Microplasticity Detected by an Acoustic Technique

Evidence for the formation of slip lines and slip bands has usually been obtained from slip-line replica and etch-pit techniques. An apparatus has been built to detect the formation of small slip events within a crystal by monitoring small longitudinal oscillations of the test specimen which occur when the load is momentarily relaxed. Each load drop results in a burst of acoustic energy, some of which are detected and recorded electronically. Results are presented of measurements of the frequency and magnitude of acoustic pulses from single-crystal specimens during plastic flow. They suggest that slip events occur cooperatively and that dislocation velocities during yielding may be as high as 103 cm/sec.