Introduction to theDesign and Behavior

of Bolted Joints

Non-Gasketed Joints

Fourth Edition

Bickford/Introduction to the Design and Behavior of Bolted Joints 8176_C000 Final Proof page i 27.7.2007 9:35pm Compositor Name: VBalamugundan

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Non-Gasketed Joints, John H. Bickford

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Bickford/Introduction to the Design and Behavior of Bolted Joints 8176_C000 Final Proof page viii 27.7.2007 9:35pm Compositor Name: VBalamugundan

Introduction to theDesign and Behavior

of Bolted Joints

John H. Bickford

Non-Gasketed Joints

Fourth Edition

CRC Press is an imprint of theTaylor & Francis Group, an informa business

Boca Raton London New York

Bickford/Introduction to the Design and Behavior of Bolted Joints 8176_C000 Final Proof page ix 27.7.2007 9:35pm Compositor Name: VBalamugundan

CRC PressTaylor & Francis Group6000 Broken Sound Parkway NW, Suite 300Boca Raton, FL 33487-2742

2008 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa business

No claim to original U.S. Government worksPrinted in the United States of America on acid-free paper10 9 8 7 6 5 4 3 2 1

International Standard Book Number-10: 0-8493-8176-2 (Hardcover)International Standard Book Number-13: 978-0-8493-8176-8 (Hardcover)

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Library of Congress Cataloging-in-Publication Data

Introduction to the design and behavior of bolted joints. -- 4th ed.p. cm.

Includes bibliographical references and index.ISBN 978-0-8493-8176-8 (alk. paper)1. Bolted joints. I. Bickford, John H., 1926- Non-gasketed joint. II. Title.

TA492.B63B5 2007621.882--dc22 2007007723

Visit the Taylor & Francis Web site athttp://www.taylorandfrancis.comand the CRC Press Web site athttp://www.crcpress.com

Bickford/Introduction to the Design and Behavior of Bolted Joints 8176_C000 Final Proof page x 27.7.2007 9:35pm Compositor Name: VBalamugundan

Dedication

Once again to my wife, Anne,

to our children David, Peter, and Leila,

and to Leilas childrenour delightful

granddaughtersZoe and Arden Sawyer.

Also to their father Hal Sawyer and to

Greg McCarthy. None of these people will

ever have to read this book, though

Hal probably will.

Bickford/Introduction to the Design and Behavior of Bolted Joints 8176_C000 Final Proof page xi 27.7.2007 9:35pm Compositor Name: VBalamugundan

Bickford/Introduction to the Design and Behavior of Bolted Joints 8176_C000 Final Proof page xii 27.7.2007 9:35pm Compositor Name: VBalamugundan

Table of Contents

Preface to the Fourth Edition .............................................................................................xxix

Acknowledgments for Volume 1 of the Fourth Edition .......................................................xxxi

Preface to the Third Edition............................................................................................. xxxiii

Preface to the Second Edition ........................................................................................... xxxv

Preface to the First Edition ............................................................................................. xxxvii

Acknowledgments for the First Three Editions ......................................................................xli

Editor..................................................................................................................................xliii

Abstract ...............................................................................................................................xlv

Chapter 1

Basic Concepts .......................................................................................................................1

1.1 Two Types of Bolted Joints ...........................................................................................1

1.2 Bolts Job .......................................................................................................................1

1.2.1 Tensile Joints ......................................................................................................1

1.2.2 Shear Joints ........................................................................................................3

1.3 The Challenge ................................................................................................................3

1.3.1 Assembly Process................................................................................................4

1.3.2 In-Service Behavior.............................................................................................5

1.3.2.1 Joints Loaded in Tension ..................................................................... 5

1.3.2.2 Shear Joints .......................................................................................... 5

1.4 Failure Modes................................................................................................................6

1.5 Design ............................................................................................................................7

1.5.1 In General...........................................................................................................7

1.5.2 Specific Goals of the Designer............................................................................7

1.6 Layout of the Book........................................................................................................8

Exercises .................................................................................................................................8

Chapter 2

Materials ..............................................................................................................................11

2.1 Properties That Affect the Clamping Force.................................................................11

2.1.1 Magnitude of the Clamping Force ...................................................................11

2.1.2 Stability of the Clamping Force .......................................................................12

2.1.2.1 Thermal Expansion or Contraction ................................................... 12

2.1.2.2 Corrosion ........................................................................................... 12

2.1.2.3 Fatigue Rupture ................................................................................. 12

2.1.2.4 Loss of Strength with Temperature.................................................... 12

2.1.2.5 Loss of Clamping Force with Temperature ....................................... 13

2.1.2.6 Elastic Stiffness of the Parts ............................................................... 13

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xiii

2.1.2.7 Change in Stiffness with Temperature............................................ 13

2.1.2.8 Brittle Fracture ............................................................................... 13

2.1.3 Miscellaneous Properties...............................................................................13

2.2 Fastener Standards.....................................................................................................14

