Hysteresis Loss Factor Research Articles

Preparation and Magnetic Properties of Low-Loss Soft Magnetic Composites Using MgO-Phenolic Resin Coating.

Optimizing the interface between a magnetic powder matrix and an oxide-insulating layer is an effective method to improve the permeability and lower eddy current loss of iron-based soft magnetic composites. In this study, in order to improve the bonding strength of the substrate and insulation layer, soft magnetic composites were prepared by pressing and heat treating with reduced iron powder as a magnetic matrix, high-temperature MgO nanoparticles as insulating coating, and phenolic resin as an adhesive. The effects of MgO content on the microstructure and magnetic properties of the composites were investigated. The results of a scanning electron microscopy and an energy-dispersive spectrometer analysis corroborate that the results obtained regarding the frequency characteristics and the resistivity of the iron powder agree with the scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) analysis and confirm their improvement by the presence of an insulating layer of MgO. The resistivity of the sample coated with 4 wt.% MgO is nearly 45 times higher than that of the uncoated sample under the same conditions. The MgO-insulating film formed on the surface of iron powder makes the coated sample have low effective grain size, high resistivity, and low magnetic loss at a high frequency. At 1 kHz, the magnetic loss of the 4 wt.% MgO-coated sample is reduced by 77.3%, and the magnetic loss is only 5.8% compared with the uncoated sample at 50 kHz. This magnetic loss separation study shows that the addition of MgO insulation material can effectively reduce the eddy current loss of the magnetic powder core. The 4 wt.% MgO-coated sample has the lowest hysteresis loss factor and relatively low eddy current loss factor, so it can be determined that the addition of 4 wt.% MgO is the optimum content to attain a low magnetic loss.

Simulation of β‐dextranase from raw natural rubber to investigate structure and properties of natural rubber/halloysite composites

AbstractThe effects of crude β‐dextranase in raw natural rubber (NR) on the structure and properties of NR/halloysite nanotube (HNT) composites are investigated by introducing external biological β‐dextranase. Results of curing tests as well as mechanical and dynamic mechanical analyses show that the curing time of the composite increases with β‐dextranase concentration and then plateaus at 6 wt%, at which the maximum values of the elastic modulus, tensile strength, and crosslink density are achieved and the lowest hysteresis loss factor at 0–80°C is observed. Morphological investigations show that the addition of β‐dextranase improves the dispersion of HNTs and enhances interfacial adhesion in the composites owing to hydrogen bonds between β‐dextranase and HNTs, as revealed by Fourier‐transform infrared spectroscopy, X‐ray diffraction, and X‐ray photoelectron spectroscopy analyses. We envision the use of β‐dextranase in NR as a novel interfacial modifier in NR composites.

Hybrid Phosphate-Alumina Iron-Based Core-Shell Soft Magnetic Composites Fabricated by Sol-Gel Method and Ball Milling Method

Novel Fe-based soft magnetic composites (SMCs) with hybrid phosphate-alumina layers were prepared by both sol–gel and ball-milling methods. The effects of the fabrication methods and the addition of Al2O3 particles on the microstructure and the soft magnetic performance of SMCs were studied. The formation of the hybrid phosphate-Al2O3 shell not only leads to the decrease of the total core loss, but also results in the reduction of the permeability and saturation magnetization. However, the degree of decrease caused by the different methods were not identical. The sample with 8% Al2O3 prepared by the sol–gel method showed the best magnetic performance, exhibiting a high-amplitude permeability (μa) of 85.14 and a low total core loss (Ps) of 202.3 W/kg at 50 mT and 100 kHz. The hysteresis loss factor and the eddy current loss factor were obtained by loss separation. The results showed that the samples with the same Al2O3 content prepared by different methods exhibited almost the same total core loss. However, the contribution of the hysteresis loss and the eddy current loss showed an obvious difference in behavior because of the change of the particle shapes and the refinement of the particle size during the ball-milling process.

