Taking into Account Glass Fibre Reinforcement in Polymer Materials: the Non Linear Description of Anisotropic Composites via the DIGIMAT to LS-DYNA Interface

In the context of light weight construction the replacement of metal parts with substitutes made from plastic plays a major role. These devices commonly are manufactured through injection moulding and reinforced by different amounts of glass fibres to enhance the strength of the material. In everyday application this poses a challenge to the engineer as due to this processing the local orientation of the reinforcements is varied on a broad scale leading to pronounced different material properties. Finally this can influence the overall stability of the part which is especially true for regions where welding lines occur. In the early stages of the virtual development of such plastic parts it is therefore significant to the take into account the material microstructure while carrying out macroscopic simulations. For explicit calculations non linear material properties, strain rate dependency and the failure of material play an important role in this context. The DIGIMAT to LS-DYNA interface allows to couple microstructure information coming from injection moulding simulations to be integrated in the structural mechanics calculation. Within this approach DIGIMAT is implemented as LS-DYNA user material and offers an independent description of the local composite in each element. The interface uses homogenization schemes which take constitutive laws for fillers and matrix, the percentage of fillers and the filler shape as an input and calculate the average macroscopic stiffness of the material based on the local microstructure. In the standard workflow of a coupled analysis several steps have to be carried out. Within DIGIMAT the constitutional laws are described by mathematical functions. These functions are fitted to the experimental measurements of the material. Usually these experiments are already carried out for fibre reinforced samples leading to the necessity that within DIGIMAT the full composite has to be reverse engineered for the fixed microstructure of the samples. The result is a set of material parameters which can then be taken for a coupled analysis connecting the injection moulding with the structural simulation for the full part under multiaxial load. As both types of simulation usually bear vastly different meshes a preparing step is required in which the local fibre orientations is mapped from the injection moulding mesh to the mesh used in the structural simulation. DIGIMAT offers all tools necessary to carry out the above described steps. In the presentation the workflow of a coupled DIGIMAT to LS-DYNA is demonstrated. Within the virtual material laboratory DIGIMAT-MF the composite is reverse engineered. The resulting parameter set is compared to coupled MOLDFLOW/LS-DYNA calculations on tensile bars under uniaxial strain as well as three point bending. For the application in explicit calculations also failure indicators can be defined within the coupling scheme. As at each step of an analysis DIGIMAT automatically offers all information about the microstructure failure criteria can be derived from the matrix phase or fibre phase separately and used for element deletion within the explicit calculation. All necessary descriptions for composites in explicit simulations can be defined within DIGIMAT, from nonlinear materials over strain rate dependency to failure. On that base the results of a coupled analysis show convincingly better results for an impact through an injection moulded plate than with the conservative approach with isotropic material.

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