Fracture toughness for mixed mode I/II of epoxy resin

We investigated the fracture locus and the direction of the crack initiation under mixed mode I/II for epoxy resin at room temperature. In order to obtain them over a whole mode mixity, we conducted asymmetric bending tests. We examined four common fracture criteria to compare them with the experimental results. Based on our experimental results, we concluded that the relaxation effect on fracture toughness varies with the mode mixity, so the common fracture criteria for mixed mode could not be applied to the epoxy resin. In contrast, the crack initiation angle can possibly be determined independently of the relaxation effect.