Accurate noncontact measurement of elastic properties of ceramics using acoustic microsopy and laser ultrasonics

Abstract

Accurate measurement of elastic properties of advanced materials is of considerable importance for the further development of such materials and their applications. For many materials, data for elastic properties are not available or are unreliable. Noncontact, nondestructive techniques are of particular interest as being suitable for process control and hostile environments. Acoustic microscopy and laser ultrasonic techniques can measure bulk acoustic wave velocities (longitudinal and shear), from which elastic properties may be extracted, but there are many problems with measuring shear wave velocity with acoustic microscopy and with generating and detecting bulk acoustic wave modes using laser ultrasonics. In this work, a dual-probe beam laser interferometer setup is used to measure the velocity of laser-generated surface acoustic waves on materials; these results are combined with measurements of longitudinal velocity obtained with a standard 50-MHz point-focus-beam acoustic microscope. The technique is illustrated and applied to a set of ceramic samples (silicon nitride, silicon carbide, alumina, zirconia). Results are compared to available data and it is shown that elastic properties of isotropic materials (Young’s modulus, Poisson’s ratio) can be measured by this noncontact, nondestructive method to accuracies of 1% or better. This compares very well to other noncontact measurement methods.