MEASUREMENT OF DYNAMIC MECHANICAL PROPERTIES OF ADVANCED CERAMICS AND CERAMIC MATRIX COMPOSITES AT TEMPERATURES ABOVE 1000°C

Summary Difficulties have been encountered in measuring dynamic mechanical properties of ceramics and ceramic composites because these materials are stiff and brittle and are to be used under extreme temperature conditions. The approaches used for testing traditional metals, polymers, and their composites may fail for testing ceramic materials if the special characteristics of ceramic materials are not accounted for. In order to avoid damaging cantilever beam vibration test samples, a precision clamping vise is required, and the clamping force must be carefully controlled. A torque wrench should be used to apply the clamping force, and find the optimum clamping force which corresponds to the smallest damping or largest modulus measurement. The extraneous energy dissipation due to the support can be reduced by either using a step beam sample with integral shoulder or using a vise with large stiffness and mass. From the economics point of view, the latter is preferred because a step geometry is costly to machine. The temperature distribution on a sample should be carefully controlled so as to minimize temperature gradients. Heat conduction from the heat chamber to the support and other possible heat losses should also be minimized if possible.