Magnetic Dipole Theory Research Articles

Micromechanism of interparticle normal magnetic attraction effect in magnetorheological suspensions based on magnetic-dipole theory

In order to reveal adsorption-regulation micromechanism and debonding micromechanism between wall surface and magnetorheological (MR) wall-climbing robot legs, an interparticle normal magnetic attraction (NMA) mechanics model was constructed based upon the magnetic-dipole theory. According to analysis of NMA mechanics, it was confirmed that the interparticle NMA could be intensified with enhancing magnetic-particle diameter but was weakened with ratio of adjacent magnetic-particles distance to magnetic-particle radius. It means that the adhesive capacity between MR wall-climbing robot legs and wall surface could be strengthened by increasing magnetic-particle size and decreasing interparticle distance. Furthermore, it was found that the NMA of the first particle in the magnetic chain was positively related to magnetic-particles number until the magnetic-particles number reached a critical value. Consequently, the adsorption ability between MR wall-climbing robot legs and wall surface could be effectively controlled by changing magnetic-particles number. Besides, the strongest NMA appeared at the middle of the magnetic chain. However, the weakest NMA locates at both ends of the magnetic chain. Thus, it could be concluded that the end of the magnetic chain would be separated from wall surface rather than fracture occurred in the middle of the magnetic chain when the MR wall-climbing robot legs divorced from wall surface.

Research on the Corrosion Detection of Rebar in Reinforced Concrete Based on SMFL Technology.

The corrosion damage of rebars is a leading cause of structural failure in reinforced concrete structures. Timely detection and evaluation of corrosion damage are crucial for ensuring structural safety. The self-magnetic flux leakage (SMFL) technology is often used due to its unique advantages in detecting corrosion damage of rebars. However, challenges persist in theoretically characterizing corrosion damage and exploring influencing factors. Therefore, the magnetic dipole theory model coupled with multiple-shaped defects is proposed and the influence of corrosion expansion force on the detection of corrosion damage is analyzed. The results show that the standard deviation of the magnetic field intensity induced by corrosion varied by up to 833%, while that induced by corrosion expansion force did not exceed 10%. So the changes in the SMFL field induced by corrosion damage play the dominant role and the influence of corrosion expansion force can be ignored. In addition, corrosion damage experiments on reinforced concrete based on the SMFL technology were conducted. The results indicate that the SFML curves of rebars change monotonically with the increasing corrosion degree. Significant variations in the curves correspond well with the locations of severe corrosion on the rebars. There is a positive relationship between the proposed magnetic parameters and the corrosion degree of the rebars. Furthermore, a corrosion damage evaluation model considering multiple parameters is developed to predict the corrosion degree of rebars. The prediction results demonstrate high accuracy, with an average absolute error of only 8.33%, which is within 10%.

Modeling and Evaluation of a Multi-Stable Hybrid Energy Harvester

This article develops a multi-stable hybrid energy harvester (MSHEH) which consists of a piezoelectric energy harvester (PEH) and an electromagnetic energy harvester (EMEH). By tuning two parameters, the MSHEH can achieve a mono-stable, bi-stable, and tri-stable state, respectively. A numerical procedure is developed to compute the EMEH’s transduction factor. The obtained result is validated experimentally. Using the equivalent magnetic 2-point dipole theory, the restoring force model of the magnetic spring is established. The obtained model is verified experimentally. The energy harvesting performances of the MSHEH under the four different configurations (linear, mono-stable, bi-stable and tri-stable) subjected to frequency sweep excitations are evaluated by simulation and validated by experiment. The comparative analysis focuses on power output, accumulated harvested energy, and effective energy-harvesting bandwidth. The optimum load resistances are investigated by Pareto front optimizations. The following key findings are obtained. When subjected to high-level frequency sweep excitation, the tri-stable configuration exhibits the widest frequency bandwidth and the highest total accumulated harvested energy. When subjected to low-level frequency sweep excitation, the bi-stable configuration is more efficient in energy harvesting. The best performance trade-off between the PEH and EMEH can be achieved by selecting the optimum load resistances properly.

