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Characterization of rolling texture by ultrasonic dispersion measurements
Ultrasonics International 87 abstracts In so-called surface skimming bulk wave devices, the transducer only couples to the horizontal shear displacement; however in the general case, it can also excite longitudinal and vertical shear vibrations, depending on the substrate. There are two main ways of solving the fundamental problem of the wave excitation. In the first one an effective permittivity is defined from the relation between the Fourier Transform of charge density and the electrical potential at the surface. This approach is mainly numerical and it is difficult to distinguish one wave from the others. The second approach is based on the classical Lamb's approach. The electrostatic potential inside the medium is computed and the mechanical displacement obtained as a forced problem. Previously mechanical displacement was evaluated asymptotically at or near the surface. In this poster a definite integral representation of the displacement is obtained at any point of the semi-infinite anisotropic solid and asymptotic formulae are obtained for the far field solution. New results will also be given for the case of more general anisotropic substrates.
A suboptimal tomography reconstruction technique
J.-P. Lefebvre and S. Nensah, CNRS, Marseille, France We present a brief note devoted to acoustic impedance tomography. Our objective is to obtain quantitative images of a medium, such as the impedance cartography, (resp. velocity) from measurements in the reflection mode (resp. transmission mode). In this way, we expose our reconstruction algorithm based on retroprojection techniques, and show how it can be optimized using numerical deconvolution and a digital filter. The latter is an empirical numerical version of the one derived by Shepp and Logan, and has been chosen because of its simplicity. Finally, to test our and all other techniques, we have built an original ultrasonic tomography system. It is computer controlled and has an accuracy which allows us to work with an RF signal up to 10 mHz. This equipment will be used to simulate experiments in the biomedical and nondestructive evaluation fields.
Characterization of rolling texture by ultrasonic dispersion measurements
Ultrasonic study of 1,1-diacetyl ferrocene and p-azoxy
E. Schneider, S. Hirsekorn, Universitat Geba'ude, Saarbru'cken, FRG
anisole in solution in non-polar solvents
A theory of ultrasonic wave propagation in textured polycrystals has been developed by one of the authors. It allows calculations of longitudinal and shear wave velocities in polycrystals of cubic symmetry with orthorhombic texture. The directions of ultrasonic propagation and vibration are not limited to be parallel to the principal axes of texture. The poster will review the theory and will deal with numerical calculations and experimental results: cold rolled and thermomechanically rolled plates with different degree of texture are considered. The expansion coefficients W/rnn of the / = 4 and / - 6 series of the orientation distribution function are evaluated and compared with X-ray results. Furthermore, correlations between the degree of texture and the texture-influenced birefringence are found and used to evaluate the residual stress states in plates with rolling texture.
G.K. Johri and D. Saxena, DAV College, Kanpur, India The ultrasonic velocity of 1,1 -diacetyl ferrocene and p-azoxy anisole liquid crystalline substances in solution in non-polar solvents has been measured at various concentrations using interferrometer techniques at 2 MHz. Viscosity, density and refractive index are also measured using Oswald viscometer, pycnometer and Abbe's refractometer, respectively. These data are used to compute adiabatic compressibility, Rao's number, Van der Waals constant and free volume. The contributions of electronic polarizability, London dispersion attractive, exchange repulsive and dipole-dipole forces to the molar volume are estimated. This study provides useful information about isotropic behaviour of liquid crystalline substances and their solute solvent interactions.
Theoretical analysis of ultrasonic interferometers for precise measurements at high pressures
T.V. Chalikian and A.P. Sarvazyan, Acad, Sci. USSR, Moscow, USSR Measurements of ultrasonic characteristics of liquids in a wide range of pressures yield important information on molecular interactions in solutions. The possibility of reaching higher values of pressures depends on the volume of the investigated object. The smallest volume of liquid required for precise measurements of ultrasonic velocity and attenuation is provided in the method of fixed path interferometer. To adapt this method to measurements at high pressures it is necessary to substitute the gaseous backing of the transduces by a liquid or solid media. A general theory of an interferometer taken as a rnultilayer system was considered and the dependences of characteristics of the interferometer upon the transducer backing parameters were calculated. The conditions under which the backing of transducers by a liquid weakly influences the Q-factor of the interferometer and high precision measurements of ultrasonic velocity and attenuation become possible were determined. Experimental results obtained by a device built according to these calculations have verified the theory.
Characterizing the microstructure of industrial steels by ultrasonic attenuation spectral analysis
R.L. Smith and L.P. Scudder, National NDT Centre, Harwell, UK In recent studies by Smith and Reynolds the ultrasonic attenuation data from well characterized ferritic steel samples has been examined. The results show that, apart from grain scattering, dislocation damping is an important attenuation mechanism in these steels. From this work a method of analysing ultrasonic attenuation data was developed; this separates the grain scattering and dislocation damping contributions so the effect of variations in grain size and distribution density can be monitored. In this poster the ultrasonic attenuation spectra were measured for samples made from commercial grades of steel. The differences in structure between samples have been interpreted from the attenuation data by using the grain scattering and dislocation damping method of analysis. These differences are compared with those shown between micrographs of the same samples. An assessment is then made of the relevance of the grain scattering and dislocation damping model for these steels.
