How does shot peening's compressive stress improve fatigue life?

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zewei1988
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How does shot peening help improve fatigue life, or rather, how does the compressive surface stress imposed help improve fatigue life?

How does materials having high elastic moduli and large grain size prevent creep?
 
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We won't just give you the answers to homework-type questions at PF (that way nobody would learn anything), but if you give proposed answers and try to justify them, you'll likely get comments.
 
It's not a homework question, but I have no idea of how to prove it to you. It's something that was mentioned in my notes, and I tried checking Wikipedia and my recommended textbook, but I still do not understand those two points.
 
Let me try answering this way...

zewei1988 said:
How does shot peening help improve fatigue life, or rather, how does the compressive surface stress imposed help improve fatigue life?

What is fatigue, and what stress state does it involve?

zewei1988 said:
How does materials having high elastic moduli and large grain size prevent creep?

What is the atomic mechanism of creep? How might this mechanism be affected when the atoms are more strongly bound (which is how materials acquire high stiffness, or elastic modulus), or when there are fewer grain boundaries (look up Coble creep)?