ANALYSIS OF THE INTERLAMINAR CRACK INITIATION IN MIXED-MODE I+II COMPOSITE FRACTURE SPECIMENS

The interlaminar crack initiation in mixed-mode specimens was investigated through two- and three-dimensional finite element models. Elastic analysis was conducted to understand the crack initiation in glass-fibre/vinylester composites. The MMF and CLS specimens were used for the two-dimensional plane strain models. Simplified 3D micro-mechanical models were constructed to investigate the effect of the fibres on the stress distribution based on the square fibre arrangement. The mixed-mode conditions were produced by changing the ratio of the crack opening and crack shearing displacement components. It was concluded that the fibre/matrix interface plays critical role in the direction of the crack propagation path. The propagation path was described by the crack angle determined by the peak stresses in the crack front and in the fibre/matrix interface. The critical fibre/matrix interface stress was also determined and found to increase with the mode-I contribution. The tensile stresses ahead of the crack-tip were examined and experienced as increasing with the mode-I contribution