Equivalent crack growth model for correlation and prediction of fatigue crack growth under different stress ratios

An equivalent crack growth model that accounts for the effect of stress ratio is proposed for the correlation and prediction of crack growth under different stress ratios. A previously proposed equivalent driving force Delta Keq that yields the same growth rate (da/dN)R as combined applied stress intensity factor range Delta KR and stress ratio, R is modified, and its corresponding equivalent growth rate (da/dN)eq is derived. This yields an equivalent crack growth model of (da/dN)eq versus Delta Keq capable of collapsing data of different R-ratios unto a common curve. The model was validated with excellent agreement between the model and published data.