A new viscoplastic model and experimental characterization for thermosetting resins

Abstract

Resins as matrix materials for structural composites show nonlinear rate-dependent mechanical behaviors. In the present work, a new viscoplastic constitutive equation based on a potential function is proposed to predict the mechanical response of an epoxy matrix to any three-dimensional loading condition. The proposed potential function is a combination of the second and third invariants of the deviatoric stress tensor as well as the first invariant of the stress tensor, i.e. the hydrostatic stress. Series of tensile and shear constant-rate straining tests were performed on epoxy resin specimens up to the fracture. Under shear loading, the nonlinearity of the stress-strain curve and the rate dependency of the initial modulus and strength are more significant than that under tensile loading. The viscoplastic model parameters are derived from the experimental data, and the fracture patterns of the specimens under tensile and shear loadings are studied. Further, the model predictions are compared with a known rate-dependent model to show the accuracy of the presented model.