A simulation study on fatigue with single and block overloads

Abstract

An investigation into crack retardation behavior for variable magnitude single overloads and block overloads is conducted on some aluminum alloys. Plasticity zone interactions and plasticity induced crack closure has been used to obtain fatigue crack growth rates in the simulation study of this investigation. The relationship between Over Load Ratio (OLR) and retardation parameter is developed and provides an insight into nonlinear behavior of overloads on fatigue growth. Thus, the lacunae in Wheeler's model pertaining to single overload applications and block overloads are addressed from the viewpoint of dependence of retardation phenomenon on the magnitude of overload ratio. The importance of introduction of overload ratios in the governing equations is emphasized. Thorough calibrations have been performed with the experimental results from various sources in open literature and the model is capable of simulating fatigue crack growth, delay cycles due to single over load and block overloads and the fidelity of the model is established. The predictions on number of delay cycles, Fatigue Crack Growth (FCG) and Fatigue Crack Growth Rate (FCGR) of the model are representative retardation behavior and agree with the experimental data. The computational analysis of load-interaction effects on fatigue crack growth is presented. The model shows that a combined effect of plasticity and crack closure is a controlling mechanism of crack growth for single overload and block overload problems. Model development is presented in Fig. 1 and some plasticity zones are given in Fig. 2, while other results obtained are provided in Figs.3, 4, 5 and 6.