Fracture Behavior of a Si3N4-BN Fibrous Monolith Ceramic

摘要

The two different microstructures of Si3N4-BN fibrous monolith ceramic material were compared to each other and to monolithic Si3N4 in order to evaluate the fracture behavior and effect of cell size on the mechanical performance of the material. The room temperature behavior was evaluated through fast-fracture tensile testing of straight-sided, dogbone, and modified single- edge notched specimens with various notch lengths. Load-unload and cyclic fracture tests were performed along with several non-destructive evaluation (NDE) techniques including x-ray radiography, thermography, ultrasonic c- scanning, and acoustic emission to determine critical stages of damage evolution in each. The Si3N4-BN materials tested showed non-catastrophic fracture behavior compared to the monolithic Si3N4 in tension and demonstrated to be insensitive to stress concentrations imparted by the notches. The influence of individual cell size on the fracture behavior of the FM materials was not evident as the cell bundles formed by the processing technique, not the individual cells, were the dominate microstructural feature. Cell bundle size in the materials tested was shown to influence the behavior as the displacements, extent of damage, and fracture energies were higher with larger cell bundles.