Evaluation of Residual Stress Induced by Shot Peening on Aircraft Structural Components

The purpose of shot peening (blasting) process is the induction of residual compression stress on the surface of components subject to fatigue loads. This is obtained impacting a surface with shots (round metallic, glass, or ceramic particles) with a force sufficient to create plastic deformation. It is similar to sandblasting, except that it operates by the mechanism of plasticity rather than abrasion. This process has been used for many years on special steel automotive (shift gears, connecting rods and suspension components) and aerospace components, in titanium alloys and light alloy steel.
The characterization of the shot peening process is defined by specific parameters, according to legislation, such as the intensity (expressed in Almen), the diameter of the particles and the degree of coverage. When used on components made of a material different from the Almen specimen (steel), the stress field in the component structure cannot be easily estimated. In that particular case we rely on bibliography for the definition of the process parameters. By use of X-ray diffraction with a new type of instrument, the authors were able to measure the real tensile stress induced by shot peening, carried out with two different parameters on aeronautical structural components (aluminum alloy).