2.3 Selecting an Appropriate Standard ............................................................................14

2.4 Bolting Materials........................................................................................................16

2.5 Tensile Strength of Bolting Materials ........................................................................16

2.5.1 General Purpose=Automotive Group............................................................172.5.2 Structural Steel Group ..................................................................................17

2.5.3 Petrochemical=Power Group.........................................................................172.5.4 Metric Group ................................................................................................17

2.5.5 Extreme-Temperature Materials ...................................................................18

2.5.5.1 American Society for Testing and Materials (ASTM)

F2281 Materials.............................................................................. 18

2.5.5.2 Traditional High-Temperature Materials ....................................... 18

2.5.6 Corrosion-Resistant Group...........................................................................19

2.5.7 Two New ASTM Bolting Standards.............................................................19

2.5.7.1 Room Temperature Strengths of ASTM F2281

and F2282 Materials....................................................................... 20

2.6 Metric Fasteners.........................................................................................................20

2.7 Equivalent Materials ..................................................................................................21

2.8 Some Comments on the Strength of Bolting Materials .............................................21

2.8.1 In General .....................................................................................................21

2.8.2 Shear Strength...............................................................................................21

2.8.3 Bearing Yield Strength..................................................................................23

2.8.4 Hardness versus Strength..............................................................................23

2.9 Nut Selection..............................................................................................................24

2.10 Effects of Temperature on Material Properties..........................................................26

2.10.1 Thermal Expansion .......................................................................................27

2.10.2 Miscellaneous Temperature Problems...........................................................31

2.11 Other Material Factors to Consider...........................................................................32

2.11.1 Fatigue Properties .........................................................................................32

2.11.2 Corrosion ......................................................................................................32

2.11.3 Miscellaneous Considerations .......................................................................32

2.12 Joint Materials ...........................................................................................................32

Exercises ...............................................................................................................................35

References and Bibliography................................................................................................35

Chapter 3

Stress and Strength Considerations......................................................................................39

3.1 Types of Strength .......................................................................................................39

3.1.1 Tensile Strength ............................................................................................39

3.1.2 Thread-Stripping Strength ............................................................................39

3.1.3 Shear Strength...............................................................................................40

3.1.4 Brittle Fracture Strength...............................................................................40

3.1.5 Strengths at High and Low Temperatures ....................................................40

3.1.6 Fatigue Strength............................................................................................40

3.1.7 Stress Corrosion Cracking Strength..............................................................40

3.2 Bolt in Tension...........................................................................................................41

3.2.1 Elastic Curves for Bolts in Tension...............................................................41

3.2.2 Elastic Curves under Repeated Loading .......................................................42

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xiv

3.2.3 Stress Distribution under Tensile Load ........................................................42

3.2.4 Stress Concentrations....................................................................................43

3.2.5 Magnitude of Tensile Stress ..........................................................................43

3.2.6 Stress in the Nut ...........................................................................................45

3.3 Strength of a Bolt.......................................................................................................48

3.3.1 Proof Strength...............................................................................................48

3.3.2 Tensile Stress Area ........................................................................................49

3.3.3 Other Stress Area Equations.........................................................................50

3.3.4 Stress AreasMetric Threads.......................................................................51

3.3.5 Strength of the Bolt under Static Loads .......................................................53

3.4 Strength of the Joint ..................................................................................................54

3.4.1 Contact Stress between Fastener and Joint...................................................54

3.4.2 Stresses within and between the Joint Members ...........................................56

3.4.3 Static Failure of the Joint .............................................................................56

3.5 Other Types of Load on a Bolt..................................................................................57

3.5.1 Strength under Combined Loads ..................................................................59

Exercises and Problems ........................................................................................................59

References and Bibliography................................................................................................59

Chapter 4

Threads and Their Strength .................................................................................................61

4.1 Thread Forms ............................................................................................................61

4.1.1 Thread Forms in General .............................................................................61

4.1.2 Inch Series Thread Forms.............................................................................61

4.1.3 Metric Thread Forms....................................................................................63

4.2 Thread Series..............................................................................................................63

