Keywords: fabrics, textiles, finite element analysis, forming, preforming, interlock fabrics.

Composites materials have more and more applications especially in aeronautics where high resistance to weight ratio are needed. Because of delamination sensitivity, composites are nowadays mainly limited to non structural parts. To balance this problem and extend composites applications, interlock fabrics where developed [1]. In those specific applications, forming feasibility and material properties of the composites parts have to be precisely known. Fibres orientations in the final part are key information to determine anisotropic properties for dynamic or damage analysis [2]. Numerical simulation of interlock reinforcement forming allows conditions for feasibility of the resin transfer moulding process to be determined and above all the position and orientations of fibres in the final composite part to be known.

For this forming simulation, specific hexahedral finite elements made of segment yarns are proposed. The simulation method is based on a dynamic explicit scheme of resolution in finite strain. Displacement approximation in elements is Lagrangian, which imply no macroscopic sliding between yarns. This hypothesis has been experimentally verified. This allows the forming simulation of a whole composite structure (thousands of yarns) whereas mesoscopic scale (or yarns scale) simulations [3] are limited to tens of yarns because of the contact computation.

In this three-dimensional element, the behaviour of the interlock preform is divided in two different contributions.

• The first order of this behaviour is the discrete contribution of each yarn segment in tension. The media is here considered at mesoscopic scale (or yarn scale). This avoids determination of an anisotropic homogenized equivalent continuous law that would be very difficult considering the complexity of the weaving.
• The second order of behaviour is the transverse properties of the fabric that is taken into account within a hypoelastic constitutive equation. An objective derivative of the Cauchy stress is calculated from the strain rate [4]. The scale is now macroscopic and the media is considered as continuous. Properties of this hypoelastic material are determined with a shear test (such as a Bias test [5]) and a compression test.

A set of three-dimensional interlock fabric forming simulations shows the efficiency of the proposed approach.

1

A.P. Mouritz, M.K. Bannister, P.J. Falzon, K.H. Leong, "Review of applications for advanced three-dimensional fibre textile composites", Composites Part A, 30, 1445-1461, 1999. doi:10.1016/S1359-835X(99)00034-2

2

P. Boisse, B. Zouari, J.L. Daniel, "Importance of In-Plane Shear Rigidity in Finite Element Analyses of Woven Fabric Composite Preforming", Composites Part A, 37(12), 2201-2212, 2006. doi:10.1016/j.compositesa.2005.09.018

3

D. Durville, "Numerical simulation of entangled materials mechanical properties", Journal of Materials Sciences, 40, 5941-5948, 2005. doi:10.1007/s10853-005-5061-2

4

Y.F. Dafalias, "Corotational rates for kinematic hardening at large plastic deformations", Trans. of the ASME, Journal of Applied Mechanics, 50, 561-565, 1983.

5

K. Potter, "Bias extension measurements on cross-plied unidirectional prepreg", Composites Part A, 33(1), 63-73, 2002. doi:10.1016/S1359-835X(01)00057-4

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