Threshold and Variable Amplitude Crack Growth Behavior in 350WT Steel Available to Purchase

A number of models are currently available for the prediction of fatigue crack growth (FCG). Among them, Zhang and Hirt model has been identified as the most promising, based on the fact that it requires knowledge of only the basic mechanical properties of the material and the threshold stress intensity factor (K_th). To determine an appropriate value for K_th, an experimental program was designed to investigate the crack growth threshold behavior of 350WT steel. The resulting K_th was found to be similar to that suggested by other workers. However, our investigation showed that when used in conjunction with the Zheng and Hirt model, the experimentally determined K_th yields poor fatigue life predictions (FLP). An experimental testing program was also developed to investigate the fatigue crack growth behavior of center-cracked 350WT steel specimens when subjected to semi-random loading comprised of various combinations of intermittent tensile overloads and compressive underloads. Taheri et al. [1] proposed an exponential delay model for the prediction of crack growth behavior under the influence of intermittently applied tensile overloads. The current investigation proposes a modification to the exponential delay model to include the effects of not only overload ratio, but also stress ratios and overload/underload ratios. The modified delay model predictions proved to be in good agreement with the experimental data.