INFLUENCE OF NOTCHES AND CRACKS ON LIFETI ME OF 2,25CR-1MO STEEL UNDER FATIGUE CREEP CONDITIONS

The lifetime of notched and cracked cylindrical and flat specimens of a 2,25Cr-1Mo steel was studied under high-cycle-fatigue/creep conditio ns. The lifetime for the constant maximum stress conditions was shown to be dependent on the stress ratio R = sigma(min)/sigma(max) in nonmo notonous way with a well pronounced maximum. Under the fatigue/creep c onditions characterized by a small cyclic stress component the lifetim e could be described simply by the stress dependence of the time to fr acture for pure creep using the corresponding mean stress. Higher cycl ic stress components have negative effect on the lifetime. Increasing cyclic stress component results in fatigue crack propagation and sever e decrease of the lifetime. The time to fracture of notched bodies wit h the same stress concentration factor depends not only on R, but also on the degree of the stress triaxiality at the notch root.