Exam Question

(a) Influence of Stress Level and Cyclic Frequency on Operating Life:
Fatigue is progressive and localised structural damage caused by cyclic loading, where the maximum stress is below the ultimate tensile strength. The relationship between stress level, cyclic frequency, and operating life depends on whether the fatigue is high-cycle/low-stress or low-cycle/high-stress.
High-cycle fatigue (low stress-high cycle):
This occurs at lower stress levels over a high number of cycles, resulting in elastic deformation. The component can withstand more cycles at these lower stress levels, and its life expectancy is determined by the S-N curve, which predicts the number of cycles before failure at a given stress level. For example, fatigue in turbocharger blowers often results from prolonged vibration over numerous cycles.