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Abstract

The third order elastic constants of polycrystalline aluminum (purity of 99.79%) and copper (purity of 99.98%) were determined by measuring their ultrasonic velocities under uniaxialy applied stress and the results were discussed by comparing with the previous data.The travel time of ultrasonic waves (5MHz) in a specimen of 10mm thickness was measured precisely with a singaround system. The longitudinal and shear waves polarized parallel or perpendicular to the uniaxial stress axis were propagated perpendicular to the axis.Since the traveling time under zero stress varied slightly in the experiment, the traveling time was measured before and after periodical stress and no plastic strains were observed.The results are summarized as follows:(1) The traveling time did not change linearly with applied stress. The deviation toward longer travel times was very large for copper both in tension and compression.However, the deviation for aluminum was a little. This is inferred to be the dislocation contribution. (2) To separate the measured traveling time change into two parts, one caused by the lattice anharmonicity and the other by dislocations, the measurements in both tensile and compressive conditions are needed.(3) The values of third order elastic constants measured for aluminum were in good agreement with the previous data, but not for copper.The present values, however, were most close to those calculated from the data of single crystal without containing dislocation contributions.

Low-Temperature Acoustic and Thermal Properties of Plastically Deformed, High-Purity Polycrystalline Aluminum

“…[37] using the elastic constants of Kanemochi et al [21]. For a dislocation density N d % 3 Â 10 13 m --2 , a thermal resistivity W ds % 10 m K W --1 is obtained at T ¼ 0.1 K, which is rather small compared to the experimentally observed value of about 3 Â 10 3 m K W --1 .…”

“…where s 0 is the yield stress at which plastic deformation starts, G is the shear modulus (G ¼ 24.8 GPa; Kanemochi et al [21]) and b is the Burgers vector (b ¼ a 0 /2 [110]; a 0 ¼ 4.04 Â 10 --10 m being the lattice constant). From eq.…”

A Finite-Difference Time-Domain Technique for Nonlinear Elastic Media and Its Application to Nonlinear Lamb Wave Propagation

“…The displacement distribution is analyzed by two-dimensional Fourier transform in the frequency-wave number plot U(K, f), where K and f are the wave number (inverse of wave length) and the frequency, respectively. The two-dimensional Fourier transform is calculated as , e ) , ( (17) In this analysis, we choose X = 45 mm and T = 5 μs. Figure 3 shows a result of the two-dimensional Fourier transform analysis at  X 88 mm,  t 26 μs.…”

Noncontact ultrasonic spectroscopy on deforming polycrystalline copper: Dislocation damping and acoustoelasticity

“…In Figure 5, we separately plot the dislocation and acoustoelastic contributions to the velocity change. [13,14,15] But, such a separation has never been realized before because of their similar responses to stress. By fitting the linear function to the velocity change due to the acoustoelasticity, we can calibrate C A for the three bulk waves.…”

“…By fitting the linear function to the velocity change due to the acoustoelasticity, we can calibrate C A for the three bulk waves. Kanemochi et al [15] adopted the compressive and tensile stresses to remove the dislocation effect and derived the third-order elastic constants of polycrystalline copper. A number of efforts have been made to remove the dislocation effect from the as-measured velocity change to determine the higher-order elastic constants of metals based on the acoustoelastic theory.…”