Shot Peening

Shot peening is a cold working process that strengthens a metal or composite surface by striking it repeatedly with small round particles, called shot, made of steel, glass or ceramic, with enough force to plastically deform the surface and leave it under a layer of compressive residual stress. The compressive stress helps prevent cracks from starting and spreading, and the process is widely applied to components under cyclic loading, such as automotive crankshafts and connecting rods, and in the repair of aircraft parts. American engineer John Almen made a key contribution to the field by developing the Almen strip, a standardized measurement device used to gauge and control the intensity of a shot peening treatment, which helped make the process measurable and repeatable across industries; SAE International has since established a series of formal shot peening standards for aerospace and other sectors. The source consulted for this entry gives no specific date or original inventor for shot peening itself, only for Almen's later measurement innovation, so none is recorded here.