Evaluation of mode-I SIF, T-stress and J-integral using displacement data from digital image correlation - Revisited

J-integral evaluation is essential for elasto-plastic fracture mechanics (EPFM) studies. Curve fitting the local displacement data is necessary for J-integral evaluation and suitable polynomial function and grid size need to be selected. Theoretical study carried out in this work showed that a third order polynomial fitted to displacement data in a local grid of size 0.5 mm (approximately ten times the plastic zone size) gave accurate J values even for paths of small radius (closer to crack-tip) where strain gradients are very high. Using these parameters, J-integral is obtained for epoxy (brittle polymer) and polycarbonate (ductile polymer). For polycarbonate, a method has been suggested to determine the Dugdale plastic zone size from the measured J-integral and out-of-plane displacement results.