Short‐Crack Mechanical Properties and Failure Mechanisms of Si3N4‐Matrix/SiC‐Fiber Composites

Abstract

SiC‐fiber‐reinforced Si3N4 composites were fabricated by hot pressing. The indentation‐strength technique was applied to study the mechanical properties of these composites. This enabled the investigation of short‐crack behavior of continuous‐fiber ceramic composites (CFCCs). The flaw tolerance of composite ultimate strength, matrix‐cracking stress, and work‐of‐fracture were investigated. Scanning electron microscopy was used to examine crack–fiber interactions. The ultimate strength was found to be independent of indentation load at a fiber volume fraction f= 0.29, while at f= 0.14 it exhibited a transition from flawsensitive to flaw‐independent. The work‐of‐fracture was found to be independent of indentation load at both fiber volume fractions. The matrix‐cracking stress was found to correspond to the first load‐drop on the load–displacement curve. It decreased with increasing flaw size and therefore is the steady‐state matrix‐cracking stress. A failure mechanism transition from catastrophic failure to non‐catastrophic failure, coupled with the transition from flawsensitive to flaw‐tolerant behavior, was observed by varying the preexisting flaw size and the fiber volume fraction. These transitions were explained by analyzing the relations between ultimate strength, matrix‐cracking stress, fiber volume fraction, and preexisting flaw size of the composite materials. Experimental results were compared with predictions from available models.