A semi-empirical model for predicting overload-affected fatigue crack growth in steels

The ability of semi-empirical crack closure models to predict the effect of overloads on fatigue crack growth in low-alloy steels has been investigated. The CORPUS model developed for aircraft materials and loading spectra has been checked first by comparison between the simulated and observed results. The CORPUS predictions of crack growth under several types of simple load histories containing overloads appeared generally non-conservative which prompted the authors to formulate a new model, more suitable for steels. With the latter approach, the assumed evolution of the crack opening stress during the delayed retardation stage has been based on the experimental results reported for steels. For all the load sequences considered, the predictions of the proposed model appear to be far more accurate than those from CORPUS. Based on the analysis results, the capability of semi-empirical prediction concepts to cover experimentally observed trends reported for sequences with overloads is discussed. Finally, possibilities of improving the model performance are considered.