I just ran a fatigue test to compare shot peened and non shot peened 17-4PH material. To my surprise, the shot peened material had a lower endurance limit. This seems really strange. Could residual stresses (due to a forging process prior to shot peening) cause this to happen? Also, the critical area to be shot peened had a 90 degree bend and a .015" radius.
Has anyone else had negative results due to shot peening? If so why?
