JEC COMPOSITES MAGAZINE - Issue #60 - Special JEC Asia - October 2010 - 64

KNOW-HOW
Design tool
g…/… Modelling of textile composites

(forming and impregnation) and structural analysis of the completed composite part. Figure 1 also gives an idea of “horizontal” integration of the models along the production chain (forming – impregnation) and, further on, towards the part’s in-service behaviour. The various meso-level models shown in Figure 1 are implemented, for example, in the WiseTex software suite of K.U. Leuven [1-3], presented in Table 1. WiseTex’s geometrical and micro-mechanical component has been integrated into ESI Group’s Virtual Performance Solution product, namely the SYSPLY structural analysis tool, to serve in macro-level structural analysis of composite parts [4].
Table 1: WiseTex software (K.U. Leuven) – virtual textiles and textile composites

Description
Internal geometry and deformability of textile reinforcements Visualisation – virtual reality* Permeability

Software
WiseTex Lam Tex VRTex FlowTex

Description
Micromechanics – stiffness prediction Link to meso-FE modelling

Software
TexComp

FETex MeshTex**

Fig. 2: Geometrical models of textile reinforcements created by the WiseTex software: (a) generic model of a woven fabric with internal structure parameters, input: p – yarn spacing; calculated: h – crimp height, z(x) – yarn middle line; d1,d2 – yarn cross section; ΔZ – distance between middle planes of the fabric layers for 3D fabrics; Q – interaction forces of the yarns; specific reinforcement types (from left to right, top to bottom): (b) cross-ply laminate; (c) 2D woven laminate; (d) 3D woven non-crimp fabric; (e) 3D woven angle interlock; (f) biaxial braid; (g) triaxial braid; (h) non-crimp fabric; (i) weft knitted fabric

*in collaboration with T.U. Liberec ** in collaboration with Osaka University The article focuses on the integrated design tool’s “performance” component, i.e. the prediction of mechanical properties (stiffness, strength, fatigue) of textile composites.

Because the internal geometry model in relaxed state is built based on a description of mechanical interaction between the yarns, the same model can be used to calculate the geometry of the unit cell in the deformed fabric – by compression, shear or biaxial tension. The external loading enters into equilibrium equations of the yarns. Alternatively, the relaxed geometry can be transformed into geometry under load using finite element modelling of dry fabric deformation [6].

Internal architecture models of textile laminates and 3D woven textile composites
The geometrical model of a fabric translates the interlacing topology (woven, braided, knitted…) into actual yarn placement in the unit cell space and calculates yarn dimensions and waviness (crimp). Such a model accounts for the interaction between the yarns in the relaxed or loaded state of the fabric, which is defined by the forces due to bending and compression of the yarns and to external loads. The following input data are given to the geometrical model: 1. Fabric interlacing topology – for example, 2D and 3D weaves are coded by a weave matrix [5] 2. Compression and bending behaviour of warp and weft yarns (there can be any number of different types of yarns in both warp and weft) 3. Spacing of warp and weft yarns (which can be non-uniform). The algorithm solves equations of equilibrium between yarns under forces created by bending and compression of the yarns, or equations expressing the minimum energy condition, with constraints given by the interlacing. The resulting geometry is presented using a unified data format for different types of the textile (Fig. 2).

Fast prediction of the elastic properties of textile composites, integrated with structural analysis of composite parts
Once a geometrical model of a textile composite is ready, the homogenized stiffness can be calculated using the inclusion method, implemented in the TexComp software [1, 2, 7]. The yarns in the unit cell are subdivided into a number of smaller segments, where each yarn segment is geometrically characterized by its total volume fraction, spatial orientation, cross-sectional aspect ratio and local curvature (all these parameters are readily provided by the geometrical model). Next, Eshelby's equivalent inclusion principle is applied to transform each heterogeneous yarn segment into homogeneity with a fictitious transformation strain distribution. The solution uses a short-fibre equivalent, which physically reflects the drop in axial load-carrying capability of a curved yarn with respect to an initially straight yarn. The interaction problem between the different reinforcing yarns is solved in the traditional way, by averaging out the image stress sampling over the different phases, using a Mori-Tanaka scheme. Fast homogenization with the inclusion model is well-suited to meso-macro calculations, implemented in ESI Group’s latest SYSPLY software, which incorporates WiseTex libraries. Performance

jec composites magazine / No60 October 2010

JEC COMPOSITES MAGAZINE - Issue #60 - Special JEC Asia - October 2010

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #60 - Special JEC Asia - October 2010