The adiabatic elastic moduli of single crystals of aluminum have been measured from 4.2° to 300°K by using the ultrasonic pulse-echo technique. The values obtained by extrapolation to 0°K are C11=11.430, C12=6.192, and C44=3.162 in units of 1011 dyn/cm2. The Debye temperature obtained from the 0°K modulus values is 430.3°K, in excellent agreement with the value from heat-capacity measurements.
Articles you may be interested inLow-temperature anomalies in the dynamic elastic moduli of cubic AIIBVI crystals with 3d-transition metal impurities Low Temp.
The three elastic moduli of 99.999+% pure copper and their associated internal frictions have been measured at Mc frequencies between 4.2 and 250°K both before and after fast neutron bombardment. The changes produced by the irradiation were used to determine the dislocation contributions to the damping and moduli as a function of frequency and temperature. The dislocation damping showed the maximum predicted by Granato and Lücke to arise from the heavily damped bowing of dislocation loops. By calculating the resolved shear stress factors and measuring the dislocation density by etch pit counts, it was possible to determine the coefficient B which describes the viscous drag on a moving dislocation as well as the effective loop length l. The factor B was found to be 8×10−4 d sec/cm2 at 300°K and to decrease linearly with decreasing temperature, as predicted by Leibfried. The effective loop length appeared temperature independent and had a value of 3×10−4 cm in the sample examined most carefully.
Cold-worked single crystals of the same copper were also studied. Two Bordoni type peaks in the damping vs temperature curves were located at 135 and 60°K at 10 Mc. Activation energies of 0.113 and 0.05 ev were determined by using low-frequency data taken from the literature.
It is well established that elastic waves may be generated in a metal without physical contact through the reaction of a static magnetic field and dynamically induced eddy currents. The technique can significantly reduce the time needed in certain ultrasonic inspection problems because there is no need to re-establish a mechanical bond at each point of measurement. However, it has not yet received sufficient attention to determine its potential in actual industrial problems. This paper describes a feasibility study of the application of direct electromagnetic transduction to the inspection of gas pipelines from within the pipe. Experimental results are presented demonstrating the generation and detection of 130 kHz antisymmetric Lamb waves in 3/8 in. thick steel plate and pipe. The sensitivity of the process to various design parameters is discussed as well as the amplitude of signals reflected from defects. The experimental results for transduction and reception efficiencies are compared to a theoretical model.
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