engineering design handbook · 2013-02-05 · 2 3 6l2 -~ ·, ·'" !~ it:cq t tb 9 1 19lt...
TRANSCRIPT
. ~ . 2 3 6L2 -~ ·, ·'" !~ it:CQ t tB 1 9 19lt
DARCOM PAMPHLET DARCOM-P 706-316
10~023
ENGINEERING DESIGN
HANDBOOK
JOINING OF ADVANCED COMPOSITES
US ARMY MATERIEL DEVELOPMENT AND READINESS COMMAND MARCH 1979
Documentlllo. Handbook !Used by DOC lllo. 70&· and IIITISl
201 AOA-022 007 202 AOA-033 216 203 AD901 657 204 AD-785 000 205 ADA-020 020 210 AD-889 245 211 AD-389 295 212 lSI AD-389 331 213 !Sl AD-389 330 214 lSI AD-389 333 215 AD·389 296 235 AD-894 910 238 ADA-023 513 240 !CI AD-386 896 242 AD-801 509 244 AD-830 290 245 AD·389 304 247 AD-830 296 248 A0-830 284 249 AD-830 266 250 AD-830 303 251 AD·838 748 252 AD-830 297 2531 255 AD-818 532 260 AD-868 578 270 ADA-016 716 280 AD-840 582 281 iSRDI AD-389 352 283 A0-830 377 284 AD-389 298 285 A0-861 082 286 AD-830 267 290 AD·501 329 300 AD·905 372 312 ADA-013 178 313 ADA-015 181 327 A0-830 809 329 A0-879 465 331 AD·830 275 340 A0-830 276 341 . A0-830 277 342 A0-830 281 343 A0-830 393 344 A0-830 396 345 ADA-003 347 346 A0-830 301 347 A0-830 291 350 AD·881 357 355 A0830 268 356 AD-817 023 357 AD-873 103 3591 ADA-035 445 360 A0-783 697 361 AOA-013 769 4101 AOA-038 803 411 lSI ADC-008 827
412 ICl AOC-008 828 4131SI ADC 008 829
4141Sl ADC·008 830 415/SI ADC·008 831 4161Sl ADC-008 832 417 IS/I 445 AD-903 789 4701 ADA-029 902
"UNDER PREPARATION-not ava1lable "REVISION UNDER PREPARATION
ENGINEERING DESIGN HANDBOOKS (cont'd)
Title IIIllS Price
Helicopter Engineering, Part One, Preliminary Oesign. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $17.50 Helicopter Engineering, Part Two, Detail Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $20.00
• • Helicopter Engineering, Part Three, Qua~fication Assurance . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $12.00 Helicopter Performance Testing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $10.75 Timing Systems and Components.......... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $17.50 Fuzes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $ 9.25 Fuzes, Pro1imity. Electricel, Part One. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ........................ $ 4.75 Fuzes, Pro1imity, Electrical, Part Two lUI........... . ...................................... . Fuzes, Pro1imity, Electrical, Part Three lUI. . . . . . . . . . . . . . . . . ............................ . Fuzes. Pro•imity, Electrical. Part Four lUI. . . . . . . . . . . . . . . . . . . . . . . . . . . .............................. . Fuzes, Pro1imity, Electrical, Part Five. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....................... $ 6.25 Hardening Weapon Systems Against RF ~nergy.................. .. .. . . . .. ............................ $10.75 Recoilless Rifle Weapon Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ........................... $20.00 Grenades lUI . . . . . ........................ · .... · . · · · · · · · · · · · · · · · · · · · · · · · · · · · · Design for Control of PrOJectile Flight Characteristics..... . . . . . . . . . . . . . . . . . . . . . . . . . .......................... $ 7.25 Ammunition, Section 1. Artillery Amftllnition-General, withTableof Contents, Glossary, and lndet for Series ................. $ 6.00 Ammunition, Section 2, Design for Terminal Effects. .. .. .. . . . .. .. . . . . . .. .. .. . . . . .. ...................... $12.50 Ammunition, Section 4, Design for Projection. . . . . . . . . . . . . . . . . . . ................... $ 9.00 Ammunition, Section 5,1nspection Aspects of Artillery Ammunition Design. . . . . . . . . . . . . . ........ $ 4.50 Ammunition, Section 6, Manufacture of Metallic Components ot Artillery Ammunition. . . . . . . . . . . . . . . . . . ......... $ 5.25 Guns-General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $ 6.00 Muule Devices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... $ 7.25
"'GunTubes.......... ........... ............................................... .. .... $6.50 ' Breech Mechanism Design .. . . .. .. . . . ............................................... .
Spectral Characteristics of Muzzle Flash. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....................... . Automatic Weapons . . . . . . . . . . . . . . . . . . . . . . . . ............................................ . Propellant Actuated Devices. . . . . . . . . . . . . . . . . . . . . . ...................................... .
• • Design ot Aerodynamically Stabilized Free Rockets . . .......................................... .
. ... $ 6.50 $12:00
. $12.50 $ 9.25
Weapon System Effectiveness lUI. . . . . . . . . . . . . . . . . . . . . ......................................... . Aerodynamics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $ 6. 00 Trajectories. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...................................... $ 6.50 Elements of Aircraft and Missile Propulsion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ................ $21.25
\Structures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ................. $ 6.00 Warheads-General.......................................... . .......................... $12.50
• • • Fabric Design !limited Document). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .......................... . Rotational Molding of Plastic Powders. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ......................... $15.00 Short Fiber Plastic Base Composites................................. . ............................ $12.50 Fire Control Systems-General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .......................... $15.25 Fire Control Computing Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....................... $15.00 Compensating Elemants. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .................... $ 6.50
•' Carriages and Mounts-General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .................. $ 4.50 • • Cradles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $ 5.25 • ·Recoil Systems................ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............ $ 6.00 • • Top Carriages........ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....... $ 4.50 " Bottom Carriages. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .......... $ 4.50 " Equilibrators. . . . . . . . . . . . .................. ·' . . . . . . . . . . . . . . . . . . . . . . . ....... $ 4.75 •' Elevating Mechanisms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... $ 4.50 " Traversing Mechanisms.. .. . .. .. .. . .. .. .. .. .. .. . .. . .. . .. .. . $ 4.50
Wheeled Amphibians. . . . . . . . .. .. .. . . . .. .. .. . . . .. .. . . .. . . .. ................ $13.25 The Automotive Assembly. . . . . . . . . .. . . . . .. .. . . . . . . . .. . . .. . . . .. .. .. .. . .. .. .. .. . . . .. .. .. . . . .. $15.25 Automotive Suspensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $14.50 Automotive Bodies and Hulls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... $13.25 Analysis-and Design of Automotive Brake Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $15.00 Military Vehicle Electrical Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $16.50 Military Vehicle Power Plant Cooling. . . . . . . . . .................................................. $20.00 Electromagnetic Compatibility IEMCI............... . .. .. .. . . . .. .. .. . . . .. . . .. .. . . . .. .. .. . . .. ... $22.50 Vulnerability of Communication-Electronic and Electro Optical Systems !Except Guided Missiles) to Electronic Warfare, Part One, Introduction and General Approach to Electronic Warfare Vulnerability lUI ... Part Two, Electronic Warfare Vulnerability of Tactical Communications lUI. ................ . Part Three, Electronic Warfare Vulnerability of Ground-Ba•ed and Airborne Surveillance and Target Acquisition Radars lUI. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ......... . Part Four. Electronic Warfare Vulnerability of Avionics lUI. . . . . . . . . . . . . . . . . . . . . . . . . . ............... . Part Five. Optical/Electronic Warfare Vulnerability of Electro-Optic Systems lUI ....................................... . Part Si1. Electronic Warfare Vulnerability of Satellite Communications IU). . . . . ......................... . Vulnerability of Guided Mi•sile Sy•tems to Electronic Warfare lUI . . . . . . . . . . . . . . . . . ............... . Sabot T ethnology Engineering . . . . . .............. . $11.00 Metric Conversion Guide . . . . .............. . . ...................... $ 9.00
"'limitod Documents are not for sale by NTIS I DARCDM-P 706·
Document Ia. Handbook IUatHI by DDC lo. 706· and ITISJ
201 ADA 022 007 202 ADA·033 216 203 AD·901 657 204 AD-785 000 205 AOA-020 020 210 AD·889 245 211 A0·389 295 212 lSI AD-389 331 213 lSI AD·389 330 214 lSI AD·389 333 215 AD·389 296 235 AD·894 91D 238 ADA·D23 513 240 ICI A0·386 896 242 A0·801 509 244 AD·830 290 245 AD·389 304 247 AD·830 296 248 A0·830 284 249 A0·830 266 250 AD·830 303 251 A0·838 748 252 A0·830 297 2531 255 A0·818 532 260 A0·868 578 270 AOA·Ol6 716 280 A0·840 582 281 ISROI A0·389 352 283 A0·830 377 284 AD·389 298 285 A0·861 082 286 A0·830 267 290 AD·501 329 3DO A0·905 372 312 ADA·013 178 313 ADA·015 181 327 A0·830 809 329 AD879 465 331 AD·830 275 340 A0830 276 341 AD·830 277 342 A0·83D 281 343 AD·83D 393 344 A0·830 396 345 AOA·003 347 346 AD·830 301 347 A0·830 291 350 AD·881 357 355 A0830 268 356 A0·817 D23 357 A0·873 103 3581 ADA·035 445 360 AD·7B3 697 361 ADA·013 769 4101 AOA·038 803 411 lSI AOC·008 827
412 ICI ADC·OOB 828 413iS) ADC·OOB 829
414 lSI ADC·008 830 415 lSI AOC·008 831 416 lSI AOC·008 832 417 !Sit 445 AD·9D3 789 4701 AOA·029 902
"UNDER PREPARATION-not available ""REVISION UNDER PREPARATION
ENGINEERING DESIGN HANDBOOKS (cont'd)
Title
Helicopter Engineering, Part On a, Prelirrinary Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. .. .. t17. 50 Helicopter Engineering. Part Two, Detail Design ..................................................... , . . . . . . t20.00
• • Helicopter Engineering, Part Three, Qualificetion Assurance ........................................... , . . . . . . . . t 12.00 Helicopter Performance Testing ........................................................................ t1 0. 75 Timing Systems end Components ...................................................................... t1 7.50 Fuzes ......................................................................................... t 9.25 Fuzes, Proximity, Electrical. Part One .................................................................... t 4.75 Fuzes, Proximoty, Electricel, Part Two lUI. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ................ . Fuzes, Proxirrity, Electrical. Pert Three lUI ........................................................•........ Fuzas, Proxirrity. Electrical. Pert Four lUI. .............................................................•..• Fuzaa. Proxirrity, Electrical, Pert Fin .................................................................... t 8.25 Hardening Weapon Systems Against RF Energy ............................................................. t10. 75 Recoilless Rille Weapon Systams ....................................................................... t20.00 Grenades lUI ........................................ · ........................ · ...... · · · .. · ...... · Dosign for Control of Projectile Flight Characteristics ......................................................... t 7.25 Amrrunition, Section 1, Artillery Amrrunition-General, with Table of Contents, Glossary, and Index for Series .................. t 8.00 Amrrunition, Section 2, Design for Terrrinal Effects. . . . . . . . . . . .............................................. t12.50 Amrrunition, Section 4. Design for Projection .............................................................. t 9.00 Amrrunition, Section 5, Inspection Aspects of Artillery Amrrunition Design .......................... , ..........•.... t 4.50 Amrrunition, Section 6, Manufacture of Metallic Components of Artillery Amrrunition ............•..................... t 5.25 Guns-General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . t 8.00 Muzzla Devices. . . . . . . . . . . . . . . . . . . . . . . . . . ...................................................... , t 7.25
• • Gun Tubes.. .. .. .. .. .. .. .. . . . . . . . ............................................................. t 8.50 • Breech Mechanism Design . . . . . . ..........................................................•......•.
Spectral Characteristics of Muzzle Flash .................................................................. t 8.50 Automatic Weapons ........................................................................•••.... t1 2.00 Propellant Actuated Devices ..............................................................•......•.... t12.50
• • Design of Aerodynarrically Stabilized Free Rockets . . . . . . . . .. .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. .. . . . . .. .. .. .. . t 9.25 Weapon System Elf activeness lUI .................................•...................................•. Aerodynamics ...............................................................................•...• t 8.00 Traiot•ries ................. , . . . ...............................................•....•...... t 8.50 Elements of Aircraft and Missile Propulsion .................................................•....•........• *21.25 Structures .............................................................................•........ t B.OD Warheads-Ganeral. ............................................................................•.. t12.50
• • • Fabric Design llirritad Document) .......................................................... , ........... . Rotational Molding of Plastic Powders ............................................................•.•.... t15.00 Short Fiber Plastic Basa Composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . t1 2.50 Fire Control Systems-General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . t15.25 fi11 Control Computing Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . t1 5.00 Compensating Elements ............................................................................. t 8.50
• • Carriages and Mounts-General ............................................................•........•.. t 4.50 • • Cradles. . . . . . . . . . . . .................................................................... t 5.25 • • Recoil Systems .............................................................................•..... t 6.00 • • Top Carriages............. . .........................................................•....... t 4.50 • • Bottom Carriages. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...........•............................. t 4.50 • • Equilibrators. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ................................................ t 4.75 • • Elevating Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . • . . . . . . . . . . . . . . . . . . . . . . . . . • . t 4.50 • • Travarsing Mechanisms .........................................................................•... t 4.50
Wlleeled Amphibians. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . • . . . . . . . . . . . . ...............• t13.25 The Automotive Assenilly. . . . . . . ................................................................... t15.25 Automotive Suspensions .........................................................................•.. t14.50 Automotive Bodies and Hulls .....................................................................•.•.. t13.25 Analysis and Design of Automotiva Brake Systems . . . . . . .. .. .. . . . . . . . . . . . . . . . . . . . . . .. .. . . .. . . . . . . . . . . . . . . . .. t1 5.00 Military Vehicle Electrical Systarns . .. . . .. .. .. . . . . . . .. . . . . . . . . . . . . . . . . . .. . . . . . . .. .. . . . . . . . . . . . . . . . . • .. .. t1 8.50 Military Vehicle Power Plant Cooling ...............................................•.................... t20.00 Electromagnatic Compatibility IEMC) .................................................................... t22.50 Vulnerability of Conmmication·Eiectronic and Electro·Dptical Systems lhCIIIt Guided Millilal to Electronic Warfare, Part One.lntroduction and G-al ApproKh to Electronic War1ere Vulnerability IUJ ....................• Part Two, Electronic Warfare Vulnerability of Tactical Comrr~~nications lUI ..........•....... Part Three. Electronic Werf•e Vulnerability of Ground-Baled and Airborne Sllr<eiHIIIIU and Target Acquisition Radars lUI .............................................•......................... Part Four, Electronic Warfare Vulnerebility of Avionics lUI ...............................................••.•... Part Five, Opticai!Eiectronic Wer1are Vulnerability of Electro·Optic Systems lUI ...............•.............•.......... Part Six, Electronic Warfare Vulnerability of Satellite Comrrunications lUI ........................................... • Vulnerability of Guided Missile Systems to Electronic Warfare lUI ............................................... .. Sabot Technology Engineering..... . ............................................................... tll.OO Metric Conversion Guida . .. .. .. .. .. .. .. .. . .. . . . . .. .. .. .. .. .. .. .. .. .. .. .. . . . . .. . .. .. .. .. .. .. .. .. .. . t 9.00
• • "lirrited Documents are not for sale by NTIS t DARCOM·P 706·
•
DARCOM-P 706-316
DEPARTMENT OF THE ARMY HEADQUARTERS US ARMY MATERIEL DEVELOPMENT AND READINESS COMMAND
5001 Eisenhower Avenue, Alexandria VA 22333
DARCOM PAMPHLET No. 706-316
23 March 1979
Paragraph
ENGINEERING DESIGN HANDBOOK JOINING OF ADVANCED COMPOSITES
TABLE OF CONTENTS
LIST OF ILLUSTRATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1v Page
LIST OF TABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Vll
PREFACE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Vlll
CHAPTER l. INTRODUCTION 1-0 List of Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1 1-1 Advanced Composites Defined . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1 1-2 Preliminary Comments on Joint Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1 1-3 Mechanical vs Adhesive Bonded Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2 1-3.1 General ................................................................. 1-2 1-3.2 Mechanical]oints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2 1-3.3 Adhesive Bondedjoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3 1-4 Basic Joint Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3 1-4.1 General ................................................................. 1-3 1-4.2 Important BondedJoint Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3 1-4.3 Important Laminate and Adhesive Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4 1-4.4 Advanced Component Joint Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4 1-5 Surface Preparation of Advanced Composites Prior to Bonding . . . . . . . . . . . . . . . . 1-4
CHAPTER 2. COMPOSITE JOINT DESIGN 2-0 List of Sym bois . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1 2-1 Design Philosophy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2 2-2 Bonded joint Analysis and Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2 2-3 Bolted Joint Analysis and Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3 2-4 Fiber Orientation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-13
References ................................................................ . 2-30
CHAPTER 3. DESIGN DATA REQUIREMENTS 3-0 List of Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1 3-1 Baseline Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2 3-2 Laminate Mechanical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2 3-3 Mechanical Properties of Adhesives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-14
DARCOM-P 706-316
Paragraph
3-4
3-4.1
3-4.1.1
3-4.1.2
3-4.1.3
3-4.1.4
3-4.1.5
3-4.1.6
3-4.1.7
3-4.2
4-0
4-1
4-2
4-2.1
4-2.2
4-2.3
4-2.4
4-2.5
4-2.6
4-3
4-3.1 4-3.1.1
4-3.1.2
4-3.1.3 4-4 4-5
4-5.1 4-5.2
4-5.3
4-5.4
4-5.5
4-6
4-7
4-8 4-9
4-10
4-11 4-11.1
i i
TABLE OF CONTENTS (cont'd)
Design Data Generation ................................................... . Composite Mechanical Property Tests ................................... .
Tension Properties ................................................... . Compression Properties ............................................... . Interlaminar Shear Properties (In-Plane Shear) ........................ . Interlaminar Shear Properties ......................................... . Flexural Properties of Laminates ...................................... . Bearing Stress of Laminates ................... : ....................... . Test Specimen Schematics and Data Reduction Equations .............. .
Summary .............................................................. . References ................................................................ .
CHAPTER 4. BASIC BONDED AND BOLTED LAP JOINT CONFIGURATIONS
AND DESIGN VARIATIONS List of Symbols ........................................................... . General .................................................................. . BondedJoints ............................................................ .
Bonded Single-Lap Joints ............................................... . Bonded Double-Lap Joints .............................................. . Bonded Scarf Joints ..................................................... . Stepped Lap Joints ..................................................... . Bonded Joint Performance Compared .................................... . Fiber Orientation vsJoint Strength-In-BondedJoints .................... .
Bolted Composite Joints ................................................... . Single- and Double-Lap Bolted Joints .................................... .
Plain Holes .......................................................... . Bushed Holes ................................................... ~ .... . BoltedJoints With Reinforced Edges ................................. .
Bolted and Bonded Joints .................................................. . Reducing Stress Concentrations in Joints ................................... .
Model ................................................................. . Strap Modifications ..................................................... . Increased Adhesive Thickness ........................................... . Influence of Strap and Adhesive Alterations on Joint Efficiency ............ . Variable Adhesive Stiffness .............................................. .
Typical Bolted Joint Configurations ........................................ . Bolted Failure Modes ..................................................... . Typical Bonded Joint Configurations ....................................... . Bonded Failure Modes .................................................... . Weight of Joints ........................................................ · · · · Fatigue ................................................................... .
Bonded Joints ......................................................... · ·
Page 3-20
3-23
3-23
3-32
3-32
3-32
3-32
3-33
3-33
3-33
3-34
4-1
4-1
4-1
4-2
4-2
4-5
4-23
4-23
4-23 4-23 4-28
4-28 4-28 4-28 4-28
4-34
4-34
4-34
4-36
4-36
4-36
4-36
4-36
4-36
4-36
4-38
4-41
4-41
•
Paragraph
4-11.2
OARC()M-P 706-316
TABLE OF CONTENTS (cont'd)
Pa.f!.e Bolted joints and Bolted-Bondedjoints 0. 0 0 0 0 0. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0. 0. 4-42
References 0 0 0 0 ••••• 0 ••• 0 0 0 0 • 0 0 0 0 0 •• 0 ••• 0 0 0 • 0 •• 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 • 0 ••• 0 0 •••• 0 0 0 4-63 Index .. 0 •• 0. 0 •• 0 0 0 0 0. 0 0 •• 0. 0 0 0 •••• 0 •• 0. 0 0 0 •••• 0 0 0 0 0 0. 0 0 •• 0 0 0. 0 0 •• 0 ••• 0 0 0.. 1-1
Ill
DARCOM-P 706-316
Figure No. 2-1
2-2
2-3 2-4
2-5 2-6
2-7 2-8 2-9 2-10 2-11 2-12
2-13 2-14 2-15 2-1"6
LIST OF ILLUSTRATIONS
Title Comparison of Photoelastic and Computer Calculated Normal Stress on
Centerline of Doubler ................................................... . Comparison of Photoelastic and Computer Calculated Stress at Edge
of Doubler .............................................................. . Actual and Idealized Joints ................................................ . Tensile Stress Along Inner Face of Sheet at Edge of Doubler
(Computer Calculated) ................................................. . Shear Stress Distribution in Adhesive (Computer Calculated) ................ . Shear Stress Distribution in Adhesive Using Layer Properties and
Gross Properties of Composite ........................................... . Tensile Stresses in Various Layers of Composite at Edge of Doubler .......... . Symmetrical Double-Lap Joint ............................................ . Comparative Discrete Element Analytic Analyses of a Bonded Joint .......... . Predicted Joint Strength as a Function of Joint Length (Analytic Solution) .... . Shear Stress Distribution in Adhesive for Various Adherends ................. . Comparison of Photoelastic and Computed Stress Distribution for
Pin-Loaded Tension Strip ............................................... . Local Stresses in Pin-Loaded Tension Strip ................................. . Stresses in Plain Laminate ................................................. . Tensile Strength of Boron Laminates ....................................... . Stresses in Bolted Laminates ............................................... .
2-17 Principal Tensile Stresses in Bolted and Pinned Composite Joints-±¢J Patterns ............................................................ .
2-18 Tensile Stress Limits for Bolted Joints ...................................... . 2-19 Shear-Out Stress Limits for Bolted Joints ................................... . 2-20 Machined Joints .......................................................... . 2-21 Single-Lap Joints ......................................................... . 2-22 Double-Strap Joints ....................................................... . 3-1 Unidirectional Graphite/Epoxy (Type AS/3002-Batch) Longitudinal Tension
and Transverse Compression-Strain Curves at -65°F ................... . 3-2 Unidirectional Graphite/Epoxy (Type ASJ3002-Batch) Longitudinal and
Transverse Tension and Compression Stress-Strain Curves at Room
Page
2-4
2-5 2-6
2-7 2-8
2-9 2-10 2-10 2-11 2-12 2-13
2-14 2-15 2-16 2-17 2-18
2-19 2-20 2-21 2-27 2-28 2-29
3-9
Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-10 3-3 Unidirectional Graphite/Epoxy (Type AS/3002-Batch) Longitudinal and
Transverse Tension and Compression Stress-Strain Curves at 350°F . . . . . . . 3-11 3-4 Graphite/Epoxy Typical Transverse Unidirectional Tension Stress-Strain
Properties (Type AS/3002 Continuous Treated Fiber) . . . . . . . . . . . . . . . . . . . . . 3-12 3-5 Graphite/Epoxy-In-Plain Stress-Strain Properties-Crossply
[Oj±4Sj90] 8 (Type AS/3002-Batch-Untreated Fiber) . . . . . . . . . . . . . . . . . . . . . 3-13
iv
•
Fi,~;ure No. 3-6
3-7
3-8
3-9 3-10 3-11
3-12 3-13
3-14 3-15 3-16 3-17 3-18 3-19 4-1
4-2 4-3
4-4
4-5
4-6
4-7 4-8
4-9 4-10 4-11 4-12 4-13 4-14
4-15 4-16 4-17 4-18 4-19 4-20
DARCOM-P 706-316
LIST OF ILLUSTRATIONS (cont'd)
Title Page
Interlaminar Shear Strength vs Temperature for Various Orientations-Type AS/3002 Batch, Graphite/Epoxy ................................... . 3-14
Tensile Tests, Epon 828/V 40, Stainless Steel Adherends as a Function of Temperature ......................................................... . 3-16
Tensile Tests, Epon 828/V40, Stainless Steel Adherends as a Function of Bond Thickness ...................................................... . 3-17
Fracture Stress Tests, Epon 828/V40, Stainless Steel Adherends ............. . 3-18 Shear Tests, Epon 828/V 40, Stainless Steel Adherends ...................... . 3-19 Tensile Tests, EC2214, Stainless Steel Adherends as a Function
of Temperature .......................................................... . 3-20 Tensile Tests, EC2214, Aluminum Adherends .............................. . 3-21 Tensile Tests, EC2214, Stainless Steel Adherends as a Function
of Bond Thickness ...................................................... . 3-22 Precision Elastic Limit Tests, EC2214, Stainless Steel Adherends ............ . 3-:23 Shear Tests, EC2214, Aluminum Adherends ................................ . 3-24 Tensile Tests, Metlbond 329, Aluminum Adherends ........................ . 3-25 Shear Tests, Epon 9601, Aluminum Adherends ............................. . 3-26 Precision Elastic Limit Tests, Metlbond 329, Aluminum Adherends .......... . 3-27 Reduction Equations for Different Types of Specimens Tested ............... . 3-28 Single-Lap Bonded Joint Streng\h .. , ....................................... . 4-3 Effect of Et Ratio on Single-Lap Adhesive Joint Strength ..................... . 4-4 Double-Lap BondedJoint Strength ........................................ . 4-7 Effect of Et Ratio on Double-Lap Adhesive Joint Strength for Glass,
Boron/ Aluminum, Titanium Adherends ................................. . 4-9 Effect of Et Ratio on Double-Lap Adhesive Joint Strength for Stainless Steel,
Titanium, Aluminum/Composite Adherends ............................. . 4-10 Predicted Joint Strength for Double-Lap BondedJoint Using
Shell 951 Adhesive ...................................................... . 4-13 Double-Lap Joint Showing Plastic Shear Distribution in Adhesive ............ . 4-14 Stress Distribution in Actual Test Joint Based on Computer Analysis ......... . 4-15 Idealized Scarf Joint ....................................................... . 4-16 Adherend Normalized Stress Distributions in a Scarf Joint ................... . 4-17 Shear Stress Distribution in the Adhesive of a Scarf Joint ..................... . 4-18 Tensile Stress Distribution in the Adhesive of a Scarf Joint ................... . 4-19 Stress Distribution in the Adhesive of an Aluminum/Boron Scarf Joint ....... . 4-20 Scarf AdhesiveJoint Strength-Composite-to-Aluminum .................... . 4-21 Scarf Adhesive Joint Strength-Composite-to-Composite .................... . 4-22 Idealized Two-Step Lap Joint .............................................. . 4-24 Stress Distribution in the Adhesive of a Two-Step Lap Joint .................. . 4-25 Stepped Lap Adhesive Joint Strength ....................................... . 4-26 Boron-to-Aluminum Joint Strength ........................................ . 4-27 Model of a Double-Strap Joint ............................................. . 4-34
v
DARCOM-P 706-316
Figure JVo.
4-21 4-22 4-23 4-24 4-25 4-26 4-27 4-28 4-29
LIST OF ILLUSTRATIONS (cont'd)
Tztle
Ways to Reduce Strap Thickness Locally ................................... . Methods of Reducing Stress Concentration at Strap Ends .................... . Idealized Shape for Variable Adhesive Thickness ............................ . Filled Step Strap Joint ..................................................... . Variable Stiffness Adhesive Joint ........................................... . Bolted Joint Designs ...................................................... . Bolted Failure Modes ..................................................... . Bonded Joint Designs ..................................................... . Bonded Failure Modes .................................................... .
4-30 Weight Increments vs Strength of Joints .................................... . 4-31 Strength-Weight Relationships for BoltedJoints ........................... . 4-32 Total Weight Comparisons for Panels and Joints ............................ . 4-33 Fatigue Data for Adhesive Scarf Joints ...................................... . 4-34 Fatigue Data for Adhesive Double-Lap Joints ............................... . 4-35 Fatigue Life of Boron Composite-to-Aluminum Alloy Bonded Joint ........... . 4-36 Single-Lap Bonded Joint Tension Fatigue S-N Curves-Type AS/3002-Batch,
Graphite/Epoxy, 350°F ................................................. . 4-37 Single-Lap Bonded Joint Tension Fatigue S-N Curves-Type AS/3002-Batch,
Graphite/Epoxy, Room Temperature .................................... . 4-38 Bonded Symmetrical Scarf Joint Tension Fatigue S-N Curves-
Type AS/3002 Batch, Graphite/Epoxy, Room Temperature and
Page
4-35 4-37 4-38 4-38 4-41 4-41 4-42 4-43 4-47 4-48 4-50 4-51 4-53 4-53 4-54
4-55
4-56
350°F, [0±45]28 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-57 4-39 Bonded Symmetrical Scarf Joint Tension Fatigue S-N Curves-
Type AS/3002-Batch, Graphite/Epoxy, Room Temperature and 350°F, [Oj±45j90] 2s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-58
4-40 Bonded Symmetrical Scarf Joint Tension Fatigue S-N Curves-Type AS/3002-Batch, Graphite/Epoxy, Room Temperature and 350°F, [02j±45] 2s ....................................................... · 4-59
4-41 Room Temperature Fatigue S-N Curves for Various Crossplied Graphite/Epoxy-to-Steel Single-Lap Flush Head Mechanical]oints-Type AS/3002-Batch, Graphite/Epoxy . . . . . . . . . . . .. . .. . . . . . .. . .. . . . . .. .. . 4-61
4-42 Room Temperature Fatigue S-N Curves for Various Crossplied Graphite/Epoxy-to-Steel Single-Lap Protuding Head Mechanical Joints-Type AS/3002-Batch, Graphite Epoxy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-62
VI
..
