Nondestructive evaluation of advanced materials by use of electromagnetoacoustic interactions

作为本研究的基础，我们建立了具有磁弹性耦合的铁磁材料的各种磁力学行为。我们扩展了由Matsumoto提出的磁力学本构方程，将磁历史的依赖性作为更广泛类型的铁磁材料的内变量。将本构方程应用于典型铁磁材料，结果表明本构方程能较好地描述磁化曲线、磁致伸缩曲线及其应力依赖性、磁滞性和非线性。接下来，我们将磁声效应应用于应力和磁化强度的无损评估。当磁场作用于铁磁材料时，声学各向异性在磁化矢量的方向上产生。然后，通过测量在各个方向上极化的横波的速度，可以估计出磁化矢量的方向。最大和最小速度的差值与声各向异性有很强的相关性，因此也可以估计磁化矢量的大小。这种对磁化强度的无损测量可用于电磁分析的验证，有助于更准确、有效地设计电磁仪器。结果还表明，在施加磁场的情况下，传统的声弹性测量方法可以计算平面应力。作为电磁声相互作用的另一个应用，我们利用电磁声换能器（EMAT）对内部缺陷进行超声检测。首先通过波分析和电磁分析模拟了EMAT的发射和接收过程。通过在试样表面附近扫描EMAT，可以获得缺陷的超声图像。利用平滑、反卷积和阻尼效应作为波形分析，利用SAFT-UT和ALOK技术作为扫描方法，对超声图像进行改进研究。少

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