Effective Mechanical Properties of Carbon-Carbon Composites

Abstract

In recent times, composite materials have gained mainstream acceptance as a structural material of choice due to their tailorability and improved thermal, specific strength/stiffness and durability performance [1–3]. For high temperature applications, which include exit nozzle for rockets, leading edge for missiles, nose cones, brake pads etc. Carbon-Carbon composites (C/C composite) are found suitable [4–6]. Mechanical property estimation of C/C composites is challenging due to their highly heterogeneous microstructure. The highly heterogeneous microstructure consists of woven C-fibers, C-matrix, irregularly shaped voids, cracks and other inclusions. Predicting the mechanical behavior of complex hierarchical materials like C/C composites is of interest which 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 were identified as micro (single fiber with matrix), meso (fabric) and macro (laminate). Comparisons have been made with mechanical testing of C/C composites at different length scales.

Micromechanical damage analysis in laminated composites with randomly distributed fibers

“…Quantities with a prime are associated with R 0 . The displacement components (u, v, w) in the respective (x, y, z) directions obey the constraint equations (faces) as follows 12,27…”

“…3,[8][9][10][11] However, the assumptions used for analytical model development prevent them from predicting material behavior by considering actual micro-structure of FRPs in addition to accounting for different damage mechanisms. 12 On the other hand, empirical models are inadequate in terms of capturing the physics of the damage mechanisms and often times, fail to yield accurate predictions. 13 Additionally, unlike macro-scale experiments, 14,15 conducting microscale experiments to capture micro-scale damage mechanisms in FRPs is quite complex and difficult to carry out.…”

“…16 Traditionally, micromechanics principles have been used for effective property estimations of composites. 12,22,24,25 Correlating the micro-structure to the effective property is done in two ways, namely, representative volume element (RVE) approach and repeating unit cell (RUC) approach. In RVE method, the smallest volume element that replicates the composite macro-behavior is first chosen and analyzed using ''homogenization'' theory (based on a Micro-Meso-Macro principle) to yield the effective property of the composite.…”