Characterizing tensile strength of notched cross-ply and quasi-isotropic composite laminates

This study aims to investigate fracture behaviors of notched cross-ply and quasi-isotropic laminates with different stacking configurations. The fracture criterion developed by Vaidya and Sun (1997), based on the postulation that the failure was dominated by the 0 degree ply, was adopted to characterize the failure stresses of the notched laminates. The failure mechanisms of the samples were determined through X-ray examinations. It was found that for [0/90]_2s, [90/0]_2s, [0/±45/90]_2s, and [90/±45/0]_2slaminates, the strengths were quite close to the model predictions. This occurred because there were no severe damage zones observed near the crack tip; therefore, the failure stresses of the notched laminates were dominated by the stress states of 0 degree ply, which can be properly characterized using the fracture mechanics in conjunction with the laminated plate theory. However, for [0₂/90₂]_s and [90₂/0₂]_s laminates, there were severe damage zones observed near the crack tip such that the predicted failures stresses were lower than the experimental data. In contrast, for the [90₂/±45₂/0₂]_s and [0₂/±45₂/90₂]_s, because of the edge delamination taking place within the plies, the failure stresses were considerably lower than the predictions.