Effective Property Estimation of Carbon Composites using Micromechanical Modeling

Abstract

In recent times, composite materials have gained mainstay acceptance as a structural material of choice due to their tailorability and improved thermal, specific strength/stiffness and durability performance. Carbon-Carbon (C/C) composites are used for high temperature applications such as exit nozzles for rockets, leading edges for missiles, nose cones, brake pads etc. Mechanical property estimation of C/C composites is challenging due to their highly heterogeneous microstructure. Computed Tomography (CT) images (volumetric imaging) coupled with Scanning Electron Microscopy (SEM) reveal a highly heterogeneous microstructure comprised of woven C-fibers, amorphous C-matrix, irregularly shaped voids, cracks and other inclusions. The images also disclose structural hierarchy of the C/C composite at different length scales. Predicting the mechanical behavior of such complex hierarchical materials like C/C composites forms the motivation for the present work. A systematic study to predict the effective mechanical properties of C/C Composite using numerical homogenization has been undertaken in this work. The Micro-Meso-Macro (MMM) principle of ensemble averages for estimating the effective properties of the composite has been adopted. The hierarchical length scales in C/C composites has been identified as micro (single fiber with matrix), meso (fabric) and macro (laminate). Numerical homogenization along with periodic boundary conditions (PBCs) have been used to estimate the effective engineering properties of the material at different length scales. Concurrently, mechanical testing has also been carried out at macro (compression tests) and micro scale (using nano-indentation studies) to characterize the mechanical behavior of C/C composites.