Fatigue crack growth in low cycle fatigue: an analysis of crack closure based on image correlation

In this paper, the effects of crack closure on the propagation of short cracks is investigated. An experimental campaign, performed in the low cycle fatigue regime, was performed on specimens with micro-defects, considering two different strain ratios: initially, tests were performed under fully reversed straining, whereas the effect of an applied mean strain were studied by considering a strain ratio equal to 0.5. Crack closure was characterized with an innovative technique based on digital image correlation: crack opening and closing levels were measured starting from the experimental crack tip displacement fields. Finally, experimental results were compared to those computed with the analytical model proposed by Newman.