Fracture Toughness of Unidirectional Glass/Carbon Hybrid Composites

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Abstract
The results of fracture toughness of the glass/carbon fibre reinforced epoxy hybrid composites, as expressed by KIC and GIC—the critical stress intensity factor and the critical strain energy release rate respectively, in the crack open ing mode—are presented in the following paper. The tests have been conducted in the 3-point bending configuration for the specimens having a total reinforce ment content of about 55%. The K IC has been evaluated from the GIC and also from the standard expressions normally used for isotropic materials. Similarly, the GIC and KIC have been evaluated by using both Pmax, the maximum load, and PQ, the point of intersection on the load displacement curve with a line having 5% less slope than the slope of the curve at the origin. The trend of the results obtained by these two methods is considerably different particularly with increasing glass content in the hybrids. The values of GIC and KIC obtain ed from PQ exhibit a distinct positive hybrid effect. The hybrids having both the glass and carbon fibres not only have values better than those expected by the rule of mixtures but also better than those of the composite reinforced en tirely by glass or carbon fibres.