4.3 Thread Allowance, Tolerance, and Class...................................................................64

4.3.1 Inch Series Threads .......................................................................................64

4.3.1.1 Allowance ....................................................................................... 64

4.3.1.2 Tolerance ........................................................................................ 64

4.3.1.3 Class ............................................................................................... 64

4.3.2 Metric Threads..............................................................................................65

4.3.2.1 Tolerance Position (the Allowance)................................................ 66

4.3.2.2 Tolerance Grade (the Tolerance).................................................... 66

4.3.2.3 Tolerance Class (the Class)............................................................. 66

4.3.3 Inch Series and Metric Thread Classes, Compared ......................................66

4.3.4 Coating Allowances ......................................................................................67

4.3.5 Tolerances for Abnormal Lengths of Engagement .......................................67

4.4 Inspection Levels........................................................................................................68

4.5 Thread Nomenclature ................................................................................................69

4.5.1 Inch Series .....................................................................................................69

4.5.2 Metric Thread ...............................................................................................69

4.6 Coarse- versus Fine- versus Constant-Pitch Threads .................................................70

4.6.1 Coarse-Pitch Threads....................................................................................70

4.6.2 Fine-Pitch Threads........................................................................................70

4.6.3 Constant-Pitch Threads ................................................................................70

4.6.4 Miscellaneous Factors Affecting Choice .......................................................70

4.7 The Strength of Threads ............................................................................................71

4.7.1 Basic Considerations .....................................................................................71

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4.7.2 Thread Strength Equations ...........................................................................71

4.7.3 Thread Strength Computations When Le D .............................................724.7.4 Basic ProcedureAn Example .....................................................................73

4.7.5 Thread Strength Calculations When Le 6D .................................................734.7.6 Other Stress Area Formulas..........................................................................74

4.8 What Happens to Thread Form under Load? ...........................................................76

4.9 Things That Modify the Static Strength of Threads ..................................................76

4.9.1 Common Factors ..........................................................................................76

4.9.2 Which Is Usually StrongerNut or Bolt? ....................................................79

4.9.3 Tables of Tensile Stress and Shear Areas......................................................79

4.10 Other Factors Affecting Strength...............................................................................81

4.10.1 Pitch Diameter ..............................................................................................81

4.10.2 Other Thread Parameters..............................................................................81

Exercises and Problems ........................................................................................................82

References and Bibliography................................................................................................82

Chapter 5

Stiffness and Strain Considerations......................................................................................85

5.1 Bolt Deflection ...........................................................................................................85

5.1.1 Basic Concepts ..............................................................................................85

5.1.2 Change in Length of the Bolt .......................................................................87

5.1.2.1 Effective Length.............................................................................. 87

5.1.2.2 Cross-Sectional Areas of the Bolt................................................... 89

5.1.3 Computing Change in Length of the Bolt ....................................................89

5.2 Bolt Stiffness Calculations .........................................................................................90

5.2.1 Basic Concepts ..............................................................................................90

5.2.2 Example ........................................................................................................90

5.2.3 Actual versus Computed Stretch and Stiffness .............................................92

5.2.4 Stiffness of BoltNutWasher System ..........................................................92

5.2.5 Alternative Expression for Bolt Stiffness ......................................................92

5.2.6 Energy Stored in the Bolt .............................................................................93

5.3 The Joint ....................................................................................................................94

5.3.1 Basic Concepts ..............................................................................................94

5.3.2 Computing Joint Stiffness .............................................................................95

5.3.2.1 Stiffness of Concentric Joints ......................................................... 96

5.3.2.2 Stiffness of Eccentric Joints ............................................................ 97

5.3.3 Stiffness in Practice .....................................................................................100

5.3.3.1 A Quick Way to Estimate the Stiffness of Non-Gasketed

Steel Joints.................................................................................... 100

5.4 Gasketed Joints ........................................................................................................ 101

5.5 An Alternate Way to Compute Joint Stiffness ........................................................ 103

5.6 Joint Stiffness Ratio or Load Factor ....................................................................... 104

5.7 StiffnessSome Design Goals ................................................................................. 104

5.7.1 Energy Stored in the Joint Members ..........................................................104

5.7.2 Relationship between Stiffness and Stored Energy .....................................105

5.7.3 Stiffness Ratio.............................................................................................106

Exercises and Problems ...................................................................................................... 106

References .......................................................................................................................... 107

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Chapter 6

Introduction to Assembly...................................................................................................109

6.1 Initial versus Residual Preload .................................................................................. 109

