Micromagnetics of laminated Permalloy films

The edge curling wall (ECW) is observed in an optical Kerr microscope. Conditions are derived energetically favoring single transverse domains with ECWs over other multiple closure domains or single longitudinal domains that are undesirable because of their low permeability. Computed figures illustrate how the maximum permissible spacer thickness depends on Permalloy sublayer thickness, uniaxial anisotropy, width of the magnetic strip, mismatch of Permalloy thickness, and perpendicular anisotropy. The case with strip width W=100 mu m and vanishing magnetostriction or stress should require only a few sublayers. However, if W is very small, or if stress-induced or some other form of perpendicular anisotropy is excessive, then attainment of single transversely magnetized domains requires many sublayers. Some of these conclusions are supported by microscopic observations.<>     

Micromagnetics of Ni-nanowires filled in nanochannels of porous silicon

An array of ferromagnetic nanowires embedded in silicon is fabricated using an anodizing and electroplating process. During the former one oriented porous silicon channels are fabricated whereas by the latter process Ni is incorporated into these channels. The electrodeposited Ni-wires have a great pore-length to pore-diameter (aspect) ratio up to 1000 : 1 (typical diameters between 10 and 60 nm, pore-length from 10 to 30 μm). Due to this property the samples exhibit a magnetic perpendicular anisotropy. The micromagnetic properties of Ni (e.g. Bloch-wall thickness) are responsible for the peculiar magnetic behaviour of this ferromagnet/silicon nanocomposite. Structural as well as magnetic investigations like scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDXS), and SQUID-magnetometry display this nanocomposite as a bimodal ferromagnetic structure consisting of perpendicularly oriented Ni-wires and of single domain Ni-granules embedded in the silicon based matrix. The hysteresis curve outlines a two-fold magnetic switching, one at low fields (∼0.05 T) and the second at high fields (> 3 T). The micromagnetic magnetization reversal is treated in terms of an analytic formulation.     

Micromagnetics of Ferromagnetic Nano-Devices Using the Fast Fourier Transform Method

Micromagnetic simulations are widely utilized to simulate magnetic properties of magnetic materials, performance of magnetic devices, and read/write processes in recording systems. In hard disk drives, the minimum size of devices is now scaled down to the nanometer region; therefore, micromagnetics should be accurate enough to include the edge effects in these ferromagnetic nano-devices. In this work, we consider devices with flat structures. The analytical forms of demagnetizing matrices for intra-cell and inter-cell interactions are calculated for cubic and right-angle triangular prism cells respectively, which enables accurate magnetostatic interaction calculation using fast Fourier transform (FFT) method in thin film devices with arbitrary geometry. Besides, the parallel computational method is included to speed up the programs. Two examples about the switching characteristics of ferromagnetic devices are given in this paper to evaluate the accuracy of the improved FFT methods: one is a hard magnetic nano-dot; the other is a write pole tip for perpendicular recording.     

Measurement of rotating flux in silicon iron laminations

A method of calculating the magnitude and direction of the instantaneous flux density in a thin lamination of magnetic material is described. The technique was demonstrated by measuring the rotating flux in samples of mild steel, grain-oriented silicon iron, and at a point in the T-joint of a three-phase, three-limbed transformer core. The flux in the mild steel sample was found to rotate at a constant angular velocity and to be constant in magnitude. In the silicon iron sample, and at a point in the T-joint, the flux density varied both in angular velocity and magnitude. A large 150 Hz component of rotational flux was found to cause high localized power loss in the T-joint. The power loss was measured using the "initial rate of rise of temperature method" and was compared with the predicted rotational hysteresis loss.     

Optimal laminations of thin underwater composite cylindrical vessels

This paper deals with the optimal design of deep submarine exploration housings and autonomous underwater vehicles. The structures under investigation are thin-walled laminated composite unstiffened vessels. Structural buckling failure due to the high external hydrostatic pressure is the dominant risk factor at exploitation conditions. The search of fiber orientations of the composite cylinders that maximize the stability limits is investigated. A genetic algorithm procedure coupled with an analytical model of shell buckling has been developed to determine numerically optimized stacking sequences. Characteristic lamination patterns have been obtained. FEM analyses have confirmed the corresponding significant increases of buckling pressures with respect to initial design solutions. Experiments on thin glass/epoxy and carbon/epoxy cylinders have been performed. The measured buckling pressures appear to be in good agreement with numerical results and demonstrate the gains due to the optimized laminations.     

