Failure Mechanisms in Ceramic‐Fiber/Ceramic‐Matrix Composites

TLDR

In flexural loading the failure process of the SiC‑fiber/glass‑ceramic composite is more complex. The study investigates failure mechanisms in a unidirectional SiC‑fiber/glass‑ceramic composite using in situ observations during tensile and flexural loading, discusses applying conventional fracture mechanics to describe tensile failure, and explores novel methods for measuring frictional forces, residual stresses, and the effect of surface damage on strength. In situ observations during tensile and flexural loading were employed to examine failure mechanisms, while novel techniques for measuring frictional forces and residual stresses and assessing surface damage effects were investigated. Tension failure proceeds through matrix cracking, fiber fracture, and pullout; flexural testing cannot determine tensile strength but can assess matrix‑cracking stress, and the data underscore the critical role of frictional bonding between matrix and fibers.

Abstract

Mechanisms of failure in a unidirectional Sic‐fibe/glass‐ceramic composite are investigated using in situ observations during tensile and flexural loading. These experiments show that failure in tension occurs in several stages (similar to certain other brittle fiber composites): multiple matrix cracking, followed by fiber fracture and pullout. In flexural loading the failure process is more complex. Consequently, the flexural test cannot be used for measurement of tensile strength (although it can be used for measurement of the stress for matrix cracking). The application of conventional fracture mechanics to describe tensile failure is discussed. The in situ observations provide direct indication of the importance of frictional bonding between the matrix and fibers. Some novel methods for measuring the frictional forces and residual stresses are investigated, and the influence of surface damage on strength is assessed.