Table No.
1-1 2-1 2-2 3-1 3-2 3-3 3-4
3-5 3-6
3-7 3-8
3-9 3-10
3-11 3-12 4-1
4-2
4-3 4-4
4-5
4-6
4-7 4-8
4-9 4-10 4-11 4-12
4-13
4-14
4-15
DARCOM-P 706-316
LIST OF TABLES
Title
Method for Preparing Surface .............................................. . Summary of Composite Joint Strength Tests-Mechanical Fasteners ......... . Predicted Strength Ranges for Bolted Joint Specimens ....................... . Unidirectional Laminate Properties ........................................ . Summary of Theoretical and Experimental Tension Properties ............... . Summary of Theoretical and Experimental Compression Properties .......... . Summary of Theoretical and Experimental In-Plane Shear Properties ........ . Interlaminar Shear Tests Results .......................................... . Pin-Bearing Test Results .................................................. . Summary of Mechanical Properties of Adhesive Films ....................... . Average Shear Microstrain Properties ...................................... . Average Tensile Microstrain Properties ..................................... . Elastic Properties of Adhesives ............................................. . Laminate Property Determination ......................................... . Adhesive Property Determination .......................................... . Summary of Single-Lap Bonded Joint Test Results Using Shell951 Adhesive .. Summary of Double-Lap BondedJoint Test Results (1-in. Specimen Width)
Using Shell 951 Adhesive ................................................ . Joint Specimen Laminate Patterns ......................................... . Summary of Double-Lap Bonded Joint Test Results for Various Et ratios
Using Shell 951 Adhesive ................................................ . Summary of Double-Lap Bonded Joint Test Results (1-in. Specimen Width) .. . Summary of Single-Lap Bolted Joint Test Results (1-in. Specimen Width) .... . Summary of Double-Lap Bolted Joint Test Results (1-in. Specimen Width) ... . Summary of Double-Lap Bolted Joint Test Results-Bushed Holes .......... . Summary of Composite-Reinforced BoltedJoint Test Results ................ . Summary of Shim-Reinforced Bolted Joint Test Results ..................... . Summary of Double-Lap Bolted and Bonded Joint Test Results .............. . Performance of Radiused Double-Strap Joint Employing
Carbon Fiber Reinforced Plastics ........................................ . Performance of Inversed Stepped Strap Joints Employing
Carbon Fiber Reinforced Plastics ........................................ . Summary of Bonded Joint Fatigue Test Results ............................. . Summary of Bolted Joint Fatigue Test Results .............................. .
Page
1-5 2-22 2-26 3-2 3-3 3-5 3-6
3-7 3-8 3-15 3-15 3-15 3-27 3-33 3-33 4-5
4-6
4-8
4-11 4-12 4-28
4-29 4-30 4-31
4-32 4-33
4-39
4-40
4-52
4-60
Vll
DARCOM-P 706-316
PREFACE This handbook should serve as a guide to designers concerned with the technology associated with
the joining of advanced composites. It deals with basic joint design practice as well as with those practices specific to composite joining. Tabulated and graphical representations of joint property data obtained on both bonded and mechanically fastened composites are presented. These data can be used by designers to test the degree of conservatism in calculated joint properties for their composite joint designs and hopefully will impart the necessary degree of confidence or wariness in the early design stages where alterations can be made most economically.
It is hoped that the diversity of joint possibilities and the magnitude of the joint strength properties reported will prompt cautious designers of Army materiel to make use of the strength-to-weight advantages offered by advanced composites and also to recognize that the technology is available for practical implementation of these valuable engineering materials.
The handbook was prepared by Mr. Andrew Devine, Plastics Technical Evaluation Center (PLASTEC), the Defense Department's specialized information center on plastics located at the US Army Armament Research and Development Command, Dover, NJ.
The US Army DARG_OM policy is to release these Engineering Design Handbooks in accordance with DOD Directive 7230.7, 18 September 1973. Procedures for acquiring Handbooks follow:
a. All Department of Army (DA) activities that have a need for Handbooks should submit their re-quest on an official requisition form (DA Form 17, 17 January 1970) directly to:
Commander Letterkenny Army Depot ATIN: SDSLE-AJD Chambersburg, P A 17201.
"Need to know" justification must accompany requests for classified Handbooks. DA activities will not requisition Handbooks for further free distribution.
b. DOD, Navy, Air Force, Marine Corps, nonmilitary Government agencies, contractors, private industry, individuals, and others-who are registered with the Defense Documentation Center (DDC) and have a National Technical Information Service (NTIS) deposit account-may obtain Handbooks from:
Defense Documentation Center Cameron Station Alexandria, VA 22314.
c. Requestors, not part of DA nor registered with the DDC, may purchase unclassified Handbooks from:
National Technical Information Center Department of Commerce Springfield, VA 22161.
Comments and suggestions on this Handbook are welcome and should be addressed to: Commander US Army Materiel Development and Readiness Command Alexandria, VA 22333.
(DA Form 2028, Recommended Changes to Publications, which is available through normal publication channels, may be used for comments/suggestions.)
Vlll
DARCOM-P 706-316
CHAPTER 1 INTRODUCTION
Advanced composites are defined. A broad overview of joining advanced composites is presented - the efficiency of load bearing joints, advantages and disadvantages of mechanical versus adhesive bonded joints, factors affecting choice of joints, bonded joint properties, and surface preparation.
1-0 List of Symbols E = overall joint efficiency, dimensionless
EL = load bearing efficiency, dimensionless Ew = joint weight efficiency, dimensionless Lc = load continuous member can support, lb L1 load joint can support, lb
We = weight of continuous member, lb W1 weight of joined member, lb
1-1 ADVANCED COMPOSITES DEFINED
Advanced composites is a term that has come into use in recent years, suggesting composite materials which possess characteristics so superior to earlier composites as to warrant the term "advanced". It is a poor term from the standpoint of knowing what exactly is referred to when the term is used. The term "composite" taken by itself is a compound structure or material comprised of a number of parts. It must be prefixed by other terms to clarify its meaning. Terms such as glass-resin composites, graphiteresin composites, carbon-resin composites, and boron-resin composites comprise a class often referred to as "fiber reinforced composites". These fibers can be long and oriented, or short and random within the resin matrix. Composite materials can be made up of metal layers and ceramic layers, or as constructions of metal or fiber reinforced composite skins bonded to metal or paper honeycomb, or wood or foam cores. Thus the term "composite" is a loosely defined term taken by itself. When it is prefixed by "advanced", it only becomes more nebulous.
For the purpose of this handbook, and in deference to its increased use in industry, the term
"advanced composite" is employed. The scope of this handbook is limited only to the class of composites known as fiber-reinforced resin composites. These include glass, boron, and carbon or graphite reinforcing fibers. The term "advanced composite" refers to those composite materials employing high modulus reinforcing fibers in the resin matrix. In fact, the fibers serve less to reinforce the matrix than the resin serves to bind the fibers together. As a term, advanced composite is best understood when the composites described are compared with other composites employing lower modulus fibers. Advanced composites, by virtue of their high modulus fibers help make possible the strong, stiff, lightweight capability so vital to aircraft and munitions construction.
1-2 PRELIMINARY COMMENTS ON JOINT DESIGN
As a prelude to a discussion of joint design some comments should be made regarding the purpose of a joint. Very simply, the function of a joint is to unite two or more members together in order to transfer loads from one member or members to the other(s). How well a joint accomplishes this task is judged best by its overall joint efficiency E which is the product of its load bearing efficiency EL and its weight efficiency Ew.
The load bearing efficiency EL of a joint is defined as
where:
--.!2._ , dimensionless
Lc
L1 load joint can support, lb
( 1-1)
Lc load continuous member can support, lb.
1-1
DARCOM-P 706-316
The weight efficiency Ew of a joint IS
We d. . I __ , 1mens10n ess (1-2) wj
where
We weight of continuous member, Ib wj weight ofjoined member, lb
therefore
E = r~·L X f.'w, dimensionless. ( 1-3)
The joint efficiency concept is easily understood by considering the example that fol
lows. If one takes a length of material, weighs it, tests it for strength in a particular mode, and then cuts the material in two, joins it in one manner or other, weighs the entire assembly, and tests the assembly for strength in the same mode, one can employ the given equations to measure
the success of the joint design chosen in matching the structural integrity and weight of the original unjoined material. The more closely EL, Ew, and
E approach unity, the better is the joint design from a performance standpoint.
Without belaboring the obvious, an EL as close to 1 as possible is the condition to strive for because if EL exceeds 1 then it can be assumed that a weight penalty is being imposed and Ew will decrease - an undesirable trait in most designs. This situation implies that the entire structure is being reinforced, since loads cannot be transferred between members which exceed the strength of the weakest member. Such a condition would arise in the cocooning of a joint by filament winding an entire area. However, this is essentially a rebuilding or remanufacturing process to correct a major design flaw and is not solely a joining process. Where joining two dissimilar members, the joint efficiencies must, of
course, be arrived at based on the weaker of the
two members being continuous. Another factor which should be taken into ac
count is a processing factor or cost of the joint, but this is a more difficult contribution to quantify. This factor is best considered as a comparison of the cost of making one joint design versus
1-2
another, rather than between the cost of making a joint or leaving the member continuous. The latter comparison is unrealistic since joints are
certainly not employed where it would be more feasible to omit them.
1-.3 MECHANICAL VS ADHESIVE BONDED JOINTS
1-3.1 GENERAL
The adversary tone of this paragraph is justified because each joining technique produces a joint with significant differences in the manner in which they function. Mechanically fastened joints (bolts, rivets, screws, etc.) derive their strength from the strength of the fastener and the strength of members being joined such as in cases
where the members are threaded and screwed together. In mechanical joints, loads are transferred by two locked surfaces bearing against each other. Bonded joints, on the other hand, derive their load bearing capabilities via a sur
face attachment which is a function of the surface energies of the adhesive and substrate as well as the polymer chemistry of the adhesive. Loads are transferred from one member to another across a common interface or boundary created by interfacial molecular attractions. The paragraphs that follow comment on the merits and disadvantages of each type of joint.
1-3.2 MECHANICAL JOINTS
On the positive side, mechanical joints: 1. Require no surface preparation of the sub
strate or white glove operations to assure cleanli
ness. 2. Are not as adversely or irreversibly affected
by thermal cycling and high humidity as are
bonded joints. 3. Present no unusual inspection problems for
joint quality. 4. Permit disassembly without destruction of
the substrate. Mechanical joints are less favorable from the
following standpoints:
1. They require machining of holes in the members to accommodate the mechanical attachments and thereby weaken the members.
2. They concentrate stress at the bearing surfaces, thereby creating stress risers which can induce failure in the joined member.
3. They are not generally as strong as are bonded joints unless they are heavy.
4. They add weight to the joint which reduces overall joint efficiency.
1-3.3 ADHESIVE BONDED JOINTS
Adhesive bonded joints have the following positive attributes:
1. They distribute load over a larger area than mechanical joints, thereby eliminating stress risers.
2. They can be designed so as not to weaken the joined members by machining operations in the joint area.
3. They are difficult to inspect for bond quality and voids.
4. They adct a minimum of weight ·to the structure.
The drawbacks to bonded joints are: 1. They require adherend surface prepara
tion and cleaning. 2. They are subject to degradation due to the
effects of temperature and humidity cycling. 3. They are difficult to inspect for bond qual
ity and voids. 4. Disassembly cannot be effected in most
cases without destruction of the joined members.
1-4 BASIC JOINT DESIGN
1-4.1 GENERAL
Before a joint can be designed, the designer must possess some basic information. He must know the nature of the materials to be joined -physical yield strength, modulus of elasticity, thermal expansion and contraction behavior, and very often their chemistry. He must also know
DARCOM-P 706-316
the stresses which the joint is expected to withstand in service, the environment in which the joint is to function, and its expected service time.
Knowing the nature of the materials to be joined and the service the joint is to provide, the designer can proceed to his next step -the selection of the type of joint to be employed. This requires a consideration of the limitations imposed by the materials on the processing or manufacture of the joint as well as special requirements such as disassembly capability for maintenance and quality control requirements. For example, a structural joint requiring disassembly capability would probably exclude the selection of a structural bonded joint. Similarly, if the joint is to be fabricated in a facility in which a manufacturer has no proper surface preparation facility, processing considerations would preclude use of a bonded joint. If on the other hand very thin members are to be joined which cannot be machined or weakened with holes in the joint area, then a bonded joint would be in order or strength-to-weight requirements might mandate a bonded joint.
The decision whether to use a mechanical or bonded joint requires careful consideration of all variables which will effect the final outcome and requires a systems approach with the relationship between the joint and the entire structure kept in mind at all times. Once this decision has been made, then the process of configuring the joint and selecting or altering materials to meet the performance requirements of the end item can proceed. This last process is considered to be the actual design step but often it is embarked upon without proper preparation and guidance.
1-4.2 IMPORTANT BONDED JOINT PROPERTIES
Although specific test specimens have been devised to test specific end items, the basic properties to test in an adhesive ioint remain the same - tensile strength, tensile and compressive shear strengths, and peel. Other forms of tests include bending which actually creates peel
1-3
DARCOM-P 706-316
and cleavage forces .• Few of the tests used ran isolate stress modes but merely attempt to do so as nearly as possible. Some tests accomplish this better than others but the basic reason for testing joint properties is to compare one adhesivejadherend combination with another under similar loading modes and to extrapolate these data to specific configurations. No doubt a variety of tests could be devised to ascertain the behavior of a specific bonded joint under a specific test mode and this type of final design testing should indeed be done. However, the basic design properties must be determined by standard, widely accepted and used test methods so a wide range of data from many sources can be continually generated.
1-4.3 IMPORTANT LAMINATE AND ADHESIVE PROPERTIES
The strength properties of laminates and adhesives are very much time and temperature dependent so it is important to know the condi-
~
tions of service of bonded compcc.;ite joints. The environmental effects - temperature, humidity; and exposure to fuels, chemicals, and sunlight -on the properties of adhesives and composites are not fully known or quantified but can and do have detrimental effects in many instances. For these reasons data presented should be viewed as typical of the particular situation, and subject to verification and prototype testing under the actual use conditions anticipated. In addition, factors such as cure cycle, cure pressure, surface preparation, machining, and fabrication will further alter properties. It is therefore advisable to adequately characterize the specific' material design properties and their statistical accuracy before using them for design purposes. The tables and figures presented in this handbook are for guidance and comparison, and show trends. Absolute values given should be judged for their pertinence to a specific application and, if not entirely pertinent, then used with caution and with a sufficient safety factor for design purposes.
1-4
1-4.4 ADVANCED COMPOSITE JOINT CONSIDERATIONS
What has been said up to now has been general in nature and applies to composite and noncomposite alike. It should be remembered, however, that unlike isotropic materials such as metals, orthotropic materials - like advanced composites - undergo severe damage and weakening when they are cut or machined and thus become more susceptible to interlaminar shear within the substrate. For this reason bonded rather than mechanically fastened joints are most frequently employed in advanced composite joint design. More specifically, bonded joint configurations such as single and double laps or single and double strap type joints are preferred where feasible to avoid machining of the com~ posites even though a weight penalty may be imposed. Exceptions to this practice would be beveling or tapering of the ends of a lap or strap to alleviate stress concentrations at the lap or strap ends. This practice does not damage any fibers in the bond area.
Along the same line, basic design practice for adhesive bonded composite joints should include making certain the surface fibers in a joint are parallel to the direction of pull in order to minimize interlaminar shear or failure of the bonded substrate layer. On composites whose joint areas have been machined -to a step lap configuration, for example - it -is possible to have a joint interface comprised of fibers at other than the optimum 0-deg orientation to the load direction. This would tend to induce substrate failure easier than otherwise would be possible.
1-5 SURFACE PREPARATION OF ADVANCED COMPOSITES PRIOR TO BONDING
As with any bonding operation, the proper surface preparation is essential for obtaining quality bonds which fail cohesively rather than adhesively. Surface preparation for advanced composite substrates prior to bonding is accomplished best by solvent wiping to remove loose
surface dirt and grime and, then abrading the surface by hand or machine. The first step removes loosely adhered weak boundary layers, and the second increases the surface energy of the faying surface as well as increasing the bond area by surface roughening. The abrading operation should be conducted with care, however, to avoid damaging surface fibers. The purpose is to roughen the resin matrix and expose, but not rupture, the reinforcing fibers. A surface roughening method having gained wide acceptance is the use of peel ply. This technique simply involves incorporating a nylon cloth in the outer layer of the composite during lay-up. The
DARCOM-P 706-316
peel ply is torn or peeled away prior to bonding, fracturing the resin matrix and exposing a clean roughened surface for bonding. Surface roughness can to some extent be determined by the weave of the peel ply. The peel-ply method is fast and eliminates the need for solvent cleaning and removal of abraded resin dust. All abrasion treatments should have the same principles in common. These are (1) to thoroughly clean the surface prior to the abrasion step in order not to force dirt into the surface, (2) abrade, (3) remove abrasion dust, (4) clean again, and (5) Dry. One such met hod is outlined in Table 1-1.
TABLE 1-1. METHOD FOR PREPARING SURFACE
I. With a stiff brush and 2% aqueous solution of detergent at 104° to 122°F, scrub entire surface of panels.
2. Thoroughly rinse in tap water followed by immersion in distilled water. 3. Dry in forced air oven at 150°F for 30 min. 4. With 240 grit sandpaper, abrade bpnding area plus 0.5 in. margin. 5. Dust abraded area with vacuum. 6. Swab off abraded area with acetone wet clean gauze. 7. Rinse generously in distilled water (entire panel). 8. Dry in forced air oven at 212°F for 60 min, then bond parts immediately.
1-5
DARCOM-P 706-316
CHAPTER2
COMPOSITE JOINT DESIGN
The anisotropic nature of composites - a factor that must be reckoned with in joint design - is emphasized. The analysis of stress distributions of bonded joints, and pinned and bolted joints - as a function of distance along the joint - is presented in graphical form. Tables of tensile and shear strengths for mechanical and bolted joints are given for various composite fiber patterns and laminates.
2-0 LIST OF SYMBOLS
A = load area, in~ D = diameter of bolt, in. e = distance from edge of bolted joint
to center of bolt hole, in. E = elastic modulus, psi
E:r = elastic modulus of composite with fibers oriented parallel (longitudinally) to direction of applied stress, i.e.,¢ = 0 deg, psi
Ey = elastic modulus of composit~ with fibers oriented perpendicularly (transversely) to direction of applied stress, i.e.,¢= 90 deg, psi
G = shear modulus, psi Gxy = shear modulus in xy-plane, psi
K = principal stress factor, dimension-less
L = joint length, in. P = applied load, lb s = distance from side of bolted joint
to center of bolt hole, in. tl> t2 = thickness of adherends
t = thickness of adhesive layer, in. W = width of bolted joint, in.
x = longitudinal distance parallel to applied load, in.
y = transverse distance perpendicular to applied load, in.
/J.:ry Poisson's ratio of composite, relating contraction in y-direction to extension in x-direction,
dimensionless /J.yx = Poisson's ratio of composite,
relating contraction in x-direction to extension in y-direction, dimensionless
u laminate stress = Pj A, psi Uave average compressive stress based
on projected area of pin, psi uLr = tensile strength of composite with
fibers oriented parallel (longitudinally) to direction of applied load, i.e.,¢ = 0 deg, psi
ua = gross section stress level, psi urr tensile strength of composite with
fibers oriented perpendicularly (transversely) to direction of applied load, i.e., ¢ = 90 deg, psi
Uo:r applied longitudinal tensile stress, psi
u x = tensile stress at point x inches from doubler edge, psi
u :r/ U0 :r stress concentration factor at point x inches from doubler edge, dimensionless
(]1
T
Tmean
¢
tPc
=
=
=
principal stress on matrix, psi shear stress in adhesive, psi mean shear stress, psi angle between fiber laminate direction and direction of load, deg angle between longitudinal tangent to bolt hole and line drawn from corner of composite to bolt hole at tangent point of contact, deg
2-1
DARCOM-P 706-316
2-1 DESIGN PHILOSOPHY Most design techniques for joining com
posites are extensions of techniques used for isotropic materials. This approach is acceptable provided the designer remains attuned to the anisotropic nature of composites and how this can alter bulk composite properties and failure modes, depending on the working direction of the composite. By combining joint stress anlayses with material properties and failure criteria, the strength and deflection characteristics of a joint are, to some extent, predictable. For bonded joints, measurements of the strength and modulus of the composite members and cured films of the adhesive are required.
The lack of composite and adhesive property data as well as inadequate stress analyses available suggest that the best design procedure for bonded composite joints is to treat each joint as an individual structure, and test it and modify it as indicated. As more composite and adhesive data become available this process can be refined.
There are several stress analysis methods other than that discussed here. Each method, regardles~ of simplifying assumptions made, requires knowledge of the shear and tensile properties of the adhesive and adherend. These properties should reflect the pertinent joint environments of temperature and humidity for the special cure and lay-up characteristics of the composite as well as adhesive cure conditions and bond line thickness. It is unlikely, in the near future, that these data will be readily available in handbook form for quick reference-the variable combinations are too great. However, the data presented in this handbook have been assembled from several sources and do show some of the important work done as well as point out areas which require further study. Although the data available will grow with increased advanced composite and adhesive usage, it is unlikely to become available from a single source or data book.
2-2
A system needs to be established to deal with material property data generation. Ide4lly, all new data should be reported in a standardized format and placed in a centralized accessable data bank for computer-aided design and engineering purposes. The success of such a system requires the cooperation of all industry, university, and Government research and de~ign programs to insure that the design data generated for specific purposes are reported in standard format for inclusion in the data bank and availability to all. The difficulty in compiling a handbook such as this within fiscal and time constraints is that of searching for, finding, and screening data, and then putting the data on a uniform basis for comparison. It is a task requiring many man-years of effort, as a minimum, to assemble useful design data and continuous updating to keep the information complete and current.
The reliability of static test data for design purposes depends a great deal on the nature of the end product being designed. The requirements of the automotive, sporting, and aircraft industries for example, differ both for performance and safety, and therefore the consequence of a functional failure in a product will determine how tightly or reliably various components need be designed. Failure of a graphite composite tennis racket frame during competition in no way approaches a failure in a glass composite helicopter rotor blade during flight. It is with the consequences of component failure then that the designer concerns himself when he decides what design data will be required and what testing need be done to supplement that available from manufacturers and the literature.
2-2 BONDED JOINT ANALYSIS AND DESIGN
Discrete element idealizations can be established for bonded and bolted composite joints, using digital computer methods for stress
and deflection analysis. Photoelastic and computer calculated stress distributions can be compared for joints of given geometry. Once a satisfactory joint idealization is established, joint member materials and adhesives can be altered to evaluate how they effect stresses and deflections under a given load. Figs. 2-1 and 2-2 compare photoelastic and computer calculated stresses for a single strap joint (Fig. 2-3) at the centerline and edge of the strap (doubler). Figs. 2-4 and 2-5 show the results of an analysis of S-994 glass/Narmco 5505 resin composite sheet bonded to an aluminum strap (doubler) using FM-47 adhesive in which tensile stresses (J"0 x in the main member and shear stresses T in the adhesive are depicted. The spike in tensile stress will have a marked influence on fatigue life. A similar analysis using the gross and layer properties of S-994 glass/Narmco 5505 composite bonded with MB-408 adhesive is shown in Figs. 2-6 and 2-7.
Because discrete element analysis of joints consumes a good deal of time, even with the computer, a faster analytic solution using the computer was developed by McDonnell-Douglass Corp. based on an analytic solution for stresses in a symmetrical, double lap joint by Hahn.
Using this computer program to solve for stress in a symmetrical double-lap joint (Fig. 2-8), one obtained the stress distribution shown in Fig. 2-9. The assumptions made in generating this stess distribution were:
1. Only longitudin;J 1 stresses cause adherend deformation.
2. Shear stress is constant throughout the thickness of the glueline.
3. Adhesive tensile stress parallel to the glueline is negligible.
4. The adhesive stress-strain curve is constant.
It can be seen that good agreement exists between discrete element analyses and the analytical method (Hahn) except at the strap ends. Fig. 2-10 is a plot of predicted failing load vs overlap for a boron/5505 composite bonded to
DARCOM-P 706-316
aluminum using MB-408. The curve obtained; typical of such plots. Fig. 2-11 indicates that varying the metal adherends from steel to titanium to aluminum has little impact on adhesive shear stress distribution. Increased doubler modulus increases stress at one end of strap but decreases it at the other.
2-3 BOLTED JOINT ANALYSIS AND DESIGN
Computer analysis of bolted joints yields the stress distributions seen in Fig. 2-12 for pinloaded holes along with photoelastic test results. Computer predicted stress distributions in an S-994 glassjNarmco 5505 resin pin-loaded tension strip is shown in Fig. 2-13 where the elastic properties were calculated for a fiber volume content of 65% with zero voids.
The strength of composite bolted joints is dependent on the geometrical parameters edgedistance bolt-diameter ratio ej D, side-distance bolt-diameter ratio s/ D, and laminate-thickness bolt-diameter ratio tjD; and orientation of reinforcing fibers in the composite layup, and fabrication and processing methods. Even when fabrication processes are closely controlled, specimens can show large scatter.
Bearing failures account for very few bolted composite joint failing modes. Unless edge and side distance ratios are very large, full bearing stress limit is rarely achieved. Laminates comprised primarily of ±rp layers generally fail along filament lines - indicating that the interfilament strength of the matrix is the limiting factor. Laminates with 50% of the fibers oriented at 0° and 50° at ±rp usually fail along 0-deg and 90-deg lines. When rp approaches 0, failure is usually by cleavage. This does not occur in a wide joint with side-by-side bolts. Generally, the tensile strengths of bolted specimens are somewhat lower than the strength of laminates without holes, which is attributable to the effect of stress concentrations at the holes.
2-3
DARCOM-P 706-316
2-4
SHEET
0 ox
0.11
0.10
0.09
0.08
0.07
c 0.06
;:. 0.05
0.04
0.03
0.02
0.01
·2 ·1 0 2 3 4
A-.,
I y
I __ j_ I I
A_J
+ COMPUTER CALCULATED (REF. 4)
0 PHOTOELASTIC
5 6 7 8 9
Stress on Section A·A
10
Figure 2-1. Comparison of Photoelastic and Computer Calculated Normal Stress on Centerline of Doubler3
DARCOM-P 706-316
" 0 t:>
~ .... 0 ti <U .... c: .g <U !: c: .., u c: 0 u "' "' .., ....
cri
0
1.6
1.4
a or
1.2
1.0
0.8
0.6
0.4
0
0 PHOTOELASTIC (REF. 4)
0 COMPUTED
DOUBLER
~ +X
0 0 0
0
0.2~--~--~----._ __ _. ____ ~--~--~~------~----------------0.040 -0.020 0 0.020 0.040 0.060 0.080
Distance from Doubler Edge x, in.
Figure 2-2. Comparison of Photoelastic and Computer Calculated Stresses at Edge of Doubler
2-5
DARCOM-P 706-316
SINGLE STRAP JOINT
0.005 ADHESIVE LAYER
L ~1-3/8 2-3/4-----+-1
0.072
(A) Actual Joint
DOUBLER _\ I I
ADHESIVE
\SHEET
~~ ~ ........................................ ~ ~ .......... ""-.~ ':Y I
I
(B) Idealized Joint
Figure 2-3. Actual and Idealized Joints3
Failure in a bolted joint depends on the interfilament strength of the matrix. In the plain laminate illustrated in Fig. 2-14, the interfilament line AB intersects the edges of the specimen. The load components of Sand T introduce shear and tensile stresses on AB. Combined, these stresses produce a principal tensile stress on the matrix
(2-1)
where (J' == laminate stress == Pj A, psi
2-6
K == principal stress factor, dimensionless
(1/2)sin2¢(1 + y' 1 + 4 cot2 ¢).
When ¢ == 90 deg, K = 1 and the strength of the laminate becomes the ultimate tensile strength of the resin matrix. Test results indicate that laminate transverse tensile strength exhibits large scatter due most likely to varying void content and cure cycles. When ¢ approaches 0 deg, the laminate strength is limited by the combined filament strength. Fig. 2-15 shows this effect clearly
0~
'"t;" ... .9 '-' as
'"" c 0
'.::I as b c "' ~ 0 u ~
"' b [f)
DARCOM-P 706-316
1.8
' ~ SHEET (S994 GLASS/5505 RESIN)
1.6
1.
l. 4 J
I -~' DOUBLER I l
CALUMINUN) l .....__l ao%- -t- .. •1
2
L0.071 \_I
/' ~ '-0.102
FM-47 ADHESIV ., (Forest Product Lab.)
E
1. 0
0. B •\
\ 6
1\. ~
" "" r---4
0.
o.
0. 2 , -0.040 -0.020 0 0.020 0.040 0.060 0.080
Distance from Doubler Edge x, in.
Figure 2-4. Tensile Stress Along Inner Face of Sheet at Edge of Doubler (Computer Calculated)3
2-7
N I
00 l~•t--------1 •375-----------:0:o:O:':"U~B~L'='E=R----------_,.,~,
(ALUMINUM)
.g "'
I 0.4
1 ,, I \
0.005 ADHESIVE (FM·47)
SHEET ~ 0
(S994 GLASS/5505 RESIN ~e)
0.102 0. 144 (2 PLCS)
a ~~-f~~2===0~-r;i:~~
0.31 \ I ~,SYMMETRICAL I JOINT
I
0ar~~t: ~: 5~
\ \ UNSYMMETRICAL ar t if
JOINT
/~ !l::: 0.1 /
0.1 0.2. 0.6 0.5
0.3 0.4 Distance from Doubler Edge x, in.
