Abstract
Fatigue is generally a surface related phenomenon as the fatigue cracks usually initiate at the surface and propagate into the bulk material. The surface layer of residual compressive stress induced by shot peening is of primary practical importance. Roughly speaking, the residual stress acts as an applied mean stress and a compressive residual stress will therefore relate fatigue crack initiation and growth. The work hardening results in an increased dislocation density which hinders dislocation movements due to the fatigue load and suppresses localized plastic deformation which is a starting feature for crack initiation. From Mises-Henckey criterion and our previous investigation, it is expected that one of the effective way of obtaining high hardness and residual compressive stress to hard materials is high energy hard shot peening under applied tensile stress.
A systematic study of hard shot peening with water jet under various tensile stressing on surface residual stress of carburized SCM420 specimens has been conducted. As a result, the highest peak value, 1400MPa and distributions of residual compressive stress at the surface region were obtained. Also peak residual stresses increase linearly with applied tensile stress. These increments were caused by enhancing effect which is explained by Mises-Henckey criterion of shot penetration to the hardened surface due to applied tensile stress.
