THE EFFECTS OF PRESTRESSING OVERLOAD ON LOW CYCLE FATIGUE AND da/dN

The effects of prestressing overload on dow cycle fatigue and fatigue crack growth rates da/dN of titanium alloy TC-11 and Ni-base superalloy GH33A for gas turbine disks were investigated at room temperature and 633K. The experimental results show that the low cycle fatigue crack initiation life is increased by prestressing overload treatment within the range of low cycle fatigue life 5×10³ to 5×10⁴,but the effect of the prestressing overload on fatigue crack propagation life Np is not obvious. In addition, an empirical expression is formulated to estimate the fatigue life of side edge notched (SFN) specimen under prestressing overload as S^m（N_f/r） = c. When this expression is employed to estimate the fatigue life of a notched specimen prestressed, it is only necessary to know the conventional fatigue S-N curve.