On the measurement of the Young's modulus of small samples by acoustic interferometry

This paper describes and validates an interferometric technique for the measurement, of the Young's modulus of limited size samples. The technique is a generalization of the torsional guided wave interferometry introduced in a previous paper [Simonetti and Cawley, J. Acoust. Soc. Am. 115, 157-164 (2004)] for the characterization of the shear properties of soft materials. The method is based on the transmission of the fundamental longitudinal guided mode through a sample clamped between two buffer rods. The main difference with other interferometric techniques is the use of a delay line placed between the sample and one of the buffer rods. While with conventional interferometry the sample length needs to be larger than half of the shortest wavelength which can be propagated through the sample, the introduction of the delay line removes this limitation enabling the characterization of very small samples (compared to the wavelength). In addition, this method is suitable for testing highly attenuative materials which can be cut into thin specimens so reducing the energy absorption as the acoustic signal propagates through the sample. The principle of the method is discussed and measurements on a variety of specimens are presented. Results for long material specimens tested without delay line and short samples of the same material tested with the delay line agree within 1%. Moreover, measurements are in good agreement with results obtained from conventional methods and literature. (C) 2005 Acoustical Society of America.