6.2 Starting the Assembly Process ...................................................................................110

6.2.1 Assembling the Parts ......................................................................................110

6.2.2 Tightening the First Bolt ................................................................................ 110

6.3 Bolt Preload versus Clamping Force on the Joint .....................................................114

6.3.1 Effects of Hole Interference ............................................................................114

6.3.2 Resistance from Joint Members ..................................................................... 116

6.4 Continuing the Snugging Pass ...................................................................................119

6.5 Short-Term Relaxation of Individual Bolts ...............................................................119

6.5.1 Sources of Short-Term Relaxation ................................................................. 119

6.5.1.1 Poor Thread Engagement ................................................................ 120

6.5.1.2 Thread Engagement Too Short........................................................ 120

6.5.1.3 Soft Parts.......................................................................................... 121

6.5.1.4 Bending ............................................................................................ 121

6.5.1.5 Nonperpendicular Nuts or Bolt Heads ............................................ 121

6.5.1.6 Fillets or Undersized Holes .............................................................. 121

6.5.1.7 Oversized Holes................................................................................ 121

6.5.1.8 Conical Makeups ............................................................................. 121

6.5.2 Factors Affecting Short-Term Relaxation ...................................................... 122

6.5.2.1 Bolt Length ...................................................................................... 123

6.5.2.2 Belleville Washers............................................................................. 123

6.5.2.3 Number of Joint Members ............................................................... 123

6.5.2.4 Tightening Speed.............................................................................. 123

6.5.2.5 Simultaneous Tightening of Many Fasteners................................... 124

6.5.2.6 Bent Joint Members ......................................................................... 124

6.5.3 Amount of Relaxation to Expect....................................................................124

6.5.4 Torsional Relaxation ......................................................................................125

6.6 Elastic Interactions between Bolts ............................................................................. 127

6.7 The Assembly Process Reviewed ............................................................................... 132

6.8 Optimizing Assembly Results .................................................................................... 134

Exercises ............................................................................................................................. 135

References .......................................................................................................................... 135

Chapter 7

Torque Control of Preload................................................................................................. 137

7.1 Importance of Correct Preload .................................................................................. 137

7.1.1 Problems Created by Incorrect Preload..........................................................138

7.1.2 How Much Preload? ....................................................................................... 138

7.1.3 Factors That Affect the Working Loads on Bolts.......................................... 139

7.2 Torque versus PreloadThe Long-Form Equation .................................................. 140

7.3 Things That Affect the TorquePreload Relationship............................................... 142

7.3.1 Variables That Affect Friction........................................................................ 142

7.3.2 Geometric Variables ....................................................................................... 143

7.3.3 Strain Energy Losses ......................................................................................144

7.3.4 Prevailing Torque ...........................................................................................144

7.3.5 Weight Effect ..................................................................................................144

7.3.6 Hole Interference ............................................................................................ 145

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7.3.7 Interference Fit Threads ............................................................................... 145

7.3.8 The Mechanic.............................................................................................. 145

7.3.9 Tool Accuracy.............................................................................................145

7.3.10 Miscellaneous Factors................................................................................. 145

7.4 Torque versus PreloadThe Short-Form Equation................................................146

7.5 Nut Factors..............................................................................................................147

7.5.1 Some General Comments............................................................................ 147

7.5.2 Nut Factor Examples and Case Histories................................................... 148

7.5.3 Coefficient of Friction versus Nut Factor................................................... 151

7.6 Torque Control in Practice ...................................................................................... 151

7.6.1 What Torque Should I Use? ....................................................................... 151

7.6.2 Initial Preload Scatter ................................................................................. 152

7.6.3 Low Friction for Best Control ....................................................................153

7.6.4 The Lines Arent Always Straight...............................................................153

7.6.5 Other Problems ........................................................................................... 154

7.7 Some Tools for Torque Control ..............................................................................155

7.7.1 Some Generalities ....................................................................................... 155

7.7.2 Reaction Forces Created by the Tool .........................................................157

7.7.2.1 Shear Loads Created by Torque Wrenches .................................. 157

7.7.2.2 Reaction Torques ......................................................................... 158

7.7.3 In the BeginningA Search for Accuracy..................................................159

7.7.3.1 Manual Torque Wrenches ............................................................ 159

7.7.4 More Torque for Large Fasteners ..............................................................160

7.7.4.1 Torque Multipliers and Geared Wrenches ................................... 160

7.7.4.2 Hydraulic Wrenches ..................................................................... 160

7.7.5 Toward Higher Speed ................................................................................. 160

7.7.5.1 Impact Wrenches .......................................................................... 161

7.7.5.2 Pulse Tools ................................................................................... 161

7.7.5.3 Nut Runners ................................................................................. 161

7.7.6 Add Torque Calibration or Torque Monitoring......................................... 162

7.7.7 Add Torque Feedback for Still Better Control...........................................164

7.7.8 For More Information ................................................................................164

7.8 Fasteners That Limit Applied Torque ..................................................................... 164

7.8.1 The Twist-Off Bolt...................................................................................... 164

7.8.2 The Frangible Nut ...................................................................................... 165

7.9 Is Torque Control Any Good?................................................................................. 166

7.10 Testing Tools............................................................................................................166