Effects of stresses on magnetic properties of silicon-iron laminations

The magnetic properties of grain-oriented 3 1/4% silicon-iron, as used in laminated transformer cores, are extremely sensitive to mechanical stresses. Power loss and magnetostriction (the cause of core vibration and noise) are most affected by compressive stresses. The theoretical effects of different types of stress on the domain structures of silicon-iron are correlated with measurements made on single laminations and transformer cores. The ways in which stresses can arise in cores and possible methods of avoiding or eliminating them in practice, are discussed.     

Magnetic domain refinement of silicon-steel laminations by laser scribing

Laser scribing of 3% silicon steel laminations was carried out using three different lasers: a KrF excimer laser, a pulsed Nd:YAG laser and a continuous wave CO₂ laser. The processing parameters included the energy fluence at the surface of the workpiece, pulse repetition rate and pulse separation distance (for the pulsed lasers), scan separation distance and scan direction. The samples were tested for hysteresis loss, permeability, coercivity, remanence and saturation induction before and after laser treatment. An overall improvement in the core loss was observed in the laser-scribed samples. The best improvement in core loss was obtained in excimer laser scribing on the rolling direction and CO₂ laser scribing in the transverse direction. Three mechanisms were proposed to explain the improvement in energy efficiency characteristics of the silicon-steel samples: magnetic domain refinement, stress relaxation and inhibition of domain-wall movement. Domain refinement, namely the formation of subdomains, results from the shocks induced by the beam. Laser scribing also relieves the stresses that are induced in the material during manufacture. The scribe lines increase the surface resistivity of the material, resulting in reduced eddy current loss. Tensile stresses are created between the laser scribe lines that elongate the domains and serve to refine the domain-wall spacing thus inhibiting the wall movement and reducing core losses.     

Embrittlement of electrical steel laminations by nitrogen pick-up during heat treatment

Heat treated electrical steel laminations have shown evidence of low ductility behavior, characterized by a small number of bends till fracture, on repeated bending tests. The laminations were produced using a new grade of electrical steel with much lower aluminum content than usual. The problem happens when the oxygen potential (measured by the dew point of the atmosphere) of the heat treatment atmosphere is abnormally high. Furthermore, ductility can be restored by a low-oxygen potential heat treatment. Although the heat treatment resulted in a loss of ductility, the magnetic properties were not deteriorated. The low ductility samples always show intergranular fracture, whereas the un-treated laminations fracture by cleavage. The low ductility is associated with the formation of silicon–manganese nitride precipitates formed at grain boundaries, although they are not the cause of the low ductility. Ductility could be restored by a low dew point heat treatment but the inclusions remained in the grain boundaries. The low ductility and its recovery must be ascribed to the presence of nitrogen atoms segregated to the grain boundaries when the heat treatment atmosphere has a high oxygen potential. The lack of aluminum in the composition of the steel hinders the scavenging effect of this element on nitrogen atoms in solution in the steel.     

Simulation of skew domain wall bowing in SiFe laminations with asymmetric roll orientation

Cyclic motion of 180° domain walls spanning perfect monocrystalline laminations with first-order positive cubic anisotropy (like 3% SiFe) has been simulated using a finite segment technique. Only drive field, eddy field, and surface tension forces on the domain wall were considered. Calculations were made for various crystal orientations over the range between     

Finite element failure analysis of wires for civil engineering applications with various crack-like laminations

