Initiation and bifurcation mechanisms of cracks in multi-directional laminates

This work studies the behaviour of multidirectional composite laminate under opening (mode I) loading. The material used is a glass/epoxy composite. The stacking sequence +/- theta was selected to minimise coupling effects. The experimental results showed that several fracture modes depend on the angle of the ply orientation and on the applied stress type. For small angles (theta less than or equal to 30 degrees): the fracture type is delamination on the mid plane. For large angles (theta > 67 degrees), the fracture takes place by flexure at the head of the precrack. For the intermediate angles, the bifurcation phenomenon leads to a delamination in staircase. (C) 2000 Elsevier Science Ltd. All rights reserved.