/ /
0.4 0.3 0.2 Distance from Edge of Sheet, in.
0.1
I I
0 I
I 0
I
Figure 2-5. Shear Stress Distribution Adhesive (Computer Calculated)3
0.1
0 -0.02
0 > :a n 0 3:
I ., """ 0 0)
w .... 0)
DARCOM-P 706-316
0.6.---------------------------------,
~ " 0.4
SHEET (S 994 GLASS/6606 RESIN =X= 46°) 0.160 (ALUMINUM)
" ~ 0 3
" ~ '<i) .., ..c "0 -< c:: ·-<h <h .., !::
rJ)
.... "' OJ
..c rJ)
'-0
.2
"' 0::::
c c h .... " ..0
E " :::; c::
"' :::; c:: ·-<h
"' \l)
!:: rJ)
~
"' c:: "' E-
0.3
0.2
0.1
0 0 0.05 0.1 0.15
0 LAYER PROPERTIES
0 GROSS PROPERTIES
0.2 0.25 0.3 0.35
I Distance from Edge of Doubler, in.
I I I I I I I 0.35 0.3 0.25 0,2 0.15 0.1 0.05 0
Distan!'e from Edge of Sheet, in.
Figure 2-6. Shear Stress Distribution in Adhesive Using Layer Properties and Gross Properties of Composite3
as well as tests for ±¢-fiber orientations. Although both ¢- and ±¢-patterns should yield identical monolayer matrix stresses, the ± ¢pattern cannot fail along a ¢-interfilament line in one direction without shearing filaments in another. This is a synergistic advantage of crossing filaments.
Fig. 2-16 illustrates the case of the bolted laminate. The filament line AB running from the side of the hole to the edge of the specimen is a maximum when B coincides with C, the corner of the laminate; and ¢ = tPc· Test results show peak strengths at this condition~ Fig. 2-17 plots the principal tensile stresses in bolted and pinned composite joints against
±¢ from a number of referenced sources. The envelope of test results shows a fall off as ¢ approaches 0 deg or 90 deg. This is thought to result from the bolt applying load locally as filaments become unidirectional, causing shear or tension failures originating adjacent to the bolt. When 0-deg layers are used in conjunction with ±¢-layers, failures will usually be along 0-deg or 90-deg lines-the 90-deg failures thought to be secondary failure.
Tensile and shear-out stress limits for boron laminates using 0-deg and ±¢-layers are shown in Figs. 2-18 and 2-19. Table 2-1 summarizes some bolted boron composite joint strengths from referenced data sources. Table 2-2 shows
2-9
DARCOM-P 706-316
2-10
2.0
o.s
-0.04 0
DOUBLER (BORON/5606 RESINI
0.040TVP
0.005 ADHESIVE (MB-4081
SHEET (BORON! 5605 RESIN!
2,6
~ 1,5
45~ 4.8 3,7
(LAVER NO.)
Ex • 30.38 x 106 FOR LAVERS 1, 4, 5 Ia 8
Ex • 1.344x106 FORLAVERS2,3,61a7
(LAVERS 6 Ia 7 ARE ALMOST THE
SAME AS LAVER 31
0.04 0.08 0.12 0.16
Distance from Edge of Doubler, in.
Figure 2-7. Tensile Stresses in Various Layers of Composite at Edge of Doublers
Material l
Figure 2-8. Symmetrical Double-Lap Joints
....
r 0.080 0.0060
DARCOM-P 706-316
DOUBLER IBORON/6606 RESIN ~ ) ~50
1-~,---r=============~=======r==*=~
"' .., .... < ~
1:::: ·c; ....., ..,
·= .:: w .... .., >
0 "' "' .., ....
ci) .... "' ..,
..c: CFl
1::::
"' .., ::; B .., .::: "' ..,
..c: -c < .::
"' "' .., ....
ci) ....
"' .., ..c: CFl ....... 0
.g "' c:::;
ADHESIVE MB - 408 ~60 SHEET IBORON/6606 RESIN! ~
6
6
4 "' "' .., ~ .S "' 1:::: ..,
.§ -c J
.., > ·;;; .., c
..c: "' -c ..,
"' E .... .... 2
0 O.t 0.2 0.3 0.4
0 DISCRETE ELEMENT
A HAHN ICASE E)
0.6 0.6 0.7 0.8 0.9
Distance from Edge of Strap, in.
i,SYM
1.0
Figure 2-9. Comparative Discrete Element and Analytic Analyses of a Bonded Joine
2-11
DARCOM-P 706-316
0.006 ADHESIVE (MB-408}
DOUBLER (ALUMINUM}
~-=:!::::=ۤ~~- p r -P
~L 0.160 12 PLCS}
SHEET (BORON/5505 RESIN)
~oor---------------------------------------------~
500
0~----------~--------.. ----------~--------~ 0 0.6 1.0 1.6 2.0
Lt•nAth of Joint L, in.
Figure 2-10. Predicted Joint Strength as a Function of Joint Length (Analytic Solution)3
2-12
-~
DARCOM-P 706-316
0,12080/EPOXY E; 16.12 X 106 .----...L--._ p
2?----~----~---L~~ 1---:----- p
"' 0 600
X MB 408 ADHESIVE "(jj E = 139,000 0 ALUMINUM ALLOY 0.. G = 49,000 E •10.3 X 1o6 ~ 400 t- I = 0.006 -o l:l. TITANIUM "' E • 16 X 106 a ~
300 ~ .s 0 STEEL il.)
~ E • 29 X 106 :l
Q § il.)
( .:: ~
"' 200 e -v t) <l.l AVERAGE SHEAR I g ..c:
0 -o 0 0 < 1:
.... 100 "' <f)
<l.l .... en .... "' 00 0.20 0.25 0.30 0.35 0.40 0.45 0.50 "' 0.06 0.10 0.15 ..c:
ifJ Distance from Edge of Doubler, in.
Figure 2-11. Shear Stress Distribution in Adhesive for Various Adherends3
predicted strengths for vanous bolted speci- quired to produce this configuration. Figs. 2-20
mens. through 2-22 show some acceptable and unac-
2-4 FIBER ORIENTATION
As stated in par. 1-4.4, composites must not be stressed in a manner likely to induce delamination. This is why it is desirable in bonded joints to have surface fibers oriented parallel to the load direction, and to employ lap and strap joints when this is the case. The use of lap and
strap joints precludes machining the bond area.
When this is not the case, i.e., when surface fibers
are oriented at other than 0 deg to the load direction, then joints such as scarf and landed scarf
joints are useful even though machining is re-
ceptable bonded composite joints as related to fiber orientation. As can be seen, machining of bond-line areas can result in disadvantageous load to fiber orientation which ultimately would result in failure by delamination of the composite. The proper orientation of the surface fibers in a bonded composite joint should not be an accident but should be included in the de
sign. Even if a stepped lap joint is contemplated, very often it may be easier and less costly to lay
up the step configuration prior to cure. This
would eliminate the machining process and prevent damage to composite fibers.
2-13
DARCOM-P 706-316
.500
r1.21 aav•
111.13 am
-----l~----PIN LOAD
COMPUTED RADIAL STRESS DISTRIBUTION
COMPUTED NORMAL STRESS DISTRIBUTION ON TRANSVERSE SECTION
PHOTOE l.ASTIC-NORMAL STRESS DISTRIBUTION ON TRANSVERSE SECTION (REF. 8)
I
I It
a...---4-----4~---.625-------------~
aav• : AVERAGE COMPRESSIVE STRESS BASED ON PROJECTED AREA OF PIN
ac : GROSS SECTION STRESS LEVEL
0.39 ac ~:I 0.53ac
Figure 2-12. Comparison of Photoelastic and Computed Stress Distributions for Pin-Loaded Tension Strip3
2-14
COMPUTED RADIAL STRESS DISTRIBUTION
DARCOM-P 706-318
---~T"'" LOAD
~------~~---------------------1.000~----------------------~
.750
S·994 GLASS NARMCO 5505 RESIN
Ex = Er = 0.381 X .. 107 psi 1'-xy = 1'-yx = 0.352
Gxy = 0.141 X 107 psi
t :: 0.120
COMPUTED NORMAL STRESS DISTRIBUTION ON TRANSVERSE SECTION
0.24ac--J
Figure 2-13. Local Stresses in Pin-Loaded Tension Strip3
2-15
DARCOM-P 706-316
p
A
B
p
Figure 2-14. Stresses on Plain Laminate
2-16
DARCOM-P 706-316
200~~~----------------~~~~----------------~ ..,. _;r- FILAMENT STRENGTH
150
J. "' ~
(f) 100 ..:: ·;n
:::: "' E-
50
MATRIX STRENGTH
'(., FILAMENT DIRECTION
MONOLAYER: aLT = 200,000 psi
aTT = 10,000 psi
INCREASE IN STRENGTH DUE TO CROSSING OF FILAMENTS
Angle Between Laminate Fiber Direction and Load Direction t/l, deg
Figure 2-15. Tensile Strength of Boron Laminates3
2-17
DARCOM-P 706-316
Figure 2-16. Stresses in Bolted Laminates8
2-18
DARCOM-P 706-316
II ' D
SYMBOL AEF TEST D D t REMARKS
X 2 1ST SEAlES 2.67 3.33 1.88 PINNED
+ 2 2ND SEAlES 3.00 2.67 2.24 PINNED
0 2 2ND SEAlES 3.00 2.67 2.24 BOLTED
[!] 3 3AD SERIES 3.00 2.67 1.12 PINS AND BOLTS
* 3 4TH SERIES 3.00 2.67 1.12 CSK BOLTS
4 TABLES 4.80 3.00 2.60 PINNED • XLIX AND L
w 4 TABLE L 2,00 3.00 2.60 PINNED
A 5 2.00 2.38 4.80 PINNEO
18r---------------------------------------------------------------..,
0 14
X )C
12 t: i + + ~ t + ....
·u; • .><:
"' "' " ... cii ..!::! ·u; = 8 ..,
E-<
6 CSK BOLTS
4 PLAIN BOLTS AND PINS
Angle Between Laminate Fiber Direction and Load Direction <b, deg
Figure 2-17. Principal Tensile Stresses in Bolted and Pinned Composite Joints -±t/1-Patterns3
2-19
DARCOM-P 706-316
~r-----------------------------------------------------------~
TENSILE STRESS LIMITS 0° ANO ±~PATTERNS
40
30
·:;; ...:.:
TENSILE STRESS = P![t(W - D)]
;i <I> !:: r.n
-= ·;;; c "' ......
20
10
Angle Between Laminate Fiber Direction and Load Direction <b, deg
Figure 2-18. Tensile Stress Limits for Bolted Joints3
2-20
"<ii -"' <£ "' l1l !:: (fJ .. "' l1l ...c:
(fJ
SHEAR-OUT STRESS LIMITS
o0 AND :te/)PATTERNS
DARCOM-P 706-316
20r-----------------------------------------------------------------------~
18
' '100'lHC/)
PREDICTION RANGE
12
8
6 - SHEAR-OUT STRESS • P/(2et)
4 ~- t I I e
2 _j
! p
10 20 60 70 80 90
Angle Between Laminate Fiber Direction and Load Direction rb, deg
Figure 2-19. Shear-Out Stress Limits for Bolted Joints3
2-21
DARCOM-P 706-316
TABLE 2-1 SUMMARY OF COMPOSITE JOINT STRENGTH TESTS-MECHANICAL FASTENERS2
CALCULATED STRENGTH LIMITS, tb
TEST DATA SOURCE PATTERN MINIMUM MAXIMUM LOAD, tb FAILURE MODE
REF. 2 0 704 s 1056 s 1040 SHEAR FIRST SERIES 697 s 1045 s 1045 (CLEAV ACE) (PINNED)
±IS 1000 s 1480 .s 1410 ALONG 1010 s 1493 s 1420 FILAMENT ....
LINES
±30 1260 s 1831 s 1730 1283 s !870 s 17.10 1213 s 1762 s 1660
±45 950 s 1694 s 1565 960 s 1712 s 1545 970 s 1730 s 1730
±60 878 T 1240 T 1130 878 T 1240 T 1150 878 T 1240 T 1165
±75 494 T 815 T 815 4gs T 799 T 780 474 T 783 T 750
±90 2171 T 542 T 300 TENSIO!'i 291 T 586 T 317 284 T 568 T 284
REF. 2 0 712 s 1070 s 715 CLEAVAGE SECOND SERIES (PINNED) ±10 910 s 1.170 s 1025 ALONG
920 s 1380 s 1110 FILAMENT LINES
±15 1010 s 1498 s 1120 1010 s 1498 s 1140
±20 1040 s 1643 s 1140 1027 s 1626 s 1170
±25 1107 s 1583 s 1130 1120 s 1600 s 1140
±30 1227 s 1780 s 1255 1240 s 1800 s 1240
±.15 1226 s 1903 s 1320 1226 s !903 s 1290
±40 1083 s 1614 T 1180 1096 s 1611 T 1200
±45 988 T 1.191 T 990 999 T 1407 T 1060
±50 835 T 1198 T 1040 (cont'd) 844 T 1210 T 1102
.. S Ar\D T INDICA' IE WHETHER SHEAR (S) OR TENSION (T) LIMITS ARE CRITICAL.
(cont'd un next page)
2-22
DARCOM-P 706-316
TABLE 2-1 (cont'd)
CALCULATED STRENGTH LIMITS, I b
TEST DATA SOURCE PATTERN MINIMUM MAXIMUM LOAD, lb FAILURE MODE
REF. 2 ±60 577 T !!20 T 5KO SEC:< )NJ) SERIES 570 T lll2 T 74!! (PINNED) (!'Ont'd)
±75 .~14 T 51!! .,. 315 317 T 524 T 424
±90 201 T 401 T 217 TE:\'SION
REF. 2 ±10 9111 s I 3()() s 1300 ALONG SlCOND SERIES ± 15 990 s 1463 s 1390 FILA:v!ENT (BOLTED) ± 20 1 120 s 1620 s 1520 LINES
±35 1227 s 1902 s 1655 ±411 1 JHO T 161:1 T 1555 ±45 9HO T 1190 T 1:155 ±60 SiD T H30 T H20 ±75 31H T 524 T c., I 0
REF. 2 () 1:164 s 2024 s 1620 SHI':AR THIRD SERIES 13.D s 20011 s 2000 (CLEA V/\GE) (PINNED & 1341 s 21110 s 2010 NOTED)
Oj15/-15JO J9BO s 2930 s 2410 ALONG (BOLTED) 1923 s 2845 s 2270 0° AND 90°
1979 s 2910 s 2530 LINES
OJ30J-30JO 24!!0 s 3600 s 2960 2425 s 3520 s 3190
Oj45j-45JO J9BO s 3882 s 3310 1926 s 3775 s 3715 1938 s 3796 s 3550
OJ60j-60JO 1756 s 3660 T 3615 (BOLTED) 1710 s 3560 T 3560
1727 s 3600 T 3400
0/90 2046 T 2480 T 2050 2036 T 2470 T 2050
REF. 4 ±45 1748 T 2456 T 2453 ALO:-\G (PINNED) 1763 T 2480 T 2456 FILA:v!E:-IT
1715 T 2412 T 2346 LI:-\ES
OJ60j-60 2855 s 4290 T 4250 BEARI:-\G 2630 s 3950 T 393) 2815 s 4225 T 3HSO
0/90 2520 T 3060 T 2915 TEI\'SIOI\ 1960 T 2380 T 2352 2030 T 2460 T 2347
OJ60J-60JO 2550 s 3825 T 3685 TENSI0:-1 3640 s 5470 T 5170 TENSION 2280 s 4890 s 4550 SHEAR 1520 s 3260 s 3255 TENS lOr\
0/90 1990 T 2416 T 2334 TENSIO:\ (coni 'd) 1363 s 2416 T 1450 TENSION
S AND T INDICA IE WHETHER SHEAR (S) OR TENSION (T) Ll~IITS ARE CRITICAL
(coni 'don next page)
2-23
DARCOM-P 706-316
TABLE 2-1 (cont'd)
CALCULATED STRENGTH LIMITS, lb
TEST DATA SOURCE PATTERN MINIMUM MAXIMUM LOAD,lb FAILURE MODE
REF. 4 0/45j-45 3640 s 7125 s 5190 TENSION (PINNED) 2273 s 4450 s 4370 SHEAR (cont'd) 151) s 2970 s 2970 SHEAR
±45 1760 T 2474 T 2445 TENSION 1053 s 1882 s 1277 SHEAR
0/15/-l:i 5700 s 8460 s 5700 BEARING 3910 s 5800 s 4000 SHEAR 2443 s 3624 s 2540 SHEAR 1630 s 2416 s 1960 SHEAR
REF. 5 e = 2
s =1 303 s 367 T - - 310
(PI;\INED) D IJ 2 303 s 593 s 303 0/45/-45 3 303 s 593 s 383 PATTERN 4 303 s 593 s 445
e I 356 T 367 T 360 - = 1 D 2 394 s 772 s '\56
3 394 s 772 s 489 4 394 s 772 s 535
f ~ 4 I 356 T 367 T 367 - 606 s 1148 T 712 D 2
3 606 s 1187 s 820 4 606 s 1187 s 711
e 2 757 s 1148 T 820 - = 5 D 3 757 s 1484 s 835
4 757 s 1484 s 871
REF. 5 0/% 672 s 857 s 702/813 (PINNED)
0/90 504 s 643 s 5os;sso
±45 504 s 887 T 600/644
Z3824815 ( -1) 2620 s 5130 s 4440 SHEAR (1/4 in. DIA PIN) 0/45/-45/0 2620 s 5130 s 3620
2615 s 5120 s 4230
( -503) 3590 HEARING 0/45/-45/90 3640
3800
(-507) 0/45/-45/0 2650 s 5190 s 2960 SHEAR
2%SiC/ A 1,0, 2646 s 5180 s 4500 NOT FAILED WHISKERS 2646 s 5180 s 3620 SHEAR/TENSION
(-509) 0/45/-45/0 2585 s 5060 s 3710 HEARING
1 %SiC/ A 1202 2594 s 5080 s 3910 SHEAR WHISKERS 25HO s 5050 s 3670 SHEAR
(-511) 0/45/-45/0 2620 s 5130 s 4200 BEARING A 1203/ AI N 2620 s 5130 s 4050 BEARING
WHISKERS 2620 s 5130 s 3660 l\OT FA! LED . ' SANDT INDICATE WHE1 HER SHEAR (S) OR TEl\iSION (I) LIMITS ARE CRITICAL.
(cont 'd on next pa~e)
2-24
DARCOM-P 706-316
TABLE 2-1 (cont'd)
CALCULATED STRENGTH LL\1ITS, lb
TEST DATA SOURCE PATTERN MINIMUM MAXIMUM LOAD, lb FAILURE MODE
OTHEK E!'JD (1/2 in. HOLE)
Z3H24815 (-I) 2910 s 'i700 s H40 ;\;UT F:\1 LED (In in. DL\ PIN) Oj4Sj-45jtl 2910 s ')700 s 3620
2900 s 5700 s 4230
(-50:1) 3590 Oj4Sj-45j90 3640
3HOO
(-SO?) 2944 s 5780 s 2960 l'iOT FAILED 2%SiC/ 1\ 1,0, 2940 s 5760 s 4.500 BL\KI!\:G WHISKEKS 2940 s 5760 s 3620 !\lOT F.\! LEU
(-509) Oj45j-4Sj0 2873 s 5630 s 3710
I %SiC/:\ 1,0, 2880 s 5650 s 3lJIO WHISKEKS 2865 s 'i620 s \670
(.;I I) 0/45/-45/0 2910 s 5700 s 4200
2%;\ 1,0,/ AIN 2910 .s ')7()() s -+050 NOT F.\ILED WHISKERS 2910 s 5700 s 3660 SHf.\K
SANDT INDICATE WIIETHE.K SHEAR (S) OR TENSION (T) LI:-Ill·s :\KE CRITIC.\L.
2-25
DARCOM-P 706-316
TABLE 2-2 PREDICTED STRENGTH RANGES FOR BOLTED JOINT SPECIMENS8
PREDICTED LOAD, lb
DRAWING NO. PATTERN A* r, in. I, in. MINIMUM
z 3824831 50 0.75 012 1745 s 33 1/3
z 3824832 50 0.50 0.12 1163 s 50 0.16 1552 s 33 1/3 0.12 1163 s 25 0.16 15.'i2 s
z 38248.'\1 so 0.75 0.12 1745 s 50 0.16 2328 s 33 1/3 012 !745 s 25 0.16 2328 s
z 3824834 so 1.25 0.12 2910 s 51l 0.16 3880 s DljJ 0.12 2910 s 25 () 16 3880 s
WITH 5/16 IN BUSHINGS
50 0.50 0.12 1163 s 50 0.16 1552 s 3.1 1/3 () 12 1163 s 25 016 1552 s
50 0.75 0.12 1745 s 50 0.16 2328 s 33 l/3 0.12 1745 s 25 0.1& 2128 s
50 125 0.12 2910 s so 0.16 3880 s 33 1/3 0.12 2910 s 25 0.16 3880 s
•A INDICATES% FIBERS AT ±45°. BALANCE OF FIBERS AT oo •• ASSLMED BEARING STRESSES: 150,000 PSI FUR 50% AT ±45°
200,000 PSI FOR 33 1/3% AT ±45° 225,000 PSI FOR 25% AT ±4.'i 0
.
MAXIMUM
3420 s
2280 s 3040 s 2280 s 1040 s
3420 s 4560 s 3420 s 4560 s
4580 T 6110 T 45RO T 6110 T
22RO s 3040 s 22KO s 3040 s
3420 s 4560 s 4320 s 4560 s
3880 T s 170 T 3880 T 5170 T
S AND T INDICATE WHETHER SHEAR (S) OR TE!'<SION (T) LL'viiTS ARE CRITICAL.
2-26
BEARING LIMIT, lb**
1375 4500
337.i 4500 4500 6750
.D75 4500 4500 6750
3375 4500 4500 6750
5625 7500 7500
11250
5625 7500 7500
11250
562S 7500 7500
11250
•
DARCOM-P 706-316
-~ -~ -~ -® -® -
h~>ud lirw
~ () ' ) ') I) () ( )
0 0 0 0 c 1)
u 0 0 0 0 0
() 0 0 0 () ()
I) ') 1 ) I) () ') :) () () I) () 0 ()
(II) Sl':trl
/bond line· / rc·srn
0 0 0 J r) r J U 0 r J 'J CJ 0 0"' J iJ r,..
i~~ig&~ijtiE~~~6~6 000000000 000000
, .... •., ,·. ·,·.•,•.•.•, -,· •,· .. ,, .•. ·.· ·.•.w .• ,-.-.·,.·.--:-·- -~-.-··--, ...
0000000000000 bOOUO
() () 0 0 (J 0 0 0 () 0 0 0 1! p () 0 0 0
.·ltTt'jJ!uiJh· !liJ.('hirlt'd ,ioint nniliguralion:-. with nunprDmi .... ing load dirc·l'lion !IJ fit1er ori~·nla!ion.
fiLns
r b l I Olll ine
11 ·•'· ''•'•' · .. -;:•:.: .. -.---··- • •,-,r
0000 )00 0 ooooooooovoooo 0 0 0 c 00 00 0.00 0 0000(!)000 0
0 0
00 0 0
v-W·'-""··• ,, . .., .. .,. ..• ,.,, .•.·
oo 0000000 0 u pooooooo 0 0 0 0 00 0 00 0 0 )0000000
0 0 0000 0 00 0 0 booooooo ·-·-·-·-.. ·-··.·'"·,··-· ·.-.-·-·-··· ·····.·.·· ..... -.·.·-··-·-·--:--.··-:-
(C) Steppt'(l Lap
Unac!'eptab/e bt•cause of possibility of having load bearing surfaet• fjl.J,·rs perpendi<·ular to load.
® - fiber ori('nlation normal to page
4-+- fiber orientation para I I~ I to page
Figure 2-20. Machined Joints
fihe rs
- resrrr
2-27
N ' N 00
bonrl lirw () u u u 0 ~) 0 0 0 0 0 :) 0 0 0 0
o_o n n :) o o o o o t) o r:) o o o
res;~~~~_;,....;;;.....;;1~0c(,:., ~(=_;:Q:\c,_:, =Ot:C":;:c_,:,:C~J~C=J~o~:~' ~:,~'dO~;O~. ~o~· •0~0;it~J fibers .... . , .... ·.·.-§··· . . ..... {··· ... +---~: ''"•··{
(A) Poor--ourlare fibers normal to load
fibers
(B) Good--surface fibers paral!t:-1 to load
Figure 2-21. Single-Lap Joints (no machining)
•
•
0 )> :XI (') 0 3: ' '"0
"'-1 0 0)
w ... 0)
N I
N '0
.. !4---- composite or other material
U J C_J_ J 0 0 0 () IJ () _(_) ........................... fibers
(jr ',_)()_(!
c J J 0 u () ()..._() 0 u
l
(A) Poor--surface fibers normal to load
(B) Good--surface fibers parallel to load
Figure 2-22. Double-Strap Joints (no machining)
0 )> ::a 0 0 ~ ' "g
""" 0 Ol
I w ... Ol
DARCOM-P 706-316
REFERENCES
1. K. F. Hahn and D. F. Fauser "Methods for Determining Stress Distribution in Adherends and Adhesives", Symposium of Adhesives for Structural Applicahon, M. J. Bodnar ed., Picatinny Arsenal, Dover, NJ, 1961.
2. Structural Airframe Application of Advanced Composite Materials General Dynamics Fourth Quarterly Progress Report for Contract AF33 (615-5257, Wright-Patterson Air Force Base, OH, June 1967.
3. G. M. Lehman and A. V. Hawley Investigation of Joints in Advanced Fibrous Composites for Aircraft Structures, AFFDL-69-43, Air Force Flight
2-30
Dynamics Laboratory, Wright-Patterson Air Force Base, OH, June 1969.
4. F. Wilson, Research on Resin-Impregnated, Collimated Boron Filaments and Improved HighModulus, High-Strength Filaments and Compositions, Whittaker Corp., AFML-TR-6 7-20, Wright-Patterson Air Force Base, OH, January 1967.
5. V. H. S~.ffire, Applications of Advanced Fibrous Reinforced Composite .Mate rials, General Electric Co., AFML-TR-66-272, Wright-Patterson Air Force Base, OH, September 1966.
DARCOM-P 706-316
CHAPTER 3
DESIGN DATA REQUIREMENTS Graphs and tables of values of the ultimate strength and stress/ strain behamor of composite joints in tension, compres
sion, shear, and bearing are presented as a function of various fiber orientations and fibers. Graphs of bond strength as a functirm of temperature are presented. Properties of various adhesives also are presented.
3-0 LIST OF SYMBOLS
A = area of joint, in~ E = elastic modulus, psi
EL = elastic modulus of composite with fibers parallel (longitudinal) to direction of applied stress, i.e., ¢ = 0 deg, psi
E1,,. = compressive elastic modulus of composite with fibers parallel (longitudinal) to direction of applied stress, i.e., ¢ = 0 deg, psi
EL, tensile elastic modulus of coihposite with fibers parallel (longitudinal) to direction of applied stress, i.e., ¢ = 0 deg, psi
Er elastic modulus of composite with fibers perpendicular (transverse) to direction of applied stress, i.e., ¢ = 90 deg, psi
ETc compressive elastic modulus of composite with fibers perpendicular (transverse) to direction of applied stress, i.e., ¢ = 90 deg, psi
ET, tensile elastic modulus of composite with fibers perpendicular (transverse) to direction of applied stress, i.e., ¢ = 90 deg, psi
Ex elastic modulus in direction of applied load, psi
FLc compressive strength of composite with fibers parallel (longitudinal) to direction of applied load, i.e., ¢ == 0 deg, psi
FL, tensile strength of composite with fibers parallel (longitudinal) to direction of applied load, i.e.,¢= 0 deg, psi
F. = in-plane shear strength, psi Fr,. = compressive strength of composite
with fibers perpendicular (transverse) to direction of applied load, i.e.,¢ = 90 deg, psi
Fr, = tensile strength of composite with fibers perpendicular (transverse) to direction of applied load, i.e., ¢ = 90 deg, psi
fbru ultimate bearing strength, psi f'u ultimate compressive strength, psi pt" interlaminar shear strength, psi PSI" ultimate interlaminar shear strength,
psi
r shear stress, psi ru ultimate shear strength, psi f~" = ultimate shear strength of adhesive
joint, psi f 1
" ultimate tensile strength, psi G = modulus of rigidity (shear) of adhe
sive, psi
La P= S= t=
W=
/'xy
l
shear modulus with fibers parallel (longitudinal) to direction of applied shear, psi shear modulus in xy-plane, psi length of specimen, in. distance between fulcrum and load, in. length of adhesive joint, in. loads (as indicated in text), lb distance, in. thicknesses-i.e., of ply, adherend, specimen as indicated in text-in. width, in. shear strain, in./in. shear strain in xy plane, in.jin. strain, in.jin.
3-1
DARCOM-P 706-316
JJLT Poisson's ratio with stress applied parallel (longitudinally) to fiber orientation of composite, dimensionless
JJ.rL Poisson's ratio with stress applied perpendicularly (transversely) to fiber orientation of composite, dimensionless
(J pure tensile strength of adhesive, psi T pure shear strength of adhesive, psi ¢ angle between fiber laminate direction
and direction of load, deg
3-1 BASELINE DATA
An essential part of joint design is to characterize the properties of the members to be joined. This means that the ultimate strength and stressstrain behavior should be ascertained in tension, compression, shear, and bearing. Similarly, when a bonded joint is contemplated, the important adhesive properties to characterize are those in shear and tension. This information will characterize adherend stiffness and adhesive strength adequately.
3-2 LAMINATE MECHANICAL PROPERTIES
The laminate properties of interest can be obtained from the results of tension tests, compression tests, in-plane (edgewise) shear tests, interlaminar shear tests, and pin bearing tests.
