Abstract
In order to control the surface mechanics of a metallic material, mechanical treatment of the surface, such as by shot peening, water jet peening, cavitation peening or laser peening, is often done. In this review paper, we discuss the mechanical properties of such treated surfaces and the effect of the treatment on fatigue strength. Although there is a detrimental increase in surface roughness introduced by the various treatments, the positive effects, such as the introduction of compressive residual stress and/or work hardening, i.e., an increase in the yield stress, outweigh the negative effects, then treatments improve the fatigue strength. The compressive residual stress introduced by the various treatments is closely related to the crack closure and crack initiation. If the same peening process is used, the fatigue strength can be estimated from the residual stress distribution. However, when the mechanical surface treatments were different, the residual stress distribution of the specimen at the same fatigue strength was totally different. Namely, when different peening processes are applied to the surface, the compressive residual stress only shows a tendency to improve the fatigue strength, and the fatigue strength cannot be evaluated precisely from the residual stress distribution, Thus, a fatigue test is required to evaluate the fatigue strength. As the fatigue strength strongly depend on the crack initiation, an evaluation of the threshold level of the stress intensity factor range of a treated surface is valuable, and it can be possible by a plate bending fatigue test using a notched specimen.
