.,------------------------,

Total relaxation of residual stress was observed [7] for the residual stress component in the z-direction, a 1., as measured on a cross-sectioned sample in the plastically deformed (subsurface) region by making two additional slots with a separation of 2 mm, extending partly through the plastically deformed subsurface region, as schematically illustrated in Fig. lOb. These carefully ground slots through the elastically deformed surface layer (z = 0 to z = 0.08 mm) and into the plastically deformed region (up to 0.2 mm), release the as measured tensile residual stress in the surface normal direction, as indicated in Fig. lOb.