Papers by Keyword: Ferromagnetic Material

Abstract: Barkhausen noise (BHN) measurement is one of electromagnetic testing methods that is suitable for ferromagnetic materials. It has a sensitivity to different material properties such as microstructure, composition, residue stress, hardness, etc. which can also be used to determine the hardness case depth of a hardened layer. The measurement is intriguing because of its time and cost-effectiveness. The aim of this work was to study and select a suitable method to evaluate and predict the hardness case depth of induction hardened S50C steel based on Barkhausen noise measurement. Signal processing of BHN signal was performed and extracted features were validated with the actual hardness case depth according to the destructive method of Vickers hardness and metallography in order to achieve the most accurate hardness case depth evaluation model. The results showed that the hardness case depth prediction model could be used to indicate the hardness case depth of induction hardened steel significantly at the correlation coefficient (R) of 0.97 and root mean squares error of estimation (RMSEE) of 3.56%.

Abstract: In the NDT procedure is very important to be informed about modification happened in structure in particular in the ISI. The prediction life can be studied by using the inverse problem. In our study an efficient method, called the inverse distribution function, for calculating the magnetic field strength H from the flux density B through the Preisach model is developed. According to this technique, H can be obtained from B by determining the parameters of the proposed distribution function using genetic algorithms. Various distributions functions will be studied to determine which function gives the best distribution for modeling the hysteresis loop and give maximum information with minimum error on what happened in the microstructure.

Abstract: With the initial permeability testing technique, early evaluation on stress concentration and fatigue damage can be realized by measuring initial permeability of the ferromagnetic material. The variation of detection signals with initial permeability is researched via the ANSYS FEM simulation and the tensile testing of 45 steel. The results indicate that the detection signals have a linear relation with initial permeability of the ferromagnetic material. It is seen that initial permeability testing technology can give effective and accurate evaluation of the ferromagnetic material.

Abstract: The structure, electronic and magnetic properties of full-Heusler alloy Co₂TiGa are investigated by means of the full potential linearized augmented plane-wave method. Our results show that the ground state of Co₂TiGa is of the nearly half-metallic ferromagnetism with a magnetic moment of 1.00218 μ_B per unit cell, which are contributed by the atoms Co and Ti. Meanwhile, the spin polarization around the Fermi level is up to 93.2%, almost 100%, which indicates that full-Heusler alloy Co₂TiGa with the well magnetism and spin polarization would be possibly applied to the field of the material engineering and information technology.

Abstract: Metal magnetic memory testing (MMMT) technique is a kind of new NDT technique. It is interested by NDT area in recent years for its own advantages: early diagnosis, preventing sudden fatigue failure of equipments and the testing samples do not need to be magnetized. In order to find out the variation law of the residual magnetic strength of ferromagnetic material processed by different cutting method, axial tension tests about milling and flat surface grinding samples are completed in elastic and plastic deformation phase. The experimental results indicate that the magnetic strength variation law of two kinds of sample makes a great difference in the same deformation phase. The magnetic strength and standard deviation variation law of the grinding and milling samples are almost reverse. But there is a common ground of the two samples that when the material reaches yield phase, turning point occurs on both the residual magnetic strength and standard deviation curve. So we can identify whether there is plastic deformation according to the residual magnetic strength variation law of ferromagnetic material.

Abstract: It has previously been reported that when a fatigue crack grows in ferromagnetic materials, abnormal magnetic signals are spontaneously emitted, which can provide a powerful tool for fatigue crack life prediction. However, there is no physical model yet available to explain the mechanism for the formation of these self-emitting magnetic signals. In the present research, tension-tension fatigue tests of center-cracked sheet specimens were performed. The variations in the normal component of the self-emitting magnetic signals, Hp(y), on the surfaces of the specimens were measured during the fatigue test. The differences in peak-to-peak value, Hp(y), before and after failure of a specimen, were characterized. Consequently, a physical model based on magnetic charge was proposed, which was in good agreement with the experimental results. The model is helpful for understanding the inherent mechanism of the self-emitting magnetic signals.

Abstract: In this study, the coil-less fluxgate effect in Co₇₁Fe₁Mo₁Mn₄Si₁₄B₉ amorphous ribbon was investigated. The coil-less fluxgate is a new type of fluxgate sensor without a coil. It is based on helical anisotropy and deep circumferential magnetic saturation in the ferromagnetic fluxgate core. Coil-less fluxgate measurements were performed in as-cast and annealed ribbons at 480 mA current with 3, 12.5 and 25 rad/m torsion. The second harmonic of the output voltage detected from the ends of the wire show a linear variation in the low magnetic field region. The sensitivity of the current annealed ribbons in the presence of 25 rad/m torsion is about 570 V/T, which is comparable with previously reported fluxgate sensitivity values. The presented sensor has no coil so it is much easier to reduce the size of the sensor and easy to fabricate it.

Abstract: Powders of Ñî-Ð alloy with ultradispersed corundum (Al₂O₃) and detonation nanodiamond (DND) precipitates were synthesized by chemical reduction. The products were characterized by X-ray diffraction and scanning electronic microscopy. The shape of the particles was spherical and they were ferromagnetic. Magnetization dependence on field in applied fields of up to 40 kOe and magnetization dependence on temperature in the temperature range from 2 to 300 K were measured. Influence of precipitates on magnetic properties was studied.

Abstract: A new non-contact sensor with three magnetic pole based on magnetoelastic effect was designed, and its operation principle and mathematical model of induced voltage output were given. The output characteristic of the sensor affected by field current intensity, frequency, and the gap between the probe of the sensor and the surface of the material tested was analyzed by testing. The calculation result based on the output model found by the paper accord basically with the test result. The results of the test have showed that the measuring precision and sensitivity of the sensor can meet the demands of the general practical application.

Abstract: When a steel etc. a ferromagnetic material is subjected to the external loads, the internal force will develop, that is, stress will develop inside the material, which will lead to a corresponding change in the magnetic permeability of this material when magnetized. In this paper, according to this unique property of the ferromagnetic material, in the light of the mainly stressed and deformation characteristic of a long span steel structure etc. defect sensitive structures, by the use of stress sensitivity of magnetization, a mathematical physical model of relationship between the change in the magnetic permeability and stress is studied and put forward when a ferromagnetic component is under the action of a simple stress, a linear dependency relation of the component’s stress and its permeability is obtained, and the fundamental theory of the magnetic non-destructive testing of a safe state and its engineering application method is also established for a long span steel structure etc. defect sensitive structures, which provides a definite basis for guaranteeing safety of this kind of structures. Additionally, in this paper through the comparison of the theoretical analysis results with results of the related experiments, the dependency relation of change in the magnetic permeability and stress etc. theoretical research results is verified. Both these results exhibit a good consistence, which demonstrates that the research and the application of the non-destructive safe testing method for a defect sensitive structure based on the magnetic effect is feasible and valid and the future will see a certain engineering application prospect in this research and this testing method.