Research on Spatial Magnetic Field Distribution of Magnetic Fluids Based on Microstructure.

This study focuses on the spatial magnetic field distribution of magnetic fluids, an extraordinary class of fluids composed of magnetic nanoparticles (MNPs), employing the Monte Carlo method to simulate the microstructure of magnetic fluids under an external magnetic field. On that basis, a model was established through magnetic dipole theory to delve into the spatial magnetic field distribution of magnetic fluids. The findings reveal that the application of a magnetic field leads to the formation of chain-like structures within the magnetic fluids, resulting in inhomogeneous spatial magnetic field distribution. The size and concentration of MNPs are crucial determinants that significantly affect the microstructure of magnetic fluid and its spatial magnetic field distribution. Furthermore, environmental conditions such as external magnetic field strength or temperature can also regulate the positions of MNPs within magnetic fluids and the spatial magnetic field distribution of the magnetic fluids. These observations enrich the comprehension of the fundamental mechanisms of magnetic fluids and their response to diverse factors, advancing the growing comprehension on the characteristics and applications of these remarkable magnetic fluids.

A physics-guided deep learning model for predicting the magneto-induced mechanical properties of magnetorheological elastomer: Small experimental data-driven

Magnetorheological elastomer (MRE) is a novel intelligent material, which shows excellent potential in vibration control applications. Previous researches have fully demonstrated that the magneto-induced shear storage modulus of MRE largely determines the vibration control effect. However, both existing theoretical and experimental ways to measure the magneto-induced shear storage modulus of MRE face their own shortage. Therefore, a novel physics-guided deep learning model is proposed to efficient predict the magneto-induced mechanical properties of MRE based on Magnetic Dipole theory and data-driven methods. A small database is built by collecting the magneto-induced shear storage modulus of MRE with different material ratios tested on a special shear rheometer. The proposed model trained with small training samples and its prediction results fit well with experimental values (average R2 of 0.99) which is superior to existing constitutive models. The training only takes 25 s, which significantly shortens the time compared to the experiment. Furthermore, the proposed model effectively predicts the magneto-induced storage modulus of MRE and has good generalization and superior transfer performance.

Precipitation mechanism of abrasive particles in magnetorheological polishing fluid and experimental verification

This study aims to address the issue of poor workpiece surface machining quality due to inadequate abrasive particle precipitation during the processing of magnetorheological polishing fluid. The paper employs magnetic dipole theory and molecular dynamics theory to establish a microdynamics model for magnetorheological polishing fluid and conducts kinematic and dynamic analyses of magnetic and abrasive particles. The chaining process of magnetic particles in magnetorheological polishing fluid was simulated under an external magnetic field, and the precipitation process of abrasive particles under the action of magnetic particles was simulated and analyzed. Furthermore, we established a microscopic observation experimental platform for magnetorheological polishing fluid and verified the precipitation law of abrasive particles under the action of dynamic magnetic field. The study findings indicate that the magnetic particles will form a chain structure, when the rotating magnetic field has an effect on the magnetorheological polishing fluid, and the abrasive particles will precipitate from the magnetorheological polishing fluid and adhere to the upper end of the magnetic chain. Moreover, the precipitation rate of abrasive particles is also affected by the magnetic field strength, the volume fraction of magnetic particles, and the rotating magnetic field speed, with the abrasive particles’ precipitation rate specifically increasing with higher magnetic field strength. At a magnetic field strength of 100 kA/m, the abrasive precipitation rate reaches 80 % in approximately 90 s, which increases to 80 % in only 60 s at a magnetic field strength of 200 kA/m. Additionally, with the increase of magnetic particle volume fraction, the precipitation rate of abrasive particles decreases. Within the first 40 s of the test, the magnetic particle volume fraction increases from 10 % to 30 %, and the precipitation rate of abrasive particles decreases by about 11 %. Similarly, the abrasive precipitation rate is affected differently by the rotating magnetic field speed. As the rotating magnetic field speed increases, the abrasive precipitation rate shows a trend of first increasing and then decreasing. When the rotating magnetic field speed increases from 20 r/min to 40 r/min, the abrasive precipitation rate of the first 40 s increases by about 25 %. When the speed continues to increase to 60 r/min, the precipitation rate of abrasive particles gradually decreases.

