Fatigue is one of the main causes of crankshaft failure.
a) Indicate on a sketch the most likely location of a fatigue crack.(4)
b) Explain how a fatigue failure is identified.(4)
c) Describe how a fatigue crack may be initiated.(4)
d)Describe, with the aid of sketches, the methods used to inhibit fatigue cracks.(4)
Reference Answer
### a) Location of a Fatigue Crack A fatigue crack in a crankshaft is most likely to initiate at a point of high stress concentration. The highest stresses occur at the geometric discontinuities where the crankpin or main journal joins the crank web. Specifically, the crack will almost invariably start at the **fillet radius** between the journal/pin and the web. This is because: * **Bending Stress:** The crankshaft is subjected to significant bending moments from the gas pressure acting on the piston. These moments are highest at the transition to the web.
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