'Ultra'-Fast Fracture Strength of Advanced Structural Ceramics at Elevated Temperatures: An Approach to High-Temperature ‘Inert’ Strength

The determination of “ultra”-fast fracture strengths of a total of 17 advanced ceramics at elevated temperatures has been made by using constant stress-rate testing in flexure with a series of “ultra”-fast test rates. The test materials included two aluminas, eleven monolithic silicon nitrides, two SiC whisker-reinforced composite silicon nitrides, and two silicon carbides. Of the 17 ceramic materials tested, 15 advanced ceramics exhibited elevated-temperature strengths that approached (within 90%) their respective room-temperature strengths at an “ultra”-fast test rate of 3.3 × 104 MPa/s. This indicates that slow crack growth responsible for elevated-temperature failure can be eliminated or minimized by using a sufficiently fast test rate. These ongoing experimental results have shed light on laying a theoretical and practical foundation on the concept and definition of elevated-temperature “inert” strength behavior of advanced ceramics. The elevated-temperature, “inert” strength of a ceramic material could be determined by using test rates equal to or greater than the “ultra”-fast test rate of 3.3 × 104 MPa/s