. By referring to a sketch showing a stress concentration, describe the phenomenon of crack initiation in high cycle fatigue and comment on the proportion of fatigue life that is used in initiating a crack under these conditions
Design Against Fluctuating Loads
Machine elements are subjected to varieties of loads, some components are subjected to static loads, while some machine components are subjected to fluctuating loads, whose load magnitude tends to fluctuate. The components of a machine, when rotating at a high speed, are subjected to a high degree of load, which fluctuates from a high value to a low value. For the machine elements under the action of static loads, static failure theories are applied to know the safe and hazardous working conditions and regions. However, most of the machine elements are subjected to variable or fluctuating stresses, due to the nature of load that fluctuates from high magnitude to low magnitude. Also, the nature of the loads is repetitive. For instance, shafts, bearings, cams and followers, and so on.
Design Against Fluctuating Load
Stress is defined as force per unit area. When there is localization of huge stresses in mechanical components, due to irregularities present in components and sudden changes in cross-section is known as stress concentration. For example, groves, keyways, screw threads, oil holes, splines etc. are irregularities.
7. By referring to a sketch showing a stress concentration, describe the phenomenon of crack initiation in high cycle fatigue and comment on the proportion of fatigue life that is used in initiating a crack under these conditions.
8. By considering a notched metal bar as an example, explain (with the aid of diagrams), how you would reduce the probability of fatigue failure by applying self-stresses.
9. Describe, with sketched examples, how the stress-raising effect of circular and elliptical holes can be considered qualitatively as being analogous to liquid flow.
10. By considering a circular hole in a thin elastic sheet, explain (with the aid of any diagrams as appropriate) how a stress concentration can magnify stress.
11. Explain the principles of designing alloys for oxidation resistance.
12. Describe and explain (with the aid of a sketch) how crack propagation is enhanced through stress corrosion cracking
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