Bruce B. Chick

Dislocation Contribution to the Second Harmonic Generation of Ultrasonic Waves

The experimental evidence and the associated theory are presented for the dislocation contribution to the generation of the second harmonic of an ultrasonic wave in solids. The contribution is measured through the changes, as a function of static bias stress, in the amplitude of the second harmonic of a fundamental wave (10 Mc/sec compressional wave) propagating in the specimen.In aluminum single crystals the amplitude of the second harmonic, for a given amplitude of the fundamental, changes markedly with static bias stresses ranging from 0 to 106 dyn/cm2. In alloys, there are essentially no changes of the amplitude of the second harmonic even for bias stresses up to 107 dyn/cm2. These observations are consistent with the predicted dependence of the amplitude on dislocation loop length and on the static stress. The effects of small amounts of plastic deformation were consistent with the proposed model.

Ultrasonic Attenuation Unit and Its Use in Measuring Attenuation in Alkali Halides

An instrument for measurement of ultrasonic attenuation and velocity in the frequency range from 5–200 mc/sec is described. The unit incorporates pulsed rf oscillator, superheterodyne receiver, exponential wave‐form generator, precision time delay generator (useful in velocity measurements), CRT display circuits, and appropriate synchronization circuits. Ultrasonic attenuation measurements made in single crystals of NaCl and KCl during deformation and recovery at several temperatures are reported here.An instrument for measurement of ultrasonic attenuation and velocity in the frequency range from 5–200 mc/sec is described. The unit incorporates pulsed rf oscillator, superheterodyne receiver, exponential wave‐form generator, precision time delay generator (useful in velocity measurements), CRT display circuits, and appropriate synchronization circuits. Ultrasonic attenuation measurements made in single crystals of NaCl and KCl during deformation and recovery at several temperatures are reported here.

Sensitivity of Ultrasonic Attenuation and Velocity Changes to Plastic Deformation and Recovery in Aluminum

Measurements of changes in ultrasonic attenuation together with changes in ultrasonic velocity have been made concurrently with load strain measurements in tensile tests on the same specimen of aluminum. The results of such measurements taken during loading of the specimen, during relaxation or recovery at constant strain, and during unloading show a number of interesting effects. These observed effects are interpreted in terms of dislocation behavior for the various stages of the experiment. The experimental results for attenuation α and velocity change Δv/v permit the calculation of changes in dislocation density and loop length based on a dislocation damping theory developed in this laboratory to include both megacycle and kilocycle frequencies. The strain due to dislocation motion was calculated with a simple model and with dislocation loop lengths and densities obtained from the data and the theory just mentioned. The comparison of the calculated strain and the measured strain lends support to the us...

Electrical‐Charge Study in Sodium Chloride during Plastic Deformation

Electrical charges developed during plastic deformation of sodium chloride were investigated. Experiments are chosen (orientation and shape of the crystals; direction of applied stress) to enable the edge and screw components of dislocation loops to emerge separately on two different pairs of the external surfaces of the specimen. The experimental results indicate that an electrical charge is associated only with the edge components of dislocation loops. It is also found that in tensile experiments of a bent specimen (accidentally or intentionally) negative charge appears on the concave side and positive charge appears on the convex side, and the negative charge is larger, in absolute value, than the positive charge, in the early stages of deformation. A model is proposed to explain these results.

High‐Sensitivity Logarithmic Recorder of Ultrasonic Attenuation

A sensitive instrument for measuring and recording the amplitude ratio of two video pulses from an ultrasonic echo train is described. The instrument has been designed primarily for ultrasonic attenuation studies using pulse‐echo techniques but may also be used for through transmission, and/or single echo measurements. The unit selects two pulses from the echo train, peak detects them, and measures their amplitude difference in a differential logarithmic voltmeter calibrated in decibels. The resultant output may also be applied to an external recorder. Provisions for zero suppression are included to permit the use of the most sensitive meter range (0.01‐dB resolution) when small changes in attenuation are to be measured against a large background attenuation. Automatic gain control, operating from the first selected echo, has been incorporated in order to maintain operation in the linear portion of the receiver dynamic range.

Use of the Interaction of Thermal and Ultrasonic Waves to Study Radiation‐Induced Defects in Quartz

Evidence is presented showing that the interaction of high‐frequency stress waves with lattice vibration waves provides a means of studying crystal perfection. This discussion is concerned specifically with quartz single crystals, but the method has been found to apply to other materials as well.

Ultrasonic Attenuation in Al2O3 at Ultrahigh Frequencies and Low Temperatures

Ultrasonic propagation in Al2O3 at low temperatures and high frequencies (to 3000 Mc/sec) is discussed in terms of the relations given by Woodruff and Ehrenreich. Phonon relaxation times calculated from thermal conductivity measurements are used. The measured low‐temperature attenuation values at 1315 Mc/sec agree with the calculated values. A comparison of attenuation as a function of frequency is made among Al2O3, Ge, Si, and quartz. On comparing experimental values of attenuation for pure Al2O3 and impure Al2O3 (ruby) it is found that impurities lead to an increase in the attenuation as would be predicted from the corresponding effect of impurities on the thermal phonon relaxation time.

The Metals Research Laboratory and the development of instrumentation for acoustics research at Brown University

People I worked with and instrumentation that was developed during 30+ years at the Metals Research Laboratory at Brown University, and what that original instrumentation has led to.