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Short Fiber Reinforced Polymers: Part II - Anisotropic Extensions of the SAMP-Model

In this contribution, a new anisotropic elastic-viscoplastic constitutive model for simulating short fiber reinforced polymers is presented. The new anisotropic SAMP-model addresses the same main features as the isotropic SAMP model (MAT_187 in LS-DYNA). These are in particular pressure dependent yielding allowing different yielding in tension, compression, shear and biaxial loadings, tabulated input of hardening data for each stress state and a non-associated flow rule for a correct prediction of volumetric plastic strains. Hence, the anisotropic material models represent a consistent further development of the isotropic SAMP material model (SAMP-1 or MAT_187 in LS- DYNA 971). ) The anisotropy is incorporated by an invariant formulation using so called structural tensors. This provides interesting modeling techniques for short fiber reinforced thermoplastics. The fiber orientation tensor is directly integrated into the constitutive equations and an automated homogenization is performed. That is the fiber orientation tensor “weights” the structural tensors representing the preferred directions and in the limiting case “all fiber directions equally distributed in all directions”, the isotropic SAMP model is recovered as a special case. As an example, simulation results of material characterization tests of PA6GF60, a short fiber reinforced polyamide with 60% glass fibers, are presented and discussed. The characterization consists of quasi-static and dynamic tensile tests, compression and shear tests and quasi-static and dynamic bending tests which are performed by the 4a-Impetus test system. The importance of regarding triaxiality and anisotropy in the constitutive equations as a crucial feature of the new developed material model is demonstrated and discussed. For future developments, the process chain mold flow simulation –> crash simulation will be addressed. Therefore, a new feature in LS- DYNA, a so called *PART_POLYMERE is proposed, which enables to regard the typical layerwise fiber distribution and which offers the possibility to provide the fiber orientation tensor as an additional information in each Gauss point.