This work introduces a material modelling approach for explicit finite element simulations of injection moulded short fibre reinforced thermoplastics. The material model considers linear-elastic behaviour and non-linear orthotropic stress-state dependent viscoplastic deformation for arbitrary fibre distributions. Regarding elasticity and the initial yield surface, a micro-mechanical Mori-Tanaka based approach is applied. On the matrix level an isotropic quadratic yield surface is introduced which is transferred into a Tsai-Wu yield surface on the composite level. An analytical expression for non-linear hardening and a simplified consideration of strain rate dependency is presented. The constitutive equations were verified with the experiments of a self-compounded PPGF30 material regarding regarding tension, compression and shear at different orientation distributions.

A requirement for the safe design of thermoplastic parts is the ability to precisely predict mechanical behaviour by finite element simulations. Typical examples include the engineering of relevant components in automotive applications. For this purpose adequate material models are essential. In this context, the present work introduces a material modelling approach for short fibre reinforced thermoplastics (SFRTPs). SFRTP parts are processed cost-effectively by injection moulding and show a varying degree of anisotropy due to the locally inhomogeneous fibre distributions that arise during the moulding process. The presented material model considers linear-elastic behaviour and non-linear orthotropic stress-state dependent viscoplastic deformation for arbitrary fibre distributions. The constitutive equations are verified with the experiments of a PPGF30 material regarding different stress-states and orientations.