In service, a rotating steel shaft is subjected to an alternating stress of +/-

ID: 1862079 • Letter: I

Question

In service, a rotating steel shaft is subjected to an alternating stress of +/- 350 MPa. Which of

the following would increase the fatigue lifetime of the component? (Choose all that apply.)

a. Apply a surface treatment (e.g. carburization) that places the outer surface of the shaft in

compression.

b. Increase the rotational frequency (RPM) of the shaft.

c. Apply an additional tensile stress along the axis of the shaft.

d. Increase the diameter of the shaft.

e. Replace the steel with an aluminum alloy.

Answer is A and D

A because u create a compressive surface stress to suppress growth of cracks at surface

D because increase in diameter means u decrease the amount of stress concentrating on the material

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