Generalized formulation for the description of hysteresis in softmagnetic materials

Presents a phenomenological formulation that broadens the range of applicability of the Basso-Bertotti hysteresis model to include soft magnetic materials with very gradual saturation, such as commercial manganese-zinc (MnZn) power ferrites. The formulation also enables the Basso-Bertotti model to better characterize both the major loop and the minor loops of these soft magnetic materials. The formulation introduces a model parameter m_t that defines the transition between low fleld/minor loops and high field/major loop. An explicit expression for magnetization in term of domain-wall position was synthesized to make the hysteresis model numerically attractive. The formulation was verified by experimental data of commercial MnZn ferrites     

通过改进的制备工艺提高FINEMET纳米晶磁粉芯的磁性能及其机理

通过对比实验研究了改进的制备工艺下FINEMET纳米晶磁粉芯的磁性能,并探讨了其相应的物理机制。采用扫描电镜、透射电镜和X射线衍射仪检测磁粉的表面形貌、内部结构和晶格畸变,采用B-H分析仪检测磁粉芯的动态磁性能。结果表明,改进的制备工艺能够有效降低磁粉芯的损耗,提高磁导率和频率应用范围。延长非晶粉末的球磨时间能够降低磁粉芯的磁滞损耗和涡流损耗,最佳的球磨时间为8h。通过对比磁粉的晶格畸变,发现通过改进工艺制备的磁粉的晶格畸变相对较小,该工艺提高磁性能的原因在于磁粉残余内应力的有效释放。     

Analysis of Minor Hysteresis Loops of Cold Rolled Low Carbon Steel

Minor hysteresis loops of cold rolled low carbon steel have been analyzed in connection with the rolling reduction. We found several simple relations between parameters of minor loops and obtained minor-loop properties that are independent of magnetic field amplitude and magnetic field. The properties increase with increasing rolling reduction and are in proportion to coercive force of the major loop. The present analysis method using minor loops can be applied to quantitative nondestructive evaluation of dislocation density in ferromagnetic materials     

Low Temperature and High Magnetic Field Dependence and Magnetic Properties of Nanocrystalline Cobalt Ferrite

The DC magnetic hysteresis loop measurements were carried out for temperatures varying from 5 to 300 K over a field range of ±10 T on nanocrystalline (～35 nm) cobalt ferrite samples (crystallized to \(Fd\bar {3} m\) space group with cubic symmetry) to validate the law of approach at low temperature for the nanocrystalline cobalt ferrite. A magnetocrystalline anisotropy constant and saturation magnetization have been obtained by analyzing the magnetization curve in saturation using the “law of approach (LA) to saturation.” The magnetocrystalline anisotropy constant is found to be almost constant in the temperature range of 5 to 150 K due to the freezing of spin at low temperature. Also, spin freezing leads to a decrease of coercivity with the increase in the temperature.     

The Dominant Influence of Plastic Deformation Induced Residual Stress on the Barkhausen Effect Signal in Martensitic Steels

The paper presents the results of investigation of the influence of plastic deformation on the magnetic properties of martensitic steel (P91 grade). The properties of the hysteresis loops as well as of the Barkhausen effect (BE) signal are analysed for both tensile and compressive loading up to \(\varepsilon = 10\)% of plastic deformation. The choice of the steel and of the deformation range is unique, since for such combination one can expect high residual stresses (both compressive and tensile) in the material that does not exhibit saturation of the BE intensity as a function of elastic stress. The obtained relationships show that for the low level of deformation the dislocation density changes may play a dominant role, yet for higher deformation level the residual stress becomes a dominant factor. It leads to the strong decrease of the BE signal for tensile deformation and an increase for the case of compression. It agrees well with the assumption that the tensile plastic deformation results in the compressive stresses appearance in the soft (magnetically active) sub-regions of the material whereas for the compression one can expect a residual stress of a tensile nature in those areas. Both deformation modes result in the increase of coercivity of the samples, yet the increase observed for the tensile deformation is significantly higher since both the residual compressive stress and increase of dislocation density have a strong effect on the material coercivity. The change of the hysteresis loops steepness agrees well with the notion of the dominant role of residual stresses too.     

Temperature compensation and scalability of hysteretic/anhysteretic magnetic-property sensors

Non-destructive/noncontact stress sensors based on magnetoelastic principles have numerous applications for monitoring cable stress. However, their widespread use is hampered by problems related to temperature compensation and to scaling of calibration data to large cables, which is the domain of greatest interest. In this paper, experimental magnetic property and thermal response data are obtained and analyzed to address these problems. The magnetic property data include initial curves, major hysteresis loops, and anhysteresis curves, all obtained quasistatically. The thermal response data are presented in the form of a dimensionless correlation which is valid over a range of Reynolds numbers. Comparison of data indicates the feasibility of using absolute magnetic property measurements as the basis for direct calibration of large sensors.     

