Fatigue fracture toughness and fatigue crack propagation curve.

Abstract

Fatigue crack growth rate of several high strength steels has been examined in laboratory air at different stress ratio, covering almost entire range of stress intensity, from nearly threshold stress intensity to fatigue fracture toughness Kfc. It is cleared that this crack propagation behaviour can be well expressed by four parameter Weibull function. The fatigue characteristic stress intensities, Ke and Kv, are proposed to define the transition behaviour of fatigue crack growth rate, from so called region I to II, and from region II to III, indicating that the maximum stress intensity, Kmax, is reached to the constant values, Ke and Kv respectively. The correlation between Kfc, which is one of the four parameters in the Weibull function, and the other three parameters is also analysed and, hence, the stress ratio dependency of the fatigue crack propagation curve can be predicted successfully.