Research And Optimization Design For Thermal Expansion Properties Of 3D 4-directional Braided Composites

The structures and properties of 3D braided composites are designable; and the braiding parameters are very important to them. In this paper, the thermal expansion properties of 3D braided composites are researched:Firstly, theoretical research of thermal properties of 3D braided composites. Many theoretical calculation method of thermal expansion coefficients of fiber reinforced composites are introduced; combined the fiber strand cylinder model and the method of stiffness equalization, the elastic properties of fiber strands and 3D braided composites are calculated; Use the Rosen-Hashin method and volume-average method, the thermal expansion properties of fiber strands and 3D braided composites are obtained based on their elastic properties.Secondly, numerical modeling of thermal expansion properties of 3D braided composites. The corresponding periodic finite element RVE of 3D braided composite micromechanics fiber inclination model and diagonal model are established; the application of displacement periodic boundary conditions are researched; then, use FEM software, the equivalent coefficients of thermal expansion of these two models are calculated; finally, compare the FEM solutions with the experiment solutions seperately, the results of the compare show that, the fiber inclination model and displacement periodical boundary conditions are more suitable for thermal expansion modelingThirdly, research and optimization design of thermal expansion properties of 3D braided composites. Use the fiber inclination model and periodical boundary conditions which have been proved in last part, the thermal expansion properties of 3D braided composites with different braiding angleθand different fiber volume friction V_f are researched, and the relationships between the thermal expansion properties and braiding angleθand fiber volume friction V_f are obtained. Then, base on the work which has been done in this part, zero thermal expansion 3D braided composites with most homogeneous thermal stress is optimization designed.In this paper, the thermal expansion properties of 3D braided composites are researched by theoretical method and finite element method, the relationships between the thermal expansion properties and braiding angleθand fiber volume friction V_f are obtained, then, the zero thermal expansion 3D braided composites are optimization designed.