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-Al₂O₃ 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.