Nondestructive Measurement of Stress and Material Properties using Electromagnetic Fields

本研究的主要目的是发展研究者提出的磁声弹性，实现更实用的无损应力评估技术，为非磁性材料提供一种新技术。提出了具有磁滞的非线性铁磁材料的本构方程，并从理论上分析了磁滞对超声波传播的影响。我们还提出了塑性铁磁材料的本构方程，并证明了可以将塑性变形和磁弹耦合对超声波速度变化的影响分离开来。由此可以将磁声弹性理论应用于受较大应力作用的材料。为了考虑更广泛的材料类别和变形，我们提出了磁性本构方程，可以描述磁率和各向异性的影响。磁场作用下的应力和材料性能无损评价研究表明，利用超声波在磁场作用下的速度变化，可以分离材料的织构和应力各向异性，从而更准确地评价材料的应力，这是传统方法难以做到的。我们进一步研究了在磁场作用下，可以通过测量一种超声波的速度变化来评估试样的平面应力。我们研究了由烧结材料的波速分布可以得到材料密度或弹性常数的分布。磁声弹性的推广利用压电或电致伸缩效应将磁声弹性推广到非磁性材料。目前还没有对理论研究进行实验验证，留待以后的课题研究。

The main purpose of the research was to develop magnetoacoustoelasticity proposed by the investigators, and to achieve more practical nondestructive techniques of stress evaluation and a new technique available for nonmagnetic materials.1. Establishment of nonlinear electromagnetoelastic constitutive equations and their verificationWe proposed the constitutive equations of nonlinear ferromagnetic materials with hysteresis and theoretically analyzed the effects of magnetic hysteresis on the propagation of ultrasonic waves. We also proposed the constitutive equations of plastic ferromagnetic materials and proved that we can separate the effects of the plastic deformation and the magnetoelastic couplings on the speed shift of ultrasonic waves. From the result, it becomes possible to apply the magnetoacoutoelasticity to materials subjected to larger stresses. In order to take into account wider classes of materials and deformations, we proposed the magnetic constitutive equations which can describe the effects of magnetic rate and anisotropy.2. Nondestructive evaluation of stress and material property under magnetic fieldWe showed that from the speed shift of ultrasonic waves under the magnetic field, it becomes possible to separate the texture and the stress anisotropies and to evaluate more accurate stress which has been difficult by conventional techniques. We further examined that by applying the magnetic fields to the specimen, the plane stress can be evaluated by measuring the speed shift of one kind of ultrasonic wave. We examined that the distribution of the material density or the elastic constants can be obtained from that of the wave speed for sintered materials.3. Extension of magnetoacoutoelasticityWe generalized magnetoacoutoelasticity to noumagnetic materials by using the piezoelectric or electrostrictive effects. Verification of the theoretical study by experiments has not been done and left for the future subject.