4The generation of residual stresses in hard machining has been investigated bymany researchers [Field 1971, Brinksmeier 1982, Mittal 1998, Liu 1998, andJacobson 2002]. It is reported that residual stresses on the machined surface areknown to influence the service quality of the component, such as fatigue life and,tribological properties, and distortion. The profile (magnitude and depth) of theresidual stresses can greatly influence the fatigue life of a component. It isbelieved that compressive residual stresses are more favorable for rolling contactfatigue life than tensile residual stresses.Shot peening is a cold working process in which the surface of a part is bombardedwith millions of small spherical media, called “shot”, which are made of steel,glass or ceramic. It is known that after the peening treatment a layer withcompressive residual stress will present under the surface. The compressiveresidual stress underneath increases the fatigue life and wear resistance of, andprevents stress corrosion cracking and fretting fatigue of the treated components.