Class 2 (2nd Engineer) MEKG 📅 Apr 2023

Exam Question

With reference to fatigue of engineering components:

(a) Explain the influence of stress level at cyclical frequency on expected operating life.

(b) Explain the influence of material defects on the safe operating life of engineering component.

(c) State the factors which influence the possibility of fatigue cracking of an auxiliary boiler feed water pump shaft and explain how the risk of such cracking can be minimized.

Reference Answer

### (a) Influence of Stress Level and Cyclical Frequency on Expected Operating Life
Fatigue is the progressive and localized structural damage that occurs when a material is subjected to cyclic loading. The maximum stress values are lower than the ultimate tensile strength (UTS) and often below the yield strength of the material. The relationship between stress, frequency, and life is best described by the material's S-N curve (Stress vs. Number of cycles to failure).
**1. Influence of Stress Level:**
The level of cyclic stress is the most critical factor determining fatigue life. The relationship is inverse and non-linear:

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