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An improved characterisation of long-fibre thermoplastics for numerical simulation of components

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  • Long-Fibre Thermoplastic
  • Lft
  • Numerical Simulation
  • Anisotropic Material Behaviour
  • Bilinear Mode
  • Design


In recent years long-fibre reinforced thermoplastics (LFTs) have gained major importance, especially in the automotive sector. LFTs are increasingly used in structural and semi-structural components. So-called direct processes in which semi-finished products are avoided and parts are produced directly from the raw materials such as glass fibres, polymers and appropriate additives have gained significant market shares. The components are produced in an inline compounding direct process. In this manufacturing process, the rheological behaviour has a considerable influence on the mechanical properties. However, this is not taken into consideration during component design. Usually, an elastic, isotropic material model will be used but this is only a rough approximation of the real material behaviour of LFTs. The aim was to improve the understanding of the material behaviour to come to a numerical model which is closer to reality and to maintain and enlarge the lightweight construction potential of LFTs. In this manufacturing process, the bearing area of the extrudate is usually smaller than the component area, so the extrudate is flowing during the compression process. The fibres align with increasing flow length. So for structures with large flow lengths the anisotropic material behaviour is not negligible. For structures with flow lengths below 100 mm, the material behaviour can be regarded as quasi-isotropic. It was further established that the material is stiffer under tension than under compression. Fibres subject to compression can buckle and thus lose their reinforcing effect. Because of these two perceptions two material models can be used. For components with large flow lengths this is an approach where the properties are dependent on the fibre direction (orthotropic or transversely isotropic ). Therefore you have to know the fibre orientation and the corresponding mechanical properties. For components which are basically subject to compression the use of a nonlinear material model is advisable; in the simplest case a bilinear model where you use Young´s Modulus and the compressive modulus.

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