Abstract

Based on the strip-yield model for propagating cracks, the current paper proposes a new method for the evaluation of crack-tip opening loads. It is based on the theoretical analysis of shapes of the compliance offset curves for various applied stress levels and R-ratios, which indicates that the inflection point of the curve is a good approximation of the initiation of the crack tip opening. The method avoids uncertainties and drawbacks associated with the selection of empirical thresholds or criteria to identify the value of opening load, which is often utilised to calculate the effective stress intensity factor range or fatigue crack driving force. Careful experimental studies also confirm the ability of this proposed method to negate R-ratio effect on fatigue crack growth rates for a wide range of loading conditions.