An inelastic constitutive model of blood vessels

Summary The present paper is concerned with the formulation of a constitutive model describing the hysteresis loops of stress-strain relations of blood vessels under cyclic loading conditions. It is assumed that the hysteresis loop is composed of elastic deformation and viscoplastic deformation. Hence the total strain is expressed as the sum of the elastic part and the inelastic part on the basis of a finite deformation theory. Then the elastic part is established by postulating a strain energy function of an exponential type, while the inelastic part is formulated by modifying the nonlinear kinematic hardening rule in the viscoplastic model proposed by Chaboche et al. A comparison of the numerical result with the literature shows that the present model can describe the hysteresis loop qualitatively.     

Spin Turbulence Made by the Oscillating Magnetic Field in a Spin-1 Spinor Bose-Einstein Condensate

We numerically study spin turbulence made by the oscillating magnetic field in a two-dimensional homogeneous spin-1 spinor Bose-Einstein condensate. We confine ourselves to the case of the ferromagnetic interaction, where the ground state is ferromagnetic. By the oscillating magnetic field along some direction makes the system unstable. At first, the spin density vector revolves in the plane perpendicular to the magnetic field, exciting long-wavelength modes. Secondly, appear some vector components along the magnetic field. Finally, the system becomes spin turbulence. In terms of the energy spectrum of the spin-dependent interaction energy, the peak appears first at low wave number region. Gradually, the peak shifts from low to high wave number region. Eventually, the spectrum exhibits the ?7/3 power law. The ?7/3 power law is confirmed by the scaling analysis using the hydrodynamic equation of the spinor Bose-Einstein condensate.     

磁悬浮运动中电磁铁磁滞特性的非线性影响研究

超精密磁悬浮运动控制中,电磁铁铁心及衔铁导轨中存在的磁滞特性是导致电磁力难以实现精确控制的重要原因之一.研究磁滞特性对电磁力的非线性影响规律并建立其非线性模型具有重要意义.通过研究磁悬浮精密运动中电磁铁磁滞特性对气隙处磁感应强度的影响,分析了带气隙磁路磁滞特性建模原理,建立了包含Jiles Atherton模型的电磁铁磁浮力非线性模型,并采用粒子群优化算法对该模型参数进行实验验证.结果表明,磁悬浮精密运动中电磁铁磁滞特性不容忽视,采用经参数辨识得到的新模型比采用传统模型计算得到的气隙磁感应强度值更精确、更接近实测值.研究结果为提高磁悬浮精密运动中电磁力的精确控制提供了重要参考价值.     

Identification method for a circuit model of scalar static hysteresis

We present a new identification procedure for a hysteresis model based on nonlinear circuit cells. The response of elementary cells is equal to a generalized play operator. The procedure identifies exactly the limit symmetric hysteresis loop and can minimize the reconstruction error on minor loops. We present test cases for three different soft magnetic materials with peculiar behavior and we discuss the results.     

Magnetic properties of GdBa2Cu3O7crystals in high magnetic field

The magnetic properties of single crystals of GdBa₂Cu ₃O₇ were investigated in a magnetic field of up to 20 T applied parallel to the c axis in the 1.7-300 K temperature range. In the superconducting state, the field and temperature dependences of the critical current densities were deduced from the hysteresis of the half-cycle using Bean's critical state model. The Gd³⁺ paramagnetic moment was then studied. Above about 20 K, the M(H) isotherms were found to be given, at different temperatures, by the Brillouin function of the free Gd³⁺ ion. Below 20 K, the average magnetization does not obey the Brillouin law. The normal-state susceptibility was described by the free-ion Curie-Weiss law     

Scaling law for the ac losses of multifilament superconductors

It is experimentally and theoretically shown that the overall losses of a multifilament superconductor in an applied ac magnetic field can be described by a general scaling law. The losses depend only on a reduced frequency. This scaling law makes the prediction of the ac losses and the design of multifilament superconductors easier.     

Rotational hysteresis in ticonal alloy

Anisotropy constants and rotational hysteresis have been investigated at different stages of optimal heat treatment on 8-mm-diameter spherical samples. The changes in the uniaxial anisotropy constant obtained upon tempering are in good agreement with the respective changes in coercive force. Rotational hysteresis has been measured in the range from 400 to 28 800 Oe. Two maxima have been obtained on the curves of the rotational hysteresis versus field after all heat treatments. The first maximum is interpreted in terms of reversal magnetization of single-domain precipitates in a low magnetic matrix. The nature of the second maximum is not clear.     

