ʹUltraʹ-fast fracture strength of advanced ceramics at elevated temperatures

An attempt was made to determine elevated-temperature, `ultraʹ-fast fracture strengths of one alumina, two silicon nitrides and one silicon carbide by using constant stress-rate (`dynamic fatigueʹ) testing with a series of `ultraʹ-fast test rates. Of the materials tested, the alumina exhibited a convergence of strength at stress rates below 3.3×104 MPa s−1. The strength approached approximately the room-temperature inert strength. By contrast, the silicon nitrides and silicon carbide did not reveal a strength approach, but exhibited elevated-temperature strengths 10 and 20% lower than their respective room-temperature strengths. Although the analytical results imply that the elevated-temperature `inertʹ strength of a ceramic material can be obtained by using sufficiently high stress rates, the experimental testing rates were only sufficient to demonstrate convergence for the alumina.