Mechanism of creation of compressive residual stress by shot peening and its effect on fatigue strength: Analysis of residual stress produced by a single shot

In order to clarify the mechanism by which compressive residual stresses are created during shot peening, a 76.2 mm diameter steel ball was repeatedly dropped against selected spots on a flat steel plate. In addition, static indentation of the plate by the same steel ball was also carried out. After the first drop and static indentation, a tensile residual stress was found near the center of the ball indentation mark and the peak of compressive residual stresses was found outside of the indentation. With increasing in the number of drops, the tensile residual stress became compressive. Furthermore, a steel ball attached to a cylindrical weight was dynamically dropped on the center of a fatigue test specimen and a rotating-bending fatigue test was carried out to investigate the effect of residual stresses on the fatigue strength. The fatigue strength of the specimens containing the indentation produced by a dynamic shot decreased remarkably compared to those of unpeened specimens.