IN-SITU MEASUREMENT OF THE YOUNG MODULUS OF AN EMBEDDED INCLUSION BY ACOUSTIC MICROSCOPY

Alumina-silicate inclusions (shot) have been found to adversely affect the mechanical properties of a short alumina-silicate fiber reinforce d aluminum alloy (A356). To better understand the differences between the responses of the shot and fibers to applied loads, the Young's mod ulus of the shot is measured and compared to that of the fibers. The R ayleigh wave speed in the shot particle (cross-sectional area of 200 m u m x 150 mu m), measured in situ to be 4041 m/s using a scanning acou stic microscope, was used to calculate the Young's modulus of the shot particle (132 GPa). The accuracy of the technique and the experimenta l arrangement used was verified to be better than four percent by inde pendent measurements of the Rayleigh wave speeds in the aluminum alloy matrix and an embedded sapphire fiber. The fiber modulus was estimate d to be 225 GPa based on a comparison of previously measured composite modulus with micromechanical predictions. Thus, shot was Sound to hav e a Young's modulus 40 percent lower than that of the fibers. The appl icability of the V(z) technique has been demonstrated for measuring th e elastic properties over a microscopic area, even when the target mat erial is an embedded inclusion.