Compressive Instabilities in Braided Textile Composites

This paper discusses the results of a finite element (FE) based study of the compressive instabilities of braided glass fiber composites. The micromodel was based on a 2-unitcell size 3-D FE model. Computational tests were carried out to first determine the elastic moduli of the system. Once the computational model was validated with experimental data for the elastic moduli, the compressive response of the micromodel was established using the RIKS method option available in the ABAQUS commercial FE code. The present approach is different from that reported in the literature where classical methods based on the technique of homogenization is used to model the elastic and inelastic response of braided composites. In the present work, explicit account of the braid microstructure (geometry and packing) and the inelastic properties of the matrix are accounted for via the use of the FE method. The macromechanical data pertaining to the braided composites were obtained through traditional means. Tensile tests were performed on the composites through the usage of ASTM D 3039 standard to obtain the macroscopic orthotropic moduli and response. For each test, 3 samples were used to ensure accuracy and the average data is reported in this paper. A separate test was conducted to obtain the in-situ matrix properties of the glass braided composites. The computational model provides a means to assess the compressive strength of braided composites and its dependence on various microstructural parameters. It also serves as a tool to assess the most significant parameter that affects compressive strength. Furthermore, the model is useful to understand the response of braided composites under multiaxial loads.