Estimating tensile creep rate of ceramics from flexure data

Abstract

A new model of ceramic creep in four-point bending is proposed to determine the creep rate that corresponds to tensile creep at an elevated temperature. Based on the assumption that ceramics creep only in tension and there is no creep in compression, the tensile creep rate which is invariant with time in the secondary mode is calculated in a simple way. Since the initially applied maximum tensile stress does not correspond to the stress at the secondary creep range, the creep-induced stress at the time of measurement is calculated based on beam deflection. Then, the calculated tensile creep rates from fourpoint bending data are compared with observed tensile creep rates for both an alumina ceramic at 1000 °C and a silicon nitride ceramic at 1200 °C. This study shows the usefulness of flexural creep tests not only to verify the accuracy of tensile creep tests, but also to obtain the tensile creep data in a less expensive and easier way.