Abstract
In this study, we discussed the fracture criterion for mixed mode of the epoxy resin at the room temperature. We conducted the three- and four-point bending tests to determine the fracture toughness under mixed mode loading and compared the experimental results with three theoretical fracture criteria: maximum hoop stress theory, minimum strain density theory, and maximum energy release theory. At lower mode mixity, namely closer to mode I, the fracture envelope and the crack initiation angle could be roughly predicted by the theoretical criteria. However, at higher mode mixity, especially at the vicinity of mode II, the fracture envelope followed neither theoretical nor empirical criteria, which could be due to the effect of thermo-viscoelastic relaxation phenomena, even when the crack initiation angle followed the maximum hoop stress criterion.
