Nondestructive evaluation of advanced materials by use of electromagnetoacoustic interactions

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As the foundation of the present research, we formulated various magnetomechanical behaviors of ferromagnetic materials with magnetoelastic couplings. We extended the magnetomechanical constitutive equation proposed by Matsumoto to include the dependence of magnetic histories as internal variables for wider classes of ferromagnetic materials. Applying the constitutive equations to typical ferromagnetic materials, we have shown that they can describe in good accuracy the magnetization curve, the magnetostriction curve including their stress dependence, hysteresis and nonlinearity.We next applied the magnetoacoustic effects to the nondestructive evaluation of the stress and the magnetization. When the magnetic field is applied to a ferromagnetic material, the acoustic anisotropy is induced in the direction of the magnetization vector. Then the direction of the magnetization vector can be estimated by measuring the speed of the transverse wave polarized in each direction. The difference o … More f the maximum and the minimum speeds has a strong correlation with the acoustic anisotropy, so that the magnitude of the magnetization vector can be also estimated. Such a nondestructive measurement of the magnetization can be applied to verification of the electromagnetic analysis, which contributes to more accurate and effective design of electromagnetic instruments. It is also shown that conventional acoustoelastic measurement enables us to evaluate plane stress if the magnetic field is applied.As another application of electromagnetoacoustic interactions, we visualized the internal defects by ultrasonic inspection using electromagnetic acoustic transducer (EMAT). We first simulated the transmitting and the receiving processes of EMAT by the wave analysis and the electromagnetic analysis. An ultrasonic image of defects can be obtained by scanning EMAT near the specimen surface. Improvement of the ultrasonic image was studied by employing smoothing, deconvolution and damping effect as waveform analysis, and SAFT-UT and ALOK techniques as scanning method. Less