Effect of combined loading on cracks in graphite/epoxy composites

Moiré Interferometry technique has been used to study the effect of combined loading on crack displacement in graphite epoxy plates. Specimens with central cracks of various orientations were subjected to uniaxial tensile loads. Thus, the cracks were under biaxial-stress fields, mode I (tension stress) and mode II (sliding stress). The obtained fringe patterns represented contours of constant-in-plane displacements. Based on these fringe patterns, two types of displacements were determined at the crack center, crack opening displacement (COD) and crack shearing displacement (CSD). The effect of combined loading on COD and CSD as well as the behavior of the material under these conditions was investigated in more detail. Experimental data were compared with the linear elastic fracture mechanics (LEFM) solution.