An approach to solving the effect of background in fluidized bed on electromagnetic tomography

As a non-invasive measurement technique, electromagnetic tomography (EMT) system based on tunneling magneto resistance (TMR) can detect the distribution of medium in the gas–liquid–solid fluidized bed by the difference of permeability. The distribution of medium in the three-phase fluidized bed is not uniform, and the solid clusters and bubble clusters are formed in the background of the gas–liquid–solid mixture. Since the effect of the background in the pipe of the fluidized bed on the boundary measurement data of the TMR-EMT system is much greater, it is difficult to detect solid clusters and bubble clusters when the image is reconstructed directly using the boundary measurement data. In order to improve the detection of clusters by the TMR-EMT system, a method to weaken the effect of the background is proposed. The equivalent magnetic circuit model is used to estimate the background permeability. Then the magnetic dipole theory and demagnetization effect theory are utilized to establish a simple background compensation model based on the estimated background permeability. Using the compensation model, the effect of the background is weakened from the boundary measurement data and the cluster distribution information is highlighted. Simulation and experimental results demonstrate the effectiveness of the proposed method.

Material removal model for magnetorheological polishing considering shear thinning and experimental verification

To establish a more accurate magnetorheological polishing material removal model, the shear thinning effect of magnetorheological polishing solution under high shear rate conditions was analyzed based on magnetic dipole theory, and the two-particle chain junction model was used to analyze the force of magnetic particles in magnetorheological polishing solution, and the shear yield stress of magnetic chain under tilted condition was obtained, and the magnetorheological polishing material removal model considering shear thinning was established by combining the modified Preston equation. The effect of shear thinning on the magnetorheological polishing material removal model was analyzed. The calculated results of the model are compared with the experimental data of magnetorheological polishing material removal, and the results show that the material removal model considering shear thinning can accurately predict the material removal rate of magnetorheological polishing, especially the trend of decreasing material removal rate of magnetorheological polishing at high shear rate is effectively predicted.

Non-contact electromagnetic controlled metamaterial beams for low-frequency vibration suppression

To address the challenge of suppressing extremely-low frequency vibration and noise in precision instruments and equipment, a novel non-contact metamaterial beams is proposed in this paper. The resonators of the metamaterial beams integrate negative stiffness mechanism and electromagnetic damping tuning system. Based on the magnetic dipole theory and the electromagnetic induction law, the mechanical model of magnetic resonator is established. The band structure and transmission spectrum of the metamaterial beams are obtained by transfer matrix method. Besides, the results of numerical simulations are used to verify the accuracy of theoretical results. The result shows that the negative stiffness can be controlled by nonlinear magnetic force among the magnets. Based on this mechanism, the bandgap frequency can be reduced to a minimum of 50Hz. Then, the method of combining electromagnetic damping and negative impedance circuit is proposed to form a tuning system which can reduce the initial frequency of the bandgap to 4Hz. Interestingly, the proposed bandgap control mechanism achieves the extremely-low bandgap while broadens the bandwidth relatively, which overcomes the deficiency of traditional quasi-zero-stiffness metamaterials that reduce the bandgap frequency while causing the bandwidth to narrow. This study is expected to provide valuable ideas for the application of metamaterials in the field of low-frequency vibration and noise reduction.

