2 fcp fracture case studies
TRANSCRIPT
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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ME 431Failure Analysis
of Mechanical Components