Experimental investigation of two-dimensional Mode-II delamination in composite laminates

The two-dimensional (2D) delamination growth in composite laminates under the Mode-II fracture condition was experimentally investigated using a novel set-up. Circular plate specimens with a centrally embedded pre-crack of two sizes were semi-clamped along the edge allowing sliding movement and loaded transversally at the center. In addition, one-dimensional (1D) experiments were conducted on specimens of the same material in an endloaded split set-up for comparison. For 2D experiments, the whole delamination process could be divided into three stages, i.e., crack initiation, slow propagation and subsequent rapid propagation. The corresponding load-deflection response, crack-length changes, stiffness and compliance variations in each stage were discussed. In contrast to 1D experiments, the load continued to increase in 2D cases even after rapid crack propagation due to the increasing crack-front length. Under post-inspection with a digital microscope, a much longer fracture process zone, including large-scale fiber bridging, was observed in 2D compared to 1D specimens.