Loading rate effects on mixed-mode I/II fracture envelope of epoxy resins with nonlinear behavior

The tangential stress contour (TSC) method in combination with the equivalent material concept (EMC) was used to predict the fracture load, fracture initiation angle, and fracture resistance of an epoxy resin with nonlinear and ductile behavior. In this analysis, both the loading rate and mode mixing effects were taken into account to obtain the fracture envelopes of the tested resin. Based on the considered approach, only a tensile test performed on dogbone specimens and a pure Mode I fracture toughness test using semi-circular bend (SCB) samples are required to predict the ultimate load and crack initiation angle of the resin at different mode mixities. According to this technique, the non-linear ductile behavior of the tested epoxy is simulated by a virtual brittle linear response, which greatly simplifies the problem. The predicted fracture envelope was validated by experimental results. A very good agreement between the prediction and the experimental data was obtained.