An equivalent driving force model for crack growth prediction under different stress ratios

An equivalent driving force (EDF) model is proposed for the correlation and prediction of crack growth under different stress ratio, R, values. The equivalent driving force defines a completely-reversed stress intensity range that is expected to yield the same crack growth rate as a given stress intensity range ΔK and stress ratio R. Thus, the suggested equivalent driving force (EDF) model seeks to unify the crack growth data into a single master curve for fatigue design. The EDF depends on a single factor known as the mean-stress-sensitivity factor, which can be readily determined from experimental data. Application of the EDF model to the published data of Titanium and Aluminum alloys indicates that there exists an R-value below and above which the mean-stress-sensitivity factor differs. It was found that for −1 ⩽ R ⩽ 0.3 the mean-stress-sensitivity factor was much higher than for 0.3 < R ⩽ 1. This difference in mean-stress-sensitivity to crack growth behavior in the two R-regimes could be explained in terms of the dominant mechanism controlling damage/crack growth rate.