The Propagation of Short Fatigue Cracks at Notches
SourceCenter-notched plate specimens and single-edge-notched specimens of a low-carbon steel were fatigued under axial and bending loads. The growth behavior of a short fatigue crack near the notch tip was analyzed based on the measurement of crack closure. The crack closure develops as a crack grows; the effective fraction of the applied stress decreases. This accounts for the decrease of the crack growth rate with increasing crack length. The relation between growth rate and the effective stress intensity range is unique, and nearly identical to that for a long crack, meaning that the effective stress intensity range is a good measure of the crack driving force. The results on the threshold of crack growth are compared with the model proposed by Tanaka and Nakai. The variations of the threshold values of the stress intensity range and the effective stress intensity range, and the crack closure at the threshold with the length of nonpropagating cracks, agree well with the model prediction.