7. (2 points) For brittle materials under static loading, stress concentration f

Question

7. (2 points) For brittle materials under static loading, stress concentration factors a must be applied b. must not be applied c. can be applied or omitted 8. (2 points) For materials under dynamic loading, stress concentration factors a must be applied b. must not be applied c can be applied or omitted 9. (2 points) All materials have an endurance limit. a. True b. False 10. (2 points) Fatigue loading makes metals more brittle over time. That's why they break by sudden fracture. a. True b. False

Explanation / Answer

7) a) must be applied

8) a) must be applied

9) b) False

This is due to the composition of each material. The majority of non ferrous alloys don't have an endurance limit. Steel does. The reason steels have an endurance limit is due to the presence of carbon in the alloy. If you submit a metal to certain stresses, dislocations will tend to appear. In steels, they don't appear (if the stress is low enough) because the carbon will prevent the dislocations from moving and consequently prevent cracks from growing.

Other material's structure don't have that strengthening mechanism that carbon provides, so even at very low stresses the material will eventually fail after many many cycles.

10) a) True

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