An invariant-based anisotropic material model for short fiber-reinforced thermoplastics: Coupled thermo-plastic formulation

This paper presents the development of a new fully-coupled thermo-mechanical invariant-based elasto-plastic constitutive model for short fiber reinforced composites (SFRPs). The invariant-based character of the current formulation under quasi-static multiaxial loading conditions allows the incorporation of the anisotropic (transversely isotropic) response of these materials, which results from the employed injection molding process for their production. From the modeling point of view, the thermo-mechanical nonlinear behavior of these materials is performed through the definition of a thermal-dependent anisotropic yield surface and a non-associative plastic potential function. This novel coupled formulation is accordingly derived and implemented into the FE code FEAP by means of the user capability UEL, i.e. the constitutive model is integrated within an user-defined element. The performance of the model is first assessed using a set of benchmark computations, and subsequently validated with available experimental data, showing the potential applicability of the proposed formulation.