The cyclic R-curve method for predicting fatigue crack growth threshold based on modified strip-yield model of plasticity-induced crack closure under fully reversed loading

A strip-yield model modified to leave plastically deformed stretch in the wake of the advancing crack tip is applied to simulate the buildup of plasticity-induced crack closure with crack extension from precracks with various lengths under fully reversed loading. Two types of pre -cracks are examined: open precracks which remain open even under cyclic compression, and closed precracks which may close under compression. The effects of precrack type and length on fatigue thresholds were systematically examined. Because of a sharp increase of crack opening stress with crack extension, the effective stress intensity range Delta Keff drops initially and then turns to increase. Assuming a constant threshold value of Delta Keff for steels, new master curve equations are proposed for the cyclic R-curve. The effect of the precrack type on fatigue thresholds is successfully derived for different precrack lengths.

Automated summary

A modified strip-yield model is used to simulate plasticity-induced crack closure in the wake of advancing cracks, with different lengths of precracks, under fully reversed loading. Two types of precracks, open and closed, are examined to understand their effects on fatigue thresholds. The results show that the crack opening stress and effective stress intensity range Delta Keff have significant influence on fatigue thresholds, and new master curve equations are proposed for the cyclic R-curve.