Matrix crack initiation in ceramic matrix composites Part II: Models and simulation results

Abstract

In Part I of this work, matrix cracking in unidirectional fiber-reinforced ceramic matrix composites was studied experimentally in the Nicalon/LAS, carbon/borosilicate and SiC/borosilicate systems. The objective was to study the inter-relationships between the matrix cracking mechanisms and influencing factors in the composite microstructure. In order to control some of the factors, the SiC/borosilicate system was processed in-house with the fiber content being made to vary from 0 to 50 vol%. Three-point-bend tests were conducted to induce matrix cracking. Several examination techniques were used to discern the details of the cracking processes at the microstructural scale, including tests conducted inside the chamber of a scanning electron microscope. The experiment provided a considerable amount of matrix cracking data and confirmed that matrix cracking initiates in the matrix between fibers, which may or may not lead to the formation of the so-called fiber-bridged matrix cracks. The present paper is a continuation of Part I. Here, however, the matrix cracking problem is addressed from the modeling point of view. First, an in-depth review of the current matrix cracking models is given, with the emphasis being placed on the fundamental assumptions made in the cracking mechanisms, the microstructure, the cracking criteria and the key factors involved in the model formulation. Special attention is paid to the disposition of and the roles played by the fiber-matrix interface conditions. These current models are then applied to predict the matrix cracking initiation stresses in the composites tested in Part I. A comparison is made between the predicted and the experimental results.