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Resonant ultrasound spectroscopy (RUS) and pulse-echo (PE) superposition techniques have been used to determine the three independent elastic-stiffness constants C 11 , C 12 , and C 44 as a function of temperature for single crystals of 70Fe-15Ni-15Cr alloy. The values of the elastic moduli determined using RUS and PE are in very good agreement within the range of uncertainties. This particular ternary composition of Fe, Ni, and Cr undergoes an fcc-bcc structural phase transformation near 190 K resulting in a low-temperature ferromagnetic phase. The Debye characteristic temperature was determined to be 447 K from PE and 451 K from RUS measurements. The Zener elastic anisotropy A ϭ 2C 44 /(C 11 Ϫ C 12 ) is nearly constant: A ϭ 3.53 Ϯ 0.16 in Fe-Ni-Cr alloys with similar compositions. For these alloys, only small variations are observed in the Grüneisen parameter, ␥ Ϸ 2.08, and in the Poisson ratio, v [hkl] ϭ 0.293 Ϯ 0.013.

The miscibility of a diluted polymer blend under steady shear has been investigated in the twophase region using fluorescence and phase-contrast microscopy. Critical exponents describing the shape of the coexistence curve and the shift of the critical temperature DT c ͑ ᠨ g͒ were compatible with expectations based on renormalization group and mode-coupling theories, but the introduction of a reduced variable description of DT c suggested a tendency for T c to saturate at high shear rates.[S0031-9007 (97)02774-9] PACS numbers: 83.80.Es, 64.75. + gThe effects of shear on the critical temperature T c has been studied in small molecule binary mixtures as well as polymeric blends [1][2][3][4]. Because of the relatively large influence of shear and the slow dynamics of polymeric systems, it has been possible to perform more comprehensive measurements on bulk [3] and diluted [4] polymer blends using a combination of small angle neutron scattering and dynamic light scattering techniques. A comparison [5] of experimental results obtained in the one phase region with the theory of Onuki and Kawasaki [6] indicates a remarkable consistency. However, many questions remain about the influence of shear on the phase stability of mixtures. For example, the combined influence of additives (e.g., solvent for the blend) and shear on the phase stability of mixtures and the nature of mode-coupling effects in the unstable regime have received limited attention. The present paper considers these problems based on the existing Onuki-Kawasaki framework.Previous measurements [2] on diluted polymer blends in the unstable regime under conditions of steady shear showed a marked decrease of scattering intensity at high rates of shear. This shear-induced "homogenization" effect was interpreted in terms of a shift of the phase boundary with shear, as in earlier shear-scattering measurements on small molecule mixtures in the one-phase region [1]. The effect of droplet distortion on the shear-scattering measurements was minimized by considering the projection of the scattering data along the vorticity direction. Estimates of the integrated intensity along this direction from shear light scattering measurements showed a tendency to strongly decrease and then to saturate at high shear rates. The characteristic shear rate ᠨ g c , corresponding to this saturation point, was then employed along with theoretical arguments to estimate the shift of the phase boundary with shear. While this procedure led to estimates of the critical temperature shifts with shear that were apparently consistent with the Onuki-Kawasaki (OK) theory [6], it seems unclear to us whether the diminished scattering intensity ("homogenization") reflected a true shift of the phase boundary or merely the breakup of droplets under shear to a scale undetectable by light scattering measure-ments. Since this kind of scattering intensity measurement depends on the history of the shearing measurement, the procedure of extrapolation, and the sensitivity of the detection system, it seems nece...

Using low-stress pseudoshear deformation, we measured the ambient-temperaturecreep-recovery behavior of polycrystalline indium. The &+J diagram shows three regions with increasing stress: stress exponents of 1.05, 7.4, and 2.0. The diagram resembles remarkably the dislocation-velocity-shear-stressdiagrams reported for various materials by many authors, who interpreted the diagrams by dislocation dynamics. Applying an extended Burgers model (two Kelvin-Voigt elements) gave for the three regions the following relaxation times z2 and .c3 (in seconds):(1) 11, 123; (2) 10, 132; (3) 12, 154. Thus, z, is nearly stress independent, and .c2 increases with increasing stress. Laplaceantransformation of our ~( t )measurements to get the retardation-time distribution function g(In z) indicates in all three regions a strong peak near .c2 = 3 s and a weaker, broader peak near 23 = 150 s. These agree surprisingly well with the Burgers dashpot-spring-model results. We analyzed the recovery part of the strain ~( t ) to obtain e-lcf) curves.

Using a method used mainly by geophysicists for small specimens--acousticresonance spectroscopy (ARS)--we measured the elastic-stiffness constants of centimeter-size copper specimens with rectangular-parallelepiped shapes. The polycrystal consisted of heavily twinned 75-1tm crystallites. From the specimens' macroscopic resonance-vibration frequencies (midkilohertz to low-megahertz), we calculated the least-squares elastic-stiffness coefficients, two and three for the two cases. Using the same specimens, we augmented the ARS measurements with conventional pulse-echo-method measurements. Using rod specimens, we measured the Young modulus E and torsional modulus G, and we calculated the bulk modulus B. The less direct and less familiar ARS method gives the same results as a usual pulse-echo method and a rod-resonance method. The small difference between polycrystal and monocrystal values may arise from mobile twin boundaries that contribute a small reversible plastic strain to the intrinsic elastic strain. We list 16 advantages of the ARS method to measure elastic constants.