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An axial residual compressive stress due to a manufacturing process is present on the outer surface of a rotating shaft subjected to bending. Under a given bending load, the fatigue life of the shaft in the presence of the residual compressive stress is
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- decreased
- increased or decreased, depending on the external bending load
- neither decreased nor increased
- increased
Correct Option: D
As we can see from the Gerber’s parabola, the endurance strength remains constant at maximum value irrespective of the compressive load. Whereas for tensile load it decreases sharply with increases in σm and stress in the shaft, its strength in fatigue increases. 
