Nondestructive Estimation of Stress and flaws by combining Magnetic Field and Ultrasonics

本课题的目的是发展研究人员提出的磁声无损技术，以包括强应力和断裂的情况。项目实施期间取得的成果如下：1.用磁声弹性评价应力我们证明了通过施加合适的磁场，可以分离出超声波速度变化中的织构和声学各向异性。通过选取外加磁场，提出了仅用纵波估算平面应力的新方法。应力作用下的磁声发射(MAE)我们对磁性材料(低碳钢)施加应力，直到塑性区域，在磁场周期性变化的情况下，测量了各个应力水平下的MAE。发现在一个周期的磁场中MAE信号的总数随着弹性区域中的应力的增加而减少。结果表明，利用MAE对应力进行无损评价，适用于弹性区的低应力水平。除了拉伸试验外，我们还测量了MAE在压缩试验下的应力相关性。结果表明，磁场一周内的MAE数相对于单轴应力符号是对称的。MAE估计缺陷的可能性将作为未来的主题。磁性材料的本构方程对于磁化强度的速率依赖关系，我们提出了一个速率型本构方程，并验证了磁化强度的纵向响应与实验数据相符。我们还研制了二维磁化测试的实验仪器。结果表明，所提出的具有非线性、各向异性和磁滞效应的三维本构方程较好地描述了旋转磁场下的磁化实验结果。

The purpose of the subject is to develop the magnetoacoustic nondestructive techniques proposed by the investigators in order to include the cases of strong stresses and fractures. The obtained result during the term of the project is the followings.1. Stress evaluation by MagnetoacoustoelasticityWe showed that it is possible to separate the texture and the acoustic anisotropy in the speed change of ultrasonic waves by applying a suitable magnetic field. We proposed new technique of plane stress evaluation only by longitudinal waves by choosing the applied magnetic field.2. Magnetoacoustic Emission (MAE) under the stressWe applied the stress to the magnetic material (low carbon steel) up to the plastic region, and measured MAE at each stress level under the periodic change of the magnetic field. The total count of MAE signals during one cycle of the magnetic field, is found to decrease according to the stress in the elastic region. In a result, the nondestructive evaluation of the stress using MAE is suitable for low stress levels in the elastic region. In addition to the extension test, we also measured the stress dependence of MAE under compression test. It is shown that the MAE count during one cycle of the magnetic field is symmetry with respect to the sign of the uniaxial stress. Possibility of flaw estimation by MAE is left as a future subject.3. Constitutive Equations of the magnetic materialsAs for the rate dependence of the magnetization, we proposed a rate type constitutive equation and verified that the indential response of the magnetization agrees with the experimental data. We also created the experimental instrument of two-dimensional magnetization tests. We showed that the proposed three-dimensional constitutive equations with nonlinear, anisotropic and hysteretic effects well describes the experimental results of magnetization under rotating magnetic field.