shotpeened

Shotpeened is a surface condition produced by shot peening, a mechanical surface treatment in which a stream of small, hard spherical media is accelerated and directed at a component surface. The impacts plastically deform the surface and create a gradient of residual compressive stress in the near-surface region, enhancing fatigue resistance.

Media and equipment vary, but common shots are steel, stainless steel, tungsten carbide, or ceramic, typically in sizes from about 0.1 to 2 millimeters. Peening can be performed with air-nozzle, wheel, or hammer-type equipment. Process parameters include shot size and material, velocity, coverage, and Almen intensity, used to quantify energy imparted to the surface.

Effects include the introduction of surface compressive residual stress and slight work hardening, which together improve fatigue life and resistance to crack initiation and growth. Shot peening can also modify surface roughness and remove micro-notches. Overpeening or excessive velocity may cause surface damage or dimensional change, requiring careful process control.

Applications span aerospace, automotive, and heavy machinery parts such as gears, springs, valve trains, turbine blades, and fasteners. QC commonly employs Almen strip tests and residual-stress measurements to verify coverage and intensity, ensuring the treated surface meets design specifications before service.