CHARACTERIZING TENSILE STRENGTH OF NOTCHED CROSS-PLY AND QUASI-ISOTROPIC COMPOSITE LAMINATES

This study aims to investigate fracture behaviors of notched cross-ply and quasiisotropic 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](2s) laminates, 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 [0(2)/90(2)](2s) and [90(2)/0(2)](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 [90(2)/+/- 45(2)/0(2)](s) and [02/+/- 45(2)/90(2)](s), because of the edge delamination taking place within the plies, the failure stresses were considerably lower than the predictions.