Abstract: A process of compression stressing shot pellets to increase the fatigue strength or resistance thereof to brittle fractures by impact of the pellets during shot peening and cleaning operations wherein the elastic radial tensile stress at the surface of the pellets is maintained at a safe low value during initial compression stressing and preparation for and performance of peening and cleaning operations. The process entails subjecting the pellets initially to compression stresses of sufficiently low value to avoid the spontaneous formation of superficial or surface cracks in pellets formed of notch sensitive material and then subjecting the pellets to stresses normal in shot peening and cleaning operations.

Abstract: A process of compression stressing metals to increase the fatigue strength or resistance to brittle fractures thereof by shot peening or surface rolling wherein the elastic radial tensile stress of the metal is maintained at a safe low value at the time when subsurface yield incident to initial compression stressing occurs. Initial processing entails compression stressing of the metal under conditions imparting compression stresses of sufficiently low value to avoid the formation of superficial or surface cracks in notch-sensitive metals followed, where required, by final processing wherein the metal is subjected to compression stressing under conditions imparting compression stresses of sufficiently high value to produce a favorable distribution of residual compression stress and residual tensile stress for increase of the fatigue strength of the metal.