Reading a broken metal part: fatigue, fracture, corrosion, creep

Questions

1. 1
   Not answered. A part has broken in service. Before anyone replaces it, why is the fracture surface photographed?
2. 2
   Not answered. This aluminium specimen was pulled until it broke. What does the narrow waist just below each broken end tell you?
3. 3
   Not answered. These cast-iron halves have flat, grainy faces and still measure the full original diameter. What kind of failure is this?
4. 4
   Not answered. Why does the outer rim of a ductile tensile fracture slope at roughly 45° to the pulling direction?
5. 5
   Not answered. This fracture surface is covered in shallow cavities a few micrometres across. What formed them?
6. 6
   Not answered. This surface is a patchwork of flat, shiny facets, each with a fan of fine lines. Which mechanism made it?
7. 7
   Not answered. What distinguishes a transgranular fracture from an intergranular one?
8. 8
   Not answered. What are the fine, parallel ridges covering this fatigue fracture surface called?
9. 9
   Not answered. In the regime where striations form, how many load cycles does a single striation represent?
10. 10
    Not answered. Which statements about beach marks and striations are correct?
11. 11
    Not answered. This aluminium bicycle crank broke during ordinary riding. Most of the face is bright and rough, and a darker region along one edge has curved lines on it. What happened?
12. 12
    Not answered. Two identical shafts both failed by fatigue. One face is almost all fatigue zone with a thin sliver of final fast fracture. The other is mostly final fast fracture. What does the difference tell you?
13. 13
    Not answered. A bracket carries a repeated load whose peak is comfortably below the alloy's yield strength. Can it still fail by fatigue?
14. 14
    Not answered. Where should you look first for the origin of a fatigue crack?
15. 15
    Not answered. A steel bracket and an aluminium bracket both survive ten million cycles on the test rig. Why is that result worth less for the aluminium one?
16. 16
    Not answered. On the left is a coated, buried gas pipeline. On the right is the same spot after the corrosion product was blasted off. Why do engineers worry more about pitting than about uniform rusting?
17. 17
    Not answered. Galvanised steel pipework is joined directly to brass and copper fittings, with water inside. Which metal corrodes?
18. 18
    Not answered. Two joints sit in seawater: steel bolts holding a large copper plate, and copper bolts holding a large steel plate. Which one is the dangerous design?
19. 19
    Not answered. Fine branching cracks run out from a welded collar in this vessel wall. What has to be present at the same time for stress corrosion cracking?
20. 20
    Not answered. A steel part with a long, clean service record starts failing early after the equipment moves to a damp, salty site. The duty cycle is the same. What is the likeliest explanation?
21. 21
    Not answered. A turbine blade under a constant load well below its yield strength slowly stretches over thousands of hours in service. What is that called?
22. 22
    Not answered. Creep becomes a design concern above roughly what fraction of a metal's absolute melting temperature?
23. 23
    Not answered. Why does the strain rate speed up in the tertiary stage of creep?
24. 24
    Not answered. Which of these failure modes typically give little or no outward warning before the part separates?
25. 25
    Not answered. A shaft snaps after three years in service. Two thirds of the face is smooth with fine curved lines, and the rest is rough. There is no necking anywhere. What is the diagnosis, and where should the fix go?