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TRENDS IN COMPUTATIONAL STRUCTURES TECHNOLOGY
Edited by: B.H.V. Topping, M. Papadrakakis
Strength of Textile Composites in Multiscale Simulation
R. Rolfes, M. Vogler, G. Ernst and C. Hühne
Institut for Structural Analysis, Leibniz University of Hannover, Germany
R. Rolfes, M. Vogler, G. Ernst, C. Hühne, "Strength of Textile Composites in Multiscale Simulation", in B.H.V. Topping, M. Papadrakakis, (Editors), "Trends in Computational Structures Technology", Saxe-Coburg Publications, Stirlingshire, UK, Chapter 7, pp 151-171, 2008. doi:10.4203/csets.19.7
Keywords: multiscale analysis, textile composites, voxel meshing, damage, failure, anisotropy, material model.
Due to the complex three-dimensional structure of textile composites experimental determination of material parameters is not an easy procedure. Especially through-thickness parameters are hardly quantifiable. Therefore, in addition to real material testings, virtual material testings are performed by use of an information-passing multiscale approach. The multiscale approach consists of three scales and is based on computation of representative volume elements (RVE's) on micro-, meso- and macro-scales. The micromechanical RVE enables the determination of the stiffness and strength parameters of unidirectional fiber bundle materials. The homogenized material parameters of the microscale are used as input data for the next scale, the mesoscale. In the mesomechanical RVE, the fiber architecture, in particular fiber undulations and the influence of through-thickness reinforcements, are studied. The obtained stiffnesses and strengthes are used as input for the macroscale. On the macroscale, structural components are analysed. On each scale, numerical results are compared with experimental test data for validating the numerical models.
Special care has to be taken to find a good representation of the characteristics of epoxy resin and fiber bundles. Therefore, two material models are developed. Epoxy resin is modelled with an isotropic elastoplastic material model regarding a pressure dependency in yield and failure surface. Thus, different behavior under uniaxial tension and compression and under shear can be regarded. A non-associated flow rule with a special plastic potential is chosen to control volumetric plastic straining. For fiber bundles, a transversely isotropic elastoplastic material model is developed. The constitutive equations for the description of anisotropy are derived in the format of isotropic tensor functions by use of structural tensors. In both material models, softening is computed with a strain energy release rate formulation combined with the voxel-meshing approach to alleviate mesh dependency. As a special feature, hardening is considered via tabulated input, i.e. experimental test data is used directly without time consuming parameter identification.
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