For a specific glass and boron composite, the elastic moduli in tension and compression are given in Tables 3-1 through 3-3. Table 3-4 reports the shear moduli for the same glass and boron composite obtained from in-plane shear tests. Some interlaminar shear test data can be found in Table 3-5 and pin bearing strengths in Table 3-6. The pin bearing results are for both boron and glass composites with a nominal pin diameter of 0.25 in., an edge-distance boltdiameter ratio ej D = 4.5, and a side-distance bolt-diameter ratio sj D = 3.
For Type AS/3002 graphite composite the tensile and compressive strengths and moduli are presented in Figs. 3-1 through 3-4. In-plane shear stress strain data are given in Fig. 3-5 and interlaminar shear strengths are given in Fig. 3-6.
TABLE 3-1. UNIDIRECTIONAL LAMINATE PROPERTIES 1
S-994 FIBERGLASS BORO"l'
82H-1 031 N!\RMCO SSO'i BIJ:v!A-MI\A
RESIN RESIN Ni\RMCO 5505 RESIN
EXPERI:VIENT LITERATURE* EXPERIMENT LITERATURE*
ELASTIC PROPERTIES Ec, I 06 psi S.HS-'J .. 10 7.65 (I) Er, 106 psi 1.59-2.25 2.24 (1) GLT• 1 o• psi 0.84-1.4.1 0.78 (I) /hr 11248-0.308 0.270 (I) !lrL 0.027-0.075 0.079 (I)
STRENGTH PROPERTIES FL, 1 C!' psi 17 5.3-242.0 2M 0 (I) FL" I 03 psi -- 1730{1) Fr,. 103 psi 7. 96-9.61) 7.5 (.1) Fr,.IO'psi -- 29.0 (I) F., I 0' psi 9.62- n.s8 8.5 (I)
(1) Data from Ref. 4, page 2:W. Ftberglass/828-1031 BDMA-:VfN,\ Lammate. (2) Data from Ref. 5. (3) Data estimated from Rei. 6.
24.8-29.6 30.00 (2) 1.90-2.21 3.00 (2) 0. 73-0.88 1.10(2)
0.163-0.266 0.380 (2) 0.018-0Jl29 0.038 (2)
152-1'!0.7 200.0 (2) 0 - 2'10.0 (2)
(>.80-8 . .1 7 7.0 (3) --- 20.0 (3)
11.04-15.00 12.0 (3)
*Data from literature were used in analysis. These gave better correlation of predicted properties with test results for multidirectional laminates used in specimens.
3-2
LA~II!';.\ Tt: PATTER,'\
ALL0°
ALL 90°
0°(45°(-45°(0°
u-.
~ oo /45°/-45°/0° "' 0 ;.,
§ "' z 0°/45°(-45°/00 2 2 0 45° ;oo ;oo /-45° :Q
oo(45o /-45o ;oo
0°/45°/-45°/0°
0°/45°/-45°/90°
0°/45°/-45°/90°
TABLE 3-2 SUMMARY OF THEORETICAL AND EXPERIMENTAL TENSION PROPERTIES1
ELASTIC COJ'\STA!'\TS STRE~GTH PROPERTIES VOLUl\!E FRACTIO:'IlS
PREDICTED ACTUAL PREDICTED ACTUAL
FIRST LA~!l!';ATE FAILURE ULTIMATE ULTIMATE
THICK!':ESS E" E,, STRESS, STRESS, STRESS, 10. 1 o• psi Jll'"y 108 psi 1-l:cy ksi ksi ksi FILAME~T RESJ:--1 VOIDS
0.030 h50 0.250 158.5 24.80 0.241 158.5 27.20 0266 171.0 25.80 0.164 190.7 27 60 0.167 180.0 29.60 0.163 152.0 0.595 0.381 0.024
AVG26.75 AVG 0.209 AVG 168.5
0.050 2.21 0018 7.15 2.03 0.029 6.80 1.90 0.021 8.37 0.621 0.324 0 055
AVG201 AVG 0.023 AVG 7.44
0.040 16.80 0.722 95.0 16.10 0.714 99.5 17.40 0.745 88.0 0.636 0.332 0.032
17.13 0.688 AVG16.90 AVG0.727 94.0 J()J. 5 AVG 94.2
0.040 14.8 0.704 1000 15.7 0.706 95.0 0.545 0.412 0.043
17.13 0.688 AVG15.3 AVG0.705 94.0 101.5 AVG'17.5
0.080 15.1 0.710 98.2 14.7 0.616 102.5 0.5~7 0.436 0.027
17.13 0.688 AVG14.9 AVG 0.663 94.0 1015 AVG100.4
0.120 17.0 0.687 102.0 16.7 0.720 104.3 0.612 0.342 0.046
17.13 0.688 AVG 16.9 .\VG 0.704 94.0 101.5 AVG 103.2
0 160 17.2 0.777 93.3 17.0 0.700 98.5 0.597 0 .'\30 0.073
17.11 0.688 AVG 17.1 AVG 0.738 94.0 101.5 AVG 95.9
0.040 11.5 0.331 60.0 11.5 0.312 43.8 112 0.329 53.8 0 602 0.342 0.056
11.87 0.336 AVG11.4 AVG0.324 31.1 66.4 .'\VG 52.5
0.120 10.8 0.394 66.0 l) 7 0.200 57.4 0.609 0.346 0.045
11.87 0.336 AVG 10.3 .'\ VG 0.298 31.1 66.4 AVG 61.7
(cont'd on next page)
0 l:o :c (")
0 ~
LAMINATE LA~-.1!NATE THICKNESS PATTERN in
ALL0° 0.060
0.030
"' 0 ALL90° 0.060 "' "' c u § 0.050
"' z ~ "' (3
.... "' oo /45o /-45o ;oo 0.080 "' r),
0°/45°/-45°/90° 0.080
TABLE 3-2 (cont'd)
ELASTIC CO!\STANTS STRENGTH PROPERTIES
PREDICTED ACTUAL PREDICTED ACTUAL
FIRST FAILURE ULTIMATE ULTIMATE
E,, E,, STRESS, STRESS, STRESS, 10' psi !lry 10' psi jlxy ksi ksi ksi
7.70 0.308 7.80 0.248 9.30 0.26J'"
5.85 0.266 175.3 6.56 0.288. 203.3 6.40 0.260 242.0
AVG 7.27 AVG 0.272 AVG 206.8
2.20 0.075 7.48 2.19 0.068 8.00
2.25 0.063 8.17 1.84 0.027 7.96 1.59 0.071 9.60
AVG2.01 AVG0.061 AVG 8.24
4.55 0.591 120.0 4.06 0.575 143.4 5.77 0.577 137.0
5.10 0.453 AVG4.79 AVG0.581 19.6 115.3 AVG 133.4
3.66 62.6 3.80 55.4 3.75 57 3
3.92 0.308 AVG3.74 6.6 65.3 AVG 58 4
VOLUME FRACTIONS
FILAMENT RESIN VOIDS
0.548 0.411 0.005
0.548 0.411 0 005
0.594 0.401 0.005
0 ,. ::IJ n 0 s: . "D ..... 0 m w ... m
TABLE 3-:3. SUMMARY OF THEORETICAL AND EXPERIMENTAL COMPRESSION PROPERTIES1
ELASTIC CONSTANTS STRE~GTH PROPERTIES
ELASTIC MODULUS POISSON"S RATIO E JJ.:rl· PREDICTED .\CTL\L
CONFIGURATION SPECIMEN PREDICTED ACTUAL FIRST F.\ILCRE l"L Tl~l.\TE CLTI:'-1.\TE Z38248l8 NUMBER 10' psi to• psi PREDICTED ACTC.\L STRESS. ksi STRESS. ksi STRESS. ksi Rnl.\RKS
-1 1 17.1 17.0 0.688 0.638 <J3.2 I.HS 9~ ~
0°/41°/-45'/0' 2 17.1 16.1 0.688 09'i0 9~.2 13U -1=0120in 2 16.4 13.3 0.688 O.i3S " lJ:'.2 lHS 105.6 SECO~D LO.\Dl~G
BORONjNARMCO SS05 3 I~ J 17.4 0.688 0.169 9=i 2 13~.8 !00.9
-501 I 5.1 5.0 0.453 0.130 .17 ~ 80 .. i 86 0 0°/45' /-45'/0' 2 5.1 5.0 0.453 0.095 .F~ 86.5 89.3 I= O.J21lin S-994/NARMCO 5505 3 5.1 4.12 0.453 0.119 3-.~ 80s H9.)
-503 I 19 7 14.3 0.439 0.063 l'iO.O 1-6.0 100 H P.\ TTER~ CO~SISTED OF PATTERN NOTED ~ll'o CIRCl"L.\R. 20"", .\T I= O.IODin 2 19.7 18.8 0.439 0.09J iStl.O 1-6.0 105.0 ±~5' .. \~D Oll""o BORONjNARMCO 5505 LO:\C!Tl 01~.\L-CIRCl·-AND NOTED 3 J 9.7 24.7 0.4J9 0.0)5 l:iO.ll 1-6.0 1-u L.\R \\"R.\PS \\"ERE S-99~
-505 J 5.65 6.5 0.247 0.06o ~6.:::. II 0.- 990 P.\ TTER:\ CO:\SISTED OF PATTERN NOTED 2 s 61 5.0 0.247 0 06) -l6.:) 110.- 99.5 2tl"", CIRCTL.\R. 2ll""o .\ T I= 0.100 ±~o' .. \.\;D 60", S-994/1\ARMCO 5505 3 5.65 4.76 0.247 ll.ll:il ..f6 .. 1 Jill.~ T3 LO.';GITl"Dl~.\L
-507 I 17.1 20.0 0.688 (I 173 96.2 13~.8 l :i~ H 0'/45'/-45'/00 SiC-.\ I.\; WHISKERS 1 = 0.120in. 2 17 I l 5.14 0.6HH 0 tOO 9<>.:: l.q H t.1.i - .\ODED TO L.\:1.11:\.\ TE .\T BORON/NARMCO 550.1 ~,.,OF RES!:\ \\"EIGHT +NOTED WHISKERS .3 17.1 17.24 ll.68H ll.l6ll 96.2 1.>~. H tr-
-S09 I' J7.1 11.10 0.688 0.111 9:).2 (qH tr .. >• 0'/4S 0 /-4S'/0' SiC-.\1:-.: WHISKERS 1 = 0 120in. 2 17 l 14.10 0.6HH 0.13H 9-) 2 l.1~.H 161.(> .\DOEll TO L.\~11:\.-\TE .\ T IIORON/NARMCO S.\0.1 l'"o OF RESIN WEICHT +NOTED WHISKERS .1 17.1 12.20 0 llHH 0.171 9:,.2 ~-~.8 (.=)9_9
-511 I 17.1 16.2 0.088 o. !_;~ 9_=i_2 U~.S nu O' /45' j-4S' jO' .-\1,0,--.-\1:\ WHISKER~ 1 ~ 0.120 in 2 17.1 IM.H li.6HS 0 IHH l):'.2 1.1~.H l ~-l.2 .-\DIJE!l TO L\:\II.';.YrF. AT BORON/l':ARMCO SSOS 2'';, OF RESI:\ \\"EIGHT + NOTED WHISK 1-:RS .1 17.1 13.2 0.6HH 0.1.39 l)_~.2 lq H l(l).J
•N,etammg: rmg fatlrd
0 J> ::D 0 0 :!:: . , ..... i . w ... CD
TABLE 3-4 SUMMARY OF THEORETICAL AND EXPERIMENTAL IN-PLANE SHEAR PROPERTIES 1
ELASTIC CONSTANTS STRENGTH PROPERTIES
SHEAR :V!ODULUS, G PREDtCTED ACTUAL VOLUME FRACTIONS
THICKNESS, PREDtCTED, ACTUAL, FIRST FAILURE liLTI\>lATE FIRST FAILURE ULTIMATE :>,IATERIALS PATTERN in. 10' psi 10' psi STRESS, ksi STRESS, ksi STRESS, ksi STRESS, ksi FILAMENTS RES!!'\ voms
S-994/N.\R~!CO 5505 .\LL oo 0.100 1.43 8.3 13.58 - 0.91 - - 7.1 11.0
0.84 6.0 9.62 0.627 0.365 0.008
AVE 1.06 AVE 7.1 AVE1140
0°/±45°/0° !.52 2.03 10.7 46.6 34 . .'i 1.79 - 42.1 !.50 34.9
AVE 1.77 AVE 372
oo; ±41° /90° 1.52 2.08 10.7 46.6 )4 8 2.24 - 34.2 1.93 33.7
AVE 2.08 AVE 34.2
BORO:'I.'/N.\R~!CO 5505 .\LL 0° 0.100 0.88 NONE 15.00 0.77 6.9 12.50
- 0.73 - - 7.3 11.04 0.589 0.367 0.044
AVE0.79 AVE i I AVE 12.84
0°/ ±45°/0° 4.45 6.22 20.4 52.0 46.0 6.17 41.} 6.05 41.0
AVE6.15 AVE 42.7
0°j±45°j90° 4.45 5 48 20.4 52.0 31.7 6.23 33.8 5 80 33.7
:\ VE 5.84 AVE331
0 l> :2:1 n 0 3:
CO:\FIGCRA-TIO~
-1
-501
-503
-505
-507
- 'i09
-511
TABLE 3-5. INTERLAMINAR SHEAR TEST RESULTS1
SPECIY!EN Y!ATERIALS GAGE, WIDTH, AREA, FAILURE LOAD, 1!\TERLAMINAR SHEAR
A~D FIBER PATTERN m. in. A, in~ P,lb STRENGTH= 3Pj(4A), psi
BOROr-:/NARMCO SS05 0.1203 0.4248 0.0511 715 10,480 0°/45°/-45°/0° 0.1194 0.4156 0.0496 657 9,940
0.1158 0.4323 0.0501 683 10,200
S-994 GLASS/NARMCO 5505 01364 0 3625 0.0494 790 12,000 0° /4S 0 /-45°/0° 0.1283 03720 0.0477 795 12,500
' 0.1384 0.3690 0.0511 845 12,400
BOROr-:jr-:ARMCO 5505 0.1179 0.3988 0.0470 488 7,780 0°/45°/-45°/90° 0.1280 0.3950 0.0477 518 8, ISO
0.1217 0.3906 0.0475 570 9,000
S-994 GLASS/NARY!CO 5505 0.1370 0.4007 0.0549 501 6,850 0°/45°/-45°/90° 0.1373 0.3648 0.0501 526 7,875
0.1278 0.3900 0.0498 519 7,805
BORON/NAR~1CO 5SOS 0.1152 0.3422 0.0394 705 13,425 SiC-AI20 3 WHISKERS AT 2o/o 0.1201 0.3620 0.0435 712 12,250 OF RESIN WEIGHT 0.1189 0.3651 0.0434 721 12,450 0°/45°/-45°/0°
BORON/NARY! CO SSOS 0.1181 0.3509 0.0414 680 12,300 SiC-AI 20, WHISKERS AT 1 o/o 0.1173 0.3548 0,0416 669 12,040 OF RESIN WEIGHT 0.1162 0.3532 0.0410 671 12.250 0°j4S 0 /-4S 0 /0°
BORON/NARMCO 5505 0.1190 0.3689 0.0439 629 10,720 AlN-AI.O, WHISKERS AT 2% 0.1242 0.3681 0.0457 661 10,830 OF RESIN WEIGHT 0.1233 0.3678 0.0453 640 10,600 00/45°/-45°/0°
0 )> :D 0 0 s:: , ..... 0 m w .... m
TABLE 3-6. PIN-BEARING TEST RESULTS 1
AVERAGE STRESS AT FAILURE
BEARING HOLE PIN BEARING ULTIMATE STRESS AT
SPECIMEN MATERIALS GAGE, DIA, DIA, AREA, LOAD, BEAR I!\/ G. SHEAR-OUT, 4%0FFSET, AND FIBER PATTERNS in. in. in. in~ lb psi ·psi psi
BORON/NARMCO 5505 0.1200 0.258 0.257 O.Q308 4,440 144,000 14.800 121,000 0°/45°/-45°/0°
0.1200 0.260 0 257 O.Q308 3,620 117,500 12,100 72,700 0.1198 0.2569 0.257 O.Q308 4,230 137,500 14,100 136,500
0.1295 0.255 7 0.255 0.0330 3,562 108,000 11,000 98,000 0.1286 0.2554 0.255 0.0328 3,723 113,500 11,500 82,400 0.1286 0.2565 0.256 0.0329 3,590 109,000 11,100 97,200
0.1260 0.2552 0.2540 0.0320 3.585 112,000 11,400 ~
0.1293 0.2565 0.2560 0.0331 3,665 110,800 11,300 ~
0.1254 0.2563 0.2550 0.0320 3,570 111,500 11,300 ~
S-994 GLASS/NARMCO 5505 0.1368 0.255 0.2550 0.0349 I ,800 53,100 5,300 48,000 0°/45°/-45°/0° 0.1260 0.255 0.2550 0.0321 1,950 60.700 6,200 29000
0.1320 0.254 0 2530 0.0334 I ,990 59,600 6,040 41,400
BORON/N ARMCO 5505 0.1200 0.260 0.25 70 O.Q308 3,590 116,500 12,000 95,500 00/45°/-45°(90° 0.1200 0.260 0.25 70 0.0308 3,640 118,100 12,100 76,000
0.1200 0.264 0.2630 0.0316 3,800 120,000 12,700 49,500
0.1150 0.2555 0.2550 0.0293 4,145 141,300 14,400 119,400 0 1150 0 2546 0.2540 0.0292 4,255 145,700 14,800 113,000 0.1190 0.2550 0.2540 0.0302 4,055 .134,300 13,600 ~
0.1182 0.2552 0.2540 0.0300 3,718 123,900 12,600 ~
0.1171 0.2550 0.2540 0.0298 4,115 138,000 14,000 --0.1192 0.2551 0.2540 0.0302 3,780 125,000 12,700 -
S-994 GLASS/NARMCO 5505 0 1250 0.255 0.2550 0.0319 1,965 61,600 6.300 25,200 0°/45°/-45°/90° 0.1390 0.255 0.2550 0.0354 2,210 62,500 6,350 46,200
0.1360 0.256 0.2550 0.0347 2,185 63,000 6,430 57,000
RORON/NARMCO 5505 0.1215 0.2569 0.2570 0.0313 2,960 96,600 9,770 56,600 SiC-AI,O, WHISKERS AT 2% OF RESIN WEIGHT 0.1212 0.2569 0.2570 0.0312 4,500 144,200 14,800 135,800 oo /45°/-45° ;oo
0.1212 0.2580 0.2580 0.0313 3,620 115,900 11,900 81,000
BORON(NARMCO 5505 0.1185 0.2569 0.25 70 O.G305 3,710 121,800 12,500 90,600 SiC-AI,O, WHISKERS AT 0.1189 0.2559 0.2560 0.0304 3,910 128,600 13,200 39,700 1% OF RESIN WEIGHT 0°(45°/-45°/0° 0 1182 0.2559 0.2560 0.0302 3,670 121,300 12,400 118,600
RORON/NARMCO 5505 0.1200 0.2610 0.2610 0.0313 4,200 134,100 14,000 79,500 AIN-AI,O, WHISKERS AT 0.1200 0.2610 0.2570 O.Q308 4,050 131,500 13,500 98,800 2% OF RESIN WEIGHT 0.1200 0.2630 0.2630 0.0315 3,660 - ~ 85,000 0°/45°/-45°/0°
0.1163 0.2570 0.2560 0.0298 3,860 129,500 13,300
l. 124,000
0.1163 0.2564 0.2560 0.0298 3,775 126,600 13,000 117,200 0.1170 0.2560 0.2550 0.0298 4,040 135,500 13,800 115,400
FAILURE MODE
COMBINED SHEAR AND BEARING SHEAR-OUT COMBINED SHEAR AND TENSION
SHEAR-OUT
SHEAR-OUT
BEARING
BEARING
REARING
BEARING
BEARIJ>;G
COMB!:\ ED SHEAR AND BEARING BEARIKG (AT y, DIAMETER LOADIKG PIN) CO:\·!BINED SHEAR AND TENSION
BEARING COMBIK ED SHEAR AND BEARING COMBINED SHEAR A;-.;D BEARING
REARING BEARING SHEAR (AT v, DIAMETER LOADI;-.;G PI:-o:)
SHEAR-OUT
TEST DATE
7j67
12/68
12j68
10/67
7 j67
12/68
12/68
10j67
12/67
12j67
'!6'
12/68
. ., ..... i
I
w -A
en
120
100
80
40
J I I
20
~//~ 0
0
1
I v I I I v
,, /~
,, /
4,000
DARCOM-P 708-318
-65°F I
l (O) 6T
SPECIMEN T-UL-7 IITR I COUPON LONGITUDINAL TENSION
i I
EL = 18.6 Msi I t i
I .. Er = 4.17 Msi _j c I I
I J i I
i ,.. .. ..... I ,.. SPECIMEN EC-UT-7 ..,P'
SANDWICH PANEL ,-"' ~.,. TRANSVERSE COMPRESSION
~,
!-''
8,000 12,000 16,000 20,000 Strain f, JLin./in.
Figure 3-1. Unidirectional Graphite/Epoxy (Type AS/3002-Batch) Longitudinal Tension and Transverse Compression Stress-Strain Curves at -65°F (Ref. 2)
3-9
DARCOM-P 706-316
200 .------r------r--- SPEC I MEN TLBB-UL I
LONGITUDINAL TENSION~ (BEAM) ~
180~----~~------~-------+'-------+----~~J' __ • ____ ~------
/
,7, ROOM TEMPERATURE
;' ;"
, .. , .. [O] 6T ,,""
160~----~---+- -+-----+~----4--~~~-4-----~
/( ,,,,.-"
,' ,1 /~SPECIMEN CLBB-ULI
,, I ----t---1----+--7 LONGITUDINAL -----1
/~ /1 COMPRESSION (BEAM)
/ I , ;' ~·
---+r---1[ l
1401---
Er = 3.1 Msi c
EL = 19.6 Msi l
EL = 16.0 Msi c
Er = 3.7 Msi l
120 ~----
/
t •' T-UL- 10
] I ~LONGITUDINAL TENSION .n / (COUPON) ~ lQQ~----~----+--~--~L__ I
ifJ I l/l,,l p I / .'/////// ~/lli/J/1:
ao~------~----~--~- -
/,// 1111111 ~ Ill ~ 1111111 I. 6 l' N .
60 1-------l~f----/;_...,.l~/-/l~-rr +:~I::: t j I I I I
40 .. • t--- SPEC I MEN CLBB-UT I ___ _
/;
" / TRANSVERSE COMPRESS ION :r~ v SPEC I MEN TLBB-UT 1 (BEAM) . -···" 1
' ~RANSVERSE TENS I ON li ............ --·····r· (BEAM) ...... .............. T-UT-10
20 ~-~--1----- 1 -- ~........ TRANSVERSE TENSION
' J? ~~-- (COrN) I I 0 ~~--~ ~ - -l- - -- - - l- -1 -
0 2,000 4,000 6,000 8,000 10,000 12,000 14,000
Strain ~. 1-1in./in.
Figure 3-2. Unidirectional Graphite/Epoxy (Type AS/3002-Batch) Longitudinal and Transverse Tension and Compression Stress-Strain Curves at Room Temperature2
3-10
"' ~
DARCOM-P 706-316
140 t-----+---+-------;---1 SPEC I.Jl-13 I I COUPON l LONGITUDINAL TENSION
~8 -+--l--l-+----+--+----t--t-----1f------t---J
(0]6T 120~--~ ~--+,~--+--~---~--~-----r---r--~-~
EL :::: 18.8 Msi
I OO t----lr----+-~-.......,/r----t----t---T EL~ :::: 14.8 Msi Er = 0.44 Msi
t
Er = 1.18 Msi
80
I c
~ J
l I !
I I I
"' I SPECIMEN CCLB-UL-10
~ SANDWICH BENDING BEAM "' 11) .... ci)
60 1---+--+------ LONGITUDINAL COMPRESS I ON -+--~----~-~-------1
ll I
Ill . 40~--~,~.--+--4------+---4--~----4----~--4---r-~,
j/ SPEC I MEN EC-UT-11 I r----!J.-1:··'~: ---t---t------t---t---r---+-- SANDWICH PANEL
• TRANSVERSE EDGEWISE COMPRESSION
20 J' .. -1 --
I __.......--......-spECIMEN T-UT-13 O ~~ •••••••••"I TRANSVERSE TENS I ON
0 4,000 8,000 12,000 Strain E, J.Lin.lin.
COUPON
16,000 20,000
Figure 3-3. Unidirectional Graphite/Epoxy (Type AS/3002-Batch) Longitudinal and Transverse Tension and Compression Stress-Strain Curves at 350°F (Ref. 2)
3-11
DARCOM-P 706-316
8 I I I I I IITRI COUPON FIBERITE PREPREG
7 TRANSVERSE TENSION [90]6T
6
5
l (ACTUAL) = 0.00767 IN/PLY (RT) /
350oF t (ACTUAL) = 0,00817 IN/PLY (3soo F) ·'
.. ' . . '
~/ • . . ;->
·;;; ..:.:
<Ji "' ., .!:::
4 IJl Ill
"' c Ill
,' ' . .. . I . .
RT . . • j . . ,.
r7 . . .. . . . ~
3 I • . , . . . . .
I~
4 ) I IIIII
I I
.... -
I • I . . . -·· I I I I I
•• -
/ . . ,~··
TEMP RT 350° F .,. .. - -
2.
I ,. .. FT, ksi 4.51 5.56 •• [ .• • -v.· ET, Msi 1.35 0.964 .• [
~ ••• 0.0266 0.0300 -
~· li-TL
I I I I I I 0 0 I ,000 2,000 3,000 4,000 5,000 6,000
Strain t, ~-tin./in.
Figure 3-4. Graphite/Epoxy Typical Transverse Unidirectional Tension Stress-Strain Properties (Type AS/3002 Continuous-Treated Fiber)2
3-12
DARCOM-P 706-318
40 -~
ll' RT
v /
'f'
/350° F t (ACTUAL) = 0.00588/PLY /i.,
~ ·~ p
35
30
25
·:;; ...><: ,.; <rJ Q.) 20 !:
CFl .... "' Q.)
...c: CFl
15
~r;'
_J~/ RT 350°F
Gxy = 2. 43 2.29 Msi
g~
I ~~
\
I/! \
'--" /: v W'
p~ '' ~\
I' RAIL \
7 SHEAR \
10
5
0 rt 0 0.004 0.008 0.012 0.016 0.020 0.024
Shear Strain -y xy• in.lin.
Figure 3-5. Graphite/Epoxy-In-Plane Shear Stress-Strain Properties-Crossply I 0/±45/90is (Type A/3002 Batch-Untreated Fiber) 2
3-13
DARCOM-P 706-316
.3-3 MECHANICAL PROPERTIES OF ADHESIVES
ture stress in a JOlnt. With regard to Young's modulus for an adhesive there needs to be re
solved the difference between the tensile modu
lus of an adhesive in free bulk, free film, and constrained film Uoint) form. Kutsha and Hofer3
assumed that the tensile modulus obtained from
The important mechanical properties to identify for an adhesive are Young's tensile modulus, shear modulus, precision elastic limit. and frac-
'<;) .... _r;
~ c:: ::: iii .... "" v
...::: (/)
.... "" c:: .E ~ 2: c:: -
32 I I I
30 - - O [O] 13T
28 r---· 0 [0/!45J ZS
0 [0/±45] 25
26 ·-r--r -¢' [0/'!'45/90] 25
24 . • [90/±45] 25
22 •[90/+45]
- 25
~ [±45] 35
20
18
16
14
12
10
--._, ~ ~ ....
~
~ I
~
v "-... .~g: Lo -+,-:-"' ~ - ":._· . ...,. ~o,, / ... i.4' ' ~ "·:· ~ ' j ! _,., """'-......,
8 ~/ -<)- ...... ~. ~L
~t-.. 1"---. ~~4. . -~-- -·
1-'& i I • ~ . - . :: .. :1::. 6
4
2
0 -100
_.,.. .. -.-r .... -J::J"'"
0
~·-+·- ~ ... '!lb. - • - • ~ I ._ .. -. ... ..., ·--4~- I I
~-.,..~~~~ .. r I --...... J ... I
100 200 300
Tl'mpl'ralure, °F
-
l
I I
I I
Figure .3-6. lnterlaminar Shear Strength vs Temperature for Various OrientationsType AS/3002, Batch, Graphite/Epoxy2
3-14
the behavior of adhesives in free film form could be used to characterize their general behavior. Table 3-7 summarizes the mechanical properties of several adhesives determined from tensile tests performed on adhesive films. Rutherford and Hughes4 maintain that the important tensile modulus to determine is the effective tensile modulus £*-the modulus of the adhesive in thin
DARCOM-P 706-316
film form constrained between two adherends. In such a constrained state the adhesive cannot deform according to its own Poisson's ratio but conforms to that of the adherend which is generally lower. Such restriction effectively increases the tensile modulus. Tables 3-8 and 3-9, and Figs. 3-7 through 3-18 show the results of their work on several adhesives. In the case of Epon
TABLE .3-7 SUMMARY OF MECHANICAL PROPERTIES OF ADHESIVE FILMS3
Tensile Maximum Deflection Chemical Type Strength, Strain, Modulus, Rate,
Adhesive Manufacturer psi % I 0' psi in.jmin
FM 1000 Polyamide Epoxy 3400 >300 1.60 0.05 American Cyanamid, Bloomingdale Division
Metlbond 400 Nylon Epoxy 7310 200 2.92 2.0* Whittaker Corp. Narmco Materials Div.
AF 131 Modified Epoxy 5300 1.15 4.82 0.05 3 .M Co.
FM47 Vinyl Phenolic 8300 1.50 6.21 0.5* American Cyanamid, Bloomingdale Division
*No strain rate efTect on modulus.