7.11 The Influence of Torque Control on Joint Design................................................... 167

7.12 Using Torque to Disassemble a Joint ......................................................................168

Exercises and Problems ...................................................................................................... 169

References and Bibliography.............................................................................................. 169

Chapter 8

Torque and Turn Control ..................................................................................................173

8.1 Basic Concepts of Turn Control ..............................................................................173

8.2 Turn versus Preload ................................................................................................. 175

8.2.1 Common TurnPreload Relationship .........................................................175

8.2.2 Other TurnPreload Curves........................................................................176

8.2.2.1 Sheet Metal Joint.......................................................................... 176

8.2.2.2 Gasketed Joint.............................................................................. 177

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8.3 Friction Effects......................................................................................................... 177

8.4 Torque and Turn in Theory..................................................................................... 179

8.4.1 Torque, Turn, and Energy ............................................................................179

8.4.2 TorqueTurnPreload Cube .........................................................................179

8.4.3 The Broader View......................................................................................... 179

8.5 Turn-of-Nut Control................................................................................................181

8.5.1 The Theory ...................................................................................................181

8.5.2 The Practice ..................................................................................................182

8.5.2.1 Structural Steel ............................................................................... 182

8.5.2.2 Turn-of-Nut Procedure in Production Operations ......................... 183

8.5.2.3 Turn-of-Nut Procedure in Aerospace Assembly ............................ 183

8.6 Production Assembly Problems ............................................................................... 184

8.7 Popular Control Strategies....................................................................................... 186

8.7.1 TorqueAngle Window Control ................................................................... 186

8.7.2 TorqueTime Window Control ....................................................................187

8.7.3 Hesitation and Pulse Tightening................................................................... 187

8.7.4 Yield Control ................................................................................................188

8.7.5 Turn-of-Nut Control .................................................................................... 190

8.7.6 Prevailing Torque Control ............................................................................191

8.7.7 PlusPermanent Records ............................................................................191

8.7.8 Meanwhile, Out in the Field .........................................................................191

8.8 Monitoring the Results ............................................................................................ 192

8.9 Problems Reduced by TorqueAngle Control ......................................................... 193

8.10 How to Get the Most Out of TorqueAngle Control..............................................193

Exercises and Problems ...................................................................................................... 194

Bibliography and References..............................................................................................194

Chapter 9

Other Ways to Control Preload ......................................................................................... 197

9.1 Stretch Control: The Concept .................................................................................. 197

9.2 Problems of Stretch Control .................................................................................... 198

9.2.1 Dimensional Variations ................................................................................ 198

9.2.2 Change in Temperature ................................................................................ 199

9.2.3 Plastic Deformation of the Bolt....................................................................199

9.2.4 Bending and Nonperpendicular Surfaces...................................................... 199

9.2.5 Grip Length ..................................................................................................199

9.3 Stretch Measurement Techniques ............................................................................199

9.3.1 Micrometer Measurements ........................................................................... 199

9.3.1.1 Irregular Measurement Surfaces..................................................... 199

9.3.1.2 Operator Feel ................................................................................. 200

9.3.1.3 Measurement Accuracy Required .................................................. 200

9.3.1.4 Depth Micrometers ........................................................................ 200

9.3.2 Other Techniques .......................................................................................... 201

9.3.2.1 Dial Gages...................................................................................... 201

9.3.2.2 Commercially Available Gage Bolt ................................................ 202

9.3.2.3 Ultrasonic Measurements............................................................... 202

9.4 How Much Stretch? ................................................................................................. 202

9.5 Problems Reduced by Stretch Control..................................................................... 203

9.6 How to Get the Most Out of Stretch Control ......................................................... 204

9.7 Direct Preload ControlAn Introduction...............................................................204

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9.7.1 Strain-Gaged Bolts...................................................................................... 205

9.7.2 Strain-Gaged Force Washers ......................................................................205

9.7.3 Direct Tension Indicators ...........................................................................205

9.7.4 Squirter Self-Indicating DTIs......................................................................207

9.7.5 Twist-Off Tension-Control Bolts ................................................................ 207

9.7.6 Alternative-Design Fasteners ......................................................................208

9.8 Bolt Tensioners ........................................................................................................ 208

9.8.1 The Hardware .............................................................................................208

9.9 Bolt Heaters ............................................................................................................. 210