The effects of stress on a ferromagnet on a minor hysteresis loop

Reversible and irreversible changes in magnetization due to stress on a minor hysteresis loop were studied at various magnetic field strengths. It was found that the irreversible changes were not always directed toward the principal anhysteretic, contrary to Jiles and Atherton's hypothesis (1986). Also, two different demagnetization methods were used within the minor loop to test the existence of postulated offset anhysteretic curves. The results of asymmetric demagnetizations seemed to support this suggestion     

Constitutive and damage modelling of H11 subjected to low‐cycle fatigue at high temperature

Hot‐work tool steel H11 is extensively applied in extrusion industries as extrusion tools. The understanding of its mechanical properties and damage evolution as well as failure is crucial for its implementation. In this paper, a finite element (FE) model employing Chaboche unified constitutive model and ductile damage rule is proposed to simulate the mechanical responses of H11 subjected to low‐cycle fatigue (LCF). Accumulated inelastic hysteresis energy is adopted to demonstrate the impact on damage initiation and evolution rules. A series of tension and LCF experiments were conducted to investigate H11's mechanical properties and its deterioration processes. In addition, to deeply understand the deformation and damage mechanism, scanning electron microscope (SEM) investigations were performed on the fracture section of gauge‐length part of the specimen after failure. Furthermore, the parameters in both constitutive model and damage rule are identified based on experimental data. The comparison of the hysteresis loop of the first cycle and stable cycle with different strain amplitudes demonstrates that the Chaboche constitutive model provides high precision to predict the evolution of mechanical properties. Based on the reliable achieved constitutive model, LCF behaviour prediction with damage rule was executed successfully using FE model and gains a good agreement with the experiments. It is believed that the proposed FE method lays the foundation of structure analysis and rapid design optimization in further applications.     

Ultra‐low cycle torsion fatigue of annealed copper

Torsion experiments show that pure annealed copper is able to withstand very high plastic strain amplitudes when it is loaded cyclically with less than 30 cycles to failure. Under these ultra‐low cycle fatigue conditions, the performance of copper is significantly better than that of the annealed steels A36 and AISI 304, which were also tested in this study for comparison. The dependence of fatigue life on strain range can be described by a power law. In the case of an initial overloading, fatigue life can be estimated using the Palmgren–Miner rule. The long low cycle fatigue life of copper is explained by a thermally activated softening mechanism which takes place while the material heats up as a result of the cyclically repeated plastic deformation. The softening is accompanied by a change in microstructure. The low cycle fatigue properties of copper can be utilized for designing hysteretic dampers for seismic protection.     

Computational analysis of PTFE shaft seals

An endochronic viscoplastic approach, derived from the theory of finite viscoplasticity based on material isomorphisms, is presented, in order to describe the nonlinear material behaviour of filled polytetrafluoroethylene (PTFE) in a computational analysis of PTFE shaft seals. The model allows to characterize viscoplastic material behaviour with an equilibrium hysteresis using a rate-independent elastoplastic model (with an endochronic flow rule and a logarithmic elastic law) in parallel connection with a nonlinear Maxwell model. Due to the endochronic flow rule, an elastic range limited by a yield stress is not needed in the present approach. The volumetric stress contribution is assumed to be purely elastic. The proposed model is applied to simulate the mounting process of PTFE shaft seals in an axially symmetric finite element analysis. The numerical results (radial force, pressure in the contact zone) are in fair agreement with the experimental data.     

Dynamic scaling function of polarization hysteresis in ferroelectric thin films

The scaling behavior of the polarization hysteresis dispersion in a mode spin-like system based on the three-dimensional (Φ²)² model with O(N) symmetry in the limit N → ∞, upon applying of the time-varying electric field, is investigated. We perform a simple analysis on the dynamic relaxation of the polarization and propose a scaling function in order to describe the scalability of the hysteresis dispersions over a wide range of field magnitude. The applicability of this scaling function is demonstrated by a consistent fitting to the experimental data on several types of ferroelectric thin films.     

An investigation of the hydrodynamic similarity of single-spout fluidized beds using CFD-DEM simulations

The applicability of the hydrodynamic similarity criteria (scaling law) introduced by Glicksman (1988) was investigated using fully coupled Computational Fluid Dynamics and Discrete Element Method (CFD-DEM) simulations for single-spout fluidized beds. Four test cases were performed to investigate the scaling law in a pseudo-2D spouted-fluidized bed. In addition, the applicability of Glicksman’s scaling law for simulating 3D fluidized beds was studied. In all simulations, characteristic dimensionless groups, i.e. the Reynolds number (Re), Froude number (Fr), particle-to-fluid density, bed initial height to particle diameter and bed width to particle diameter were kept constant for the both base and scaled cases. Comparing the time averaged particle velocities, gas velocities and volume fractions between the base and scaled cases indicated a very good overall hydrodynamic similarity for all test cases. A minor discrepancy observed between the simulation results of the base and scaled cases was explained by a force analysis.An advantage of the scaling approach, i.e., reducing computational time, was also presented in the last four test cases, including a large-scale simulation, showing that this approach can be considered as a promising way to simulate large-scale spouted-fluidized beds.