6 research outputs found
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Noncontacting ultrasonic and electromagnetic HTS tape NDE
Two noncontacting nondestructive evaluation techniques (electromagnetic and ultrasonic) for inspection of high temperature superconducting tapes are described. Results for Ag-clad BSCCO tapes are given
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Calculation and measurement of the critical state in superconducting tapes
An integral equation approach to solving for the flux front profile in the critical state model is described. Both nonuniform external fields and demagnetizing geometries can be accommodated as long as cylindrical symmetry is preserved. Results for a sphere in a uniform external field and a tape in the field of an external coil parallel to the tape surface are presented. 9 refs., 6 figs
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Ceramic joint interface diagnostics with ultrasonic reflection signal energies
The properties of silicon nitride ceramic joints, prepared by hot isostatic pressing, have been investigated by recording the reflected ultrasonic elastic wave off the joint interface. Experimental and theoretical analysis of the reflected signal energy has shown that properties of the joint interface such as thickness, joining compound composition, inclusions, and voids, can be imaged over the joint plane. A model incorporating plane waves shows that the reflected signal energy is a function of joint thickness, joint/host acoustic impedence and transducer bandwidth. For joint thicknesses less than the average ultrasonic wavelength in the joint, the reflected signal energy depends quadratically on the thickness. This dependence was verified by for several joints by direct measurement. In the opposite regime, where the joint thickness is greater than the ultrasonic wavelength, the reflected signal energy is independent of thickness and only a function of the joint/host acoustic impedence mismatch. This regime was not accessible with the bandwidth transducers. The results suggest that for a given range of thicknesses, measurement of the joint energy with broadband transducers with different center frequencies could provide a means of determining both the joint thickness and joint/host acoustic impedence mismatch. Joint thickness is the most prominent parameter that can be probed with ultrasonics and its effect on fracture toughness should be an important parameter in determining the quality of joints. Qualitatively, the reflected signal energy method of data analysis is a rapid means for assessing joint quality with respect to thickness, inclusions, and voids
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Direct Imaging of Anisotropic Material Properties using Photorefractive Laser Ultrasound
Anisotropic properties of materials can be determined by measuring the propagation of elastic waves in different directions. A laser imaging approach is presented that utilizes the adaptive property of photorefractive materials to produce a real-time measurement of the antisymmetric Lamb or flexural traveling wave mode displacement and phase. Continuous excitation is employed and the data is recorded and displayed in all directions simultaneously at video camera frame rates. Fourier transform of the data produces an image of the wave slowness in all planar directions. The results demonstrate imaging of microstructural isotropy and anisotropy and stress induced ansiotropy in plates