Three-dimensional properties of woven-fabric composites

A new analytical/numerical model which is simple in terms of modeling and efficient in computational effort is presented for the estimation of the effective stiffness properties of woven-fabric composites. In the present study, the analysis is carried out over the unit cell of the woven-fabric composite. The unit cell is mainly divided into three regions A, B and C depending on the tow waviness. The fiber tow geometry in these regions is easy to visualize and define through simple functions. Also, by assembling the regions A, B and C suitably, one can generate the unit cell of any woven-fabric architecture. The tow waviness in these sub-regions is assumed to be sinusoidal and the waviness in both directions is considered. The unit cell of the woven-fabric composite is discretized with three-dimensional finite elements. From the assumed tow geometry in the regions A, B and C, the tow-volume fraction and average tow inclinations in an element can be calculated. By using the tow-volume fractions and constitutive properties of each layer, the average stiffness properties of an element are calculated by effective-modulus theory. These average stiffness properties are given as input for computing the elemental stiffness matrix in the finite element formulation. The problem of estimating the Young's modulus and Poisson's ratios in all the three directions is divided into three sub-problems and the superposition method is used. From the results, it is observed that the stiffness and Poisson's ratios obtained by the present model agree very well with the available three-dimensional finite element results in the literature. The results demonstrate that the present model, which is both simple and computationally efficient, can give very accurate results compared to a complex three-dimensional finite-element model. (C) 1999 Elsevier Science Ltd. All rights reserved.