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Magnetic nondestructive evaluation (NDE) for ferromagnetic steel using spectrum analysis of induced voltage at a pickup coil and magnetic flux density has been studied. A voltage induced at the pickup coil was measured, and the corresponding magnetic flux density was calculated. Then, their frequency spectrums were obtained through a Fourier analysis. For deformed specimen, higher harmonic components decrease as compared with undeformed specimen. The wave distortion factor for the induced voltage and the magnetic flux density were defined and evaluated. Those values decrease with increasing reduction ratio of the specimen; this means the waveforms of induced voltage and magnetic flux density for a less deformed specimen has a large distortion in those waves. Those changes reflect a nonlinearity of the magnetization curves of the specimen. The results in this study indicate a potential of magnetic NDE using spectrum analysis of measurement wave forms. [ABSTRACT FROM AUTHOR]

We investigated effects of contact gap on magnetic nondestructive evaluation technique using a magnetic single-yoke probe. Firstly, we evaluated hysteresis curves and impedance related to permeability of the material measured by a single-yoke probe, when an air gap length between the probe and specimens changes. The hysteresis curve gradually inclines to the axis of the magneto-motive force and magneto-motive force at which the magnetic flux is 0 decreases with increasing the gap length. The effective permeability also decreases with increasing the gap thickness. The incremental of gap thickness increases the reluctance inside the magnetic circuit composed of the yoke, specimen and gap, which results in the reduction of flux applying to specimen. [ABSTRACT FROM AUTHOR]

We investigated the effects of DC bias current applied directly to the elements on the inclined easy axis thin-film magnetoimpedance element indicating a discontinuous impedance jump. We clarified that the DC bias current contributes to changes in the configuration of domain structure, which induces modification of impedance profiles on the 20 μm-wide element. On the other hand, 40 and 80 μm-wide elements did not show the apparent changes on the magnetoimpedance profiles. The influence of DC bias current on jumping point is not so much, which is attributed to the small bias magnetic field generated by the current; the limited bias level is not high due to Joules heating by the current. [ABSTRACT FROM AUTHOR]

This paper describes the characteristics of magnetic Barkhausen noise (MBN) and permeability on neutron irradiated Fe and Fe-Cu alloys. The plates made of pure Fe and Fe-1 wt.% Cu alloys were prepared with and without cold-rolling. Those plates were irradiated by neutron with a total fluence of 1 × 10^{24} n/m^{2}. Then MBN properties and impedance were measured using magnetic-yokes, a MBN sensor and a pick-up coil. The MBN rms voltage decreases with neutron irradiation, and the impedance increases after irradiation for cold-rolled specimen. On the other hand, the MBN properties and the impedance at lower frequency have no significant changes after irradiation for undeformed specimen. Contrary, the impedance at higher frequency for undeformed Fe-Cu alloy decreases after irradiation. The relations between those magnetic properties and the microstructure of irradiated materials were also discussed. Those results show the potential of nondestructive evaluation for neutron irradiation embrittlement in reactor pressure vessels. [ABSTRACT FROM AUTHOR]

This paper discusses a feasibility of magnetic flux leakage (MFL) method for estimation of wall thinning on tube in nuclear power plant. A single magnetic yoke is fixed on the specimen, and then a magnetic field sensor scans the leakage field between the yoke legs. The single magnetic yoke with gauss meter fixed at the center of the yoke is also scanned over specimens having a slit. From both FEM analysis and experimental measurement, it is clarified that estimation of the size of slit fabricated in the specimen using profile of leakage field is possible; this indicates monitoring conditions of wall thinning will be possible by MFL method. [ABSTRACT FROM AUTHOR]

We have examined scaling rules in magnetic minor hysteresis loops for strain-induced ferromagnetic α'-martensite in 304 stainless steels. The scaling power law between the hysteresis loss and remanence is found to be independent of volume fraction and morphology of martensite. A coefficient of the power law changes depending on size, shape and distribution of martensite. The present method can be a possible technique for integrity assessment of austenitic stainless steels because of the sensitivity and low measurement field. [ABSTRACT FROM AUTHOR]

Magnetic properties of an iron-based steel derived from its major hysteresis loop are very sensitive to its microstructures and have been, therefore, used for nondestructive evaluation (NDE) of degradation in infrastructure made by ferromagnetic materials. The permeability obtained from small ac field excitation may be a more useful parameter for NDE of ferromagnetic materials than one obtained from a major hysteresis loop from the viewpoints of electricity consumption and real-time measurements. In this paper a relation between ac permeability, calculated from impedance of coil elements, and dislocation density or grain size of pure iron were clarified. A potential of NDE using ac permeability is also discussed. [ABSTRACT FROM AUTHOR]

We have analyzed minor hysteresis loops of Fe-Cu alloys with 0.3 wt.% Cu in isothermal aging at 773 K. We found that magnetic coefficients of minor loops show a maximum around the same aging time that Vickers hardness becomes maximum. Both magnetic and mechanical properties are correlated with the microstructure of copper precipitates. These magnetic properties are very useful for nondestructive evaluation of degradation due to neutron irradiation in the nuclear reactor pressure vessels. The minor-loop properties have three advantages compared with coercive force of the major loop in view of their high sensitivity, amount of information, and a small magnetic field to be required for magnetic measurements. [ABSTRACT FROM AUTHOR]

A device for nondestructive measurement of dc hysteresis magnetization characteristics of Charpy impact test pieces was developed for investigating the correlation between changes of ductile-brittle transition temperature and magnetic hysteresis characteristic of nuclear reactor pressure vessel steel due to neutron irradiation. Operation tests verified satisfying performances of its designed functions. [ABSTRACT FROM AUTHOR]