The surface of all metal parts contains minute surface defects, blemishes, microcracks and high stress areas, induced into the part from the manufacturing and machining process. When a metal part is stressed and subjected to cyclic loading these surface defects enlarge and form cracks that propagate through the part until it ultimately fails (fatique failure).

Shot peening is a cold working process applied to the surface of metal parts to increase their resistance to fatigue failure, stress corrosion cracking, galling and fretting. Shot peening will also increase the components load carrying capacity.

The shot peening process involves bombarding the surface of the part with a high velocity stream of tiny balls manufactured from steel, glass or ceramic that are as hard as, or harder than, the surface being peened. As each particle strikes the surface, it produces a tiny round dimple and causes plastic deformation of the surface.

When complete shot peening coverage is achieved, the plastic deformation of the surface forms a layer of compressive stress which will counter any tensile stresses near the surface and prevent any cracks from enlarging. As part failure is caused by the enlargement of surface cracks, shot peening to prevent their propagation improves the service life of the component many fold.