Multi-scale analyses of 3D woven composite based on periodicity boundary conditions

In this article, two-scale 3D finite element (FE) models, the microscopic repeated unit cell (RUC) model for yarn and mesoscopic-repeated unit cell model for woven composite, are presented to predict the effective stiffness properties of 3D woven orthogonal interlock composites. The micro-RUC model for the yarn is based on a hexagonal array of fibers. Undulation of the yarns in the novel 3-D meso-RUC for the woven composite is described by Hermit-spline function. The periodic boundary conditions are applied to the two-scale models during the 3D FE analysis in order to ensure that both the displacement and stress are continuous on the boundary surfaces. Specimens are manufactured with house-made resin transfer molding (RTM) equipment and simple tensile experiment is performed. It is found that the predicted yarn properties by the micro-RUC agree well with data computed by equations with a suitable parameter determined by experiment and the predicted effective stiffness properties of 3-D woven composites by the meso-RUC are also in good agreement with the test data. Thus the correctness of the established multi-scale models and analysis method are verified.