ABSTRACT
The surface layer may be either strengthened or weakened, depending on the processing conditions. The integrity of surface is determined during the stage of finishing. The processing operations preceding it affect the surface layer as well, however, and dictate the kind of finishing method that is to follow. Among the finishing operations, producing surface layer properties that extend fatigue life, the most common are cold-working methods such as shot peening, rolling, and burnishing. The most widespread cold-work method used for surface layer strain hardening today is shot peening. The surface texture resulting from shot peening is an aggregate of a large number of superimposed indentations—traces of particle impingements. The surface roughness caused by shot peening has a favorable effect upon stress distribution. Producing low surface roughness, rolling processing increases the fatigue limit of a machine part and is applicable to external as well as internal surfaces.
