What is Shot Peening?

A. Hi.

In a way, shot peening is similar to bead blasting -- the surface is repeatedly impacted with thousands of tiny, hard, balls -- but the purpose, and therefore the operating parameters, are different.

The purpose is to indent and compress the surface, and a couple of common reasons for that would be to make it more compatible with the stresses of subsequent plating, and to make the component less sensitive to fatigue failure.

What happens with "fatigue" loading is that the stresses on the component vary, sometimes even all the way from tensile to compressive and back. This repetitive sequence, if the loading stresses are rather severe, can cause a high stress point on the surface to fail, or a very tiny existing crack, a stress riser, to get worse with every cycle until failure.

What shot peening does in this case is put a permanent compressive stress into the surface, such that even under tensile load the surface of the component never goes tensile, or at the least, stays only very mildly tensile, so that fatigue failure is not initiated. One of the best known examples of shot peened components are the landing gear on airliners.

You can search the site with additional search terms of your choice to see several dozen threads about specific aspects of shot peening.

Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
(Ted can offer longterm or instant help)
finishing.com - Pine Beach, New Jersey

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A. Critical components that are under severe stress like landing gear are in danger of suffering 'fatigue failure' whereby one tiny point on the surface of the component which is under very high tensile (pulling) loads could at some time for some reason suffer a load that is a little too high, causing a tiny rip or failure at the surface. If the loads on the component keep shifting back and forth, that initial failure point just keeps growing.

But if you properly shot peen the component, repeatedly slamming those tiny balls into its surface, you've smooshed the steel on the surface in, compressing it. Now as you apply tensile (pulling) loads on the component, its innards, its middle may be tensilely stressed but all that compressive stress on the surface has to be removed before the stress at the surface can even become tensile. The intention and overall effect is that if the outer surface never becomes highly tensilely stressed, potential stress tears don't get a chance to propagate.

Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
(Ted can offer longterm or instant help)
finishing.com - Pine Beach, New Jersey