Research on magnetoelastic coupling model based on magnetic dipole theory

In this paper, a theoretical model of a magnetoelastic coupling magnetic dipole is established to analyse the influence of stress on the magnetic signal in magnetic memory testing. Based on the theory of ferromagnetism, the equivalent field strength under the combined action of stress and the magnetic field is determined and a numerical solution for the stress magnetisation of isotropic ferromagnetic materials under a weak environmental magnetic field is obtained. Based on the assumption of a double rectangular crack in a three-dimensional problem for the magnetic signal, a theoretical analysis model of a magnetoelastic coupling-type magnetic dipole is established. Based on the theory of the magnetoelastic coupling magnetic dipole, the influence factors and rules of the magnetic signal are analysed in detail. The theoretical research shows that the solution based on the theoretical model in this paper can explain some basic experimental phenomena and laws in magnetic memory inspection. The magnetic signal of a defect-free plate shows a 'horseshoe shape'. The length, width and height of the plate will affect Hx but have no effect on Hy . In addition, the lift-off value has a great influence on the magnetic signal of the plate. When the two cracks are a small distance apart, the magnetic signal of the plate is the superposition of the magnetic signals of the two cracks. For plates with cracks, the crack size, spacing, external magnetic field strength and stress will affect the magnetic signal of the plate.

Magnetic Dipole Model and Experimental Analysis of Magnetic Signal Detection Based on Magnetic Memory

By assuming that the magnetic charge is evenly distributed in the defect groove, the linear magnetic dipole is integrated in the depth direction of the defect, and the numerical calculation is carried out by using MATLAB to establish a two-dimensional magnetic dipole theoretical analysis model of double-correlated defects, which is suitable for analyzing the influence of stress on magnetic signal in the magnetic memory detection of rectangular and V-shaped combined macroscopic crack defects. To explore the influence factors and change rules of magnetic memory signal. In order to verify the correctness of the model analysis results, tensile tests were carried out on Q235 steel plate with double associated defects with different morphological characteristics, and the Hp(y) value of the normal component of the leakage magnetic field on the surface of the member was measured. The results show that the model based on magnetic dipole theory can explain some experimental phenomena and rules in magnetic memory detection.

Microscopic modeling of magnetorheological fluids containing spherical and ellipsoidal ferromagnetic particles

Based on the magnetic dipole theory, the study of the single-chain structure of ferromagnetic particles in magnetorheological fluids(MRFs), and the analysis of the scanning electron microscope(SEM) image processing of ferromagnetic particles, a micromechanical model of MRFs containing spherical and ellipsoidal ferromagnetic particles was established. MRFs with different particle volume fractions were prepared, the shear properties of MRFs under different magnetic induction strengths were tested, and theoretical and experimental data were compared. Varying the volume fraction of the ferromagnetic particles and magnetic induction strength in MRFs at constant temperature and shear rate, the shear stress increases with increasing particle volume fraction and magnetic induction intensity. The MRF micromechanical model containing spherical and ellipsoidal ferromagnetic particles is more accurate than the model with only single-size spherical ferromagnetic particles, and the accuracy is improved by 16.85%.

Reservoir water flooding evaluation based on electromagnetic wave logging permittivity and conductivity inversion

Electromagnetic wave logging at the measurement frequency of megahertz provides two kinds of information namely conductivity and permittivity, which is helpful to solve the problem of identifying water flooding situation of oil layers after long-term water displacement development. The electromagnetic wave combination logging tool in Daqing Oilfield measures two phase difference curves at frequencies of 60 MHz and 2 MHz. At present, there is still a lack of permittivity and conductivity inversion methods for this tool that are suitable for the interpretation of water flooding situation. Based on the magnetic dipole theory of uniform medium, the study found that for the combination logging tool, the 60 MHz phase difference is affected by both the permittivity and conductivity of the formation, while the 2 MHz phase difference is mainly affected by the conductivity. The reasonable and conveniently procedure for calculating the permittivity and conductivity from the inversion of the phase difference curves is constructed. Firstly, the shale content and porosity parameters of the layers are calculated from the curves of natural gamma and acoustic time difference, while the permittivity is calculated by a formula linearly constrained by shale content based on the permittivity of mudstone and oil-bearing clean sandstone. Secondly, for 2 MHz phase difference curve, a formula for calculating conductivity with known permittivity is established. Thirdly, set the calculated permittivity as the known parameter, a formula for inversion of the 2 MHz phase difference curve to calculate the conductivity is derived. Fourthly, using the inversion calculation of the conductivity as a known input, establish a formula for inversion of the 60 MHz phase difference curve to calculate the permittivity. In the process, the permittivity calculated by the shale content constraint method is used as the initial value of the iteration, which weakens the influence of mudstone on the permittivity and ensures the accuracy of the iteration. Finally, the permittivity and conductivity calculated by inverse calculation for two sealed coring wells can reflect the flooding situation of layers. The identification standard of flooding levels was established by using the conductivity and permittivity of inversion calculation, and the coincidence rate reached 90.7%, which is suitable for the effective identification of remaining oil in the long-term fresh water displacement layers. At the same time, based on the simplified theoretical model, the inversion of 3 combination of (2 MHz, 20 MHz), (60 MHz, 20 MHz), (2 MHz, 100 MHz) is carried out respectively, and the calculated values of remaining oil saturation are consistent with the injected water sweeping area, so the universality of the research method is verified.