9.10 Problems Reduced by Direct Preload Control.........................................................210

9.10.1 Direct Tension Indicators ...........................................................................210

9.10.2 Twist-Off Bolts............................................................................................ 211

9.10.3 Hydraulic Tensioners ..................................................................................211

9.10.4 Bolt Heaters ................................................................................................ 211

9.11 Getting the Most Out of Direct Preload Control ....................................................211

9.11.1 Twist-Off Bolts and DTI Washers ..............................................................211

9.11.2 Bolt Tensioners ........................................................................................... 212

9.11.3 Bolt Heaters ................................................................................................ 212

9.12 Ultrasonic Measurement of Stretch or Tension .......................................................213

9.12.1 In General ................................................................................................... 213

9.12.2 Principle of Operation................................................................................. 213

9.12.3 How Its Used .............................................................................................214

9.12.4 Calibration of the Instrument ..................................................................... 214

9.12.5 Presently Available Instruments.................................................................. 215

9.13 Ultrasonic Measurements Using Plasma-Coated, Thin Film Transducers .............. 215

Exercises and Problems ...................................................................................................... 215

References .......................................................................................................................... 216

Chapter 10

Theoretical Behavior of the Joint under Tensile Loads .....................................................219

10.1 Basic Joint Diagram................................................................................................. 220

10.1.1 Elastic Curves for Bolt and Joint Members ................................................220

10.1.2 Determining Maximum and Minimum Residual Assembly Preload ..........220

10.1.2.1 The Equations............................................................................. 220

10.1.2.2 An Example ................................................................................ 222

10.1.3 Joint Diagram for Simple Tensile Loads ....................................................224

10.1.4 The Parable of the Red Rolls Royce........................................................... 226

10.1.5 Back to the Joint DiagramSimple Tensile Load......................................227

10.2 Details and Variations .............................................................................................228

10.2.1 Changing the Bolt or Joint Stiffness ........................................................... 228

10.2.2 Critical External Load ................................................................................229

10.2.3 Very Large External Loads.........................................................................230

10.2.4 Another Form of Joint Diagram ................................................................ 230

10.3 Mathematics of the Joint ......................................................................................... 232

10.3.1 Basic Equations........................................................................................... 232

10.3.2 Continuing the Example .............................................................................234

10.4 Loading Planes.........................................................................................................235

10.4.1 Tension Applied to Interface of Joint Members ......................................... 236

10.4.2 Mathematics of a Tension Load at the Interface........................................238

10.4.3 Significance of the Loading Planes ............................................................. 238

10.4.4 Loading Planes within the Joint Members..................................................239

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10.4.5 Modifying Our Example to Include the Effects of Internal

Loading Planes............................................................................................ 243

10.5 Dynamic Loads on Tension Joints........................................................................... 243

10.6 The Joint Under a Compressive Load ..................................................................... 245

10.7 A Warning ...............................................................................................................245

Exercises and Problems ...................................................................................................... 246

References .......................................................................................................................... 247

Chapter 11

Behavior of the Joint Loaded in Tension: A Closer Look................................................. 249

11.1 Effect of Prying Action on Bolt Loads ....................................................................250

11.1.1 Definition of Prying .................................................................................... 250

11.1.2 Discussion of Prying ...................................................................................251

11.1.3 Prying Is Nonlinear..................................................................................... 255

11.2 Mathematics of Prying.............................................................................................256

11.2.1 In General ...................................................................................................256

11.2.2 VDIs Analytical Procedure ........................................................................ 256

11.2.3 Critical Loads and the Preloads Required to Prevent Joint Separation ..... 260

11.2.4 Bending Stress in the Bolt before Liftoff .................................................... 261

11.2.5 Effects of Very Large External Loads......................................................... 263

11.3 Other Nonlinear Factors.......................................................................................... 263

11.3.1 NutBolt System ......................................................................................... 263

11.4 Thermal Effects ........................................................................................................266

11.4.1 Change in Elasticity .................................................................................... 266

11.4.2 Loss of Strength.......................................................................................... 267

11.4.3 Differential Thermal Expansion..................................................................267

11.4.4 Stress Relaxation......................................................................................... 271

11.4.5 Creep Rupture ............................................................................................ 273

11.4.6 Compensating for Thermal Effects .............................................................274

11.5 Joint Equations That Include the Effects of Eccentricity

and Differential Expansion ......................................................................................276

11.5.1 The Equations.............................................................................................276

11.5.2 An Example ................................................................................................277

Exercises and Problems ...................................................................................................... 281

References .......................................................................................................................... 281

Chapter 12

In-Service Behavior of a Shear Joint .................................................................................. 283

