Abstract
Abstract : The use of ultrasonic methods (and in some cases electrical conductivity measurements) for studying defect formation and motion in connection with deformation and stress cling experiments in aluminum and sodium chloride single crystals is the subject. Recovery in aluminum single crystals at 195 K was compared with recovery at room temperature and an interesting 'threshold effect' was observed; there appears to be a level of deformation which must be exceeded at this temperature before recovery occurs. The automatic recording time echo (or velocity) measurement unit was designed to measure the time between two successive echoes in a pulse echo train with a sensitivity of one nanosecond out of one hundred microseconds and to record the measurement as a voltage capable of driving a recorder so that dynamic changes in time will produce a record. It was found that no change in center frequency or bandwidth is seen over a 40 db range of gain control nor does an artificial change of 40 db in signal level produce a detectable change in measured time.
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