3D viscoelastic plastic model coupled with a continuum damage formulation for fiber reinforced polymers

Fiber reinforced polymers with thermoplastic matrices are increasingly used in diverse applications. As a result, ever more complex loading conditions have to be considered in their design. To improve the predictive capabilities, a recently proposed constitutive model for fiber reinforced thermoplastic (FRT), originally formulated for two dimensional (2D) loading conditions, is extended to general three dimensional (3D) loading. The model accounts for stiffness degradation, inelastic deformation as well as strain rate dependency. A comprehensive derivation of the constitutive equations is presented in combination with adaptations for unidirectionally reinforced (UD) composites, which does not necessitate introducing additional model parameters. The resulting 3D-model is validated at coupon level using quasi-static and low-velocity impact experiments. It is shown that the model generalizes well to complex loading conditions and various strain rates.