TABLE 3-8. AVERAGE SHEAR MICROSTRAIN PROPERTIES 4
,---EC-2214 ADX-41.2
-65°F 74°F 200°F -6]Cf 74°F
Virgin Moclulus, psi 301,300 2HO,fl00 L\7,900 26 7,000 lll9,000 Modulus After Stress, psi 296,300 216,300 12'i,OOO 201,(,00 140,SOO Prercision Elastic Limit, psi 134 II S <51 433 II 0 Microyield Stress, psi 1250 390 <57 17:\4 290 Fracture Stress, psi 12,904 7600 3996 41.'i0 7400 Fracture Strain 221.8 X 10 _, 206.5 x to-• 344.79 X 10 _, 2H.64 X 10 3 '!441lX I0- 3
--
TABLE .3-9. AVERAGE TENSILE MICROSTRAIN PROPERTIES'
Virgin Modulus, psi
Modulus After Stress, psi Precision Elastic Limit, psi Microyield Stress, psi Fracture Stress, psi Fracture Strain
•0.003 in. bond line .. 0.012 in. bond line
EC-2214
-670f 14° F
I ,621,300 I, 120,000
I ,402,200 1.11:1.000 - \7 50 - )360
12,.'i.'i0 11,140 1263 X JO-> 22.HO X 10 '
.----ADX-41 2
200°F -07°F 74°F
410,900 963,3(Xl HOO,HOO* 707,800••
39H,Il00 95),7()() 707,H00**
102 j l.'i3 4060 90.5X I0- 3
J210 2790 .121 () 'iHIO 15. H26 9260 20.4X 10' 17.~4 x to-•
·-
:\)()Of
29,500 2\700 <3H <38 .'\ 1.\0 S2S.O X to-•
.100°F
3.'12,400•
261,400• 7H llH 6300 82.11 X 10 _,
3-15
y> ........ o-
"' ::;
"' ::l ;:; -o
0 ::; ~ ·;;; c: ..,
E-..,
·= '-' '-'
'"'"' '"'"' ~
1.0
.8
lo ()
.6
.4
.2
0 -100 0 100 200
Temperature, °F
Figure 3-7. Tensile Tests, Epon 828/V40, Stainless Steel Adherends as a Function of Temperature4
c )> :II n 0 3: . ., ..... 0 CJ) . w ... CJ)
"' "' c "' b
"' .. u ~
700~--------~----------~----------~----------~----------~--------~
~ 500
425L---------~~--------~--------~L----------J----------~--------~ 10 20 30 40 50
Bond Thickness, mils
Figure .3-8. Tensile Tests, Epon 828/V40, Stainless Steel Adherends as a Function of Bond Thickness~
60
c J:lo ::u (') 0 3:
~ 0 ' - )> 00 :;g
(")
12 0 ~ ' "tJ
-..1 0 ~
c:., ... 10 ~
on .....:
ii 0) ...
8 tfl .., ... 3 '-'
"' ~ ~
6
4 0 5 10 15 20 25 30 35 40
Bond Thickness, mils
Figure 3-9. Tensile Tests, Epon 828/V40, Stainless Steel Adherends4
DARCOM-P 706-316
192 ............... 0
~ 160
oo~B 128
·;;; ..:.: .n
..2 ;:::
"tl 0 96 :e ... "' <l)
...<: rJJ
64
32
0 -SO
0 0
0 50 100
0
ISO 200
0 \
Temperature, °F
Figure 3-10. Shear Tests, Epon 828/V40, Stainless Steel Adherends4
828/V 40 epoxy adhesive the effective tensile modulus in a stainless steel joint is nearly twice the bulk tensile modulus. Generation of this type of effective mechanical data is essential to reliable joint design data input. Table 3-10 presents data on some additional adhesives.
The tensile property data are obtained by the tensile testing of films or cast coupons of adhesive. The effective tensile property data are yielded by circular butt tensile bonded joint specimens. The shear modulus G is obtained from napkin or torsion ring tests which provide the stress-strain behavior of the adhesive in pure shear. The shear properties of several adhesives
are presented in Tables 3-8 and 3-10 and Figs. 3-10, 3-15, and 3-17. Hughes concludes the following regarding the tensile modulus of the adhesives tested:
1. E* increases as bond line thickness decreases.
2. E* generally decreases with rising temperature.
3. Permanent adhesive strain lowers E*. 4. Increasing the strain rate for viscoelastic
adhesives raises £*. 5. Tensile and compressive moduli are the
same.
3-19
DARCOM-P 706-316
2.0
co ·;;; ~ ,; ::J 1.5 ::J co........._
-o 0 OS ~
..9: ·;;; I::
"' E-< 1.0 oo ..,
" . .;: u ~ oo .....
\ '"" 0.5 0
\
0 -100 0 100 200
Temperature, °F
Figure 3-11. Tensile Tests, EC2214, Stainless Steel Adherends as a Function of Temperature•
Hughes concludes the following regarding the shear modulus G of the adhesive tested:
1. G decreases with rising temperature. 2. Permanent adhesive strain lowers G. 3. Increasing the strain rate increases G. 4. G is independent of adhesive thickness be
tween 4 and 40 mils. It is clear therefore that the conditions under
which shear and tensile modulus are obtained for a given adhesive adherend system can alter their values and must be taken into consideration.
.3-4 DESIGN DATA GENERATION
Although there are much published data on the mechanical properties of composites and
3-20
adhesives, it will always be necessary to conduct tests on specific composite fiber orientations and on adhesives under the special environmental conditions in which a design is to provide service. Published graphical or tabulated data representations are useful primarily as a starting point for the designer but the data represented and the manner of generation may not be directly applicable to a given design. Testing for materials acceptance is also a requirement. The data obtained for a given property are a function of the test specimen configuration and the test method employed. The paragraphs that follow discuss some test methods and the type of data they yield.
2.0
·;:;; :::;: 1.5
"' -= ;;:s -c 0
:::;:
0.5
0 -100 0 100 200
Temprraturr, °F
Figure 3-12. Tensile Tests, EC2214, Aluminum Adherends4
(.).> I
N N
1.6
--. ·~ 1. 2 ::g 00 E ::s
-o 0
::g ~ .·;;; o.a c
Q.J
E-< Q.J
>
'-' Q.J
::::: ~
0.4
0 5 10 15 20 25 30 35
Bond Thickness, in. X I03
Figure 3-13. Tensile Tests, EC2214, Stainless Steel Adherends as a Function of Bond Thickness4
0 > :a n 0 s: ' "tt
.,.j 0 0)
w .... 0)
40
DARCOM-P 706-316
0
5000.
4000
<FJ c.. ...: 3000 E
...J
.=: ;;; ~ w c 2000 0
.1£:. u ..,
0::
1000
0
-100 0 100 200 Tt•mperaturt', °F
Figure 3-14. Tensile Tests, EC2214, Stainless Steel Adherends4
3-4.1 COMPOSITE MECHANICAL PROPERTY TESTS
3-4.1.1 Tension Properties
The properties of laminates m tension are usually determined either from tension coupons or sandwich bending beams. The tension coupons are either the dog bone type used in ASTM D638 Type 1, or a tab-ended, straightsided specimen or a modified bow tie (longnecked) specimen. For military applications a modified ASTM D638 Tensile Properties of Plastics is to be employed (Ref. 5) for woven fabric (bidirectional) laminates. For nonwoven (directional) laminates ASTM D-3039 Tensile Properties of Oriented Fiber Composites is the method called for
with modifications (Ref. 5). The specimen employed is commonly referred to as the IITRI (Illinois Institute of Technology Research Institute) coupon.
Another means of obtaining tension property data employs the sandwich bending beam (Fig. 3-19). The sandwich bending beam method is a more expensive method because of the nature of the specimen but the higher strengths obtained with the sandwich beam indicate that the localized stress concentrations inherent in the IITRI coupon serve to yield lower strength data. Figs. 3-1 through 3-3 present tension stressstrain data for Type AS/3002 from both IITRI coupon and sandwich bending beam tests.
3-23
-100 0 100 .2()()
Temperature, °F
Figure .3-15. Shear Tests, EC2214, Aluminum Adherends4
2.0~--------------~------~~------,-------~--------r-------,-----,
1.5
~ 1.0 ·;;;
c::: 111
E-< 111 ... c::; ~ ~ 0.5
-100
-co----o ----0 ~
0
o __ o ____ _
-o-
0 100 200
TPmpcrature, °F
Figure 3-16. Tensile Tests, Metlbond 329, Aluminum Adherends4
0 > ::a n 0 !: ' "11
..... i w .... G)
120,000
·:;; .....
"' 80,000 ::I -a
-o 0
::s .... <U
"' -= r.n
40,000
0
0 0
--- 0 ~0 ---..::0~---i
-100 0 100 Temperature, °F
Figure 3-17. Shear Tests, Epon 9601, Aluminum Adherends'
200
0 l> ;, 0 0 ~
CJ)
0..
E ;.3
·= "' __<.g .... c .s "' ·;:::: OJ ...
0...
DARCOM-P 706-316
4000
3000
2000
1000
0 0
-100 0 100
Temperature, °F
200
Figure 3-18. Tensile Tests, Metlbond 329, Aluminum Adherends~
TABLE 3-10. ELASTIC PROPERTIES OF ADHESIVES 1
MATERIAL F, psi
t\F-110 (MOD-EP) 123,<PH REI>UX K-6 (MOD-PH) .100,00() FM-47 (VINYL-PH) 125,000 MB-40!1 (NY-EP) 1.'\'). 000 FM-1000 (NY-EP) 1!10,000 EPON 422.) (EP-PH) 395,000 EP0:'\1 VIII (EP-P.-\) S0!\,000
MOD-EP = 1\.IOIJIFIED EPOXY MOD-PH = MODIFIED PHENOLIC
PH = Pll ENOLIC NY= NYLON EP = EPOXY Pi\ = PASTE
G, psi J1. T, psi u, psi SOURCE
- - -- 'J2'>H 3~1 CO~IP.\NY
1!14,000 0 . .160 !1200 !1300 FPL-011 117,000 0 .. "\!\~ .1720 4350 FPL-011 49,100 0.410 5550 !1000 FPL-011 64.100 0.40!1 7910 69'>0 FPL-011
I (J(), 000 0.294 5'\20 2560 FPL-011 I HO,OOO 0.412 6050 - FPL-011
FPL = FOREST PRODUCTS LAB 1·: = :-..tOIJULUS OF ELASTICITY G = l\.lODULUS OF RI(;IDITY JJ. = POISS()I\'S RATIO T = PURE SHEAR STRENCTH cr = PLIRETENSILESTRE;\/(;TH
3-27
DARCOM-P 706-316
E = tensile stress/tensile strain = J/ E, psi
p .. t:f'==/?=;E=w==;:!.~P'&=A~.. p
t~
pu P/ ( Wt), psi where
pu ultimate tensile strength, psi
P = failure load, lb
(1) Tension Test:
COR E
I "' (2) Compression Test:
tz
~
t P/2
J=:j_ P/2 ~·
p
J. t I
W = coupon width, in. E = elastic modulus, psi f = tensile stress, psi f = tensile strain, in./in.
(A) Tension Coupons
Jtu = Pl. ----:(;;--------..)~ , ps1
2!1 w (; + i + i
ru PJ.
J~ ( ) , psi
1 lt !2 2!2~ C+T+T
where pu ultimate tensile strength, psi ru ultimate compressive strength, psi
tb !2 laminate thickness, in.
C= core thickness, m. W= width, in.
P= failure load, lb J. = length between fulcrum and load, in.
(B) Sandwich Bending Beams
(cont 'don next page)
Figure 3-19. Reduction of Equations for Different Types of Specimens Tested
3-28
p
p
p
r I
(!) (!) I I e G)
I C!) (!)
L I I
L (!) (i)
I I (!) (!)
I I
p
CORE
DARCOM-P 706-316
G = shear stress/shear strain = .f"/ "Y = psi .f"u = Pj(Wt), psi
where G = shear modulus, psi
feu = ultimate shear strength, psi P = failure load, lb
W = width, in. t laminate, thickness
j" shear stress, psi "Y shear strain, in./in.
(C) Edgewise Compression Specimens
G = shear stress/shear strain = ri"Y j•u = Pj(Lt), psi
where G= shear modulus, psi
.f•u = ultimate shear strength, psi f"= shear stress, psi "Y = shear strain, in.jin. I' = failure load, lb L = length, in. t = laminate thickness, in.
(D) Rail Shear Specimens
p•u = 3P/ ( 4 Wt), psi where
ps1
p•u = interlaminar shear strength, psi P = failure load, lb
W = width, in. l = laminate thickness, in.
(E) Interlaminar Shear Specimens
(com'd on next page)
Figure 3-19. (cont'd)
3-29
DARCOM-P 706-316
(1) Single-Lap Joints:
j {lex: ult
where !'lex ult ultimate flexural strength, psi
P = failure load, lb S = distance between fulcrums, in.
W = width, in. t = laminate thickness, in.
(F) Flexure Specimens
ADHESIVE
NOTE: For compression sandwich specimens, there were two face sheets (one per face joint) and, hence, the equation must be divided by 2, i.e.,
jgu Pj(2WLa),psi
(2) Symmetric Double Scarf joint:
Pj (2 W La), psi
NOTE: For compression sandwich specimens, there were two face sheets (one joint per face sheet) and, hence, the equation must be divided by 2, i.e.,
j!,u P/(4 WLa), psi
(cont 'd on next page)
Figure 3-19. (cont'd)
3-30
DARCOM-P 706-316
where j;_u ultimate shear strength of adhesive joint, psi
P = failure load, lb W = width, in. La == length of adhesive joint, in.
(G) Bonded joints (Adhesive Shear Strength)
FASTENER
(1) Bearing Strength:
jbru == Pj(Dt), psi
(2) Net Tension Strength:
p
2Dt ( ~ -0.5) , ps1
(3) Shear-Out Strength:
p j•u == ---r---~-
2Dt ( ;) -0.5) , psi
NOTE: Compression mechanical joints all failed in bearing; hence, bearing strength is defined as
rru PI ( DtN), psi
(cont'd on next page)
Figure .3-19. (cont'd)
3-31
DARCOM-P 706-316
where f/Jru flu =::
j'u P== I
D e ==
s =
ultimate bearing strength, psi ultimate tensile strength, psi shear-out strength, psi load for appropriate failure mode, lb laminate thickness, in. bolt hole diameter, in. distance from edge of bolted joint to center of bolt hole, in. distance fron: side of bolted joint to center of bolt hole, in .
. N == number of fasteners, dimensionless
(H) MechanicalJoint
Figure .3-19. (cont'd)
.3-4.1.2 Compression Properties
Compression data should be obtained b~ the sandwich bending beam method (Ref. 5J for nonwoven laminates tested in tht> direction of the fibers (0-deg orientation). Woven fabric laminates tested in the 0-deg or 90-deg direction, and nonwoven laminates tested in the 90-deg direction should be tested in accordance with ASTM 0695 Compressive Propertie5 of Rigid Plastics with modifications as outlined in Ref. 5.
Another method uses a tubular specimen, as described in Ref. 1, to generate the compression data on glass and boron composites presented in Table 3-3.
3-4.1..3 Intralaminar Shear Properties (In-Plane Shear)
These properties are obtained by the use of the "rail shear test" (Ref. 5) for any angle for which shear characteristics are desired. Ultimate shear stress f'u is determined as follows:
(3-1)
where P == load on the rails, lb
3-32
t = length of specimen, in. t = thickness of specimen, in.
The shear modulus is obtained as follows:
shear stress p . G = = - ps1 (3 2)
shear strain 'Y ' -
.3-4.1.4 Interlaminar Shear Properties
These properties have been determined according to the method prescribed in ASTM 02733 lnterlamlnar Shear Strength of Structural Reinforced Plastics at Elevated Temperatures, Method A. However, for other reinforcements such as boron, graphite, and Kevlar, ASTM 02344 Apparent Hrm:;,ontal Shear Strength of Remforced Plastic by the Short Beam .i!ethod is recommended. It is suggested that the fiberglass reinforced composites be tested this way as well.
3-4.1.5 Flexural Properties of Laminates
These properties should be determined according to ASTM 0790 flexural Properties of Plastics. Like interlaminar shear, a simple beam specimen is used but the calculations differ as shown in Fig. 3-19.
DARCOM-P 706-316
3-4.2 SUMMARY 3-4.1.6 Bearing Strength of Laminates
Bearing strength determinations should be conducted according to ASTM 0953 Bearing Strength of Plastics.
3-4.1.7 Test Specimen Schematics and Data Reduction Equations
Fig. 3-19 depicts the specimens and equations to be used to obtain the materials property data needed for design.
Variations on some of the tests discussed here have been used and the data they yield may be more representative of the material than the tests recommended. What is important is that the test method used be known and that the limitations and inherent imperfections in the test and resultant data be recognized. No single data source should be regarded as infallible or absolute. Tables 3-11 and 3-12 summarize the tests used and data yielded for both laminates and adhesives.
TABLE 3-11 LAMINATE PROPERTY DETERMINATION
Test Method
Sandwich Beam
ASTM 03039 (IITRI Coupon)
ASTM 0638 (Long Bow Tie Coupon)
Tubular Compression
Rail Shear
ASTM 02733
ASTM 02344 (Short Beam)
ASTM 0953 (Pin Bearing)
Data Yielded
Tensile and Compressive Properties f'",Jc", EL, Er
Tensile Properties (nonwoven) F'", EL, Er
Tensile Properties (woven) /'", EL, Er Compression Properties j"",E
Intralaminar (in-plane) Shear JIJUt (;
lnterlaminar Shear (fiberglass only) f'lJJ
Interlaminar Shear (fiberglass, boron, graphite, Kevlar)
l'" Bearing Strength j•'
TABLE3-12 ADHESIVE PROPERTY DETERMINATION
Test Method
Napkin Torsion Ring Test
Thick Adherend Lap Shear
Circular Butt Joint
Data Yielded
Shear Properties !'", G Shear Properties !'", G Tensile Properties /'", E
3-33
DARCOM-P 706-316
REFERENCES
1. G. M. Lehman and A. V. Hawley, Investigation of Joints In Advanced Fibrous Composites for Aircraft Structures Vol 7, Technical Discusrion and Summary, Technical Report AFFDL-TR-69-43, Vol. 1, Wright-Patterson Air Force Base, OH, June 1969.
2. L. M. Lackman, et al., Advanced Composites Data for Aircraft Structural Design, Vol. IV, ~[aterial and Basic Allowable Development Graphite/Epoxy, Tech Report AFML-TR-70-58, Vol. IV, Wright-Patterson Air Force Base, OH, September 1972.
3. D. Kutscha and K. E. Hafer, Feasibility of Joining Advance Composite Flight Vehzcle Structures, Tech Report AFML-TR-68-391, USAF Contract No. AF33 (615)-3962, Wright-Patterson Air Force Base, OH, January 1969.
3-34
4. E. J. Hughes and J. L. Rutherford, Study of Micromechamcal Properties of Adhesive Bonded Joints, Pica tinny Arsenal Tech Report 3 7 44, Performed under contract DAAA 21-6 7 -C-0500 by Aerospace Research Center, General Precision Systems, Inc., Little Falls, NJ, August 1968.
5. Guidelines for the Generation and Use of Data In Mihtary Handbook 77A Part 7, PLASTEC Report R47, Picatinny Arsenal, Dover, NJ, January 1977.
6. Advanced Composite Wing Structures, Boron/ Epoxy Design Data, Vol. II, Analytical Data, Tech Report AC-SM-ST -8085, F33615-68-C-1301, Grumman Aerospace Corporation, Wright-Patterson Air Force Base, OH, November 1969.
DARCOM-P 706-316
CHAPTER4 BASIC BONDED AND BOLTED LAP JOINT CONFIGURATIONS
AND DESIGN VARIATIONS The design and strength of basic type joints -singLe Lap, double lap, scarf, stepped, boLted, and combinations- are
presented as functions of adhesives, .fiber onenlation, andjibers. Comparisons of Joint strengths and u•ei.ehts are made. Methods of reducing stress concentration in joints are presented. The response of various bonds to fatigue are presented.
4-0 List of Symbols
D = bolt hole diameter, in. e = distance from edge of bolted joint
to center of bolt hole, in. E = joint efficiency, dimensionless
elastic modulus of adhesive, psi EL = elastic modulus of composite with
fibers parallel (longitudinal) to direction of applied stress, psi
Er elastic modulus of composite with fibers perpendicular (transverse) to direction of applied stress, psi
£ 1 elastic modulus of composite, psi £ 2 elastic modulus of joined material,
ps1 fnr bearing strength, psi
pu·u ultimate bearing strength, psi n shear strength of joint, psi
f:na:r maximum shear strength of adhesive, assuming plastic shear stress distribution, psi
]"" ultimate shear strength, psi f'" ultimate tensile strength, psi
Fs average stress, psi G shear modulus, psi
La length of adhesive joint, in. N = cycles to failure P = applied load, lb R = radius, in.
.r - distance from side of bolted joint to center of bolt hole, in.
ti thickness of materials, i = I, 2, ... , in. We maximum width of plastic zone of
joint, in. a ... = tensile stress in region A, psi
a 8 tensile stress in region B, psi r shear stress in adhesive, psi
shear stress at bond line, psi
4-1 GENERAL
Designing composite JOints generally can follow the same priorities established for mechanical and bonded joints using isotropic materials. The relatively low shear strength of epoxy resin composites, however, make this property limiting in many composite joint designs - mechanical and bonded.
4-2 BONDED JOINTS
When designing a bonded joint, composite or otherwise, the bonded area should be as large as possible and as much of the bond area as possible should be working, i.e., transferring loads. This implies good strain compatibility between joint members and good stress distribution in the adhesive. The joint design should be stressed in the maximum strength mode which, for adhesives, is shear or tensile. Peel and cleavage stresses should be minimized. Good bonded joint design requires that the adherend materials, joint configuration, and load directions work toward the aforementioned aims. This serves to distribute stress and avoid stress concentrations, particularly at edges, which create peel and cleavage forces .
In selecting adhesives it is important to consider the rate at which the load is to be applied to the joint. When loads are applied suddenly, as impulse or impact loads are, the adhesive must be elastic enough to take shock loading without
4-1
DARCOM-P 706-316
failing. Often there can be conflict in this area. Thermosetting adhesives, usually rigid and of high tensile and shear strength under static and dynamic loads, are often impact sensitive and exhibit poor impact strength. Elastomeric adhesives generally possess poor shear and tensile strength but have good peel and cleavage strength and can withstand shock loads. Sustained dead loading of bonded joints can cause creep of some adhesives, and this behavior must be ascertained to avoid creep weakening of and dimensional changes in the structure.
Bonded joint strength depends greatly on the properties of the adhesive but maximum strength is achieved when the relative stiffness of the adherends is the same. This situation provides a symmetric stress distribution and the best joint efficiency. For highly loaded joints, however, the ultimate shear strength of the adhesive alone (determined from torsional ring tests) is not a good criterion for adhesive selection. Where strain incompatibility exists in the adherends, a more ductile adhesive can improve joint strength:
To achieve strain compatibility in a joint comprised of two adherends of the same material, the thicknesses of both adherends must be equaL When bonding different adherend materials it is important to match adherend stiffness by matching the products of the elastic modulus E and thickness t, i.e., Et*, of the joined materials.
When large loads are required and length L to thickness t (L/t) ratios approach 25, the interlaminar shear strength of the laminate is limiting. For improved bonded joint capability, interlaminar shear strength improvements in the laminate must go hand in hand with improved adhesive shear strength.
4-2.1 BONDED SINGLE-LAP JOINTS
This type joint is the simplest of bonded joint configurations. In joints of this type the offset loading characteristics produce the highest stress
*In subsequent discussions we will refer to "Et ratio" for convenience. The correct interpretation is "a ratio of Et's ", i.e., E,t,j(E2t2 ).
4-2
concentration factor (SCF) and carry the least load at the center of the joint. Stiffness mismatch in the adherends will serve to further aggravate an already poor stress distribution situation in the joint. Fig. 4-1 shows this effect for several combinations of boron, glass, and aluminum joints using Shell 951 adhesive (shear stress in adhesive T = 6000 psi). When the results fall along the T = 6000-psi line, the adhesive is equalizing the shear stress over the entire area. As lap length increases, stress concentrations are set up at the lap ends causing failure at lower loads. Fig. 4-2 illustrates how increased Et ratio improves the average adhesive stress in the joint. (Pattern configurations are shown in Table 4-1.) The improvement is even more pronounced for larger L/ t ratios. In addition, as lap length increases, peel stresses are introduced due to bending. The ability of the adhesive to equalize stresses over the joint area also becomes less as adherend materials are mixed (E1t1 ,.,e. E2t2 ).
When adherends are not of the same material, unfavorable thermal stresses can also be set up between adherends during adhesive cure which adversely affect joint strength. Table 4-2 summarizes some single-lap test results, using Shell 951 adhesive on boron/aluminum and fiberglass/ aluminum joints.
4-2.2 BONDED DOUBLE-LAP JOINTS The double-lap joint configuration eliminates
much of the bending and peel stresses present in the single-lap joint. Fig. 4-3 and Table 4-3 show the results of boronjaluminum and glass/ aluminum joints. It can be seen that for the boron/aluminum joints a higher average bond stress was realized probably due to the lower bending and peel forces. The same was not true for the glass/aluminum double-lap specimens.
The effect of stiffness matching in double-lap joints is clearly illustrated in Figs. 4-4 and 4-5. It is easily observed that as the Et ratio (smaller Et divided by larger Et) approaches unity, there was a general increase in joint strength. Table 4-4 summarizes test results for some composite/ metal double-lap joints of varying Et ratios.
4
3
·;;; ...:.: ~ be 0::
b lfJ 2
= 0 -.
0 0
4
3 . iii ...:.:
.rJ ~ 0:: ., ...
cil 2
0::
0
0
0
I
tl T I I I
T
PATTERN B
':'/;~: / ,_ I
5!1 I - I f:J I
PATTERN A
.r ' 0 ..
BORON/BORON
BORON I a 0.04 IN.
SHELL 951 ADHESIVE
0.5 1.0 2.0
Lap Length, in. ..
-·
~ T
g ! PATTERN A
~ ... ... I -I
"" ...
f:J· " ~ .r ""~~~ 0 ... ~ .. T .,."" !>-~ / '?
... ~ ; I I I " I I
I ; ;
J. 1 ,,
FIBER GLASS I FIBER GLASS
GLASS t 2 0.04 IN, SHELL 951 ADHESIVE
0.5 1.0 2.0
Lap Length, in.
4
3
'iii ...:.:
.rJ ~ 0:: ., !:: lfJ 2 c 0
0 0
4
3
"' ...:.:
~ 1:11)
0::
b lfJ
2 0:: '5 -.
0 0
DARCOM·P 706-316
:1 &I T' I I I I ,
•' PATTERN B . :
if 0 "(I
I
0.5
4 8 IDt II I
~ iJi
J T "( I
I I
I I
0.5
' I
BORON I ALUMINUM
BORON t ~ 0.04 IN.
ALUMINUM L = 0.063 IN.
SHELL 951 ADHESIVE
1.0 2.0
Lap Length, in .
T I
~~~~ ...... ~ '?"'~ ......... : ...... -PATTERN A
FIBER GLASS I ALUMINUM
GLASS = 0.04 IN.
ALUMINUM t = 0.0631N.
SHELL 951 ADHESIVE
1,0 2.0
Lap Length, in.
Figure 4-1. Single-Lap Bonded Joint Strength2
4-3
DARCOM-P 706-316
6 r-----------------------------------------------------------,
5
LAP LENGTH
L----------~~------------;O~.S~I:N~.----------4
·u; ..:.<
<ti if>
"' .... cFl "' > ·u;
1: 3 "C
""' "' !:>()
"' .... "' >
""' 2
2.0 IN.
0 ~----------~----------._----------~----------~--------~ 0 0.2 0.4 0.6 0.8 1.0
Ratio Et, dimensionk,;s
Figure 4-2. Effect of 1~·1 Ratio on Single-Lap Adhesive Joint Strength1
Comparing the test data of Table 4-5 with the predicted adhesive stress at failures for corresponding l.jt in Fig. 4-6 indicates that the test results generally fall below the predicted failing stress for an Et ratio of 1.00 for boron/aluminum and 0.31 for glass/aluminum. Theoreticaly, for joint lengths of less than 2/3 in. (Lj I ;:::; 8 ), the ultimate average adhesive shear stress of 6650 psi
4-4
(Shell 951) should be achieved with either glass or boron composite. The double-lap test results do not achieve the maximum design ultimate of 6650 psi but are within the range of experimentally determined results obtained on the torsion ring shear tests for Shell 951 (4640- 7220 psi). Several variables can account for this including bond line thicknesses which were only about 1/3
DARCOM-P 706-316
TABLE 4-1 JOINT SPECIMEN LAMINATE PATTERNS
LAMiNATE PATTERN
0°;±45°/0°
+45o ;oo /0°/-45°
±JSo
±45o /±45° ;oo (16 LA YERS)/±45° ji45o
±45o /±45° ;oo (24 LAYERS)j14.'i 0 /±45°
±45°/0°(8 LAYERS)/±45°
±45°/0°(12 LAYERS)j±45°
those for which the torsion ring data were obtained as well as differences in curing rates and pressures, surface condition, voids in bond line, etc. This necessitates the inclusion of a safety factor in the design to allow for such variables.
