Peened

Peening is a mechanical surface treatment used to impart plastic deformation to the near-surface region of a metal part by repeated impacts. As a cold-working process, peening introduces residual compressive stresses and a hardened surface layer, which improves fatigue strength and resistance to crack initiation under tensile loading. It is commonly applied to fasteners, gears, shafts, springs, and aerospace components.

Common methods include hammer peening, shot peening, and laser peening. Hammer peening uses a peening hammer or automated hammer to strike the surface. Shot peening blasts small spherical media at the surface, with parameters such as coverage, intensity, and exposure time controlling the effect. Laser peening uses high-energy laser pulses to generate a shock wave that plastically deforms the surface without mechanical impacts.

The process creates a pattern of shallow dimples or indentations and increases surface hardness near the surface. The induced compressive residual stresses can extend several tens to hundreds of micrometers depth, depending on method and material. In shot peening, intensity and coverage are monitored, sometimes using Almen strips as a reference standard.

Peened surfaces may alter surface roughness and can affect coatings or sealant adherence. It is not suitable for all geometries or very thin walls and must be carefully controlled to avoid over-peening, which can cause surface embrittlement or dimensional changes. Standards and specifications exist to govern process parameters and quality assessment, including various industry guidelines for different materials and applications.

As a result, peening is widely used to extend fatigue life and improve reliability in critical components, particularly in aerospace, automotive, and power-generation industries.