Elastic Properties Of Three-dimensional Braided Composites Scale Analysis

Three-dimensional braided composites, for their excellent mechanic properties, have been got more and more extensive researches and applications in the aerospace industry. Meanwhile, the analytical methods of their mechanic properties have been developed rapidly. Based on the asymptotic homogenization theory, a novel digitized cell-based finite element method (DCB-FEM) was presented in this thesis to simulate the constitutive properties of three-dimensional four-directional braided composites.Firstly, based on the theory of asymptotic homogenization, a single variational function and principal for calculating unit-cell micro-elastic properties in microscope was developed. And then the formulae of isoparametric element from single variational function were gotten.Secondly, the solution of homogenized problem was studied. The homogenization method combining with the finite element method can be applied to analyze composite materials with periodic microstructure. Because complexity of the microstructure of three-dimensional braided composites, it is quite difficult to mesh the cell model. By introducing 3D scan-conversion algorithms, a novel automatic meshing method based on the digitized cell modeling was developed for microstructure meshing of three-dimensional braided composites. The feasibility of this method has been validated by simulating the constitutive properties of single-dimensional composite materials.Finally, by analyzing the microstructure, the digitized cell model of three-dimensional four-directional composites was established. Then the mechanic properties of three-dimensional four-directional composites were calculated by the DCB-FEM. The results show a good agreement with the experimental data.In this thesis, the DCB-FEM has been developed to predict the elastic properties of three-dimensional four-directional composites. It can be applied in the parameter selection, the properties design, and the structural optimization of this material during the manufacture process, and to push the further application of three-dimensional composites in the aerospace industry. Meanwhile, the method alsoprovides a fundament to the further research of the damage problem, the strength problem and the nonlinear properties of three-dimensional composites.