The curves developed in Fig. 4-7 are based on the assumption that the adhesive is an elastic/ perfectly plastic material that becomes plastic at the joint extremities under high load. In this plastic zone the stress reaches the ultimate shear strength of the adhesive. The Width We of this zone is assumed constant for a given joint type and adhesive, and for any one-lap distance. Fig. 4-8 depicts the elastic and assumed stress distributions in the adhesive. The ultimate shear stress is determinable either from very short lap joints or, as in this case, by torsion shear tests. We is determined by testing a joint of long Lj t ratio and determining the elastic stress distribution in the adhesive. Fig. 4-8 shows the elastic stress distribution which gives the same average stress F8
as in the test joint. ru was determined to be 6650 psi. Since the stress cannot exceed j'u, the elastic stress distribution is truncated at this value and the area of the elastic distribution above ru, areas A and C, are added below as areas B and D. We then is the maximum width of the plastic zone. For identical adherends, the plastic zone
PERCENT OF PATTERN PLIES AT
DESIGNATION ±45°
A 50
B 50
c 0
D 33-1/3
£ 25
F 33-1/3
G 25
would be the same at both extremities. For different adherends andjor thicknesses, only one end achieves maximum. Other joints can then be analysed to determine the shape of the elastic distribution and, with ru and we known, the average stress F. can be determined. This is the manner in which Fig. 4-8 was prepared.
For boron and glass composites whose outer layers are oriented at 0 deg, adhesive failure is anticipated and the curves should be valid. At a 45-deg outer layer fiber orientation, there are some data to indicate failure in the laminate resin at lower stress levels.
4-2.3 BONDED SCARF JOINTS
In theory, a bonded scarf joint approaches the ideals of strain compatibility in the adherends and uniform stress distribution in the adhesive. In practice, however, one may find it difficult to realize the full potential of a scarf joint due to the peculiar processing and fabrication problems encountered in machining steep scarf angles, handling the frangible scarf ends, and applying uniform pressure to the angled bond line to control bond line thickness.
Fig 4-9 shows a finite element stress analysis for an idealized scarf joint, and Fig. 4-10 shows the adherend normalized stress distributions in a
4-5
p A T
TABLE 4-2 SUMMARY OF SINGLE-LAP BONDED JOINT TEST RESULTS
USING SHELL 951 ADHESIVE2
AVERAGE AVERAGE ADHEREND JOINT DESCRIPTION, T AVERAGE ADHESIVE TENSILE STRESS AT FAILURE
MATERIALS, AND E NOMINAL GAGES R LAP LENGTH,
in. N@ in.
SINGLE LAP A 0.50 BORON (0.040)/ A 1.00t
BORON (0 040) A l.OOtt A 2.00 B 0.50 B 100 B 2.00
SINGLE LAP A 0.50 FIBERGLASS (0.040)/ A 1.00
FIBERGLASS (0.040) A 2.00 B 0.50 B 1.00 B 2.00
SINGLE LAP A 0.50 BORON (0.040)/ A 1.00t
7075-T6 (0.063) A 100ft A 2.00 B 0.50 B 1.00 B 2.00
SINGLE LAP A 0.50 FIBERGLASS (0 040)/ A 1.00
707 5-T6 (0 063) A 2.00 B 0.50 B 1.00 B 2.00
SINGLE LAP A 1.00 BORON (0.040)/
7075-T6 (0 063) EXTERNAL SCARF
SINGLE LAP A 1.00 FIBERGLASS (0.040)/
7075-T6 (0.063) EXTERNAL SCARF
•AVERAGE OF FIVE TESTS •• (1) ADHESIVE
(2) IJI\TERLAMINAR SHEAR
ADHESIVE THICKNESS,
in.
0.0029 0.0010 0.0034 0.0024 0.0019 0.0020 0.0019
0.0017 0.0014 0.0020 0.0010 0.0010 0.0021
0.0019 0.0019 0.0030 0.0020 0.0013 0.0022 0.0019
0.0016 0.0030 0.0026 0.0034 0.0030 0.0022
0.0054
0.0035
(3) TENSION IN BASIC LAMINATE SECTION
ULTIMATE SHEAR STRESS STATIC LOAD, AT FAILURE•,
lb psi
2905 5722 3908 3875 3385 3336 3959 1957 2362 4678 3898 3868 4209 2155
2648 5087 3538 3424 3650 1794 2496 5056 2719 2665 3708 1839
2416 4738 2514 2480 3040 3016 3670 1832 2009 3570 3645 3630 3780 1928
2006 3958 2318 2229 2463 1226 2121 4100 2553 2589 3094 1560
2781 2677
2383 2306
tTESTED IN jAJI\UARY 1968 t+TESTED IN DECEMBER 1968 ®SEE TABLE 4-1
COMPOSITE, ALUMINUM, FAILURE psi poi MODEs••
72,500 NOT (1) 97,700 APPLICABLE (2) 84,000 (2) 99,000 (2) 59,000 (2) 97,500 (2)
105,000 (3)
66,300 NOT (I) 88,500 APPLICABLE (I) 91,300 (1) 62,400 (I), (2) 68,000 (1), (2) 92,700 (1), (2)
60,400 39,300 (1 ), (2) 62,700 39,900 (I), (2) 75,800 48,300 (1), (2) 91,600 58,300 (1), (2) 50,200 31,900 (2) 91,200 58,000 (2) 94,500 60,000 (2), (3)
50,100 31,800 (I) 58,000 36,800 (I) 61,500 39,100 (I) 53,000 33,700 (I) 64,800 41,000 (I) 77,300 49,000 (1)
69,500 44,200
59,500 37,900
c l> ::D (') 0 3:
10
9
8
7
·;;; .... 6 ..c
bo c: ~ 5
cii c: 4 ·o ......
3
2
0 0
o AOHEREND FAILURE ~ --·-·f !I PATTERN A
7 • - .... .l'..q
' ... ::&ty T ... ,1\16' I
.... I 6 ... I .... ... I ... ~ 5 1 0.0631N.~ I T PATTERN B
I "(ii - - -y- -- - - - - - - - -? I ...:.::
_1~1 ..l.
-5 ~ J.
4 ~ ! 0.0631N.l c:
O.OBIN. "' .... BORON COMPOSITE rfJ 3
OOOIN _};TIT ALUMINUM c: 0 ......
2 GLASS COMPOSITE
SHELL 951 ADHESIVE ALUMINUM
SHELL 951 ADHESIVE
0 0.5 1.0 2.0 0 0.5 1.0 2.0
Lap Lo·n~th, in. Lap L•·ngth, in.
(A) Boron (B) Fillt'r~lass
Figure 4-3. Double-Lap Bonded Joint Strength2
0 > :a n 0 ~
-+>-' 00
TABLE 4-3 SUMMARY OF DOUBLE-LAP BONDED JOINT TEST RESULTS
(1-IN. SPECIMEN WIDTH) USING SHELL 951 ADHESIVE2
p A T
JOINT DESCRIPTION, T AVERAGE MATERIALS, AND E NOMINAL ADHESIVE
GAGES R LAP LENGTH, THICKNESS, in. N@ in. tn.
DOUBLE LAP A 0 so 0.0011 BORON (0.080)/ A I.OOt 0.0012
7075-T6 (0.126) A I.OOtt 0.0020 A 2.00 0.0010 B 0.50 0.0015 B 1.00t 0.0012 B l.OOtt 0.0026 B 2.00 00014
DOUBLE LAP A 0.50 0.0023 FIBERGLASS (0.080)/ A 1.00 0.0033
7075-T6 (0.126) A 2.00 0.0034 B 0.50
l 0.0019
:I 1.00 0.0023 2.00 0.0025
• AVERAGE OF FIVE TESTS • • (I) ADHESIVE
(2) INTERLAMINAR SHEAR (3) TENSION IN BASIC LAMINATE SECTION (4) TENSION IN BASIC ALUMINUM SECTION
AVERAGE ADHESIVE
ULTIMATE SHEAR STRESS STATIC LOAD, AT FAILURE,•
lb psi
5769 5625 9104 4406 9746 4482 9378 2)40 5982 5793 8327 4160 9502 4751 6180 1540
5038 4986 5713 2743 5297 1347 4059 4008 4530 2257 4561 1110
tTESTED IN FEBRUARY 1968 tt TESTED IN DECEMBER 1968 @SEE TABLE 4-1
AVERAGEADHEREND TENSILE STRESSES
AT FAILURE
COMPOSITE, ALUMINUM, psi psi
72,000 45,700 113,600 72,200 122,000 77,300 117,000 74,500 74,700 47,500
104,000 66,000 118,700 75,400
77,200 49,000
63,000 40,000 71,500 45,400 66,200 42,000 50,900 32,200 56,600 36,000 57,100 36,200
FAILURE MODES""
(I), (2) (2), (3)
(3) ( 1 ), (4) (1 ), (2)
(3) (3)
(2), (3)
( 1) (I), (2) (1 ), (2)
(2) (2) (2) I
0 l> ::D () 0 ~
0
-g ...... 0 0)
w -' 0)
·:;; ..><:
"' "' ;: ci)
"' ;... ·;;;
"' .r:: -o < "' t:>O o'd .... "' ;>
<
DARCOM-P 706-316
LAYER 2 1 4 3 LENGTHWISE 1 2 3 4
PATTERN A PATTERN B
sr-------------------------------------------------------------,
4
3
2
0
X GLASS- PATTERN A +BORON- PATTERN A 0 GLASS-PATTERN B 6, BORON- PATTERN B
JOINED TO ALUMINUM AND TITANIUM ADHERENDS
0~--------~----------~----------~----------~--------~ 0 0.2 0.4 0.6 0.8
Ratio Et, dimensionless
Figure 4-4. Effect of Et Ratio on Double-Lap Adhesive Joint Strength for Glass, Boron/ Aluminum, Titanium Adherends 1
1.0
4-9
OARCOM-P 706-316
4-10
5 r-------------------------------------------------------------~
"' "' "' ;:; ci)
Q.)
;. ·;;; "-'
4
;:5 3 ...-:
2
'V 17·7 PH STAINLESS STEEL/COMPOSITE
0 TITANIUM 6 Al4V/COMPOSITE
0 ALUMINUM 7075·T6/COMPOSITE
ONE INCH OVERLAP
PATTERN A
/ /
FIBER GLASS
/ /
/ /
/
/
BORON
0~----------~----------_.------------~----------~------------J 0 0.2 0,4 0.6 0.8
Ratio Et, dimensionless
Figure 4-5. Effect of Et Ratio on Double-Lap Adhesive Joint Strength for Stainless Steel, Titanium, Aluminum/Composite Adherends2
l.O
~ I
TABLE 4-4 SUMMARY OF DOUBLE-LAP BONDED JOINT TEST RESULTS FOR
VARIOUS Et RATIOS USING SHELL 9.51 ADHESIVE2
p
A T AVERAGE T AVERAGE ADHESIVE
JOINT MATERIALS, E NOMINAL ADHESIVE ULTIMATE SHEAR STRESS AND GAGES, R LAP LENGTH, THICKNESS, STATIC LOAD, AT FAILURE,'
psi in. N@ in.
BORO:'\ (0.080)/ A 1.00 S STI.Ll (0.040)
BORON (0.080)/ A 1.00 S STL (0.050)
BORON (0.080)/ :\ 1.00 S STL (0.064)
BORON (0.080)/ A 1.00 Ti (0.064)
BORON (0.080)( ,\ 1.00 Ti (0 090) I
BOROI\i (0.080)/ i\ 1.00 Ti (0.!26)
FIBERGLASS (0.080)( A 1.00 S STL (0 040)
FIBERGLASS (0.080)( :\ 1.00 S STL (0 010)
FIBERGLASS (11.080)/ A 1.00 S STL (0.064 J
FIBEIU;t.ASS (0.080)/ ,\ 1.00 Ti (ll064)
FlllERC:t.ASS (llll80)/ A 1.00 Ti (0.090)
FIBERLCASS (0.080)/ A I 00 Ti (0126)
'AVER.'\C;E OF FIVE TESTS "(I) AllHESIVt:
(2) 11\:TERI.AI\.IINAR SHE.'\R (>) TENSION IN IHSIC L:\1\.!IN:\Tt: SECTION (4) TENSION I~ BASIC METAL SECTIO~ LIS STI. ~ STAINLESS STEEL
lR.
0.0016
0.0020
0.0045
0.0042 00036
0.0032 0.0030
0.0040
0.0012
0.0016
0 0010
0.0042
0.0027
0.0045
lb
8065 4040
8650 412)
7290 364)
6600+ 31-18 9S30tt .j746
8760+t n~o
8812t .j)7S
8100 4088
657' J21F
6460 .1230
621'> 3 I I :i
)9)7 29:i2
o8t'> 28.18
SuO~ 2691
tTESTED 1:'\ !\1.\Y 19M ttTESTEil IN J.\Nl'.·\RY 1%9 (!!SEE TABLE ~-I
(;.'\(;ES NOTED FOR l\lt:TALS INCLUDE THOSE FOR BOTH !\1£T.\L .\DHERESDS.
AVERAGE ADHEREND TENSILE STRESSES
AT FAILURE
COMPOSITE, METAL, psi psi
101.000 202.000
108.000 !73.000
91.200 114.000
B2.S0ll !03.0Ull 119.000 149.000
110.000 98.000 1\\9.'>00 9~.300
lOUllO (>4.300
B2.JOO I 1>4.)00
BO.~SO 129.\10(1
-~.Otlll q-_:lllO
-4.500 9.1.00\)
- 2.<.00 o4.:il1ll
~0.200 H.:iOl\
FAILURE MODES"
( 1 ). ,21. ( 1)
\I). \2). (31
( 1). (3 I
( l l. \:'l. 1JI
i:'l r11
,JI
(ll. (21
(I\. \2\
(I\ \~ \
(II
\I I. (2\
\I\. (2\
0 J> :a n 0 3: . ., ..... 0 ~
w .... ~
~ I ......
N
TABLE 4-5 SUMMARY OF DOUBLE-LAP BONDED JOINT TEST RESULTS
(1-IN. SPECIMEN WIDTH) 2
p A T
JOINT DESCRIPTION, T AVERAGE MATERIALS, AND E NOMINAL ADHESIVE
GAGES, R LAP LENGTH, THICKNESS, In. N@ 1n. I fl.
DOL'BLE LAP A 0.50 0.0011 BORON (0.080)/ A LOOt 0.0012
7075-T6 (0.126) A l.OO+t 0.0020 A 2.00 0.0010 B 0.50 0.0015 B lOOt 0.0012 B I OOtt 0.0026 B 2.00 0.0014
DOuBLE LAP A 0.50 00023 FIBERGLASS (0.080)/ A 100 0.0033
7075-T6 (0.!26) A 2.00 0.0034 B 0.50 0.00!9 B 1.00 0.0023 B 2.00 0.0025
• AVERAGE OF FIVE TESTS **(!) ADHESIVE
(2) ll\:TERLAMINAR SHEAR (3) TENSIO!\ IN BASIC LA:-.1!:-.iAT£ SECTION (4) TENSION IN BASIC ALUMINUM SECTION
AVERAGE ADHESIVE
ULTIMATE SHEAR STRESS STATIC LOAD, AT FAILURE.,
lb psi
5769 5625 9104 4406 9746 4482 9378 2340 5982 5793 8327 4160 9502 47 51 6180 1540
5038 4986 5713 2743 5297 1347 4059 4008 4530 2257 456! 1110
+TESTED IN FEBRUARY 1968 tt TESTED IN DECEMBER 1968 @SEE TABLE 4-1
AVERAGE ADHEREND TENSILE STRESSES
AT FAILURE
COMPOSITE, ALUMINUM, psi psi
72,000 45,700 113,600 72,200 122,000 77,300 117,000 74,500 7 4, 700 47,500
104,000 66,000 JI8,700 75,400 77,200 49,000
63,000 40,000 71.500 45,400 66,200 42,000 50,900 32,200 56,600 36,000 57,100 36,200
FAILURE MODES ..
(1), (2) (2), (3)
(3) ( 1 ), ( 4) (l ), (2)
(3) (3)
(2), (3)
(l) (I), (2) ( 1 ), (2)
(2) (2) (2)
0 Jlo :ll 0 0 s: ' '1l
..... 0 01 w ... 01
DARCOM-P 706-316
ADHESIVE SHELL 961
E = 99,500 G = 35,500
;< . k."
"' "' "' !::: lfl
Q,)
> ·v; "' ..c:
-o ...: "' lOll
~ Q,)
> ...:
7,000
6,000
5,000
4,000
3,000
2,000
1,000
~J{_j = 0.31 (S-994 GLASS/ALUMINUM) Eztz
1.00 (BORON/ALUMINUM)
SHEET FAILURE
100 KSI
0~--~----~--~--~~--~----~--~----~--~~--~ 0 6 10 15 20 25 30 35 40 45 50
Lit!
Figure 4-6. Predicted Joint Strength for Double-Lap BondedJoints Using Shell95l Adhesive8
4-13
DARCOM-P 706-316
ADHESIVE
2P
l
I
\ \
'
I I
,
"-
p
, p
L4/,2- w
L/2 ---.+-+-- L/2
Figure 4-7. Double-Lap Joint Showing Plastic Shear Distribution in Adhesive1
boron/boron composite scarf joint. Figs. 4-11 and 4-12, respectively, show shear and tensile stress distributions in the adhesive of a scarf joint. For the variable Et ratios of a boron composite/aluminum scarfjoint due to different fiber orientations present in the bond line, the adhesive stress distribution would look like that shown in Fig. 4-13.
Actual test results on boron/boron and boron/aluminum scarf joints using Shell 951 adhesive were found not to be as strong as expected and achieved just over 75% of the adhesive shear stress design value. As stated earlier it is suspected (1) that, because of the nonflat configuration, it is difficult to maintain bond line pressure during cure; and (2) that
4-14
bond quality, especially on. small overlaps with steep scarf angles, is not optimum. In addition, bond line thicknesses ( ,0.014 in.) tended to be larger by several-fold over flat lap type joints. This is probably due to the inability to control bond line pressure. Figs. 4-14 and 4-15, respectively, plot the joint strength of composite/ aluminum and composite/ composite joints versus overlap length and scarf angle.
An alternative to the scarf joint, which avoids some of the processing difficulties of scarf joint manufacture, is the external scarf or beveled single-lap joint. This joint retains the strain compatibility of the adherends but introduces the offset loading characteristics of the single-lap joint. However, improved processing ease and
DARCOM-P 708-318
4176 ~,---_.c:=:=::::;:::=:~:=:J= .060 BORON .J I I
}+-.470~ .063 AL
TEST JOINT
WIDTH • .769
F, • 5,775 PSI
1~~~----------------------------------------------------~
I I I I I I I
,....... __ We ...J
I
Figure 4-8. Stress Distribution in Actual Test Joint Based on Computer Analysis1
4-15
t I 0.00525 0.15~-0.250--..1
1-'-t-----------0.5516----------l~l
APPLIED LOADS r IDEALIZEO - STRIP
-~ -- ~ --- --- .£:" -----~ADHESIVE
Figure 4-9. Idealized Scarf Joint3
-~-, -REACTIONS\
0 l> :a n 0 3:
I 0
PROPERTIES USED
LAMINATE EL • 16.12X106
ET • 300,000
G • 109,000
ADHESIVE
oa
E .. 139,000 G • 49,000
1.0
LOAD----I
BORON/EPOXY
0.90
1.00
~ORON/EPOXY
1.15
1.10
1.00
0.90
0.80
Figure 4-10. Adherend Normalized Stress Distributions m a Scarf Joint3
REACTIONS
I 0.5516
c l> :::D n 0 3: ' .,
..... 0 ~ w .... ~
~ I ...... 00
~r-----------------------------------------~.-----------------------------------------~
7000 AVE STRESS (ENTIRE JOINT)
AVE STRESS (LOWER HALF) CALCULATED AVE STRESS
AVE STRESS (UPPER HALF)
0~--------~--------~~--------~~------~~--------~----------~--------~--------~ ·1.0 ·0.75 -0.50 ·0.25 ft. 0.25 0.50 0.75 1.0
Fraction of Distance from Center to End Joints
Figure 4-11. Shear Stress Distribution in the Adhesive of a Scarf Joint3
0 ~ :xr n 0 s:: . ., .... 0 g)
w .. g)
~.---------------------------------------~~~-----------------------------------------,
AVE STRESS
oL---------~----------~----------~--------~L---------~----------~----------~--------~ -1.0 -0.75 -0.50 -0.25 0.25 0.50 0.75 1.0
Fraction of Distance from Center to End Joints
Figure 4-12. Tensile Stress Distribution in the Adhesive of a Scarf Joint3
~ I
_.,.. I
N 0
8000 t
7000
1000
7075-TSAL
E • 10.3 X 106
G • 3.9 X 106
/'\. t t t t /
AVE SHEAR STRESS
AVE TENSILE STRESS
BORON
E o• • 30.38 X 106
E 45
• • 1.344 X 106
E t • 300,000
G • 109,000
oL-----------------------------------------------------------------------------------~ Distance Along Adhesive
Figure 4-13. Stress Distribution m the Adhesive of an Aluminum/Boron Scarf Joint3
0 J> :lJ (')
0 s: . ., ~
0 0)
w ... 0)
DARCOM-P 706-316
9 .------------------------------------r------------------------.
"' .... ..;£ bo
8
7
6
~ 5 rJ)
c ·c; -. "' ;;.
·;;; "' ;:§ 4
-..:: ..... .... .. "' rJ)
3
2
0
I
0.5 1.0
I
A
BORON/ALUMINUM PATTERN A
BORON/ALUMINUM PATTERN 8
GLASS/ALUMINUM PATTERN A
LENGTHWISE
B
FIBER PATTERNS
GLASS/ALUMINUM PATTERN B
GLASS/ALUMINUM PATTERN A
BORON/ALUMINUM PATTERN A
BORON/ALUMINUM PATTERN B
1.5 2.0 Lap Length, in.
9°05'
Scarf Angle
Figure 4-14. Scarf Adhesive Joint Strength - Composite-to-Aluminum 1
4-21
DARCOM-P 706-316
4-22
9r-------------------------------------~r-----------~
·;;; .... ..::: be s:::
8
7
6
b 5 <Fl
= 0 ,_, ., -~ "' .,
::; 4 <:
3
2
0.5 1.0
I
LENGTHWISE
A 8
FIBER PATTERN
GLASS/GLASS PATTERN B
GLASS/GLASS PATTERN A
BORON/BOFION PATTE FIN B
BORON/BORON PATTERN A
1.5
Lap Length, in.
9°os·
Scarf Angle
2.0
Figure 4-15. Scarf Adhesive Joint Strength - Composite-to-Composite1
resultant bond quality improvements can result due to the flat nonmachined bonding surfaces whose fibers can be oriented parallel to load direction.
4-2.4 STEPPED LAP JOINTS
Fig. 4-16 depicts an idealized two-step lap joint whose adhesive stress distribution is presented in Fig. 4-17. The results of tests on boron and glass composites bonded to aluminum using Shell 951 adhesive reveal, rather surprisingly, that joint strength was independent of the number of steps employed in Fig. 4-18. These results were for a joint overlap of 2 in. Joint efficiency of a two-step lap joint is improved over the single-lap joint. The center of the two-step lap is seen to carry some stress but stresses at the end seem to spike higher. The percentage of adhesive working is about the same for a twostep lap as for a single lap. If more steps and shorter Lj t ratios are employed, this configura-
• tion should prove very worthwhile. Since a scarf joint can be considered to be a multistepped lap joint in which the number of steps approach infinity, a scarf joint is considered the limiting case for a multistepped lap joint. However, due to the processing difficulties discussed for a scarf joint, it achieved only 75% of the design limit compared with about 95% for boron/aluminum stepped lap joints. For glass/aluminum stepped lap joints, only about 65% of the design limit was achieved.
4-2.5 BONDED JOINT PERFORMANCE COMPARED.
Fig. 4-19 compares the test results of single, double, and stepped lap joints with a scarf joint on boron/aluminum bonded with Shell 951. It can be seen that the single lap joint is quite efficient for low Ljt ratios but rapidly yields diminishing returns on increased lap length. In contrast, the double-lap joint is more than twice as strong as the single lap which has the highest stress concentration at lap ends and carries the least load at the center of the joint. Stepped lap
DARCOM-P 706-316
and scarf joints can potentially achieve the highest average adhesive shear strength.
4-2.6 FIBER ORIENTATION VSJOINT STRENGTH- IN-BONDED JOINTS
The fiber orientation patterns used in bonded joints are extremely important since the layers adjacent to the bond carry an increasing share of the stress as shown in Fig. 2-7. It is known that laminate modulus is a significant factor, so the nature of the substrate member is important. However, since the gross modulus is the same for a given laminate-regardless of fiber orientation- and the modulus ratio of 0-deg to 45-deg layers is approximately 10 to 1, then bond strength differences can be expected depending on outer layer fiber orientation. Since surface fiber orientation has no effect on gross laminate strength or stiffness, it is a variable which effects bond strength only. Bonded composite joint ddta must always present composite lay up patterns where possible since fiber orientation, particularly in the surface layers, has a profound effect on bonded composite joint strengths.
4-3 BOLTED COMPOSITEJOINTS
Generally only 25-50% of the basic laminate strength is achieved with mechanical fasteners. The use of metal interlayers (shims) are sometimes employed to bring joint efficiency over 50% but this results in reduced weight efficiency. Mechanical joints usually are designed to fail in bearing rather than shear-out or tension. This requires that edge-distance bolt-diameter ej D and side-distance bolt-diameter s/ D ratios higher than for metals are required to avoid shear-out or tension failures in composites. In unsymmetrical joints, such as single laps, multiple rows of fasteners are suggested to minimize bending. Generally, in order to achieve full bearing strength, Dj t ratios < 2 are recommended.
Design variations for bolted composite joint specimens can include different edge distance e,
side distance s, fastener diameter D, laminate
4-23
0 l> ::D 0 0 ~
SHELL 951 ADHESIVE
' ., 0.020 ~
0
I 7075-T6 ALUMINUM
t CJ)
w 0.040 _.
_j_ CJ) T 0.040
BORONfNARMCO 5505
1 I 0.005
REACTIONS
APPLIED LOADS
Figure 4-16. Idealized Two-Step Lap Joint2
DARCOM-P 706-316
1319w---------------------------------------------------------,
Ul 0..
oS ,.. ·:;;
"' ...<:: -o <: .5 J::
.g ::l
..0
"5 "' Ci Ul
"' "' !:: rJl .... "' "' ...<::
rJl
200
0 0
\ . \ .
' \ . \ \
~\ \ \ \ . \ \ \ . \ \ \ . \\ \ . ,, ,.
0.2
--- MOMENT ON RIGHT END - •- MOMENT ON LEFT END - - - EQUAL MOMENTS ON
BOTH ENDS
0.4 1.0 1.4
I I
2.0
Distance Along Joint, in.
Figure 4-17. Stress Distribution in the Adhesive of a Two-Step Lap Jointl
thickness t, laminate lay-up patterns, and bolt arrangements. Bolt strength should be cho~en to preclude bolt failure. When properly chosen, these parameters provide a balanced joint design in shear, tension, and bearing strengths, respectively. Because lay-up patterns can alter the
shear, tension, and bearing properties of the laminate, the optimization of joint proportions must be geared to these laminate patterns. A bolted joint differs from a pinned joint in that clamping friction is an added factor in contributing to joint strength. With friction a factor
4-25
DARCOM-P 706-316
~
..z bD ::::
"' = tl)
:::: ·c; -. "' ...
'iii .., ..<: "'0 <
4-26
12
10
8
6
4
2
COMPOSITE/ALUMINUM SHELL 951 AOHESI VE
I • 0.16
I I I I I I
I I I I I I I ,, ,,
t LENGTHWISE
A 6
COMPOSITE PATTERNS
PATTERN 8
SCARF
SINGLE LAP I I • 0.04)
oL---------~----------~--------~----------~------------------~ 0 2 4 6
Number of Steps
8
Figure 4-18. Stepped Lap Adhesive Joint Strength4
10 12
14
12
10
4
2
BORON PATTERN: 0/45/-45/0 SHELL 951 AOHESIVE
DARCOM-P 708-318
0.5 1.0 1.5
Length of Joint L, in.
2.0 2.5
Figure 4-19. Boron-to-Aluminum Joint Strength4
in bolted joint strength, the surface condition and roughness as well as bolt torques must be specified in a bolted joint.
Specimen width should be chosen to allow sufficient side-distance bolt-diameter ratios s/ D to preclude failure in tension through the bolt holes. Test results indicate that to achieve full bearing
stress, tj D ratios should not be less than about 0.5. Similarly published test results suggest that the edge distance be great enough to yield an ej D ratio ~ 5. Beyond this, bearing stress did not increase. Thus, to achieve full bearing stress, an ej D > 5 and tj D > 0.5 are suggested.
4-27
DARCOM-P 706-316
4-3.1 SINGLE- AND DOUBLE-LAP
BOLTED JOINTS
4-3.1.1 Plain lioles
Tables 4-6 and 4-7, respectively, show the strengths of single- and double-lap joints of
boron and glass composites bonded to themselves and to aluminum. These results indicate only
slight improvement in strength for the double-lap
composite/aluminum joints over the single lap. Failing modes in both cases were predominatly
shear-out of the composite with some interlaminar shear and tension failures in the com
posite for the double-lap joints. The added weight considerations may not justify the small gain in strengths obtained.
4-3.1.2 Bushed lioles
Table 4-8 summarizes the test results obtained
on double-lap joints with bushed holes. Since joint dimensions differ from the plain hole joint
results in Tables 4-6 and 4-7, direct comparison
cannot be made. However, from examining the
average laminate stresses at failure, the bushed hole joints exhibit significantly lower laminate stress bearing capability for all their excess weight; for this reason they are not efficient joints.
4-3.1.3 Bolted Joints With Reinforced Edges
Reinforcing the edges of bolted joints can be employed to reduce the edge distances needed to
develop full bolt strength and reduce shear-out failures. The reinforcement can be in the form of laminate buildup at the edge, or the inclusion of
a shim of metal or other reinforcement. Tables
4-9 and 4-10 show the results of tests on composite and steel shim-reinforced laminates,
respectively. It can be seen that the steel shimreinforced joints failed primarily by tension in
the laminate at the base of the shim and by shim deJa ruination and laminate shear-out, but occasional bolt shear did occur - indicating that reinforcement can help the joint approach full bolt strength.
