A new model for fatigue crack propagation in 4340 steel

Abstract

An investigation on fatigue crack propagation under mode I loading has been performed. Fatigue crack growth data in the case of plane strain mode I have been obtained by performing experiments on compact tension specimens of 4340 steel for increasing ΔKI, decreasing ΔKI, and constant ΔKI loading conditions. Fatigue crack extension predictions have been obtained for Khan's proposed equation [1989], together with the widely used Paris and Erdogan [1963] and Forman [1967] equations. Khan's equation overcomes the drawbacks associated with the Paris and Forman equations, such as the inclusion of all the three stages of fatigue crack propagation, the nondimensionality of the constant, “C”, and also the accuracy in life prediction. Within the context of Linear Elastic Fracture Mechanics and the types of loading performed at the crack tip, it has been shown that Khan's model can accurately predict the crack growth data from near threshold value to the unstable fracture; these predicted values are much more accurate than those from the Paris and Forman equations.