Meso-scale (unit cell of an impregnated textile reinforcement) finite element (FE) modelling of textile composites is a powerful tool for homogenisation of mechanical properties, study of stress-strain fields inside the unit cell, determination of damage initiation conditions and sites and simulation of damage development and associated deterioration of the homogenised mechanical properties of the composite. Meso-FE can be considered as a part of the micro-meso-macro multi-level modelling process, with micro-models (fibres in the matrix) providing material properties for homogenised impregnated yarns and fibrous plies, and macro-model (structural analysis) using results of meso-homogenisation. The paper discusses stages of the meso-FE analysis and proposes a succession of steps (''road map'') and the corresponding algorithms for it: (1) Building a model of internal geometry of the reinforcement; (2) Transferring the geometry into a volume description (''solid'' CAD-model); (3) Preparation for meshing: correction of the interpenetration of volumes of yarns in the solid model and providing space for the thin matrix layers between the yarns; (4) Meshing; (5) Assigning local material properties of the impregnated yarns and the matrix; (6) Definition of the minimum possible unit cell using symmetry of the reinforcement and assigning periodic boundary conditions; (7) Homogenisation procedure; (8) Damage initiation criteria; (9) Damage propagation modelling. The ''road map'' is illustrated by examples of meso-FE analysis of woven and braided composites.
In this study, we propose a FE model for dry fabric forming simulation that can express the tension dependent shear behavior in order to predict the wrinkles, one of the major forming defects. Automakers are gradually using more carbon fiber reinforced plastic (CFRP) in mass production cars, because the development of resin transfer molding (RTM) have reduced its cycle time to less than 10 minutes. Finite element analysis (FEA) is essential to the vehicle design process, so numerical simulation of CFRP is strongly desired today. Forming simulation is especially important, because the performance of the final composite part strongly depends on changes in fiber orientation during the preforming. Moreover wrinkle is one of the major defects in preforming. RTM usually involves fabric reinforcement. During forming of fabric, large in-plane shear deformations typically occur. The reason for this is that the shear resistance is very low at the initial stage, because the deformation is governed by yarn contact friction at the cross-sections. Accurately expressing the in-plane shear behavior of fabric is very important for accurate forming simulation. In most simulation models the shear resistance of fabric is assumed to be independent from the tension along the yarn. However, meso-model predictions of the picture frame and bias-extension tests suggest this to be an invalid assumption. In this study, a micromechanical model that introduces the stress component due to the yarn rotational friction is adapted to the dry fabric forming simulation. In other words, this can express the shear behavior that depends on the tensions in the yarns. The results using this micromechanical model are in good agreement with the meso-model results in the various boundary conditions. .その † 原稿受理 平成25年9月10日 Received
In this study, experimental data, geometrical models, and finite element analysis are presented for typical structurally stitched multilayer preform composed of quasi-unidirectional carbon fibre woven fabric. The term 'structural' presumes here that the stitching yarn does not only consolidate the plies (as the non-structural one does) but forms also a through the thickness reinforcement. One stitching technique, tufting, is studied, with 67 tex carbon yarn. The models account for general features of the local preform geometry and are believed to allow for a sufficient modelling on the mesoscale (textile unit cell) level. Experimental and theoretical results are presented, compared and discussed; a 'road' map is proposed for the modelling of structurally stitched preforms.
In this paper, we propose a new FE model of a carbon fiber reinforced thermoplastic (CFRTP) in order to capture the deformation during a thermoforming process because the thermoforming process of CFRTP has increased its presence in the automotive industry for its wide applicability to the mass production car. The proposed model can describe temperature dependent non-linear bending property of CFRTP by a set of elements which consists of two shell elements with membrane elements in between them. The membrane elements represent temperature dependent anisotropic in-plane behavior by calculating stress contributions of the textile reinforcement and thermoplastic in a parallel system. By applying Reuss model to the stress calculation of thermoplastic, the in-plane shear behavior which is the key deformation mode during forming can be accurately predicted. FE model is constructed based on the results of three point bending and bias-extension experiments which are conducted in the range of the process temperature. Thermoforming simulations are presented and compared to experimental results. Simulated outline and shear angle are in good agreement with experimental results. It will be shown by sensitivity study that the effect of the temperature plays an important role in deformation during a non-isothermal forming process.
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