Study on magnetostriction of ferromagnetic particles–superconducting matrix based on multi-chain model

Based on the magnetic dipole theory and the elastic mechanical plane strain method, this paper establishes a multi-chain model of ferromagnetic particle inclusions–superconducting matrix and investigates the effects of the distribution form of ferromagnetic particle inclusions and elastic parameters on the effective magnetostriction of superconductors. A dimensionless parameter is introduced to describe the spatial distribution form of ferromagnetic particles in the matrix, and the calculation is carried out using the elastic mechanical plane strain method. The change of the effective magnetostriction following the elastic parameter is given for three kinds of distribution forms: single-chain, planar–laminar, and spatial three-dimensional multi-chain, respectively. The results show that the distribution of ferromagnetic particle inclusions and the change of elastic parameters have a notable influence on the displacement and magnetostrictive distribution of superconductors.

The defect depth evaluation based on the dual-sensor strategy: Resisting the lift-off disturbance in magnetic flux leakage testing

The quantitative evaluation of defect information is the key issue in magnetic flux leakage (MFL) nondestructive testing on ferromagnetic materials. For the multi-sensor strategy with the same lift-off values, the arrayed layout of probes improves the testing efficiency, but the evaluation precision is still susceptible to the lift-off disturbance. This paper recommends a dual-sensor strategy with a given lift-off difference to resist the lift-off disturbance. Here, the reason for the possible overestimating and underestimating evaluation is clarified for the traditional single-sensor strategy using the magnetic dipole theory in MFL testing. In this paper, the effectiveness of the proposed dual-sensor strategy is demonstrated by comparison with the traditional single-sensor strategy. Analysis shows that the proposed dual-sensor strategy in MFL testing can overcome the lift-off disturbance and improve evaluation precision of the defect depth in cases with uncertain lift-off values. This study provides a path for the quantitative evaluation of MFL testing based on the dual-sensor strategy.

Magneto-controlled friction behaviors of magnetorheological elastomers with cosine-shaped surface structure

This study investigated the friction behaviors of magnetorheological elastomers (MREs) with cosine-shaped surface structures under the magnetic field. First, a magneto-controlled friction model for such MREs was proposed, and the friction coefficient was determined using the friction binomial theory and magnetic dipole theory. Then, the effects of the amplitude and wavelength, and magnetic field on the friction coefficient were analyzed. Finally, MRE-glass sliding friction behaviors were investigated by using the newly established test rig. It was found that the contact stiffness and friction coefficient of the MREs decreased with increasing amplitude and decreasing wavelength, respectively, which was consistent with the theoretical model. Moreover, the variation rate of the friction coefficient was up to 41% under magnetic field regulation.

Effect of ferromagnetic particles on the elastic and magnetostriction parameters of bulk superconductors

Based on the magnetic dipole theory and the Eshelby's equivalent inclusion theory, a theoretical model of ferromagnetic particle inclusion-superconducting matrix is established in this paper, intrinsic strain is introduced and uniform stress boundary conditions are used to calculate the mechanical properties of the composite material. The effects of changes in parameters such as the elastic modulus, volume fraction ratio, and magnetic field of ferromagnetic particle inclusions on the effective mechanical properties of bulk superconductors such as the effective elastic modulus, effective Poisson's ratio, and effective magnetostriction were compared in detail, providing a theoretical reference for the preparation of superconducting materials containing ferromagnetic particle inclusions.

