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

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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.