2 fcp fracture case studies

FCP Short CourseFracture Case Studies

Stephen D. DowningMechanical Science and Engineering

© 2001 - 2015 University of Illinois Board of Trustees, All Rights Reserved

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Agenda

Pipe Wrench Failure Truck Steering Shaft Ammonia Pressure Vessel Silver Bridge

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Chain Wrenches

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Chain Wrench In Use

* D.R.H Jones, Material Failure Analysis, Case Studies and Design Implications

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Info

Length: 1.5 meters Weight: 25 kilograms Pipe Diameter: 160 mm Broke during use Injured Worker Identify Cause Defective Part? User Overload?

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Dimensions

* D.R.H Jones, Material Failure Analysis, Case Studies and Design Implications

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Dimensions

* D.R.H Jones, Material Failure Analysis, Case Studies and Design Implications

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Failures – Link and Pin

* D.R.H Jones, Material Failure Analysis, Case Studies and Design Implications

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Failure - Handle

A B

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Force Equations

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Bending the Handle

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Bending the Handle

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Shearing the Rivet

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Fracturing the Link

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Diagnosis

Defective? No defects seen in fracture micrographs Link hardness of 250 HV consistent with good

quench and temper Overload? Force (5.15 kN) to bend the handle 5.8 times

200 lb man Double handle length and stand 3 men on the

end Slip long pipe over handle to increase leverage

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Agenda

Pipe Wrench Failure Truck Steering Shaft Ammonia Pressure Vessel Silver Bridge

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Truck Steering Shaft Failure

* D.R.H Jones, Material Failure Analysis, Case Studies and Design Implications

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Question

Did shaft failure cause accident?

or

Did accident cause shaft failure?

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Steering Shaft Failures

* D.R.H Jones, Material Failure Analysis, Case Studies and Design Implications

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Deformed Splines

* D.R.H Jones, Material Failure Analysis, Case Studies and Design Implications

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Matching Fracture Surfaces

* D.R.H Jones, Material Failure Analysis, Case Studies and Design Implications

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Shear Failure Surface

* D.R.H Jones, Material Failure Analysis, Case Studies and Design Implications

Magnification x170

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Fibrous Tensile Fracture

* D.R.H Jones, Material Failure Analysis, Case Studies and Design Implications

Magnification x325

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Polished Cross-Section

* D.R.H Jones, Material Failure Analysis, Case Studies and Design Implications

1.5 mm case

hardened

Etched 2% nital

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Hardness vs. Radius

r(mm) HV σu(MPa) τu(MPa)

0 350 1120 700

10 360 1152 720

17.5 375 1200 750

22.5 400 1280 800

Case 880 2816 1760

u

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Steering Shaft

Shear stress vs. radial distance from shaft center

* D.R.H Jones, Material Failure Analysis, Case Studies and Design Implications

curve fit

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Steering Shaft

Calculating the torsional moment

* D.R.H Jones, Material Failure Analysis, Case Studies and Design Implications

T

τuu

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Steering Shaft

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Steering Shaft

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Caused By Collision?

Steering Arm Force

Collision Force 4 g’s truck mass = 20 metric tonnes

F

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Meet Material Specs?

Yield stress = 736 MPa minimumTensile strength = 1079 to 1324 MPa

Elongation = 8% minimum

Case hardness = 59 to 63 Rockwell C

Impact energy = 59 J/cm2 minimum

* D.R.H Jones, Material Failure Analysis, Case Studies and Design Implications

Nickel-chrome-moly steel

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Spline Connections

Dimensions of the splined section

* D.R.H Jones, Material Failure Analysis, Case Studies and Design Implications

T

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Spline Connections

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Agenda

Pipe Wrench Failure Truck Steering ShaftAmmonia Pressure Vessel Silver Bridge

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Similar Tanker Truck

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Vessel Construction~6 m

* D.R.H Jones, Material Failure Analysis, Case Studies and Design Implications

Weld between the shell and end cap of the pressure vessel

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During Unloading

Fast fracture in circumferential weld End cap blown off (serious mayhem) Unloading (decanting) process Space above liquid is pressurized with

ammonia gas with compressor Pcompressor = 1.83 MPa Safety valve set at 2.07 MPa

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Fracture

* D.R.H Jones, Material Failure Analysis, Case Studies and Design Implications

Geometry of the failure

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Materials Data

y

u

f

o

712MPa833MPa22%

VH 280CVN 22lb ft 30J @ 34 C

o

oCVN 8lb ft 11J @ 34 CCVN 10lb ft 14J @ 3 C

o

o

VH 300 to 370CVN 2lb ft 3J @ 34 CCVN 5lb ft 5J @ 3 C

• ASTM A517 Grade E -HSLA steel• Samples cut from failed tank

Parent Plate

Weld Bead

HAZ

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Stresses Acting on Crack

Thin-walled Pressure Vessel – Closed Ends

Hemispherical Cap

Axial Stress on Crack

* D.R.H Jones, Material Failure Analysis, Case Studies and Design Implications

Mismatch between shell and cap

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Bending Stress

Hoop Stress

Radial Distortions - ε1

Shell

Cap

Mismatch

* D.R.H Jones, Material Failure Analysis, Case Studies and Design Implications

Mismatch between shell and cap

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Stress State of Mismatch

Assume cap is infinitely stiff End of shell is subjected to

bending moment and shear force in addition to membrane stress.

