NONCONTACT MEASUREMENT OF ULTRASONIC VELOCITY AND ATTENUATION IN POLYCRYSTALLINE PURE COPPER DURING INITIAL-STAGE OF DEFORMATION

Changes in ultrasonic velocity and attenuation were studied by noncont act and continuous measurement method for polycrystalline pure copper during deformation. This measurement, involving two ultrasonic waves a t the same time, has been made possible by electromagnetic acoustic re sonance (EMAR). Use of an electromagnetic acoustic transducer (EMAT) c an isolate the attenuation within the plate specimens. The method reli es on the Lorentz force mechanism to couple the EMAT and the specimen surfaces and then eliminates the extra losses, which otherwise occur i n the use of the piezoelectric transducers. Ultrasonic velocity and at tenuation changes are interpreted in terms of the dislocation behavior and the acoustoelastic effect. The changes in dislocation density and loop length can be analyzed using dislocation damping theory. Pure th ird-order elastic canstants, which are free from the velocity change d ue to the dislocation movement, can also be derived and compared with the existing experiments.