The Determination of the Elastic Moduli of Anisotropic Ceramics and Ceramic Composites at High Temperatures by a Novel Resonant Beam Technique

The resonant beam technique was extended for the application to anisotropic materials and to temperatures up to 2000°C. A specific equipment was developed to determine the elastic moduli from the resonance frequencies of the flexural vibrations of a beam. The elastic moduli are calculated by minimising the difference of the experimental versus the theoretical resonance frequencies. The theoretical frequencies are obtained by numerically solving Timoshenko's equation, which takes into account the influence of the shear deformation and the rotatory inertia. From the fundamental frequency and the higher modes of vibration, for every specimen one Young modulus and two shear moduli in two planes perpendicular to each other are obtained, the latter two coinciding for an elastically isotropic material. With the additional effort of cutting out specimens in specific directions, the complete elastic tensor of anisotropic materials can be measured at high temperatures. Examples of measurements on monolithic ceramics (zirconia, translucent alumina) and a fibre-reinforced ceramic matrix composite (2.5 D carbon-fibre reinforced carbon composite) are given, to demonstrate the effectiveness of the novel technique.