Bending moment tries to open crack.

What does shear do?

* D.R.H Jones, Material Failure Analysis, Case Studies and Design Implications

All mismatch taken by shell

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Effect of Shear

Roark

* D.R.H Jones, Material Failure Analysis, Case Studies and Design Implications

Shear force makes end of shell contract

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Effect of Bending

Roark

* D.R.H Jones, Material Failure Analysis, Case Studies and Design Implications

Bending moment makes end of shell expand

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Maximum Moment and Stress

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Stress Intensity (Tension)

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Stress Intensity (Bending)

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Comments

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Agenda

Pipe Wrench Failure Truck Steering Shaft Ammonia Pressure Vessel Silver Bridge

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Silver Bridge

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Statistics

Completed 19 May 1928 Connects

Huntington, VA to Middleport, OH Charleston, VA to Dayton, OH

Major east-west connection for US Route 35 Two lanes of automobile traffic 1750 feet in length Steel Eyebar Suspension Bridge Aluminum Paint (“Silver Bridge”)

A major east-west connection for US Route 35 connecting Charleston, WV and major cities in Ohio

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Ohio River

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4:58 PM December 15, 1967

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Disaster

Second most deadly U.S. bridge disaster 64 hit the water 18 rescued 46 dead or missing 31 vehicles on the bridge

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Wreckage

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Wreckage

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Wreckage

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What’s Different About Silver Bridge?

First “eyebar” suspension bridge in the U.S. First bridge that used high-strength, heat-

treated carbon steel High Risk: new structure on a new scale,

using new materials.

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Silver Bridge Collapse

Collapse, Wearne, P. TV Books, NY 1999

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Source

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Cause of Failure

Bridge Design? Eyebar Manufacturing Quality? Material Choice?

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Bridge Design at Fault?

Steel Eyebar Suspension Suspended “Bicycle Chain” Weakest Link, No Redundancy Cable Suspension has hundreds of links

Partially!

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Failed Eyebar

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Failure EvidenceJohn Bennet, US Bureau of Standards

“The Ohio River there is very heavily traveled so the U.S. Corps of Engineers had taken all the debris and just piled it on the shore – it was a terrific mess.”

“Fortunately, each piece had been photographed as they took it out.”

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Failure Evidence

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Photograph of Failed Eyebar 330John Bennet, US Bureau of Standards

“Looking at it, the fractures on the two sides were completely different.

“One side was very straight, almost like a saw cut.

“The other side was extensively deformed, the metal bent and the paint chipped off.

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Eyebar Loading

12” wide2” thickness

12

6

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Eyebar 330 Failure Sketch

12” wide2” thickness

12

6

Brittle Appearance

Ductile Appearance

1/8” corroded crack

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Crack on Eyebar 330

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Conditions of Failure

Crack formed by original forging operation Quenched and tempered steel Stress corrosion cracking 32oF ambient temperature

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Assignment

Make an estimate of the maximum allowable flaw size in the eyebar.

)lbft()CVN(2)inpsi(E

K 232

IC

)lbft(CVN5.15)inksi(KIC

)lbft(CVN35.9)inksi(K 65.1IC

Barsom-Rolfe

Corten-Sailors

Roberts-Newton

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Material Properties

u = 100 ksiy = 75 ksi = 29,000 ksi

CVN = 2.6 ft-lb at 32° F

CVN = 8.6 ft-lb at 165° F

Working stress 50 ksi

Charpy V-notch Tests

ICaK a Fb

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Estimate KIC

FatinksilbftinCVNEK oIC 326.15)(2 2

3

FatinksilbftCVNinksiK oIC 320.25)(5.15)(

FatinksilbftCVNinksiK oIC 322.45)(35.9)( 65.1

Barsom-Rolfe

Corten-Sailors

Roberts-Newton

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Assume Flaw Geometry

2

2

2K (1.12) a

a 2F (1.12) 0.799b

Two free edgesSemicircular shape

Corner crack

a a

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Critical Crack Size (Best Case)

2IC

criticalapplied

K1a0.799

= 0.045 in (using Barsom-Rolfe KIC at 32oF)

= 0.407 in (using Roberts-Newton KIC at 32oF)= 0.125 in (using Corten-Sailors KIC at 32oF)

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© 2001 - 2015 University of Illinois Board of Trustees, All Rights Reserved

ME 431Failure Analysis

of Mechanical Components