Research on magnetic signal of cracks in girth weld of ferromagnetic pipeline

The crack of pipeline girth weld is one of the most common and dangerous defects in girth weld. According to the magnetic dipole theory model, the magnetic signal model of pipeline girth weld cracks is established. By means of numerical simulation, the distribution characteristics of magnetic signals of crack defects in girth welds and the variation rules of magnetic signals of different flaw sizes and lifting heights of girth welds were studied. The simulation results show that the normal component Hy appears zero crossing and changes direction, and the tangential component Hx appears extreme value upward. Finally, the magnetic signal model of crack defects in pipeline girth weld was verified through field engineering test. The actual magnetic induction intensity detected at the flaw of pipeline girth weld was basically consistent with the theoretical calculation results, which verified the accuracy of the model.

Magneto-mechanical properties of anisotropic magnetorheological elastomers with tilt angle of magnetic chain under compression mode

Characterization of mechanical properties of magnetorheological elastomers (MREs) is essential for the design of smart materials and devices with customized features and functionalities. While the properties of MREs under shear mode have been extensively researched, MREs with tilt angle under compression mode have been less exploited. In this study, a magneto-mechanical model of anisotropic MREs is established based on magnetic dipole theory and energy method considering the reconfiguration effect of compressive strain on the microstructure of the magnetic chain. This leads to the provision of a dynamic magneto-mechanical model of the anisotropic MREs, incorporating the magneto-induced mechanical model, by using the robust fitting method. Experiments were conducted to assess the force–deflection (stress–strain) characteristics of MREs with tilt angle under compression mode, subject to the regulation of the tilt angle of magnetic chain, magnetic flux density, and mass fraction of magnetic particles. The magnetic-induced modulus, obtained from the theoretical model, is experimentally verified through magneto-mechanical testing, alongside an analysis on the dynamic mechanical properties under different dynamic strain amplitudes and frequencies. The mean square error (MSE) in terms of magneto-mechanical storage modulus in the robust fitting ranges from 2.73% to 10.86%. Experimental results also show that the range of magneto-induced stress (typically from 178 KPa to 74.6 KPa) decrease when the tilt angle of the magnetic chain increases (from 15° to 25°) corresponding to 60% mass fraction. The compression strain of the anisotropic MREs, affecting both the spacing of adjacent magnetic particles and the tilt angle of magnetic chain, causes significant changes in the magnetic-induced modulus. In addition, the hysteresis loops under different deformation (Mullins effect) show an increasing energy dissipation with decreasing tilt angle.

Magnetic field-induced variation of solid/liquid interfacial energy of solid Al2Cu and Al-Cu eutectic melt

We investigated the effect of static magnetic field (SMF) on interfacial energy of solid Al2Cu and eutectic melt both by dihedral angle and grain boundary groove method. To uncover the effect of SMF on the interfacial energy, its values were determined and calculated based on the morphologies of dihedral angles and grain boundary grooves. A variation of solid/liquid interfacial energy with SMF up to a factor of three was found experimentally. We found that the solid/liquid interfacial energy experienced a declined trend with increasing SMF under both cases. While in grain boundary groove method, the dramatic decrease of solid/liquid interfacial energy with 0.5 T magnetic field was owning to thermoelectric magnetic convection at the scale of sample. At a high intensity (12 T), thermoelectric magnetic convection at the scale of grain boundary groove and thermoelectric magnetic force in solid were supposed to be responsible for the slight increase of solid/liquid interfacial energy. Determined by two methods, the decreased intrinsic solid/liquid interfacial energy was explained with the magnetic dipole theory and structural ordering based on Ewing’s model. We clarified some conflicting and ambiguous experimental phenomena in magnetic field-induced solid/liquid interfacial energy variation. This study provides consolidate evidence that the SMF is capable of affecting the solid/liquid interface energy.