Papers by Keyword: Magnetic Flux Density

Abstract: In the paper the change of the magnetic flux density under single harmonic distortion is discussed. Presented results show the dependence of the value of the magnetic flux density in the toroidal magnetic core made from the Ni80Fe20 tape of the phase angle of higher harmonic in relation to the main harmonic of distorted magnetizing current. Moreover, the influence of higher harmonic depends from it frequency and it becomes undetectable above 15th higher harmonic, even if its level reaches 50% of the RMS value of the main harmonic of distorted magnetizing current. Laboratory tests were carried out for the magnetic toroidal core of iCT with a current ratio equal to 300 A / 5 A. The oscilloscope is used to measure waveforms of the excitation current and the secondary voltage through the voltage probes. Build in numerical integration is used to determine the magnetic flux density from secondary voltage. In the case of tested 5^th higher harmonic the highest value of the magnetic flux density is obtained for phase angle equal to 90° between main and higher harmonics, while the lowest is obtained for 270°. This depends from the initial phase of the magnetic field strength and results from the integration of distorted secondary voltage with the particular content of higher harmonics.

Abstract: In this study, anisotropic magnetorheological elastomers (MREs) mold design with capability of aligning the filler in several angles (0 ̊, 45 ̊, and 90 ̊) were developed. The mold was equipped with electromagnet coil to generate the magnetic flux. The distribution of magnetic flux density in the mold and inside the chamber was investigated by using finite element magnetic analysis. Magnetic flux density of 0.3 T was considered best value to form good particle alignment in the matrix. Moreover, the mold design was fabricated using same material as in the simulation. The magnetic flux density was taken at casing wall and measured by gauss-meter. The data was compared with simulation results. The differences between experimental and simulation is in the range of 6-40 mT. Since the difference is insignificant, it can be said that the data is valid. Finally, the model can be used for further magnetic flux density prediction inside the chamber. In the simulation, it was found that the current needed to generate at least 0.3 T inside the chamber for 0 ̊, 45 ̊, and 90 ̊ are 0.2A, 0.1A, and 3A, respectively.

Abstract: Crack propagation around the stress concentration area causes fatigue failure. Non-destructive method is necessary for monitoring structure fatigue before destruction. We focused on a magnetic non-destructive evaluation method for crack growth. In order to understand the relation between crack propagation and changes in magnetic flux density, we observed the position of the positive and negative magnetic flux density distributions around the crack of tool steel (SCM440) plate using a scanning Hall probe microscope (SHPM). We found that the vertical component of the three-dimensional magnetic flux density moved as the crack growth. Furthermore, the magnetic component which is parallel to the tensile stress appeared just before destruction of the specimen.

Abstract: Non-destructive evaluation methods using magnetic measurement systems have been developed. However, there are a few approaches to the effect of cracks on magnetic fields during whole fatigue process. In the present work, slit samples of as-received chromium molybdenum steel material (JIS, SCM440) including no retained austenite was fatigue tested. Fatigue process was observed using a scanning Hall probe microscope in order to investigate the effect of cyclic slit opening and crack growth on residual magnetic fields. It is found that the cyclic opening-closing of the slit decreases the magnetic flux density even where no tensile stress was applied.

Abstract: Nowadays power quality is a critical issue in power system. Moreover the connection of three-phase transformers through underground cables is growing fast in residential, commercial, industrial and rural applications. Due to this increasing situation, the possibilities of having a series connected capacitance and a non-linear inductance, and hence ferroresonance, become more probable. Ferroresonance can also occur in power transformers or reactors by capacitive coupling from neighbouring phases or lines. It is necessary to have a general idea about what would be the best preventive decisions to take in order to avoid unexpected surprises. It is necessary to have an accurate ferroresonance model so that a device that can smoothen the sharp effects of ferroresonance can be found. In this paper, the FACTS device, namely the static synchronous series compensator (SSSC) had been used to mitigate ferroresonance. Results show that using SSSC dramatically decreases and mitigates the ferroresonance shock as well as the instabilities of the network.

Abstract: Nowadays power quality is a critical issue in power system. Moreover the connection of three-phase transformers through underground cables is growing fast in residential, commercial, industrial and rural applications. Due to this increasing situation, the possibilities of having a series connected capacitance and a non-linear inductance, and hence ferroresonance, become more probable. Ferroresonance can also occur in power transformers or reactors by capacitive coupling from neighbouring phases or lines. It is necessary to have a general idea about what would be the best preventive decisions to take in order to avoid unexpected surprises. It is necessary to have an accurate ferroresonance model so that a device that can smoothen the sharp effects of ferroresonance can be found. In this paper, the FACTS device, namely the static synchronous series compensator (SSSC) had been used to mitigate ferroresonance. Results show that using SSSC dramatically decreases and mitigates the ferroresonance shock as well as the instabilities of the network.

Abstract: In this paper the Halbach array with different segments per pole are modeled. The dimensions of magnets among segments are different with different magnetization direction. The unified harmonic model for the magnetic flux density distribution of the Halbach array with different segments per pole is derived by using Fourier series and magnetic scalar potential. Then the Halbach array with different segments per pole can be analytically analyzed and compared by the unified harmonic model.

Abstract: Due to its good wear resistance, Al-20Si is widely used as piston. But coarse primary silicon greatly undermines the mechanical properties of Al-Si alloy. The primary silicon could be refined in pulse magnetic field with suitable magnetic flux density and magnetic field frequency. In this work, the microstructure of Al-20Si alloy with and without pulse magnetic field treatments was observed, and the influence mechanism of weak pulse magnetic on the microstructure of the alloy was investigated. The results showed that the grain size of primary silicon fluctuated with increasing magnetic flux density at 1Hz. The smallest grain size of primary silicon is obtained at 94mT. The grain size of the primary silicon decreased with increasing magnetic field frequency under the magnetic flux density of 94mT.

Abstract: In order to identify the mechanisms of changes in the magnetic flux density distribution around fatigue cracks that occur during crack propagation, JIS SCM440 specimens were fatigue tested, and the relation between crack morphology and magnetic flux density distribution was investigated. Two features were observed: a high intensity area around the crack tip, and a low intensity area around the crack root. The low intensity area grew larger for wide open cracks and disappeared when the crack was closed by external force. It was hence found that the magnetic flux density distribution is strongly affected by the crack opening.

Abstract: Crack growth under cyclic loading causes failure of machine components. Non-destructive methods that can be related to plastic deformation around crack tip are necessary to study the crack growth. In the present work, a scanning Hall probe microscope (SHPM) equipped with GaAs film sensors was used to observe the magnetic fields around the plastic deformation induced by Vicker's indentations in tool steel specimens (SKS93, JIS B 4404: 2006, equivalent to AISI W4 tool steel). The magnetic field around a 2.94N-indentation was compared to that of a 294N-indentation. It was found that the decrease in the magnetic fields depends on the plastic deformation size.