Measurement of Elastic Moduli from the Impact Sound of Engineering Ceramics and Composites at Elevated Temperatures

A simple instrumentation system is developed for determining the elastic moduli of engineering ceramics and their composites from the sound produced by the impact of a sphere on a specimen which is suspended by thin wires or ceramic threads in a furnace. The natural frequencies of the flexural and torsional vibration modes are measured from the impact noise by using a fast Fourier transform analyzer. Elastic moduli are then computed from those frequencies by using Timoshenko's beam theory and also Saint‐Venant's torsion theory. The validity of the measurementmethod is demonstrated by room‐temperature tests on ceramic and metallic specimens of known elastic moduli. SiAION and Al‐Al 2 O 3 composites are tested at elevated temperatures up to 900°C. It is shown that the Young's and shear moduli of the materials tested decrease with an increase in temperature, while Poisson's ratio remains almost constant.