ULTRA-FAST FRACTURE STRENGTH OF ADVANCED CERAMICS AT ELEVATED-TEMPERATURES

An attempt was made to determine elevated-temperature, 'ultra'-fast fr acture strengths of one alumina, two silicon nitrides and one silicon carbide by using constant stress-rate ('dynamic fatigue') testing with a series of 'ultra'-fast test rates. Of the materials rested, the alu mina exhibited a convergence of strength at stress rates below 3.3 x 1 0(4) MPa s(-1). The strength approached approximately the room-tempera ture inert strength. By contrast, the silicon nitrides and silicon car bide did not reveal a strength approach: but exhibited elevated-temper ature strengths 10 and 20% lower than their respective room-temperatur e strengths. Although the analytical results imply that the elevated-t emperature 'inert' strength of a ceramic material can be obtained by u sing sufficiently high stress rates, the experimental testing rates we re only sufficient to demonstrate convergence for the alumina. (C) 199 8 Elsevier Science S.A.