Class 2 (2nd Engineer) MEKG 📅 Feb 2018

Exam Question

With reference to fatigue of engineering components:

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

(b) Explain the influence of material defects on the safe operating life of an engineering components

(c) State the factors which influence the possibility of fatigue cracking of a bed-plate transverse girder and explain how the risk of such cracking can be minimised

Reference Answer

(a) Material defects can significantly reduce the safe operating life of engineering components because defects serve as stress concentrators that increase local stress around the defect. This leads to premature failure as the material cannot withstand the same level of cyclic stress as a defect-free component.
Surface roughness, porosity, inclusions, and abrupt section changes all create stress concentrations, lowering fatigue strength.
Coarse grain size, specific chemical compositions, and cold working introduce residual stresses that reduce fatigue resistance.
Corrosion, erosion, and decarbonisation weaken the material and accelerate fatigue crack initiation and propagation.

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