Analysis of Hinge’s Hysteresis Based on Response Surface Method

The hinge, a key component of deployable space mechanism, has a significant influence on the precision of the whole mechanism. Hysteresis is one of the uncontrollable factors affecting the precision of the hinge. However, much work so far has focused on the equivalent model of hysteresis, which is far from the actual situation. In this paper, the hysteresis model of the general rotary hinge was established via the finite element method (ABAQUS/Standard 6.14-4). The correctness of the model was verified by experiments, and the loss factor was defined to measure the size of hysteresis. The response surface method was then used to establish the response surface of the hysteresis loss factor of the general rotary hinge. Results show that the hinge was optimised. By comparing the response surfaces of the two types of hinges, the modified hinge can effectively reduce hysteresis loss factor. Importantly, the repeatability of the hinge can be effectively improved by reducing hysteresis loss factor through repeatability experiments. Using this method, the response surface of the hinge's hysteresis loss factor can be established accurately, and the hysteresis loss factor can be reduced through optimal design to improve the precision of the hinge. This method can provide reference and guidance for the hinge design of the high-precision deployable mechanism.

Experimental Characterization of the Temperature Influence on the Stiffness and Damping of a Field-Cooled Superconducting Magnetic Suspension

Superconducting magnetic levitation has been used in contactless mechanical components for different applications like bearings or positioning devices. This technology is currently being investigated for its potential use as a vibration isolation and thermal disconnect passive mechanism to support the focal plane array of the ESA ATHENA scientific telescope. Although it is well known that superconducting levitation properties depends on temperature, theoretical models have difficulties with complex bearing geometries or capturing inhomogeneity in material properties. In addition, experimental studies focused on the characterization of the mechanical properties of superconducting magnetic bearings are scant and mostly carried out with zero-field-cooled thrust bearing configurations. In order to increase the maturity of the technology for its potential use in space applications, further experimental research of the superconducting levitation properties at different temperatures is required. In this paper, we present the results of an experimental study of the levitation mechanical properties of a journal superconducting suspension in a high vacuum and temperatures from 90 to 12 K. Axial stiffness quadratically increases at lower temperature and linearly in the radial direction. However, the hysteresis loss factor decreases when decreasing the temperature for both axial and radial directions of displacement. These results demonstrate that the temperature influence on superconducting levitation systems is significant, and thus, mechanical engineers must consider it for design of superconducting levitation systems subjected to temperature variations.

Prediction of colloid detachment in a model porous media: hydrodynamics

Understanding the mobility of colloids through porous media is important in both engineered and natural applications. This study employed a model system to explore physically based colloid detachment. Polystyrene colloids were attached in the primary minimum to glass beads in a packed column, and a residually attached fraction was subsequently detached via hydrodynamic shear. Colloid fractions released from the surfaces in the porous media were experimentally quantified. A flowrate of 75 ml/min detached 50% of the residual colloid fraction from the surface. The residual colloid fraction released was predicted with a model incorporating an interaction energy distribution and system physics. In this model, detachment is realized when the applied rolling moment from hydrodynamic shear overcomes the resistance associated with rolling. With the exception of one parameter, the hysteresis loss factor, system characteristics were described a priori. Using the hysteresis loss factor and interaction energy distribution developed from extended-DLVO theory, the detachment of the residual colloid fraction from the packed bed was well predicted. This work decomposes colloid detachment into the constitutive mechanisms dependent upon thermodynamics and hydrodynamics.

An Investigation of Free Rolling Resistance at Light Loads

This paper presents the results of an investigation into the resistance to free rolling, under light loads, of a ball bearing ball on a flat track of unhardened En 31 steel using a pendulum arrangement in partial vacuum (5 – 50 Pa). The effect of air resistance (from experiments conducted in air) is demonstrated and results of tests at different frequencies and loads are presented. These include estimates of the effective hysteresis loss factor and of the coefficient of rolling resistance. A detailed examination of the amplitude decay curves shows that the damping, under the experimental conditions described, (i) can be represented neither by the Coulomb nor the viscous models; (ii) is practically independent of frequency (within the limited range possible with the apparatus); (iii) is appreciably dependent on contact load and oscillation amplitude, especially at the higher end of the load range investigated where a gradual transition to plastic behaviour is evident.

