Shot Peening is an operation that improves fatigue life and stress corrosion resistance by creating beneficial residual surface stresses that inhibits and/or delays crack initiation and propagation. It is a method of cold working in which compressive stresses are induced into the exposed surface layers of metallic parts and structures by impingement to improve the fatigue life of metal components.
The most common mechanical method used to treat the surfaces is shot peening, where spherical media is propelled by air or a centrifugal wheel and directed at a metal surface at high velocity and controlled parameters.
A void or heavy tooling mark in the surface of a part is a stress concentration point or stress riser, such that its crack propagates and migrates (sometimes to failure) in a part with fatigue loading.
The shot peening process has been a standard mitigating remedy in most cases for post-machining, deburring/polishing and heat treating of high fatigue components.
Common peening media are cast steel shot, conditioned cut wire, ceramic and glass beads.
Note: Shot peening is not applied in order to compensate for deficiencies in other steps of the manufacturing process.