12.1 Bolted Joints Loaded in Axial Shear .......................................................................283

12.1.1 In General ...................................................................................................283

12.1.2 Friction-Type Joints.................................................................................... 284

12.1.2.1 Bolt Load in Friction-Type Joints .............................................. 284

12.1.2.2 Stresses in Friction-Type Joints .................................................. 285

12.1.3 Bearing-Type Joints .................................................................................... 285

12.1.3.1 Stresses in Bearing-Type Joints................................................... 286

12.2 Factors That Affect Clamping Force in Shear Joints ..............................................286

12.3 Response of Shear Joints to External Loads ........................................................... 288

12.4 Joints Loaded in Both Shear and Tension ...............................................................288

12.5 Present DefinitionsTypes of Shear Joint .............................................................. 290

Exercises ............................................................................................................................. 290

References .......................................................................................................................... 291

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Chapter 13

Introduction to Joint Failure .............................................................................................293

13.1 Mechanical Failure of Bolts ...................................................................................293

13.2 Missing Bolts..........................................................................................................294

13.3 Loose Bolts............................................................................................................. 294

13.4 Bolts Too Tight ...................................................................................................... 295

13.5 Which Failure Modes Must We Worry About?.....................................................295

13.6 Concept of Essential Conditions ............................................................................ 295

13.7 Importance of Correct Preload ..............................................................................297

13.7.1 Corrosion ................................................................................................ 297

13.7.2 Stress Corrosion Cracking....................................................................... 297

13.7.3 Fatigue Failure ........................................................................................297

13.7.4 Mechanical Failure..................................................................................297

13.7.5 Self-Loosening of Fastener......................................................................297

13.7.6 Leakage ................................................................................................... 297

13.8 Load Intensifiers ....................................................................................................298

13.9 Failure of Joint Members....................................................................................... 298

13.10 Galling....................................................................................................................300

13.10.1 Discussion ...............................................................................................300

13.10.2 Removing Galled Studs...........................................................................300

Exercises .............................................................................................................................301

References .......................................................................................................................... 302

Chapter 14

Self-Loosening ....................................................................................................................303

14.1 The Problem........................................................................................................... 303

14.2 How Does a Nut Self-Loosen?............................................................................... 303

14.3 Loosening Sequence ...............................................................................................306

14.4 Junkers Theory of Self-Loosening.........................................................................306

14.4.1 The Equations ......................................................................................... 307

14.4.2 The Long-Form Equation in Practice .....................................................308

14.4.3 The Equation When Applied Torque Is Absent .....................................308

14.4.4 Why Slip Occurs? .................................................................................... 309

14.4.5 Other Reasons for Slip ............................................................................ 310

14.4.6 Other Theories of Self-Loosening............................................................310

14.5 Testing for Vibration Resistance............................................................................ 310

14.5.1 NAS Test................................................................................................. 310

14.5.2 Junker Test .............................................................................................. 311

14.6 To Resist Vibration................................................................................................ 312

14.6.1 Maintaining Preload and Friction........................................................... 313

14.6.1.1 Conventional Wisdom............................................................. 313

14.6.2 Preventing Relative Slip between Surfaces .............................................. 314

14.6.3 Countering Back-Off Torque .................................................................. 315

14.6.3.1 Prevailing Torque Fasteners ................................................... 315

14.6.3.2 Nord-Lock Nuts and Washers ................................................ 318

14.6.3.3 In General ............................................................................... 318

14.6.4 Double Nuts............................................................................................ 319

14.6.5 Mechanically Locked Fasteners ..............................................................319

14.6.5.1 Lock Wires and Pins ............................................................... 319

14.6.5.2 Welding ................................................................................... 319

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14.6.5.3 Stage 8 Fastening System ........................................................... 319

14.6.5.4 Huck Lockbolt............................................................................ 320

14.6.5.5 Honeybee Robotics..................................................................... 320

14.6.5.6 A-Lock Bolt and Nut ................................................................. 321

14.6.5.7 Omni-Lok Fasteners ................................................................... 322

14.6.6 Chemically Bonded Fasteners ..................................................................... 322

14.6.6.1 Rust ............................................................................................ 322

14.6.6.2 Anaerobic Adhesives .................................................................. 322

14.6.7 Vibration-Resistant Washers ...................................................................... 323

14.6.7.1 Washers That Maintain Tension in the Fastener ....................... 323

14.6.7.2 Toothed Washer ......................................................................... 323

14.6.7.3 Helical Spring Washer ................................................................ 324

14.6.7.4 Nord-Lock Washer..................................................................... 324

14.6.8 Comparison of Options ..............................................................................324

Exercises ............................................................................................................................. 324

References and Bibliography..............................................................................................325

