Class 4 (4th Engineer) MEKM 📅 Nov 2022

Exam Question

(a) With reference to crankshaft and piston crowns outline the main stresses to which these parts are subjected (4)

(b) In each case explain how the stresses are generated and how they vary in magnitude and direction during one cycle (6)

(c) With respect to the whole engine describe how stresses may be accommodated by good design and influenced by poor maintenance (6)

Reference Answer

### (a) Main Stresses on Crankshaft and Piston Crowns
**1. Crankshaft Stresses:**
The crankshaft is a complex component subjected to multiple, simultaneous stresses that vary throughout the engine cycle:
* **Bending Stresses (Tensile & Compressive):** Generated by the gas pressure and inertia forces of the reciprocating parts acting on the crankpin. The crankshaft acts as a beam supported by the main bearings. As it rotates, any given point on the journal surface experiences alternating tensile and compressive stresses once per revolution. The bending moment is highest midway between the main bearing supports.

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