Analytical model and numerical analysis of the elastic behavior of triaxial braided composites

This paper is concerned with elastic behavior of a triaxial braided composite by using a three-dimensional analytical model and mesoscale finite-element (FE) analysis, in conjunction with experimental observations. The analytical method and FEM take into account the actual fabric structure by considering the fiber undulation and actual architecture parameters. A representative unit cell model of the triaxial braided architecture is first identified based on fiber volume ratio, specimen thickness, and microscopic image analysis. Detailed geometric parameters for axial and bias fiber bundles are obtained, which provide precise information to enable the development of analytical and FE models. A general three-dimensional analytical model based on realistic architecture is developed with consideration of axial and bias fiber undulation. A typical study on the effect of axial fiber undulation is presented through the analytical model and axial tensile test. The prediction of effective elastic constants of the composite are presented and are compared with the experimental data. Edge damage, which is identified through FE simulation and experiments, is found to occur periodically along the free edge and to result in reduced transverse properties. The edge effect on the elastic modulus is studied through FE simulation with various numbers of unit cells. The axial fiber undulation and edge effect explains the discrepancy between the analytical and computational predictions and the experimental results.