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Anisotropic Extensions of the SAMP-Model for the Simulation of UD-Composites and Organic Sheets

In this contribution, new anisotropic elastic-viscoplastic constitutive models for simulating unidirectional reinforced fiber matrix composites and textile fabrics are presented. These are in particular a transversely-isotropic constitutive model for UD-composites and an anisotropic constitutive model for textile fabrics. The new material models address 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 offers a very nice possibility to regard misalignments of the yarns in a textile fabric. When considering textile fabrics, the two main directions representing the directions of the rovings do not necessarily need to be perpendicular to each other. An initial misalignment of the yarns due to the draping process and also a loading induced misalignment of the yarns due to the forming process can be incorporated easily, letting the structural tensors rotate against each other. The applicability of the anisotropic SAMP models will be shown with two examples. First, simulation results of quasi-static and dynamic off-axis compression tests and triaxial tests of a carbon epoxy IM7-8552 are presented, predicting the experimentally observed pre-failure nonlinearities. Secondly, the applicability of the orthotropic SAMP-model to organic sheets is discussed. The experimentally observed highly non-linear behavior under shear dominated loadings and the quasi brittle behavior in uniaxial tension and compression in the main directions can be predicted. In future developments, the whole process chain drape simulation -> forming simulation -> crash simulation will be addressed. Therefore, a new development in LS-DYNA, a so called *PART_FABRIC is proposed, enabling to regard the preliminary misalignments and the loading induced fiber misalignments. That is, after the forming simulation, the reorientation of the yarns (regarded by a rotation of the vectors a and b) can be rewritten into the *PART_FABRIC and are thus available in the subsequent crash simulation.