Shot peening is a special metal surface treatment used to extend the fatigue life of most metals. The surface of all metal parts contain some form of micro-cracking, tooling marks, discontinues or tiny cracks. Key high stress areas are corners, holes, scratches, key ways, splines or any other interruption on to the smooth surface of the metal.
Most long term failures are due to tensile stress; these stresses attempt to pull the surface apart which will eventually lead to cracking. Shot peening has many uses within industry especially in the production of gears, chains, welded parts, aerospace and more.