Research On Multi-scale Properties Of 2.5D Woven Composites

3D woven composites have been widely used in the areas of aeronautics and astronautics due to their excellent properties of anti-delaminating, damage tolerance and ability of making near net shape structural components. 2.5D woven composites, as an important branch of 3D woven composites, have owned a lot of attentions. In order to effectively design and use 2.5D woven composites, a deep research on their mechanical properties must be made.In this dissertation, three-scale models such as microscopic repeated unit cell(RUC) model for yarn, macroscopic RUC model for woven composites and macroscopic structure have been researched for 2.5D woven composites. Three models for three-scale RUC & component, and perform 3D finite element method are made respectively to predict the stiffness properties. For microscopic RUC of yarn, in the basement of hexagonal array of fibers, a model was established. Through it, the stiffness of RUC is analyzed under different load conditions, the distribution of stress and stress-strain curve are received, and comparisons are made with forecast values of empirical formula. For macroscopic RUC of woven composites, in allusion to the interlock structure of this paper, the geometry parameters of yarns and interlock styles between yarns are calculated through current theoretical formula. At last a RUC model for analyzing is established. For macroscopic structure, regard the properties of woven composites RUC as material properties of the structure. By analyzing the structure, the distribution of stress & strain and dangerous point under test load are received.The periodic boundary conditions are applied to the former two scale models during the 3D FEM analysis in order to ensure that the displacement and stress are continuous on the boundary surfaces. The result indicated that the periodic boundary conditions coincide with actual situation due to considering of stiffness distributing inhomogeneous of component materials.