Fracture Energy and Tensile strength of Silicon Nitride at High Temperatures

Abstract

The work-of-fracture (WOF) tests were conducted for hot-pressed silicon nitride at high temperatures above 1000°C to investigate displacement rate (D-rate) dependence of effective fracture energy, and then the bridging stress at a crack interface was estimated from the increment of fracture resistance with crack extension (R-curve behavior) to discuss its correspondence to tensile strength. The effective fracture energy and the bridging stress increased with lowering D-rate, and then decreased, probably due to the activated pulling out work of grains and its sensitivity to change in D-rate. The bridging stress was shown to correspond to a great part of tensile strength in the range where a plasticity was seen in the stress-displacement (S-D) curve, implying a large contribution of grain bridging toward bearing an applied tensile stress during slow crack extension.