Exam Question

(a) Fatigue cracks are most likely to initiate in areas where there are changes in section or where there is a concentration of stress. The most likely location for a fatigue crack is indicated at the fillet radius (the transition curve) between the crankpin and the web. This area experiences high stress concentration due to the change in geometry. Another possible location is across the web itself, especially if there's a shrink fit involved
(b) Fatigue cracks are often difficult to detect initially because they start as small, invisible cracks. However, there are a few telltale signs:
Visual inspection: The crack surface will have a smooth, polished finish, while the remaining material will show a granular texture.
Crack pattern: The fatigue crack surface will display a series of curved visible lines, which are a result of the cyclical loading and stress.