Shot peening consists of bombarding the surface of a metal part with calibrated media (steel, ceramic, glass) projected at high velocity by a centrifugal wheel or compressed air jet. Each impact causes highly localized plastic deformation at the surface: the underlying material resists, and the end result is a residual compressive stress field that impregnates the first 150 to 400 microns of the part.
These compressive stresses delay the initiation of fatigue cracks (which preferentially start in tension) and slow their propagation. The fatigue life gain is typically ×2 to ×5 depending on the material, geometry and loading mode. Shot peening does not consume material, does not significantly alter dimensions, and applies equally to new parts and to parts under maintenance.
The master parameters — Almen intensity (transferred energy), coverage (percentage of surface impacted) and media selection — are monitored and documented at every intervention per AMS 2430 (automated process), AMS 2432 (manual process) or AMS 2546 (ultrasonic peening).