Hey 340, Wiki first states that it adds compressive stress then later says relives stress. Thats the stuff that i'd like to get to the bottom to. Which one add/relieve? An old mentor of mine that was McDonnell Douglas ball bearing top dog said it added stress. I'm on same page as Transman.
There are several good answers here and I didn't write the Wiki page. I'm thinking if you have some residual tensile stresses on the surface of a part, then peening would add compressive stresses to relieve the tensile stresses. My SWAG on the matter. Now I'm wondering how a machinist can tell if a part was double shot peened?
Answer:
https://www.shotpeener.com/library/pdf/2013029.pdf
