Numerical evaluation on the influence of void defects and interphase on the thermal expansion coefficients of three-dimensional woven carbon/carbon composites

In order to evaluate the influence of void defects and interphase on the thermal expansion properties of three-dimensional woven carbon/carbon composites, a multi-scale numerical model was proposed to predict the effective thermal expansion coefficients considering void defects and interphase. On micro-scale, the effective thermal expansion coefficients of fiber bundles with void defects were predicted. On meso-scale, the effective thermal expansion coefficients of three-dimensional woven carbon/carbon composite with voids and interphase were predicted through a two-step homogenization procedure based on the asymptotic homogenization method and finite element method. The numerical model was validated by comparing with experimental measurements. Moreover, the influences of voids fraction and interphase modulus on the effective thermal expansion coefficients were examined quantitatively. The results indicate that the voids fraction has a negative impact on the coefficients of thermal expansion. The thermal expansion coefficients tend to decrease approximately linearly with the increase of voids fraction in fiber reinforcement and matrix, and decrease nonlinearly with the increase of voids fraction in interphase. The effective coefficients of thermal expansion increase as the increase of interphase elastic modulus, and the influence of interphase voids fraction on the coefficients of thermal expansion is becoming weaken as the increase of interphase elastic modulus.