Secondary creep in tension was characterized by power-law functions of stress that were evaluated from load-point displacement on four-point flexure specimens and published compressive creep data for two ceramic materials. The flexural creep of 99 % mass fraction alpha silicon carbide with less than I % porosity was measured at 1500 [degrees]C, and the flexural creep of 25 % mass fraction silicon carbide whisker-reinforced alumina with 4.9 % porosity was measured at 1200 [degrees]C. The neutral axis and curvature were represented as functions of the applied momentand the power-law functions of stress in both tension and compression. The curvature was estimated from the load-point displacement by numerical double integration of the curvature along the length of the specimen, where the applied moment was assumed constant within the minor span of flexure and to decrease linearly between the minor and major spans. The power-law functions of stress in tension were estimated by least-squares fits to the load-point displacement of the two ceramic materials, using power-law functions of stress in compression that were estimated from published creep data of these materials. The resulting creep rates in tension are approximately four and forty times as great as those obtained for the two materials, respectively, by the customary assumption that the neutral axis is located midway along the flexure specimen.
Citation: Journal of the American Chemical Society
Pub Type: Journals
flexure specimen, load-point displacement, power-law function of stress, secondary creep, silicon carbide, silicon carbide whisker-reinforced alumi