Hysteresis losses in rolling and sliding friction

Previous work on the mechanism of rolling friction has shown that it is mainly due to elastic hysteresis losses in the rolling elements. Under conditions of uniform tension or torsion it is generally assumed that the energy dissipated by hysteresis is a constant fraction (the hysteresis loss factor) of the elastic energy introduced during the cycle. This elastic input energy has been calculated for a hard cylinder or sphere rolling on rubber, and with the above assumption expressions have been obtained for the rolling friction. These expressions predict correctly the dependence of rolling friction on load, ball or cylinder diameter and elastic constants of the rubber. However, the absolute values of the frictional force are too small. The experimental values are two to three times the theoretical estimates. This suggests that it is invalid to use the hysteresis loss factor, as measured in a simple deforma­tion cycle, for more complex cycles such as those involved in rolling. For a thin-walled rubber tube to which tensional and torsional stresses could be applied, the hysteresis energy losses for complex stress cycles were measured. In such a system there are two relevant shear stresses which contribute to hysteresis losses; if these are plotted graphically, a deformation cycle can be expressed by a stress diagram which, in general, will form a closed loop. A hypothesis is put forward which suggests that the losses in the cycle are proportional to the square of the length of this loop. An investigation of different types of stress cycle show that this hypothesis may be used fairly reliably to estimate energy losses in complex stress cycles. In particular it may be shown that if the rubber is deformed in such a way that its elastic strain energy is constant throughout the cycle, marked hysteresis losses occur. The earlier concept would predict no energy loss. This result is of general importance and explains the earlier discrepancies between theoretical and experimental values for the friction of rolling cylinders and spheres. Although this hypothesis has limitations (these and alternative hypotheses are discussed) it is applicable to the deformation of material by a hard roller and an analysis is given for a long cylinder rolling on rubber. It is shown that the losses are over three times as great as those deduced from the earlier concept and for a spherical roller the loss is about twice as great as earlier estimates. This is in good agreement with experiment. The analysis is extended to the case of rolling over short distances and it is shown that the resistance increases linearly from zero as a cylinder, starting from rest, commences to roll. An experimental study indicates that this is approximately true. Only when each element has passed under the roller and out of the contact region does the hysteresis loss reach its maximum steady-state value. For minute displacements of a roller, there is evidence that adhesion may not be entirely destroyed, and though, in general, rolling friction is dominated by hysteresis losses, it is suggested that under these limiting conditions the effect of adhesion may not be negligible.

Natural Rubber Compounds for Intermittent Low Temperature Service

Abstract The changes in physical properties of rubber vulcanizates on approaching the so-called second order transition temperature are discussed and distinction is drawn between these phenomena and those associated with crystallization. A simple apparatus of the torsional pendulum type is used to determine the dynamic stiffness and hysteresis loss factor at a frequency of about 0.5 c.p.s. of vulcanizates in the temperature range 20 to −120° C. A large number of liquids are examined as potential plasticizers for lowering the rubber to glass transition temperature and a number are shown to have a high order of efficiency in this respect. Of these materials some also conform to the overriding requirements of low volatility and adequate compatibility with rubber. The loss in physical properties consequent on increase of plasticizer content is not markedly different for most of the plasticizers. Di-iso-octyl adipate is representative of the liquids which give useful low temperature plasticization and a number of commercial type compounds are developed using this plasticizer with carbon black or silica reinforcement, some of these have transition temperatures approaching those of the silicone rubbers but with a better level of general physical properties. A tentative theoretical treatment for the low temperature plasticization of nonpolar rubbers is discussed and this leads to a law which has been found to predict fairly well the transition temperature of a plasticized natural rubber compound in terms of the index of variation with temperature of the plasticizer viscosity.