Formulation of the Viscoplastic Behavior of Epoxy-Glass Fiber Composites

The tensile behavior of epoxy-glass fiber composites is examined experimentally and theoretically, in terms of a 3-D viscoplastic model, appropriate for material anisotropy. For the kinematic description, the multiplicative decomposition of the deformation gradient tensor has been used, while a flow rule for an orthotropic material, based on a dyadic of vectors parallel to the material axes, is introduced. Moreover, a functional form expressing the rate of plastic deformation, developed for polymeric materials in earlier works, is applied in the case of polymeric composites. A satisfactory agreement with the experimental results of the off-axis specimens is found, while the strain rate effect is described in terms of a scaling rule, valid in the viscoplasticity.