Ultrasonics 1987 Vol 25 Nove~mber
379
A suboptimal tomography reconstruction technique
J.-P. Lefebvre and S. Nensah, CNRS, Marseille, France We present a brief note devoted to acoustic impedance tomography. Our objective is to obtain quantitative images of a medium, such as the impedance cartography, (resp. velocity) from measurements in the reflection mode (resp. transmission mode). In this way, we expose our reconstruction algorithm based on retroprojection techniques, and show how it can be optimized using numerical deconvolution and a digital filter. The latter is an empirical numerical version of the one derived by Shepp and Logan, and has been chosen because of its simplicity. Finally, to test our and all other techniques, we have built an original ultrasonic tomography system. It is computer controlled and has an accuracy which allows us to work with an RF signal up to 10 mHz. This equipment will be used to simulate experiments in the biomedical and nondestructive evaluation fields.
Characterization of rolling texture by ultrasonic dispersion measurements
Ultrasonic study of 1,1-diacetyl ferrocene and p-azoxy
E. Schneider, S. Hirsekorn, Universitat Geba'ude, Saarbru'cken, FRG
anisole in solution in non-polar solvents
A theory of ultrasonic wave propagation in textured polycrystals has been developed by one of the authors. It allows calculations of longitudinal and shear wave velocities in polycrystals of cubic symmetry with orthorhombic texture. The directions of ultrasonic propagation and vibration are not limited to be parallel to the principal axes of texture. The poster will review the theory and will deal with numerical calculations and experimental results: cold rolled and thermomechanically rolled plates with different degree of texture are considered. The expansion coefficients W/rnn of the / = 4 and / - 6 series of the orientation distribution function are evaluated and compared with X-ray results. Furthermore, correlations between the degree of texture and the texture-influenced birefringence are found and used to evaluate the residual stress states in plates with rolling texture.
G.K. Johri and D. Saxena, DAV College, Kanpur, India The ultrasonic velocity of 1,1 -diacetyl ferrocene and p-azoxy anisole liquid crystalline substances in solution in non-polar solvents has been measured at various concentrations using interferrometer techniques at 2 MHz. Viscosity, density and refractive index are also measured using Oswald viscometer, pycnometer and Abbe's refractometer, respectively. These data are used to compute adiabatic compressibility, Rao's number, Van der Waals constant and free volume. The contributions of electronic polarizability, London dispersion attractive, exchange repulsive and dipole-dipole forces to the molar volume are estimated. This study provides useful information about isotropic behaviour of liquid crystalline substances and their solute solvent interactions.
Theoretical analysis of ultrasonic interferometers for precise measurements at high pressures
T.V. Chalikian and A.P. Sarvazyan, Acad, Sci. USSR, Moscow, USSR Measurements of ultrasonic characteristics of liquids in a wide range of pressures yield important information on molecular interactions in solutions. The possibility of reaching higher values of pressures depends on the volume of the investigated object. The smallest volume of liquid required for precise measurements of ultrasonic velocity and attenuation is provided in the method of fixed path interferometer. To adapt this method to measurements at high pressures it is necessary to substitute the gaseous backing of the transduces by a liquid or solid media. A general theory of an interferometer taken as a rnultilayer system was considered and the dependences of characteristics of the interferometer upon the transducer backing parameters were calculated. The conditions under which the backing of transducers by a liquid weakly influences the Q-factor of the interferometer and high precision measurements of ultrasonic velocity and attenuation become possible were determined. Experimental results obtained by a device built according to these calculations have verified the theory.
Characterizing the microstructure of industrial steels by ultrasonic attenuation spectral analysis
R.L. Smith and L.P. Scudder, National NDT Centre, Harwell, UK In recent studies by Smith and Reynolds the ultrasonic attenuation data from well characterized ferritic steel samples has been examined. The results show that, apart from grain scattering, dislocation damping is an important attenuation mechanism in these steels. From this work a method of analysing ultrasonic attenuation data was developed; this separates the grain scattering and dislocation damping contributions so the effect of variations in grain size and distribution density can be monitored. In this poster the ultrasonic attenuation spectra were measured for samples made from commercial grades of steel. The differences in structure between samples have been interpreted from the attenuation data by using the grain scattering and dislocation damping method of analysis. These differences are compared with those shown between micrographs of the same samples. An assessment is then made of the relevance of the grain scattering and dislocation damping model for these steels.
Ultrasonics 1987 Vol 25 Nove~mber
379