Chapter 15

Fatigue Failure ................................................................................................................... 327

15.1 Fatigue Process ........................................................................................................327

15.1.1 Sequence of a Fatigue Failure..................................................................... 327

15.1.1.1 Crack Initiation .......................................................................... 327

15.1.1.2 Crack Growth............................................................................. 328

15.1.1.3 Crack Propagation...................................................................... 328

15.1.1.4 Final Rupture ............................................................................. 328

15.1.2 Types of Fatigue Failure............................................................................. 328

15.1.3 Appearance of the Break ............................................................................329

15.2 What Determines Fatigue Life? ............................................................................... 329

15.2.1 SN Diagrams.............................................................................................330

15.2.2 Material versus The Part.........................................................................332

15.2.3 Summary.....................................................................................................332

15.3 Other Types of Diagram .......................................................................................... 333

15.3.1 Constant Life Diagram ............................................................................... 333

15.3.2 Center Portion of Constant Life Diagram.................................................. 334

15.3.3 Approximate Constant Life Diagram ......................................................... 334

15.3.4 Endurance Limit Diagram .......................................................................... 336

15.3.5 Fatigue Life Data for Fasteners..................................................................337

15.4 Influence of Preload and Joint Stiffness................................................................... 338

15.4.1 Fatigue in a Linear Joint............................................................................. 338

15.4.2 Nonlinear Joints.......................................................................................... 339

15.4.3 What Is the Optimum Preload? ..................................................................341

15.4.4 Fatigue and the VDI Joint Design Equations............................................. 341

15.5 Minimizing Fatigue Problems .................................................................................. 343

15.5.1 Minimizing Stress Levels............................................................................. 344

15.5.1.1 Increased Thread Root Radius................................................... 344

15.5.1.2 Rolled Threads ........................................................................... 344

15.5.1.3 Fillets .......................................................................................... 345

15.5.1.4 Perpendicularity .......................................................................... 345

15.5.1.5 Overlapping Stress Concentrations............................................. 345

15.5.1.6 Thread Run-Out ......................................................................... 345

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15.5.1.7 Thread Stress Distribution........................................................ 345

15.5.1.8 Bending ..................................................................................... 347

15.5.1.9 Corrosion .................................................................................. 347

15.5.1.10 Flanged Head and Nut ............................................................. 347

15.5.1.11 Surface Condition ..................................................................... 348

15.5.2 Reducing Load Excursions .........................................................................348

15.5.2.1 Prevent Prying........................................................................... 348

15.5.2.2 Proper Selection of Preload ...................................................... 348

15.5.2.3 Control of Bolt-to-Joint Stiffness Ratios .................................. 348

15.5.2.4 Achieving the Correct Preload.................................................. 348

15.6 Predicting Fatigue Life or Endurance Limit ............................................................348

15.7 Fatigue of Shear Joint Members ..............................................................................349

15.8 Case Histories ..........................................................................................................351

15.8.1 Transmission Towers ..................................................................................351

15.8.2 Gas Compressor Distance Piece.................................................................. 351

Exercises .............................................................................................................................352

References and Bibliography.............................................................................................. 352

Chapter 16

Corrosion ...........................................................................................................................355

16.1 Corrosion Mechanism.............................................................................................. 355

16.1.1 Galvanic Series............................................................................................ 355

16.1.2 Corrosion Cell.............................................................................................356

16.1.3 Types of Cells.............................................................................................. 357

16.1.3.1 Two-Metal Corrosion ............................................................... 357

16.1.3.2 Broken Oxide Film ................................................................... 358

16.1.3.3 Stress Corrosion Cracking ........................................................ 358

16.1.3.4 Crevice Corrosion ..................................................................... 359

16.1.3.5 Fretting Corrosion .................................................................... 359

16.2 Hydrogen Embrittlement ......................................................................................... 360

16.2.1 Stress Cracking Failure Modes ...................................................................360

16.2.2 Hydrogen Embrittlement Mechanism of Failure ........................................360

16.2.3 Susceptible and Safe Materials.................................................................... 361

16.2.4 Testing for Embrittlement...........................................................................362

16.2.5 Fighting Hydrogen Embrittlement..............................................................363

16.3 Stress Corrosion Cracking ....................................................................................... 363

16.3.1 Mechanism of Failure ................................................................................. 363

16.3.2 The Concept of KISCC ................................................................................. 364

16.3.3 Factors Affecting KISCC ..............................................................................365

16.3.3.1 Bolt Material............................................................................. 365

16.3.3.2 The Environment ...................................................................... 365

16.3.3.3 Thread-Forming Procedure ...................................................... 365

16.3.3.4 Bolt Strength or H