New instrument for continuous and simultaneous recording of changes in ultrasonic attenuation and velocity.

The study of microplasticity of pure single crystals at low temperatures (i.e., the study of the first movements of dislocations) implies the measurement of elastic and anelastic characteristics during tensile tests. Hence a new method has been developed for continuous and simultaneous recording of changes in ultrasonic attenuation and velocity. The attenuation measurement is obtained by the usual pulse-echo technique. The relative velocity measurement is obtained by automatic comparison between a reference square pulse and the attack front of a selected echo. The relative accuracy is 6x10(-6) with a sensitivity of 30 mV ns(-1) for frequencies up to 40 MHz. Application to dislocation studies in aluminium is reported.