Answer the following questions and very briefly explain your

Answer the following questions, and very briefly explain your answer

i)   Why does polishing the surface of a metal extend fatigue life?

ii)   Will small, finely dispersed precipitates reduce or accelerate fatigue crack

growth?

iii) Why is it particularly important to avoid stress concentrations such as changes in

section with sharp corners in fatigue applications?

Solution

1) Fatigue occurs at surface due to surface defects

By polishing we reduce or mitigate these defects so fatigue life increases.

2) Small dispersed precipitates will reduce fatigue crack growth as they try to close the crack which is created by various mechanics.

3) Stess concentrations are points of geometrical discontinuities which have increased intensity of stress field. So they fail by fatigue.