4-4 BOLTED AND BONDED JOINTS
Bolted and bonded joints yield strengths which are superior to either bolted or bonded joints of
similar configuration when used alone. Table 4-11 shows that the bolted and bonded
glass/aluminum joints were three times as strong as their bolted-only counterparts, and bolted and
bonded boron/aluminum joints were five times
TABLE 4-6 SUMMARY OF SINGLE-LAP BOLTED JOINT TEST RESULTS
' (1-IN. SPECIMEN WIDTII)*•
AVERAGE LAMINATE STRESSES AT FAILURE
LAMINATE ULTIMATE -JOINT DESCRIPTION THICKNESS, STATIC LOAD••, SHEAR-OUT TENSION,
AND MATERIALS in. lb psi psi
SI~GLE LAP FIBERG LASS/7075-T6 0.112 2523 15,200 28.030
SINGLE LAP BOR0Nj7075-T6 0.116 2823 16,160 29,640
SINGLE LAP FIBERGLASS/ FIBERGLASS 0.114 2087 12,430 23,SAO
SINGLE LAP BORON/BORON 0.116 2560 14,720 27,210
'-----
•0.190-IN. BOLT DIA:\1ETER, 0. 750-1~. EDGE DISTAI\CE, Pi\ TTERN A. TABLE 4-1. ••AVERAC;E OF FIVE TESTS
4-28
BEARING, psi
119,920
127,740
98,120
115,240
FAILURE MODE
SHEAR-OUT
SHEAR-OUT
SHEAR-OUT
SHEAR-OUT
TABLE 4-7 SUMMARY OF DOUBLE-LAP BOLTED JOINT TEST RESULTS
(1-IN. SPECIMEN WIDTH) 2
I ULTIMATE AVERAGE LAMINATE STRESSES STATIC LOAD, AT FAILURE
LAMINATE EDGE AVERAGE JOINT AND THICKNESS, DISTANCE, OF 5TESTS, SHEAR-OUT, TENSION, BEARING MATERIALS in. tn. PATTERNt lb psi psi pst
DOUBLE-LAP 0.100 0.50 A 1862 18,600 23,000 98,000 FIB ERG LASS/707 5-T6 0.102 0.75 A 2359 15,400 28,600 122,000
0.104 1.25 A 2583 9,900 30,700 131,000 0.110 0.50 F 1133 10,300 12,800 54,200 0.102 0.75 F 1630 10,600 19,700 84,000 0.108 1.25 F 2226 8,200 25,400 108,500
0.148 0.50 A 2559 17,300 21,300 91,000 0.138 0.75 A 3244 15,700 29,000 123,000 0.146 1.25 A 3782 10,400 32,000 136,500 0.13R 0.50 G 1340 9,700 12,000 51,100 0.151 0.7) G 2302 10,200 18,900 80,000 0.143 1.25 G 2600 7,300 22,400 95,500
DOUBLE-LAP 0.128 0.50 A 2189 17,100 21,200 90,000 BOROI'\/7075-T6 0.117 0.75 A 3028 17,200 32,000 136,000
0.120 1.25 A 3420 11,400 35,200 150,000 0.133 0.50 D 1524 11,500 14,200 60,600 0.115 0.75 D 2059 11,900 22,100 94,500 0.116 1.25 D 3107 10,700 33,000 141,000
0.168 0.50 A 2621 15,600 19,200 82,000 0.160 0.75 A 4214 17,500 32,500 138,700 0.163 1.25 A 4756 11,700 36,000 154,000 0.166 0.50 E 1648 9.900 12,300 52,100 0.157 0.75 E 2604 11,000 20.500 87,500 0 165 1.25 I E 4317 10,500 32,300 138,000
* (1) SHEAR-OUT r SEE TABLE 4-1 (2) TENSIO;-.; AT SECTION THROUGH BOLT HOLE (3) BEARING (4) INTERLAMINAR SHEAR
**THESE STRESSES COMPUTED AS THOUGH ADHESIVE WAS 1'\0T INCLUDED.
FAILURE MODE•
( 1 ), ( 4) (1), (4) (3),(4) (1), (4) (1), (4) (1), (4)
(1),(4) (1), (4) (3), (4) (1), (4) (1 ), (4) (1),(4)
( 1) (1)
(1), (2), (4) (1) (1) (1)
( 1) (1),(2)
(1),(2),(4) (1) (1) ( 1)
c )> ::n (") 0 s: ' "'0 ....,
0 en w ..... en
TABLE 4-8 SUMMARY OF DOUBLE-LAP BOLTED JOINT TEST RESULTS- BUSHED HOLES2
ULTIMATE AVERAGE LAMINATE STATIC LOAD STRESSES AT FAILURE
JOINT DESCRIPTION, LAMINATE BOLT EDGE FIBER AVERAGE OF MATERIALS, AND THICKNESS, DIAMETER, DISTANCE, ,. AT '45°, 5 TESTS, SHEAR-OUT, TENSION, BEARING, SPECIMEN WIDTH in. m. in. PATTERN* o/o lb psi psi psi
DOUBLE LAP 0.171 0.3125 1.0 A 50 4773 11,690 24,670 74,800 BOR0:-.1-ALUMINUM 0.171 0.3125 1.5 A 50 4524 8,820 27,930 84,640
0.176 0.3125 2.0 A 50 4565 6,480 27,360 83,020 I .250-IN. 0.127 0 3125 1.0 A 50 3595 13,460 28,820 86,100
SPECIMEN 0 126 0.3125 1.5 A 50 3865 10,220 32,340 9fl,OOO WIDTH 0.127 0.3125 2.0 A so 4683 9,230 39,240 118,240
DOUBLE LAP 0.167 0.3125 1.0 A so 4253 12,710 26,860 81,380 FIBER- 0.166 0.3125 1.5 A 50 4889 9,820 31,490 94,260 CLASS/ALU~1INUM 0.146 0.3125 2.0 A 50 5001 8,590 37,210 110,000 1.250-IN. 0.128 0.3125 1.0 A 50 3487 13,660 29, !90 87,480
SPECIMEN 0.122 0.3125 1.5 A 50 3825 10,480 33,740 100,540 WIDTH 0.121 0.3125 2.0 A 50 4174 8,810 37,120 110,200
t (I) SHEAR-OUT (2) TENSION AT SECTION THROUGH BOLT HOLE (3) BEARING FAILURE •
*SEE TABLE 4-1
FAILURE MODESt
(I) (2)
(I), (2) (I), (2) (1 ), (2) (I), (2)
(I) (3) (3) ( 1) (3) (3)
c J> ::D (") 0 ~ ' "V ....,
0 01 ' w ....
01
TABLE 4-9 SUMMARY OF COMPOSITE-REINFORCED BOLTED JOINT TEST RESULTS2
JOINT DESCRIPTION, LAMINATE BOLT EDGE MATERIALS, AND THICKNESS, DIAMETER, DISTANCE,
SPECIMEN WIDTH •n. m. in. PATTERNt
DOUBLE-LAP 0.278 0.190 0.50 A BORON/STEEL•• 0.279 0190 0. 75 A 0.750-IN. 0.279 0.190 125 A
SPECIMEN WIDTH 0.292 0.190 0.50 D 0.301 0.190 0. 75 D 0.289 0.190 1.25 D
DOUBLE-LAP 0.283 0.190 0.50 A FIBERGLASS/ 0.268 0.190 0.75 A
STEEL"" 0.275 0.190 1.25 I A 0.750-IN. 0.257 0.190 0.50 F
SPECIME]'; WIDTH 0.274 0.190 0.75 F 0.257 0.190 1.25 F
DOUBLE-LAP 0.366 0.250 0.75 A BOROJ';jSTEEL•• 0.373 0.250 1.00 A l-IN. 0.361 0.250 1.50 A
SPECIMEN WIDTH 0.346 0.250 0. 75 E 0.373 0.250 1.00 E 0.343 0.250 1.50 E
DOUBLE-LAP 0.381 0.250 0. 75 !\ FIBERGLASS/ 0.151 0.250 1.00 A
STEEL•• 0.324 0.250 0.75
I G
l-IN. 0.342 0.250 1.00 G SPECIME]'; WIDTH 0.353 0.250 1.50 G
"(1) SHEAR-OCT tSEE TABLE 4-1 (2) INTERLAMINAR SHEAR (3) TENSION AT SECTION THROUGH BOLT HOLE
""RIGID TEST FIXTURE
ULTIMATE AVERAGE LAMINATE STRESSES STATIC LOAD AT FAILt:RE
FIBER AVERAGE OF AT'45°, 5 TESTS, SHEAR-OUT, TENSION, BEARING,
% lb psi psi psi
50 4,602 16,500 28.600 87,300 50 6,910 16,600 44,300 130,000 50 7,215 10.400 45,900 137,000 43 3,885 13.300 23.500 70,000 43 6,785 15.000 39,700 118,500
" 43 7,140 9,900 43,600 130.000
50 5,975 21,100 37,500 111,000 50 6,390 15.800 42,400 125.500 50 6.725 9,800 42.900 129,000 43 4,763 18.500 33,100 97,500 43 6.470 15,700 41,800 124,000 43 6.420 10.000 44,500 131,000
so 9,179 16,700 33,500 100,000 50 11.914 15.800 42.000 126,000 50 12,021 1!, 100 44,400 133,000 39 6.284 12,100 24.200 72,500 39 10,715 14,400 38,300 115.000 39 10,300 10,000 40,000 120,000
50 10,796 18,900 37,700 113.000 50 11.200 15.900 42,500 127,700 39 7,463 15.300 30.700 92,000 39 8,742 12,800 34,100 102.000 39 10,430 9,800 39,500 118,000
FAILURE MODES"
(I)
I ( 1 ), (3)
I (1),(3)
(1) ( 1) ( 1 )
( 1 ), (2) (I). (2) (I). (2) (I). (2) ( 1 ), (2) (1 ), (2)
(I) ( 1 ), (3) ( 1 ), (3)
( 1) ( 1) (I)
( 1 ). (2) ( 1 ), (2) ( 1 ), (2) ( 1 ), (2) ( 1 ), (2)
0 )> :a n 0 ~ . "V .... 0 G)
w ... G)
TABLE 4-10 SUMMARY OF SHIM-REINFORCED BOLTED JOINT TEST RESULTS2
ULTIMATE AVERAGE LAMINATE STRESSES STATIC LOAD
]01:'\T DESCRIPTION, LAMINATE BOLT EDGE AND MATERIALS, AND THICK!'iESS, DIAMETER, DISTANCE, NO. TESTS, SHEAR-OUT,
SPECI:\1EN WIDTH m. Ill. in. PATTERN+ lb psi
DOLHLE-L\P 0.192 0.100 0.37) A 6.'J38 (5) 4'J,100 BORO:'\jSTEEL .. 0.192 0.1'JO 0.500 ,\ 6,670 (4) 34,700 (!750-I:'\. (J.192 0.100 1.000 A 7,H!3 (5) 20,400 SPECI\IE:'\ \\lOTH I) 192 0.190 0.375 D 6,8'J3 (5) 4 7, HOO
0.192 0. 190 0 500 D 7,600 (5) 40.000 0.192 0.190 1.000 D 8,360 (4) 21,800
DOLBLE-L\P 0.192 0.100 0.375 A 4,550 (4) 31,60(1
FIBERGLASS/ 0. JCJ2 0.190 0 500 t\ 5,300 (5)
I 27,600
STEEL* (I 192 0 190 1. 000 A 5,006 (5) 13,000 0.750-l:'\. (). 1 CJ2 0.190 0 )7) F 4,070 (5) 2H,200 .SPECI\IE:'\ WIDTH run 0 100 0.500 F 5,354 (5) 27,900
0 192 (J190 !.000 F 5,316 (5) 13,800
DOLBLE-LAP 0 260 () 250 0.43 7 5 A 11,905 (5) 52,500 BORO:'\/STEEL ** 0.260 0. 250 0 500 A 12,H20 (5) 49,400 1-1:'\. 0.2i>fJ 0.250 (J750 A 12,800 ( 4) .'l2,KOO SPECI\11:::'\ \VIDTH 0.260 0 250 (J437S E 10,800 (3) 47,500
0.260 0.250 () 500 E 11 ,HI 'i (5) 4'i ')()()
0.260 0.250 0.750 E 14,\100 (5) 38,200 0.260 0.2SO 1.250 E 14,HSO (2) 22,KOO
DOLBI.E-LAP (J 260 () 250 0.500 A 7,172 (5) 27,600 FIBERGLASS/ (L260 0.250 0.750 A H,HHH (5! 22,800 STEEL** 0.260 0.2'i0 0.500 G 7,1 ()() (5) 27.400 1-I:'\ (J 260 0.250 0.750 G 7,3\12 ('i) 1H,90() SPECI\IE:'\ WIDTH 0 260 0.260 1.250 G K, 142 ('i) 12,500
* 1. BOLT SHEAR t SEE TABLE 4-1 2. TE:'\SIO:'\ 1:'\ LA\-11:'\ATE /\T HASE OF SHI~S 3. SHI\1 DELA\1I:'\ATIO:'\ A:'\IJ LA:V11NATE SHEAR-OUT 4. TJ::i'\SIO:\ I:\ LA\11:'\ATE A:--.:D SHI\-1 OF SECTION THROUGH FASTENER HOLE ). TE:\SIO:\' I:\ LA.\11:'\/\TE A:'\D O:'>.'E SHI\-1. TENSION AND SHEAR-OCT IN SECOND SHIM 6. SHEAR-OUT OF LA.\11NATE AND ONE SHI\1, TE.\JSION IN SECOND SHIM 7. TENSIO;-.; 1;--.; OLTER PLIES OF LA\-1INATE AT BASE OF SHIMS AND AT SECTION
THROUGH FASTESER HOLE IN PLIES BETWEEN SHIMS; PARTIAL DELAMINATION OF SIIIMS. •• RIGID TEST FIXTURE
AT FAILLRE
TENSION, BEARING, pst pst
64,)00 191,000 62,000 184.000 72,600 215,000 64,000 1H'),500
71 '50() 212,000 77,800 130.000
42,400 125,000 49.400 146,000 46,500 137,500 37,')0() 112,000 49,800 147,400 49,400 146,000
61,300 1K4,000 6),800 107,000 65,700 197,100 :; 'i' )()() 166,000 6(),(,()0 184,000 7(J,500 229,000 76,200 228,000
36,800 110,000 45,500 137,000 36,500 109,400 37,900 113,700
41 '700 12.'i,OOO
FAILURE MODES*
I (2), (3), (4) (2), (3), ( 4)
(2), (7) I (2), (3) I
(2). (1) ( 1), (3)
(2), (3) (2), (.\) (2), (3)
(2), (3), (4) (2)
(2), (3)
(4) ( 4 ), (5)
(4) (6)
(3 ). (4) (2), (3), (4)
(I )
(3 ), ( 4) (3) (3) (3)
0!. (4)
c )> ::JJ C')
0 3: I -g .... 0 en c., ... en
TABLE 4-11 SUMMARY OF DOUBLE-LAP BOLTED AND BONDED JOINT TEST RESULTS2
LAMINATE EDGE JOINT AND THICKNESS, DISTANCE, MATERIALS lfi. in.
DOUBLE-LAP FIBERGLASS/7075-T6 0.!20 0.75 BOLTED AND BONDED
DOUBLE-LAP BORON/7075-T6 0.120 0.75 BOLTED AND BO:-.IDED I
• (I) TENSION AT SECTION THROUGH BOLT HOLE (2) INTERLAMINAR SHEAR
ULTIMATE STATIC LOAD, AVERAGE OF
5TESTS, PATIERNt lb
A 7470
A 12,875
l
••THESE STRESSES COMPLTED AS THOUGH ADHESIVE WAS NOT INCLUDED.
tSEE TABLE 4-1
AVERAGE LAMINATE STRESSES AT FAILURE
SHEAR-OUT, TENSION, BEARING, psi psi psi
41,500 .. 77,000 .. 328,000 ..
71,500** 132,000** 564,000**
FAILURE MODE•
(1), (2)
(I), (2)
c J> ::D 0 0 s: ' "'0
...... 0 G)
w ..A
G)
OARCOM-P 706-316
as strong as bolted only. The presence of a bolt in a bonded double-lap joint of 3-in~ area is seen to increase average bond shear stress in glass from 1800 psi to 2717 psi, and in boron from 3300 psi to 4300 psi. There is, therefore, a synergistic effect of the bolt and adhesive on one another.
4-5 REDUCING STRESS CONCENTRATIONS IN JOINTS
4-5.1 Model
The double-strap joint pictured in Fig. 4-20 will be used to illustrate some of the things which can be done to reduce stress concentrations due to stress risers resulting from abrupt configurational changes in bonded joints.
Assume undirectional composites with fibers parallel to load direction, then three types of failure are likely:
1. Tensile failure of main member of region A 2. Tensile failure of strap through region B. 3. Bond failure and shear-out originating at
points C. The stress diagrams in Fig. 4-20 show the
stress concentrations in the main members, straps, and bond line as cr A, CTs, and r, respectively.
4-5.2 STRAP MODIFICATIONS
Strap and main member failures can be minimized by proper sizing of members -e.g.,
:>I-
t T
making straps the same thickness as the main member (if the strap and main member are the same materials) to reduce strap failures, and increasing strap length to eliminate bond failure and shear-out. Main member failures at region B can be alleviated by reducing the stress concentrations in this area due to the abrupt load transfer between strap and main member. This can be done in several ways -by reducing strap thickness at the strap ends or by increasing adhesive thickness at the strap ends. Fig. 4-21 shows a number of ways to reduce strap thickness locally.
The stepped strap configuration (Fig. 4-21 (A)) affords greater n~xibility and reduced stress concentration at the strap/main member boundary. While this reduces the probability of ~a in member failure in the aforementioned location, the steps create stress risers in the strap thus introducing a new possible mode of failure- strap delamination originating at the step corners. Fig. 4-21 (B) shows a tapered strap which accomplishes the same stress concentration reduction as the stepped strap but in a continuous fashion. Finite element analysis by Sage5 showed that stress concentration factors as low as about 1.1 were possible for a taper angle of under 5 deg with no step at the strap end. However, the end produced by machining to this angle is so frangible as to cause problems in machining, handling, and bonding. This led Sage to a radiused strap
r = shear si:Tess at bond line a A = tensile si:Tess in region A a8 = tensile si:Tess in region B
aa--+
Figure 4-20. Model of a Double-Strap Joint
4-34
DARCOM-P 708-318
(A) Sl!~pp!'d Strap--Good
(8) Tapned Strap--Better
•
(C) Radiu~ed Strap--Best
Figure 4-21. Ways to Reduce Strap Thickness Locally
configuration (Fig. 4-21 (C)) which solved anum
ber of problems. First, the tangent to a large enough radius can easily approximate the 5-deg taper at the strap end and thereby meet the reduced stress concentration requirement. Second, a straight taper of this angle would require the removal of a large mass of strap and is not necessary after a modest distance from the strap end. Third, a flat strap can be bonded on and the radius machined afterward, allowing for uniform pressure application during cure and
eliminating the handling problems. Small radii were found to cause interlaminar shear failure in the strap skin similar to that cautioned against in
the stepped strap configuration. Larger radii circumvented this failure mode. The following equation suggests the minimum radius R to avoid this failure mode:
( pu ) t .
R = fsu X 2, m. (4-1)
pu = ultimate tensile strength of the composite, psi
ru = ultimate shear strength of the
composite, psi t = thickness of the joined composite
members, in.
4-35
DARCOM-P 706-316
A factor of 2 was built into this equation in an effort to make R large enough to eliminate tensile failure as well. Fig. 4-22 shows us that a key advantage of the radiused strap is that, even for a short strap length, the favorable 5 deg angle at the strap end can be achieved for lowered stress. A modified straight taper is also shown which might offer a further advantage over the radiused strap yet avoid the difficulties of a straight taper.
4-5.3 INCREASED ADHESIVE THICKNESS
Another way to overcome the stress concentration at the ends of a strap is to increase the adhesive thickness at the main member I strap end interface. This avoids the abrupt load transfer in a manner much the same as reducing strap thickness or reducing stiffness in the region, thereby relieving rather than restraining stresses and distributing them more efficiently over the whole joint area. Fig. 4-23 is the configuration suggested by Sage to accomplish this in a doublestrap joint.
Machining of the straps depicted in Fig. 4-23 would be rather tedious so a stepped strap configuration (Fig. 4-24) is suggested.
By forming the steps in the strap using prepreg, the machining of steps can be eliminated; however, filling the steps with adhesive is required. The performance of these joints is illustrated in Table 4-12. Load bearing efficiencies of greater than 100% have been achieved. This means that failure occurred outside the joint area in the main member. Thus, the joint could be considered too efficient from ·a load bearing standpoint and perhaps weight could be saved by design refinements.
4-5.4 INFLUENCE OF STRAP AND ADHESIVE THICKNESS ALTERATIONS ON JOINT EFFICIENCY
Tables 4-12 and 4-13 summarize the results of tests on type I and II carbon fiber reinforced plastic double-strap joints conducted by Sage.
. The load bearing efficiencies can be observed to
4-36
respond to strap length, strap composition, strap radius, or step filler; and failure modes reflect the stress concentrations which result from the different configurations.
4-5.5 VARIABLE ADHESIVE STIFFNESS
Another means of reducing stress concentration at joint extremities is by the use of two adhesives of varying stiffness (Fig. 4-25) in the bond line. A lower stiffness adhesive at the joint ends will provide better stress distribution by relieving itself of the higher stresses at the joint ends and transferring the load into the center of the joint where a higher stiffness adhesive can carry a larger share of the load.
4-6 TYPICAL BOLTED JOINT CONFIGURATIONS
Several examples of bolted joint configurations are presented in Fig. 4-26. Variations on these basic joints can involve varying bolt placement on large joints but little else.
4-7 BOLTED FAILURE MODES
The types of failures which can occur in bolted joints are shown in Fig. 4-27. Bolted joints usually are designed to fail in bearing rather than tension or shear-out but all types of failure are encountered - usually a mixture of several modes. Another possibility, though rarely encountered, is bolt failure. Bolt strength should always be chosen to preclude this type of failure.
4-8 TYPICAL BONDED JOINT CONFIGURATIONS
Bonded joint design alternatives are more numerous than for bolted joints and are depicted in Fig. 4-28. Included are single and double laps; single and double straps; scarfs; and pinned, keyed, and variable stiffness and thickness adhesive types.
4-9 BONDED FAILURE MODES
Bonded joints should ideally fail cohesively since that indicates the adhesive has been stressed to its ultimate in load transfer
All can provide for an ex = 5 deg at strap end but a radiused or modified straight taper permits a shorter more practical strap length.
Figure 4-22. Methods of Reducing Stress Concentration at Strap Ends
0 l> :a () 0 !:
DARCOM-P 706-316
Figure 4-2.3. Idealized Shape for Variable Adhesive Thickness
Figure 4-24. Filled Step Strap Joint
capability. Adhesive failure indicates that,poor adhesion is present due usually to poor processing or to adverse environmental effects such as moisture displacing the adhesive at the adhesive/ adherend interface. Interlaminar shear failure in the composite is encountered frequently due to the anisotropic nature of laminates and the many processing parameters which can induce flaws in the composite. Fig. 4-29 depicts possible failure modes.
4-10 WEIGHT OF JOINTS
As discussed in Chapter 1 the weight of the joint is critical to its overall efficiency and ultimate usefulness. Load carrying efficiencies of 100% or more are possible but excessive weight is the price paid. A load carrying efficiency of 100% accompanied by a weight efficiency of 50% yields an overall joint efficiency E of just 50% as defined by Eq. 1-3. High joint efficiencies are achieved by keeping the load carrying capability of the joint design as close to that of the continuous unjoined member while keeping the weight increment added as small as one can.
4-38
A weight study conducted on different boron composite and aluminum joints (bonded and bolted) 1 yielded data on weight added to achieve different joint strengths. The results (Fig. 4-30) show that a weight increment of about 0.04 lb/in. of bonded joint width was required to obtain a single-lap joint strength of about 3500 lb/in.; double-lap joint strength, of about 5500 lb/in.; and a scarf joint strength, of about 20,000 lbjin. Just 0.01 lbjin. of joint width yields a strength of 20,000 lb/in. for a four-step lap joint. Thus a stepped lap or scarf joint is seen to be much more efficient than a double- or single-lap joint. Data from the bolted joint study (Fig. 4-31) show an almost linear relationship between strength, and weight, i.e., those bolted configurations which were the strongest were also the heaviest. It is significant to note that the incorporation of adhesive into a bolted lap joint raised joint strength approximately threefold with no weight penalty as shown in Fig. 4-31. Fig. 4-32 compares the weight added by different joint designs to achieve the same load. The bonded scarf and stepped lap joint are shown to add little or
TABLE 4-12 PERFORMANCE OF RADIUSED DOUBLE-STRAP JOINTS EMPLOYING CARBON FIBER REINFORCED PLASTICS5
STRAP DIMENSIONS, mm RADIUS R, FIBER TYPE MAIN MEMBER STRAP LENGTH WIDTH THICKNESS mm
FAILURE MODE UNDER STATIC AXIAL TENSION
JOINT EFFICIENCY
76 24
76 24
grp• 76 24
grp 76 24
50 24
II II 76 24
II II 76 24
II II 76 24
• grp- glass reinforced plastic
t crfp - carbon reinforced plastic
1.27 200
1.27 76
1.27 76
1.27 200
1.27 76
1.27 76
1.27 200
1.27 200
Tension in main member away from joint area
Tension in main member away from joint area
lnterlaminar shear in grp strap close to bond
lnterlaminar shear in grp strap close to bond
Tension in strap at center
Shear in strap
Tension in main member a\·•ay from joint area
Tension in main member and strap at strap end
0.7
0.7
0.7
COMMENT
Failure outside joint indicates o1·er design and excess weight. Shorter strap length is possible.
Same as abO\·e.
Strap strength is too low. Lower stiffness grp chases stress to joint center.
Same as abo\"e.
Increased stress concentrations due to shorter strap length
Radius is insufficient to alle1·iate stress concentration in the stiffer Type II crfp. t
Shorter strap length is possible. Larger radius chased failure back to main member outside of joint.
.\F-130 adhesi\"e used. ~lore brittle than BSL 312/3 used on others
FIBER TYPE MAIN MEMBER STRAP
II II
II II
•carbon reinforced plastic
TABLE 4-13 PERFORMANCE OF INVERSED STEPPED STRAP JOINTS EMPLOYING CARBON FIBER REINFORCED PLASTICS~
FAILURE MODE LOAD BEARING STRAP DIMENSIONS, mm FILLING UNDER STATIC EFFICIENCY
LENGTH WIDTH THICKNESS IN STEPS AXIAL TENSION E COMMENT
127 24 1.00 crfp• Tension in main member Joint overdesigned. Shorter strap could cut weight.
90 24 1.00 crfp Tension and shear at 0.7 crfp fibers transverse to load unable to with-strap end stand increased stress at this strap length.
127 24 1.00 Adhesive Tension in main member Larger strap length with adhesive step filler BSL 312/3 outside joint area yields same result as with crfp filler.
Some strap length between 127 mm and 90 mm seems optimum.
90 24 1.00 Adhesive Tension and shear at 0.9 Failure mode similar to crfp filler at this BSL 312/3 strap end strap length but higher failing load and
shear location indicate isotrophic adhesive filler cohesively stronger than transverse crfp.
90 24 1.00 crfp Tension and shear at 0.7 Same as configuration 2. strap end
90 24 1.00 Adhesive Same as configuration 4 but higher strength BSL 312/3 main member fails at higher load.
0 )> ::0 0 0 3: ' .,
...., 0 en c:., ... en
DARCOM-P 706-316
higher stiffness adhesive
Figure 4-25. Variable Stiffness Adhesive Joint
/ I
(A) Single Lap (B) Double Lap (including bushings)
(C) Reinforced Edge
(D) Shim Joint (E) Bolted-Bonded
Figure 4-26. Bolted Joint Designs2
no weight whereas the bonded double-lap and bolted double-lap joints added in excess of 30% to the basic panel weight.
4-11 FATIGUE
4-11.1 BONDED JOINTS
The fatigue behavior of several types of glass/aluminum and boron/aluminum bonded joints is shown in Table 4-14. Clearly, although the scarf joints had among the highest average adhesive shear stress by comparison with the
other joint types, the low stress concentration factor (SCF) in the scarfed configuration resulted in less severe stressing of the joint. This is graphically depicted in Fig. 4-33. S-N (StressNumber of Cycles to Failure) curves for boron/aluminum bonded scarf and double-lap joints are shown in Figs. 4-34 and 4-35. Similar curves for a graphite/graphite single-lap and graphite/titanium scarf joints are shown in Figs. 4-36 through 4-40 for both room temperature and 350°F. Elevated temperature is seen to reduce fatigue endurance substantially.
4-41
DARCOM-P 706-316
(A) Shear Out (B) Tension
(C) Bearing (D) Tension/Shear Out
(E) Bearing/Shear Out (F) Bearing/Tension/Shear Out
Figure 4-27. Bolted Failure Modes
4-11.2 BOLTED JOINTS AND BOLTED-BONDED JOINTS
A tabulation of single- and double-lap boron and glass bolted joint fatigue results is presented in Table 4-15 as well as data on bolted and bonded glass/aluminum and boronjaluminumjoints. Double-lap bolted joint fatigue endurance was greater than for the single lap. Failure was through the aluminum bolt hole not the boron bolt hole. Direct comparisons between the bolted
4-42
and the bonded joints are not possible because of the different configurations but, generally, the maximum loads on the bolted joints were less than those on the bonded joints.
Adding adhesive to the bolted joint permitted the maximum and minimum load on the joint to be increased 250% with good results. Failures in the configuration were a mixture of laminate and aluminum through the bolt hole, and aluminum through the basic section.
