ULTRASONIC ASSESSMENT OF POISSONS RATIO IN THIN RODS

It is shown in this paper that longitudinal guided modes propagating in a thin rod can be exploited to determine the axial Poisson's ratio of the material. The feasibility of two versions of the guided wave method have been studied. The first technique determines Poisson's ratio from the low-frequency dispersion of the axial guided mode in the free rod. It is well known that the velocity of this mode in a thin rod decreases with increasing frequency by a small amount that is proportional to the square of Poisson's ratio. The second technique is based on measuring the excess attenuation of the same mode due to leaky losses when the rod is immersed in water. The leaky attenuation, which is caused solely by the normal component of the surface vibration, is also proportional to the square of Poisson's ratio in the specimen. The main goal was to verify the results of this novel leaky-attenuation technique by comparing them to those of the more conventional first technique. The experimental results indicate that both techniques can be used to determine Poisson's ratio in thin (0.3-1.5)-mm-diam metal wires in the 200 KHz-2 MHz frequency range. The measured Poisson ratios were generally higher than the corresponding values in isotropic materials, which is indicative of the significant anisotropy characteristic of such specimens. (C) 1995 Acoustical Society of America.