BMFB 4283 NDT & FAILURE ANALYSIS
description
Transcript of BMFB 4283 NDT & FAILURE ANALYSIS
![Page 1: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/1.jpg)
BMFB 4283NDT & FAILURE ANALYSIS
Lectures for Week 10
Prof. Qumrul Ahsan, PhD Department of Engineering MaterialsFaculty of Manufacturing Engineering
![Page 2: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/2.jpg)
10.0 Fatigue Failure
10.1 Introduction10.2 Factors Causing Fatigue Failure10.3 S-N Curve10.4 Fatigue Crack Growth10.5 Factors Influence Fatigue Properties
Issues to address
![Page 3: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/3.jpg)
Failures occurring under conditions of dynamic loading are called fatigue failures.
metal subjected to a repetitive or fluctuating stress will fail at a stress much lower than that required to cause failure on a single application of load.
Fatigue Failure
Fatigue failure is characterized by three stages Crack Initiation Crack Propagation Final Fracture
![Page 4: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/4.jpg)
Ken Youssefi MAE dept., SJSU 4
Hawaii, Aloha Flight 243, a Boeing 737, an upper part of the plane's cabin area rips off in mid-flight. Metal fatigue was the cause of the failure.
![Page 5: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/5.jpg)
Appearance of Fatigue Fracture Surface
![Page 6: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/6.jpg)
1.0-in. diameter steel pins from agricultural equipment.Material; AISI/SAE 4140 low allow carbon steel
Fracture surface of a failed bolt. The fracture surface exhibited beach marks, which is characteristic of a fatigue failure.
![Page 7: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/7.jpg)
The final fracture area is clearly identified by its colour - the surface of the crack will be dull due to the effects of air and moisture being in contact and setting up mild corrosion, while the newly failed surface will show signs of new, clean brittle failure
![Page 8: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/8.jpg)
![Page 9: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/9.jpg)
![Page 10: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/10.jpg)
![Page 11: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/11.jpg)
![Page 12: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/12.jpg)
![Page 13: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/13.jpg)
![Page 14: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/14.jpg)
Fatigue Crack Nucleation
• Flaws, cracks, voids can all act as crack nucleation sites, especially at the surface.
• Therefore, smooth surfaces increase the time to nucleation; notches, stress risers decrease fatigue life.
• Dislocation activity (slip) can also nucleate fatigue cracks.
![Page 15: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/15.jpg)
Fatigue: Crack initiation and propagation • Three stages of fatigue failure:
– crack initiation in the areas of stress concentration (microcracks, scratches, indents, interior corners, dislocation slip steps, etc.). Quality of surface is important.
– incremental crack propagation– final rapid crack propagation after crack reaches critical size
• The total number of cycles to failure is the sum of cycles at the first and the second stages:– Nf = Ni + Np
– Nf : Number of cycles to failure– Ni : Number of cycles for crack initiation– Np : Number of cycles for crack propagation
High cycle fatigue (low loads): Ni is relatively high. With increasing stress level, Ni decreases and Np dominates
![Page 16: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/16.jpg)
![Page 17: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/17.jpg)
Crack propagation• Stage II a: initial slow propagation
along crystal planes with high resolved shear stress. Involves just a few grains, and has flat fracture surface
• Stage II b: faster propagation perpendicular to the applied stress. Crack grows by repetitive blunting and sharpening process at crack tip. Rough fracture surface.
• Crack eventually reaches critical dimension and propagates very rapidly and causes fatigue failure.
• Visually a fatigue fracture region is smoother than the overload fracture region
![Page 18: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/18.jpg)
![Page 19: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/19.jpg)
Indication of Fatigue Failure SurfaceCrack initiation site
Fracture zoneBeach Mark
Both marks indicate the position of the crack tip. It appears as concentric ridges (circular or semicircular
Beach Mark
• Also called calmshell marks• Can be observed using unaided eye• Components experienced
interruption during the crack propagation
• Each beachmark band represents a time over which crack growth occured
Striations
• Microscopic in size• Each striation represents crack
growth rate• stress range striations width• Multiple strations within a beach
mark
![Page 20: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/20.jpg)
![Page 21: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/21.jpg)
![Page 22: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/22.jpg)
![Page 23: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/23.jpg)
![Page 24: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/24.jpg)
![Page 25: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/25.jpg)
25
928 Porsche timing pulley
Crack started at the fillet
Fatigue at Stress Raiser• Notches decrease fatigue life
through stress concentration
• Remove stress concentrators.
bad
bad
better
better
![Page 26: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/26.jpg)
![Page 27: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/27.jpg)
![Page 28: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/28.jpg)
![Page 29: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/29.jpg)
![Page 30: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/30.jpg)
![Page 31: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/31.jpg)
![Page 32: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/32.jpg)
![Page 33: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/33.jpg)
![Page 34: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/34.jpg)
![Page 35: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/35.jpg)
corrosion either increases the rate at which material is removed from the crack tip and/or it produces material on the crack surfaces that forces the crack open (e.g. oxidation).
![Page 36: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/36.jpg)
![Page 37: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/37.jpg)
![Page 38: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/38.jpg)
Thermal cycling causes expansion and contraction, hence thermal stress, if component is restrained.
•eliminate restraint by design•use materials with low thermal expansion coefficients
![Page 39: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/39.jpg)
MAE dept., SJSU
Jack hammer component, shows no yielding before fracture.
Crack initiation site
Fracture zonePropagation zone, striation
![Page 40: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/40.jpg)
VW crank shaft – fatigue failure due to cyclic bending and torsional stresses
Fracture areaCrack initiation site
Propagation zone,
![Page 41: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/41.jpg)
This long term fatigue crack in a high quality component took a considerable time to nucleate from a machining mark between the spider arms on this highly stressed surface. However once initiated propagation was rapid and accelerating as shown in the increased spacing of the 'beach marks' on the surface caused by the advancing fatigue crack.
bicycle crank spider arm
![Page 42: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/42.jpg)
MAE dept., SJSU 42
Gear tooth failure
Crank shaft
![Page 43: BMFB 4283 NDT & FAILURE ANALYSIS](https://reader034.fdocuments.in/reader034/viewer/2022050911/56816691550346895dda6d59/html5/thumbnails/43.jpg)
43
Fatigue: summary• Initiated at surface• Fatigue failure controlled either by initiation or by
propagation• Fatigue Fracture Features: Beachmark and
Striation• Intrinsic and Extrinsic features control fatigue
failure and fatigue life.