Crack-Tip Plastic Zone Size and Shape via DIC

In this paper Digital Image Correlation (DIC) is used to characterize the crack-tip plastic zone size and shape under plane stress and plane strain situations. For that, two disk-shaped tension DC(T) specimens made of 1020 steel with thicknesses 2 and 30 mm were used in fatigue crack growth tests to simulated plane stress and plane strain conditions, respectively. Fatigue cracks were grown under quasi-constant Delta K (stress intensity factor range) and stress ratio (R) respectively equal to 20 MPa root m and 0.1. A single 100% overload was applied when the crack reached a crack length of 6 mm (i.e. total crack length/specimen width = 0.3). Experimental measurements of the monotonic plastic zone at different stages during overload application are compared with finite elements simulations to predict the size and shape of the crack-tip plastic zone. A detailed discussion is given based on the DIC measurements obtained from the current investigation, including the experimental observations of crack closure.