Abstract
Abstract 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 Δ K 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.
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