The mechanical properties of composites reinforced with woven and braided fabrics

This paper addresses an application of a versatile yet user-friendly micromechanics model, the bridging model, to simulate the mechanical properties of composites reinforced with woven and braided fabrics. The application is elaborated with a 2-D 1x1 woven and braided fabric geometry. The elastic, elasto-plastic, and ultimate strength behavior of the fabric composites under any arbitrary load condition can be easily characterized by using this model. The most important feature of the model is that the stress states generated in the constituent fiber and matrix materials are explicitly correlated with the overall applied load on the composite. Thus, the complete behavior of the composite can be treated in terms of that of the constituent materials, which are well understood in the literature. A composite failure is attained whenever either the fiber or the matrix fails. A geometric model combining elliptical cross-section and sinusoidal undulation is proposed to describe the fabric geometry, with or without inter-yam gaps. Only subdivision in the fabric plane is carried out, and the stresses in all three components (warp yarn, fill yarn, and pure matrix) of each sub-element are obtained through laminate analysis. The overall stresses in the fiber and matrix of the composite are assembled on the basis of an iso-stress assumption. Several 2-D 1x1 woven- and braided-fabric composites have been analyzed. The predicted stiffness and strength are in good agreement with available experimental data. Parametric studies have also been performed to investigate the effect of inter-yam gap sizes on the stiffness and strength of woven- and braided-fabric composites, which show useful information for composite design. (C) 2000 Elsevier Science Ltd. All rights reserved.