Numerical simulation on thermal expansion coefficient of 3D braided C/C composites

To effectively get the thermal expansion coefficient (CTE) of three-dimensional (3D) braided C/C composites and study the variations, a VC++ program with graphical user interfaces was obtained, based on the yarn unit model and numerical analysis. With the limited basic properties of carbon fibers and carbon matrix, CTE of 3D braided C/C composites is obtained at 85 C. The deviation between the simulated and experimental axial CTE of 3D braided C/C composites is no more than 11 %. The effects of different parameters (including the braiding angle of 3D braided preform, the fiber volume fraction and the porosity of 3D braided C/C composites, and the elastic modulus, Poisson's ratio and CTEs of carbon fibers and carbon matrix) were analyzed with the program. The results show that the axial CTE of C/C composites decreases with the increase of the braiding angle, the fiber volume fraction, and the porosity of 3D braided C/C composites. The transverse elastic modulus of carbon fibers has the greatest effect on the axial CTE among the studied mechanical parameters, followed by the elastic modulus and Poisson's ratio of carbon matrix.