Nondestructive Evaluation of Stress and Damage of Materials by Magnetoacoustic Effects

本课题的目的是利用在许多结构材料中可见的磁声效应，发展应力和损伤的无损评估技术。项目实施期间取得的成果如下：可变形磁性材料控制方程的推导首先推导了考虑磁弹性相互作用的磁场作用下可变形材料的本构方程。根据所提出的理论，证明了磁声现象、磁化曲线和磁致伸缩与应力有关。通过对钢和镍在磁场下的加载和声弹性试验，验证了上述预测。利用超声剪切波测量应力和磁化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的技术。当应力作用于各向异性材料时，通过应力与材料各向异性的叠加，可以得到更大的各向异性。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，就可以分离出应力对超声波速度变化的贡献。用类似的方法，我们可以通过超声剪切波在各个方向上极化的速度变化来测量磁化矢量。磁声发射（MAE）的应力依赖性研究表明，循环磁化过程中产生的磁声发射依赖于磁弹性耦合引起的应力。利用这种依赖关系，可以通过测量磁化周期内MAEs的计数来无损地估计应力。对于一种典型的铁磁材料，我们证明了MAEs的数量随应力与磁场的夹角以及应力中压缩/拉伸和弹塑性的差异而变化。研究结果表明，MAE是一种很有前途的磁性材料应力损伤无损检测方法，可提前应用于断裂损伤过程。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