Shot peening is similar to sandblasting, but removes less material, creates less dust, and operates with plasticity rather than abrasion. Using round metallic, glass or ceramic particles (shot), this cold working process spreads a surface plastically, modifying mechanical properties of metals and producing compressive residual stress layers. Shot peening uses forceful impact of shot to deform a surface, with each particle functioning as a ball-peen hammer. This process is often used in aircraft repairs to replace tensile stresses with beneficial compressive stresses.
Plastic deformation induces residual compressive stress in peened surfaces, along with interior tensile stress. Surface compressive stresses confer resistance to metal fatigue and to some forms of stress corrosion. The tensile stresses deep in the part are not as problematic as tensile stresses on the surface because cracks are less likely to start in the interior.
Shot peening can increase fatigue life up to 1000%, depending on the part geometry, part material, shot material, quality, intensity, and coverage.