Ceramic matrix composites (CMCs) exhibit process-induced defects such as matrix porosity at multiple length scales that have a considerable influence on their mechanical and failure behavior. This work focuses on the microscale mechanical behavior of single tow CMCs in the presence of microporosities that exist within fiber bundles of the composite. Microporosities in a single tow C/boron nitride (BN)/SiC CMC minicomposite fabricated by chemical vapor infiltration (CVI) have been characterized by X-ray microcomputed tomography. The porosity distribution in the scanned region has been represented by probability distribution functions (PDFs) that serve as an input to numerical homogenization. Effective elastic properties in the presence of matrix micropores have been obtained by a two-step numerical homogenization approach considering the statistical distributions of pore parameters obtained from experimental characterization. A variation of the approach has been utilized to investigate the severity of pores with respect to their location and orientation relative to the fiber reinforcement.
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.
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