Nondestructive Evaluation of Stress and Damage of Materials by Magnetoacoustic Effects

本课题的目的是利用磁声效应对结构材料的应力和损伤进行无损检测。本课题主要取得了以下成果：1.可变形磁性材料控制方程的推导首先推导了磁场作用下可变形磁性材料的本构方程，考虑了磁弹性相互作用。在此基础上，分析了磁声现象、磁化曲线和磁致伸缩与应力的关系。通过对钢和镍在磁场作用下的加载和声弹性实验，验证了上述预测。2.超声剪切波法测量应力和磁化强度我们发展了利用超声剪切波的速度和极化来测量应力和磁化强度的技术。当应力施加到各向异性材料时， 关于我们 各向异性由应力和材料各向异性的叠加给出。因此，通过从所获得的数据中减去由于材料各向异性引起的速度变化，可以分离应力对超声波的速度变化的贡献。通过类似的方法，我们可以从每个方向上极化的超声剪切波的速度变化来测量磁化矢量。3.磁声发射（MAE）的应力依赖性我们表明，在循环磁化过程中产生的MAE取决于由于磁弹性耦合引起的应力。利用该关系，可以通过测量一个磁化周期内的MAE计数来无损地估计应力。对于典型的铁磁材料，我们证明了磁声发射的计数随应力与磁场的夹角以及应力中的压/拉和弹/塑性之差而变化。结果表明，磁声发射技术是一种很有前途的磁性材料应力和损伤的无损检测方法，可用于损伤过程的断裂预报。少

The purpose of the subject is to develope nondestructive evaluation technique for stress and damage by use of magnetoacoustic effects which can be seen in many structural materials. The obtained results during the term of the project are the followings.1.Derivation of Governing Equations for Deformable Magnetic MaterialsWe first derived the constitutive equations for deformable materials under magnetic field, taking into account magnetoelastic interactions. On the vasis of the presented theory, it is showed that the magnetoacoustic phenomena, the magnetization curve and the magnetostriction depend on the stress. Such predictions were verified by loading and acoustoelastic tests for steel and nickel under the magnetic field.2.Measurement of Stress and Magnetization by Ultrasonic Shear WavesWe developed the measurement technique for stress and magnetization by the speeds and the polarizations of ultrasonic shear waves. When the stess is applied to an anisotropic material, the acoustical … More anisotropy is given by superposition of the stress and the material anisotropies. Thus by subtracting the speed change due to the material anisotropy from the obtained data, it becomes possible to separate the contribution by stress to the speed change of the ultrasonic waves. By a similar method, we can measure the magnetization vector from the speed change of ultrasonic shear waves polarized in each direction.3.Stress Dependence of Magnetoacoustic Emission(MAE)We showed that MAE generated during cyclic magnetization depends on the stress due to the magnetoelastic couplings. By means of the dependence, the stress can be nondestructively estimated by measuring the count of MAEs during a cycle of the magnetization. For a typical ferromagnetic material, we proved that the count of MAEs changes according ot the angle between the stress and the magnetic field and the difference of compression/tension and elasticity/plasticity in the stress. From the obtained result, it is found that MAE can be expected as a promising nondestrucrive method for stress and damage of magnetic materials which can be applied in advance to fracture of damage processes. Less