ULTRASONIC ASSESSMENT OF POISSONS RATIO IN THIN RODS

It is shown in this paper that longitudinal guided modes propagating i n a thin rod can be exploited to determine the axial Poisson's ratio o f the material. The feasibility of two versions of the guided wave met hod 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 de creases with increasing frequency by a small amount that is proportion al 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 cau sed solely by the normal component of the surface vibration, is also p roportional to the square of Poisson's ratio in the specimen. The main goal was to verify the results of this novel leaky-attenuation techni que by comparing them to those of the more conventional first techniqu e. 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 ge nerally higher than the corresponding values in isotropic materials, w hich is indicative of the significant anisotropy characteristic of suc h specimens. (C) 1995 Acoustical Society of America.