Fatigue accounts for ~90% of mechanical engineering fai es that may be taken to increase the resistance to fatigue of metall efly explain how each of these measures improves fatigue performa
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.
Introduction:
- If a load is continually withdrawn and restored after being of insufficient size to induce failure in a single application, failure may result.
- Fatigue is the name for this process of failure.
- In unwelded metals and alloys, the failure process begins with microscopic cracking that frequently starts at a surface feature such as a change in section, then the crack spreads and gets a tiny bit longer with each load cycle.
- Fatigue cracks are frequently very small and tightly closed at low loads, making them challenging to detect only through visual inspection.
- The cross section's unbroken area decreases as the crack widens, perhaps leading to full fracture or failure by another method like jamming or seizure.
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