High Cycle Thermal Fatigue on a Mixing Zone of Auxiliary Cooling System

An over-loading due to welding or surface finishing may be decomposed into a static stress (mean stress) and a pre-hardening (plastic strain). We show that for a stainless steel a pre-hardening enhances the fatigue life in stress control in contrast with strain control. Under high cycle thermal fatigue the presence of stripping more frequent near the weld is then related to combination of detrimental effects of pre-hardening in strain control and positive mean stress. Moreover we show that for a thin structure it is very difficult to evaluate the residual welding stress near a weld tip because of the dependence of the stress on spatial second derivative of the temperature of welding. Concerning surface finishing in the case of shot pinning we conclude that beneficial effect of a negative mean stress on fatigue life may be cancelled by the detrimental effect of pre-hardening in the case of strain control.