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 noncontact and continuous measurement method for polycrystalline pure copper during deformation. This measurement, involving two ultrasonic waves at the same time, has been made possible by electromagnetic acoustic resonance (EMAR). Use of an electromagnetic acoustic transducer (EMAT) can isolate the attenuation within the plate specimens. The method relies on the Lorentz force mechanism to couple the EMAT and the specimen surfaces and then eliminates the extra losses, which otherwise occur in the use of the piezoelectric transducers. Ultrasonic velocity and attenuation 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 third-order elastic canstants, which are free from the velocity change due to the dislocation movement, can also be derived and compared with the existing experiments.