Mode I fracture of epoxy bonded composite joints: 1. Quasi-static loading

Mode I constant displacement rate tests were conducted on epoxy-bonded CFRP joints at –50, 22 and 90°C. A comparison of experimental compliance and different beam theory approaches indicated that care needs to be taken when applying beam theory approaches across a wide temperature range. Temperature was seen to influence the mode of fracture which progressed from stable, brittle fracture at low temperatures to slip-stick fracture at room temperature and finally to stable ductile behaviour at elevated temperatures. This behaviour has been attributed to the dependence of critical strain energy release rate on crack velocity for epoxy adhesives and a model for the fracture behaviour of viscoelastic materials has been used to explain these results. The critical strain energy release rate was seen to increase with temperature and the failure locus transferred from predominantly in the composite substrate to predominantly in the adhesive.