Nondestructive Estimation of Residual Stresses by Magnetoacoustoelasticity

本学期的研究总结如下。分析了广泛用作结构材料的钢铁等铁磁性材料在轧制等加工过程中产生的磁各向异性。结果表明，即使在轧制具有正交各向异性磁对称的板材的情况下，由于磁化曲线的非线性，也有可能产生高阶各向异性。通过碳钢板材的平面磁化实验验证了预测的正确性。为了估算强磁场作用下铁磁材料的声弹性应力，我们考虑了磁场对超声波传播的影响。对于无磁滞的软铁磁材料，我们用传统的磁弹性材料连续介质模型的广义理论很好地解释了磁场与超声波传播速度之间的复杂关系。为了在强磁场下进行更实用的无损检测，我们研究了磁滞效应对超声波传播的影响。结果表明，由于磁滞效应和磁弹性效应，速度和声弹常数随磁场的变化存在滞后现象。通过对低碳钢在磁场作用下的声弹性实验，验证了理论结果。结果表明，磁滞和磁弹性耦合引起了波形的失真和波的衰减。开发一种利用波形分析的影响进行应力估计的新技术是一个未来的课题。

The summary of the research in the term is the followings.1. We analyzed the magnetic anisotropy, induced by working such as rolling, of ferromagnetic materials like steel which are widely used as structural materials. It is shown that there is a possibility that higher order anisotropy is generated due to the nonlinearity in the magnetization curve, even in the case of rolling plates with orthotropic magnetic symmetry. The prediction is verified by the plane magnetization experiment of a carbon steel plate.2. For acoustoelastic stress estimation on ferromagnetic materials under the strong magnetic field, we considered the influences of the magnetic field on the propagation of ultrasonic waves. For soft ferromagnetic materials without magnetic hysteresis, we showed that a complicated relation between the magnetic field and the speed of the ultrasonic wave is well explained by a generalized theory of the conventional continuum model of magnetoelastic materials.3. For the purpose of more practical nondestructive measurements under the strong magnetic field, we studied the influences of the magnetic hysteresis on the propagation of ultrasonic waves. In a result, it is shown that from the magnetic hysteresis and the magnetoelastic effect, there occurs a hysteresis in the speed and the acoustoelastic constants with respect to the change of the magnetic field. The theoretical result is verified by the acoustoelastic experiment on low-carbon steel under a magnetic field.4. It is found that the distortion of the wave form and the attenuation of the wave are induced by the magnetic hysteresis and the magnetoelastic couplings. The development of a new technique utilizing the effect by wave form analysis for stress estimation is left as a future subject.