Quote:
Originally Posted by cadandcookies
Sorry, not super familiar with the manufacture of bolts, but could you explain what you mean by "compressive strain?"
On another note, in 2012, 2220 used grade 5 stainless 1/2-20 (if I remember correctly) bolts as axles on our robot. We made it the entire season without bending an axle significantly. Not saying it was a good idea, but it worked in our case.
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http://en.wikipedia.org/wiki/Shot_peening this has some decent non-jargon explanation of the principle.
Essentially introducing residual compressive stress on the surface through plastic deformation leads to prevention of crack propogation, increasing fatigue life.
With a rolled thread you are also increasing strength through
cold working (strain hardening) the material, which improves both fatigue and tensile strength, but makes the material more brittle. This is also why form tapped holes are stronger than threaded holes produced with a cut tap.