...
DARCOM-P 708-318
L ~ 7 simple
/ I [;?'
beveled (external scarf)
22 ~ 7 < radiused
(A) Single-Lap Joints
simple
beveled
radiused
(B) Double-Lap Designs
(cont'd on next page)
Figure 4-28. Bonded Joint Designs
4-43
DARCOM-P 706-316
--------~~ ~ ce;r tc----.----rtr ___ f?? single strap
double strap
beveled straps
radiused straps
I recessed double strap
(C) Strapped Joints
(cont'd on next page)
Figure 4-28. (cont'd)
4-44
DARCOM-P 706-316
r/ z ,: CJ I
simple stepped lap
z c ~ () ..-.. recessed stepped lap
c/ : ~ v scarf (single taper)
/ I z (?)
scarf (double taper)
increased thickness scarf joint
landed scarf
(D) Stepped Lap and Scarf Joints
(cant 'd on next page)
Figure 4-28. (cont'd)
4-45
DARCOM-P 706-316
variable adhesive thickness
variable stiffness adhesive
pin
key
(E) Adhesives
Figure 4-28. (cont'd)
4-46
DARCOM-P 706-316
5 T~ I
l_
(A) Cohesive
-
I (B) Adhesive
(C) I nterlaminar Shear
Figure 4-29. Bonded Failure Modes
4-47
DARCOM-P 706-316
0.18 r-----r---------,.-----------~....,
SHELL 951 ADHESIVE
0.16
Q. 0,14 a.. j c(
_I w w ...J _I en (.!) :::l 2 0 Ui Q
0.12
<:::
.:0
e; 0.10 <1
= ., E ~ u
= ..r: 0.08 bC
"' ~
0.06
Joint Strength, (lb/in. of bonded joint width) X w- 3
(A) Weight Increments for Bonded Joints in Boron Panels
Figure 4-30. Weight Increments vs Strength of Joints2
4-48
c::
:?i
~ <l
c (l.J
E "' ... (.)
..:; -C
tl.O (l.J
ss
0.03 .---~-
0.02
O.D1
SHELL 951 ADHESIVE
NO. OF STEPS = 4
5 10
DARCOM-P 706-316
15 20
Joint Strength, (lb/in. of bonded joint width) X 10 ~ 3
(B) Comparison of Weight Increments for Stepped Lap Joints
Figure 4-.'30. (cont'd)
S-N curves for f1ush head and protruding head bolted graphite joint configurations are shown in Figs. 4-41 and 4-42, respectively. Fatigue behavior is not predictable at present based on mechanical property data. Factors which affect fatigue life are numerous. They include joint type and configuration, fiber orientation, adhesive type, processing variables for laminate manufac-
ture, surface preparation of laminate if it is to be bonded, adhesive cure schedule, and environmental effects of temperature and humidity. These factors make prediction of static strength of joints difficult and the introduction of dynamic cyclic loads compounds the difficulty. For this reason S-N curves must be developed for a joint design representative of the end item.
4-49
DARCOM-P 706-316
16.----------------------------------------------------------------------
"' I 0
X
...... 0
.5 g
14
12
..c 6 bo c: 01)
t: en
2
UNREINFORCED D • 0.190 l =0.120
BOLTED +BONDED
D = 0.190 I = 0.120
SHIMMED D = 0.250 I = 0.160
\_ REINFORCED- D = 0.250
·, = 0.160
D = 0.190 t = 0.120
0=0.190 I = 0.120
0~--------~--------~--------~--------~--------~--------~--------~--------~
0 O.Q1 0.02 0.03 0.04 0.05 0.06 0.07 0.08
Weight Increment AW, lb/in.
Figure 4-31. Strength - Weight Relationships for Bolted Joints2
4-50
...
::9
..c:: 1:lD Q)
~
~ 0 .....
DARCOM-P 706-316
ALUMINUM AND BORON PANELS 24r-----------------------------LOAD = 10,000 LB/IN.
B
4
DOUBLE LAP BONDED
> X 0 Q,
u; z 0 a: 0 Ill
DOUBLE LAP BOLTED
> X 0 Q, w :Z 0 a: 0 Ill
PANEL WIDTH = 20 IN.
PANEL LENGTH = 60 IN.
SCARF STEPPED LAP BONDED BONDED (N = 4)
> > X X 0
~ Q, w tJ,l :Z z 0 0 a: a: 0 0 Ill Ill
Figure 4-32. Total W,tight Comparisons for Panels and Joints2
4-S 1
.... I U1 N
TABLE 4-14 SUMMARY OF BONDED JOINT FATIGUE TEST RESULTS•2
MAX!Ml!M ~1ATERIALS OVERLAP "'AX!:I.H;.\1 LO.•D LOAD% ot-· A:-;D GAGES, LEXGTH, "1!~!.\ft:M LOAD STATIC
JOI:\TTYPE in. in. lb/lb l:LTIMATE
BORO:-..-f_\L L'~II:\LC.I I I~IJ0j90 72
(() 040)/10063) SI:\C, LE L\P
FIBERCL\SSj_\LV,IL'\L\1 I 1600/RO 69
((1_040)/10.063)
BUR( l:\/ ALL\11.'\L:...I I 6•HJOj260 70
(0081J;ji1J 126)
I 4200/ZIJO 73
FIBERC;L\'iSf-\LL:-..11:'\L'\1 DOLBLE L\P
IIJ OHIJ J/ 10.121J!
I 341JOj171) 60
BORO:\f_\ L L .\II:\ L :...1 2 6600j331J 56
11!.160;/ 10.16111
2 8200/410 7()
llORO:\/ ,\ LL:-..11:\L\1 II!. 161! )/ (() 160;
Ff JL'R-STEP PATJ'ER:\ C L\P 2 6(,()()(_)\0 .J/
Fl BERC ;L\SSj,\LL\11:'\L\1 2 IJ61JO/-).l1J 75
IIJ JI,IJJ/111.160)
llO RO:\j ;\ l.l':'-.11 :\L :'.I I 3300/ 16.) 7()
(fJ.I{J()Jj((J liJIJ) -:,\RF
II BERC; LAS.'i/ ALL\11:\L'\1 I .1HorJjiWJ 7[)
(fJ.IIJIJJ/(0.160)
1-1:\ SPECI~1E:\ WIDTH -, R = ,0.05
VE LA.\11:\ATE PATTERN A, SEE T'\BLE 4-1
(SCF) X ADHESI\'l AVERAGE STRESS AT STRESS AT "'AXl:l.lt::\.1 APPROXI\IATE .\!AXI.\Il!\1
LOAD, SCFI:\ LOAD, TESTS p!oi ADHESIVE P"
5 1.800 4.H H,600
5 - - --
5 .UOIJ .14 10900
2 - - -
3 - - -
3 .1.11!0 3.1J 11,9()1)
2 4, IIJ() 1 () 14,7011
2 .1. )iii! l.iJ 11, 111!1)
j - - --
s _),}()() 14 4,(,(1(1
s - - ~
R.,:-;GE OF CYCLES TO FA!Lt:RE
FAILCRE \lODE
8,000 l() ADHESIVE
35,000
I 10,700 f'() ADHESIVE
19 400
480 Til r\llHESI\'E
I ,K60
I, /01! j'() :\llHESI\T
2_:llliJ
1,600 j'() ADHESIVE
H,SOIJ
1,1!00 '10 .\llHES!\'1::
.o,ooo
7:)0
'" ,\lli!ES!VE 2,1JIJ()
7,)1!1! ")41 1\ll!IESI\'E
12,721!
201!
'" 1\lliiESIVE 100
1\000 J() AllllESIVE
ll'J,()()()
I ,400 jl) A Ill! E~ IV 1·.
20,000
.... tO .,
..<::: ifJ
3.5
3.0
DARCOM-P 706-316
.-------~---- -------------- --- ------
SPECIMEN
Z3824858-501 I11NCHI
'o ' b.
SPECIMEN
Z3824858-1 {1-1/2 INCH)
0 .0
0 0
b.
BORON/NARMCO 5505 LAMINATE TO 7075 T6 AL. STRESS RATIO. R - •005 SHELL 951 ADHl.SIVE
~-------6----.~ 2.5 "' .,
..<::: -o < ., ~
"' .... ., ;>
<
·;;.; ..><:
-o
"' 0 ...... E ::l E
•;< "' ::E '.;
"' "' ., !:::
ifJ .... 01 .,
..<::: ifJ .,
;> ·:n ., ..<::: -o < ., ~ tO .... ., ;>
<
0 DENOTES 1-IN. SCARF
b. DENOTES 1-1/2-IN. SCARF
CLOSED SYMBOL DENOTES RUNOUT
2.0 ~-----------L----------------~------------------L---------------~
1.5
1.0
0.5
104
Cycles to Failure N Figure 4-33. Fatigue Data for Adhesive Scarf Joints1
SPECIMEN
Z382486Q--503 (1 INCH} 0/45/-45/0
SPECIMEN Z382486Q--1 (2 INCH} 0/45/-45/0
'b. b. SPECIMEN -..... 6 6
0
BORON/NAAMCO 5505 LAMINATE TO 7075 T6 AL STRESS RATIO. R = +0.05 SHELL 951 ADHESIVE
•
. .. 0 ••
Z3824860-501 (2 INCH} -..._b. b. 6
------
0~
0 DENOTES 1-IN. LAP. 0/45/-45/0 PATTERN
0 DENOTES 2-IN. LAP, 0/45/-45/0 PATTERN
b. DENOTES 2-IN. LAP, 45/0/0/-45 PATTERN
CLOSED SYMBOL DENOTES RUNOUT
b.----•:. •
0 ~----------~------------~--~----------------L---------------~ 10
4 105 106
Cycles to Failure N
Figure 4-34. Fatigue Data for Adhesive Double-Lap Joints 1
4-53
DARCOM-P 706-316
CONSTANT AMPLITUDE R • +0.05
SCARF JOINTS
105
SINGLE LAP ~ JOINTS ., ... ..2 ·o;; ~
104
.8
FOUR STEP LAP JOINTS
1 I
<ll .., u >.
u DOUBLE FOUR STEP LAP JOINTS LAP JOINTS
103 I 1
4 4 6 8 10 12 14 16
Average Maximum Cyclic Stress X (SCF), ksi
Figure 4-35. Fatigue Life of Boron Composite-to-Aluminum Alloy Bonded Joints6
4-54
~
' U• \.JI
·u; ....:
~ :2 ::: ;)
.... "' 01
-"' rJ)
""0 c: 0
IXl
E "' E ,., "' ~
2.0
' ' 1.8
1.6 '~"-· .......
1 • 4
1.2 ). -1.0
0.8
0.6
0.4
0.2
' -....~
~
"' Ill.. '
GRAPHITE/EPOXY TO GRAPHITE/EPOXY
350°F
IlL I R = 0.05 /AOH~SIV~ I II I " Nx _, ~ METLBOND 329-7
I ~ ,_ La --+j 0, 5 \+-- N
X
- -..... """~'... l J l .. ... 411_ ..........
~ --
1 10
I
-~
- -
!
i
.._, -~~ ... .....
.... ·-. .... ~ - - -
I
I I I
~ ~l fa'== N) La u [0/:!:45) s
"""""' ' o- - [0/:!:45/90)5 ··~oo. r ···;
"""""' ~ .. ..... :... ~~~~... 0······-- [0 /:!:45]
r-.. jt • .......,. 2 s - ~ - .. ~-.. ' • k .... ... :--~ ......... I '· n
"•r-, .. ~ f::_ .. .. .. I
~~ ~ r--~
Itt~
I
Cvcle~ to Failurt• N
Figure 4-36. Single-Lap Bonded Joint Tension Fatigue S-N Curve -Type AS/3002-Batch, Graphite/Epoxy, 350°F (Ref. 7)
0 l> ::a C') 0 3: ' "Q .... 0 Gl w ... Gl
2. 3
2.0
"' ..>(
~ "' 1 • "' "'
5 !::: rJl ... "' <l)
.;::: rJl ""0
= 0 ~
E :l E
"' 1. 0 "' ~
I
1---·
I
0. 5 -->
I
N. -I
I I
f.' == N.f La - - -- --
I
I I
I
I I I
GRAPHITE/EPOXY TO GRAPHITE/EPOXY ROOM TEMPERATURE
R 0 05 "" I -,· f
ADHESIVE
L 1..----METLBOND 329-7 , ___
L" -+I 0.51+-- N,
I s:s
,-w- 0- -
' 0 •••••••
('\
" \.
' "\
~' '~ " r ~,.,. ' """--..., ...._
'· ..... ~ ~
-~ -~ .... "-' ""' .... "'-~ .....
'· -.. ~ .. " .0
.......... r---.. .. -w J-r--.... .... .... -....
,...., ...... --~ .r "-' ~. --...
.. r----. ...,' --I I
i
I I
Cycle,; to FailurP N
Figure 4-37. Single-Lap Bonded Joint Tension Fatigue S-N CurveType AS/3002-Batch, Graphite/Epoxy, Room Temperature7
(0/±45) 5 (0/±45/90)5
(02/±45)5
............. ...... r--.; ... ~~ ~ ...... ..
... ~ ~
0 l> ::1:1 (') 0 s:
'
GRAPHITE/EPOXY TO TITANIUM
5.0 R = 0.05
J .I I I I I I . .1 I I I
I I I I I j_ -Ti"l r-- [0
' = l\','(2L0
) Nx _. II ~ ... _
4.5
Nx 4.0 .=------:-r---1-ffr \ l -
.. "' OJ
3.5
(J5 2.5 "'0 t: 0
a:!
~ 2.0 § .. "' ;:g
1.5
1.0
0.5
METLBOND 329-7 1
() iolo...
ADHESIVE GRAPHITE/EPOXY
-- ...... ~ ~~ ARROWS INDICATE NO FAILURE OCCURRED ['"'. ~ 1-oo 0 ROOM TEMP ---r--. ~ ... tl 350°F ..............
-...., ........ ~ll> I .......... ~ ~
I ¢ l~ I
""" ....... u-~ ... ~- ~- ..... ..... ·--· .. ..... ~ --~ --. .. '
"·~- .... :s ....... ~- - I ........... .. , ..
I"• ·-- ..... .. . ... --·
Cycles to Failure N
Figure 4-38. Bonded Symmetrical Scarf Joint Tension Fatigue S-N Curves - Type AS/3002-Batch, Graphite/Epoxy- Room Temperature and .350°F, [0/±45hs (Ref. 7)
-
-
-
--
0 )> :a 0 0 ~ ' "0
..... 0 Gl w ... Gl
~ I
U"l 00
5.0
4.5
4.0
·;;; 3.5 ..... ~
<I> <I>
3.0 ., !::
tJl .... <"<I
"' ..r:: tJl
-c 2.5 " 0
IXl
E 2.0 "' E ... <"<I
:::; 1.5
1.0
0.5
GRAPHITE/EPOXY TO TITANIUM
R 005 = I I
I I I Ti j_ fa'= Nx/(2La) L
~ ....._ - .;:>.1 -~
Nx ......... -- ----- r- La .,_. ti .......
""" ................
............. ....... METLBOND 329-7
...... P- ADHESIVE ............... GRAPHITE/EPOXY ~
"' -... ... """' ' I
~ ~ ...
' '----- ~ ~~ ~- -· ~-- ...... .... .. ..
~· .... ['-.. ... . .. ··~· ....... .. tl .. _ .. .. r-...
L .. - -r---. .... . -·· •. It! ..... .. .J.. - INDICATE NO ~ ARROWS FAILURE OCCURRED
·- 0 ROOM TEMP.-
r-- tl 350°F ····-----·
Cycles to Failure N
Figure 4-39. Bonded Symmetrical Scarf Joint Tension Fatigue S-N Curves- Type AS/3002-Batch, Graphite/Epoxy- Room Temperature and 350°F, [0/±45/90hs (Ref. 7)
I
Nx
-~ -
0 l> :a n 0 ~ . ., .... 0 0)
(., ... 0)
·;;; -"'
~ <Jl
"' "' .... ci'i
.... "' "' ..c
Cf)
-o c: 0
lXI
E ::> E
"' "' ::E
GRAPHITE/EPOXY TO TITANIUM 5.0
4.5
4.0
3.5
) IR 0.05
I I I I I I I I T. T TT T I Ill .... = ........... ~
I I I Ti' ... fa'= N,J(2La) ~
~·-"' .. . ..
~ ~ ~-........ Nx Nx
__.-A"' f+- L -+ "f ""--~ ~ METLBOND 329-7 a t
~ ~ ADHESIVE ~
GRAPHITE/EPOXY ~~1!11..
3.0 1--' ......
~ '"' !Ill. ')
I ,.... ~,
' 2.5 ;L. •• ~ ~ ~ .... I"
1.5
2.0
~
1.0 1-
1-
0.5
0.0 0
10
"'·· '"· ~-····· I,....,__., ... __ , .•. ··:-. r--.. - r- r-. t-• ......... ..•. •.. . ,,
I "1"-.... .... . ARROWS INDICATE NO FAILURE OCCURRED -u ........
0 ROOM TEMP ss Sl 350° F ••••••••••••
Cycles to Failure N
Figure 4-40. Bonded Symmetrical Scarf Joint Tension Fatigue S-N Curves- Type AS/3002-Batch, Graphite/Epoxy - Room Temperature and 350°F, [02/±45]a:,; (Ref. 7)
....
107
0 )II ::D (') 0 ~ I
-a .... c G)
w ... G)
TABLE 4-15 SUMMARY OF BOLTED JOINT FATIGUE TEST RESULTS•2
MATERIALS AND GAGES,
JOINT TYPE in.
BORO)';jBORON
(0.120)/(0.120)
BORONj7075-T6
(0.120)/(0.160)
SINGLE L\P FIBERGLASS/ FIBERGLASS (0. 120)/ (0. 120)
FIBERGLASS/7075-T6
(0.120)/(0.160)
BORO)';j7075-T6
(0. 120)/(0.200)
DOCBLE LAP FIBERGLASS/7075-T6
(0.120)/(0.200)
BORON/7075-T6
DOL:BLE LAP (0.120)/ (0.200) BOLTED :\:'\D BO:'\DED
FIBERGLASS/7075-T6
(0.120)/(0.200)
*STRESS RATIO. R = .0.05 BOLT DIA:-.lETER. D = 0.19011\
EDGE MAXIMUM LOAD DISTANCE, MINIMUM LOAD
in. lbjlb
0. 750 1800/90
1960/98
1460/73
1765/88
2100/105
1650/83
1890/95
4950/248
0.750
4950/248
l-IN. SPECIMEN WIDTH LAMINATE PATTERN A, SEETABLE4-I.
MAXIMUM LOAD%0F RANGES OF
STATIC CYCLES TO
UlTIMATE TESTS FAILURE FAILURE MODES
4,000 70 5 TO BEARING AND SHEAR-OUT
13,000
1.000 BORON-BEARING 70 5 TO
24,000 ALL:MINUM THROUGH FASTENER HOLE
1,700 70 5 TO DELAMINATION AND
7,000 SHEAR-OUT
1,100 70 5 TO DELAMINATION AND
62,700 SHEAR-OUT
130,000 ALUMINL:l\1 THROUGH 70 5 TO FASTENER HOLE
2,677,000 NONE (RUNOL'TS)
1,000,000 70 3 TU NONE (RU:-.IOUTS)
7,591,000
I ,247,000 NONE (RUNOUTS) 80 2 TO
1,731,000 ALUMI)';L'M THROUGH FASTENER HOLE
101,000 LAM IN ATE AND ALUMINUM TO THROUGH HOLE
38 5 176,000 ALUMINUM THROUGH BASIC SECTION
11,400 66 5 TO DELAMINATION AND ADHESIVE I
49,200
c )> :J:I n 0 3: ' .,
..... 0 a» w ... 01
200
180
160
·;;; 140 ... <II "' "' ...
rfi 120 """ c
·;: .. "' lXI 100 .::: " »
u E 80 "' E
"' .. ~
60
40
20
r--
FLUSH HEAD FASTENER D = 0.19 in.
l l
-o [0/±45]45
e!D = s/D == 2.63 NOMINAL
R = 0.05
---···0 [0/!45/90]25
- --o- [02/±45]25
~ .. .. I ....... ---....a--T .. : .... --- --- -- - -·--t---~-- 1'-'
~-~
Cycles to Failure N
CYCLING RATE: 95 TO 100 Hz
1 I l l I ARROWS INDICATE NO FA I LURE
I I I I
l' = PI(Dt)
- -~ IS" •j ~---..:··· --~- ··-........ ~
, ... -( ,.... ... <0- r--or-
~
--
Figure 4-41. Room Temperature Fatigue S-N Curves for Various Crossplied Graphite/Epoxy to Steel Single-Lap Flush Head Mechanical Joints - Type AS/3002-Batch, Graphite/Epoxy'
I
0 )> :a 0 0 3:
.j>.. I
0'-N
200
180
160
·;;:; 140 .Jo<
,£
"' ., .. ~ 120 c: .. .. .,
a:l )
.::! 100 u >-u E ;;l 80 E ·;:; ..
::;:
60
40
20
PROTRUDING HEAD FASTENER D = 0.19 in. e!D == s!D = 2.63 NOMINAL
R • 0. OS
CYCLING RATE: 95 TO 1 00 Hz
I I I I l ARROWS INDICATE NO FAILURE
/' = PI(Dt)
~-- • l""l ~--· ,., .... ~ ..... ~"···- ....... - - - .......
~ :-~ - - - ·~ . . .;; ~ ----~--~ --- -~- ~-
9 .- -- ···- -···· ~ .. ~d .--~-~ --....
,...
n.
-o [D/!45Js
·-··-· 0 [0/:!:45/9Dls
- --o- [olt4S]s
J I
Cycles to Failure N
Figure 4-42. Room Temperature Fatigue S-N Curves for Various Crossplied Graphite/Epoxy to Steel Single-Lap Protruding Head Mechanical Joints -
Type AS/3002-Batch, Graphite/Epoxy7
'
I
!
_, I I
0 )> :::D C')
0 s::
I ., .... 0 m w .... m
DARCOM-P 708-318
REFERENCES 1. A. V. Hawley, et al., Investigations of]oints and
Cutouts in Advanced Fibrous Composites for Aircraft Structures, Fifth Quarterly Progress Report, Contract No. F 33615-67-C-1582, Wright-Patterson Air Force Base, OH, July 1968.
2. G. M. Lehman and A. V. Hawley, Investigations of ]oints in Advanced Fibrous Composites for Aircraft Structures, Vol. 7, Technical Discussion and Summary, Technical Report AFFD L-TR-69-43, Vol. 1, Wright-Patterson Air Force Base, OH, June 1969.
3. A. V. Hawley, et al., lnvest(r,ations of}oints and Cutouts in Advanced Fibrous Composites for Air-
craft Structures, Third Quarterly Progress Report, Contract No. F33615-67-C-1582, Wright-Patterson Air Force Base, OH, January 1968.
4. A. V. Hawley, et al., lnvestzgations of}oints and Cutouts in Advanced Fibrous Composites for Aircraft Structures, Fourth Quarterly Progress Report, Contract No. F33615-67-C-1582, Wright-Patterson Air Force Base, OH, April 1968.
5. G. N. Sage, "Some Aspects of Bonded Joint Design in CPFP", Composites 7, No. 4, IPC Science and Technology Press Ltd., Guildford, Surry, England (October 1976 ).
4-63
DARCOM-P 706-316
INDEX
A Adhesives
bonded joints, advantages/disadvantages of, 1-3 environmental effects on, 1-4 failure, 4-1, 4-2, 4-36, 4-38 important properties of, 1-4, 3-14,3-15,3-19,
3-27, 3-33 Advanced composites, definition of, 1-1
B Bolted composite joints
bushed holes, 4-28, 4-30, 4-31, 4-32 compared to bonded joints, 4-52
fatigue, 4-42 strength, 4-33 weight, 4-38
design considerations, 2-3 double lap, 4-28, 4-29 failure, 4-36 plain holes, 4-28 reinforced edges, 4-28, 4-33, 4-34 single lap, 4-28 strength, 2-22
. Bolted joints, strengths of, 2-26, 4-60 Bonded joints
compared to bolted joints, 4-28, 4-33, 4-34 fatigue, 4-41, 4-52
design considerations, 2-2, 2-3, 4-1, 4-2 discrete element analysis, 2-3 double lap, 4-2, 4-8, 4-11, 4-12, 4-23 failure, 4-36 length/thickness ratio, 4-2, 4-4, 4-5 properties, 1-3, 1-4 scarf, 4-5, 4-15 single lap, 4-2 stepped lap, 4-23 strap, 4-34, 4-35, 4-36 weight increment to achieve strength, 4-38
c Composite
advanced, 1-1 defined, 1-1 failure, 1-4, 4-36 fiber reinforced, 1-4 machining, effect of, 1-4, 2-13
properties of general, 1-4 mechanical, 3-23, 3-32 (see also: Mechanical
properties of composites) surface preparation prior to bonding, 1-4 thickness/bolt diameter ratio, 2-3, 4-23, 4-27
D Data
baseline design, 3-2 mechanical properties of
adhesives, 3-14, 3-15 (see at.ro: Adhesives) laminates, 3-2, 3-3, 3-5, 3-6 (1el! also:
Laminates) Design
bolted joints, 2-3, 2-6 bonded joints, 2-2, 2-3 data generation, 3-20 philosophy, 2-2 techniques, 2-2
Discrete element analysis of bonded joints (.rei': Bonded joints)
Double-lap joints, 4-2, 4-4, 4-5 test results, 4-8, 4-11, 4-12, 4-29 weight increment to achieve strength, 4-38
E Edge distance/bolt diameter ratio, 2-3, 3-2, 4-23,
4-27 Efficiency of joints, 1-1, 4-23, 4-36, 4-39, 4-40 F:t (product of elastic modulus E and thickness I)
ratio bonded composite/aluminum scarf joints, 4-14 bonded double-lap joints, 4-2, 4-4, 4-11 bonded single-lap joints, 4-2 comparison of bonded joint performance, 4-23 effect on joint strength, 4-2 importance of matching to equalize stress, 4-2 significance of, 4-2
F Failure
adhesives, 4-1, 4-2, 4-36, 4-38 bolted joints, 2-3, 4-36 bonded joints, 4-36, 4-38 composites, 1-4, 4-36
I-1
DARCOM-P 706-316
INDEX (cont'd)
Fatigue bolted-bonded joints, 4-42, 4-49, 4-60 bolted joints, 4-42, 4-49, 4-60 bonded joints, 4-41, 4-52
Fiber orientation, 2-13, 4-2, 4-5, 4-23 (ser aho: Laminate patterns)
J Joints
adhesive bonded, 1-2, 1-3 bolted composite (see: Bolted composite joints) bonded (.ree: Bonded joints) configurations, 4-1, 4-36 definition of, 1-1 design of, 1-3, 2-2, 2-3, 2-6, 3-2, 3-28 double lap, 4-2, 4-4, 4-5 efficiency, 1-1, 4-23, 4-36, 4-39, 4-40 mechanical (.ree: Mechanical joints) performance comparisons of different types,
4-23 scarf (see: Scarf joints) single lap, 4-2, 4-6 stepped lap, 4-23 weight
comparisons, 4-51 increments to achieve strength, 4-38
L Laminates
mechanical properties, 3-2, 3-3, 3-5, 3-6, 3-33 patterns, 4-2, 4-5, 4-25
M Machining of composites, 1-4 Mechanical joints
advantages/ disadvantages, 1-2 definition, 1-2
Moduli effective tensile, 3-14, 3-15 elastic
compression, 3-14, 3-15 tensile, 3-14, 3-15
shear adhesive, 3-14, 3-19, 3-20 laminate, 3-2, 3-6
Young's, 3-14
p Patterns, laminate, 4-2, 4-5, 4-25 Properties, mechanical, of composites, 3-23, 3-32
test methods, 3-33
1-2
tests for bearing, 3-33 compression, 3-32 flexure, 3-32 tension, 3-23
R Ratios
composite thickness/bolt diameter, 2-3, 4-23, 4-27
edge distance/bolt diameter, 2-3, 3-2, 4-23, 4-27 length/thickness, 4-2, 4-4, 4-5 side distance/bolt diameter, 2-3, 3-2, 4-23, 4-27
s Scarf joints, 4-5, 4-14
stress distribution, 4-5, 4-14 weight increment to achieve strength, 4-38
Side distance/bolt diameter, 2-3, 4-23, 4-27 Single-lap joints, 4-2
test results, 4-6, 4-28 weight increment to achieve strength, 4-38
Stepped-lap joints, 4-23 Stiffness, 4-2 Strain capability, 4-1 Strap joints, 4-34
radiused, 4-34 stepped, 4-34 straight taper, 4-35
Stress analysis, 2-2, 2-3
bolted joints, 2-3, 2-6 bonded joints, 2-2, 2-3 discrete element, 2-3 photoelastic, 2-3
concentration, 4-1 distribution of, 4-2 factor, 4-2 reduction in strap joint by, 4-34
increased adhesive thickness, 4-36 strap modification, 4-34 variable adhesive stiffness, 4-36
Surface preparation, 1-4 composite prior to bonding, 1-4 peel-ply, 1-5 purpose of, 1-5
T Testing, 3-20 (ue a/.w: Properties, mechanical, of
composite: Tests for) equations, 3-23, 3-32
methods, 3-23 specimens, 3-33
w Weight efficiency, 4-23
INDEX (cont'd)
y Young's modulus, 3-14
DARCOM-P 706-316
1-3
(DRCDE-L)
FOR THE COMMANDER:
OFFICIAL:
LTC, Adjutant General
DISTRIBUTION: Special
DARCOM-P 706-316
ROBERT L. MOORE Major General, USA Chief of Staff
<r U.S. ~Iff I'I!AITIIIG OFFICE, 19/'l-280-964/5968