Hierarchical evaluation of effective thermal conductivities of needled composites

Abstract

Thermal conductivity (TC) is essential to characterize for thin-walled parts made of needled carbon/carbon (C/C) composites in the aviation sector. This paper thus proposes a hierarchical multiscale model to predict the TCs of needled C/C composites. This model can comprehensively consider the effects of the anisotropy of pyrolytic carbon matrices and the orientation and elongation of pores. At the microscale, representative volume element models of the needled fibers and weftless plies are established, respectively, and their TCs are estimated using the finite element homogenization method. Meanwhile, a combination of the finite element and orientation average method is developed for short-cut fiber plies. At the macroscale, a generated needled laminated model consisting of the weftless plies, short-cut fiber plies, and needled region, is established, where input properties are from homogenization results of microscale models. By comparing with experimental results, the proposed multiscale model is validated. The results show that effective TCs in the directions perpendicular and parallel to needled fibers drop by 13.18% and 13.06% respectively as the porosity increases from 6% to 14%. Additionally, it is found by microstructural parameter studies that it is possible to realize needled C/C composites with isotropic TCs.