This paper presents the finite element (FE) failure predictions and analyses of a typical wire for civil engineering applications with various crack-like lamination types (Single and double), geometries (straight-end and inclined-end) and orientations (longitudinal, lateral and transverse). FE prediction and analysis of the failure of notched pre-cracked wires with a surface across-the-thickness crack-like lamination validated with experimental results are also presented. The FE predicted fracture shape for the notched pre-cracked wires that consists of a cup and cone fracture shape below the bottom tip of the surface across-the-thickness crack-like lamination agrees with the experimental fracture shape. Wires with the double straight-end and double inclined-end crack-like/line-type laminations exhibit a “slant-middle W” and a “zigzag” fractures respectively. Above and below the lateral mid-width across-the-thickness lamination, the wires with the lateral mid-width across-the-thickness lamination exhibit a combination of a transverse mid-thickness flat fracture that is perpendicular to the lateral mid-width across-the-thickness lamination and negatively inclined slant fractures on each side of the mid-thickness flat fracture at the remaining outer edges of the wire's thickness. On both the front and back sides of the transverse mid-thickness across-the-width lamination, the wires with the transverse mid-thickness across-the-width lamination exhibit a combination of transverse flat fractures parallel to the transverse mid-thickness across-the-width lamination and positively inclined slant fractures at the outer edges of the wire's thickness. FE failure analysis reveals that fracture initiations do not always begin at the termini of every longitudinal crack-like/line-type lamination as reported in a published fractographic failure analysis report of wires with longitudinal crack-like laminations. Fracture initiation only begins at the termini/tip of longitudinal inclined-end crack-like laminations and at the termini/tip of transverse and lateral laminations. FE failure analysis also reveals that wires with single straight-end, double straight-end and double inclined-end longitudinal crack-like/line-type laminations do not exhibit cup and cone fractures as reported. This work further demonstrates the need to employ FE failure analysis as a complimentary or alternative failure analysis approach where the destruction/alteration of the fracture markings by corrosion could affect the accuracy of fractographic failure analysis.     

Experimental test of loss calculations for thin laminations in the presence of normal sinusoidal flux

Recently a variational procedure was developed for calculating losses in thin laminations of any shape in the presence of sinusoidal flux directed normal to the lamination plane. The results for a variety of shapes showed that these losses do not depend on the magnetic characteristics of the lamination material but only on the resistivity. The loss formula is tested experimentally for rectangular shaped laminations for a variety of magnetic and nonmagnetic materials. We obtained good agreement with the prediction both in terms of parameter dependencies and absolute numerical values of the specific losses.     

A viscous-type dynamic hysteresis model as a tool for loss separation in conducting ferromagnetic laminations

A viscous-type dynamic hysteresis model (DHM) that is compatible with any static hysteresis model is described. In contrast to existing dynamic models, the DHM is characterized by fixed desired properties over an infinite frequency range and provides the possibility of changing the shape of the steady-state hysteresis loop. The way the DHM is combined with Maxwell equations makes it possible for the first time to separate all three components of the total loss in conducting ferromagnetic laminations. These are the static hysteresis loss, classical eddy-current loss, and the excess loss treated as a dynamic hysteresis component. The study of their frequency dependencies opens a possibility of accurate iron loss prediction based on the loss separation principle.     

Interlaminar stresses in thick rectangular laminated plates with arbitrary laminations and boundary conditions under transverse loads

In the present study, interlaminar stresses resulting from bending of thick rectangular laminated plates with arbitrary laminations and boundary conditions are analyzed analytically based on a three-dimensional multi-term extended Kantorovich method (3DMTEKM). Using the principle of minimum total potential energy, three systems of coupled ordinary differential equations with non-homogeneous boundary conditions are obtained. Then an iterative procedure is established to achieve analytical solution. The results obtained from this theory are compared with those of analytical solutions existing in the literature. It is found that the present results have excellent agreements with those obtained by layerwise theory. The results show that the multi-term EKM converges within only three terms of trial functions and the single-term EKM is not able to estimate the local interlaminar stresses near the boundaries of laminates. Finally, the power of the present approach in obtaining the interlaminar stresses in thick rectangular laminated plates with general types of boundary conditions and lay-ups is examined.     

Estimation of Parameters of Universal Distribution of Moments of Failure of Products

A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling.     

Analysis of the rate of propagation of the wave of change of boiling modes

An approximate analytical expression is derived for the velocity of the front of the wave of change of boiling modes on a rod and on a plate. The impact of the Thomson effect and of the heater orientation in the gravity field is included. Adequate agreement is demonstrated between the derived relations and experimental data.     

水三相点复现的不确定度评定

水三相点是开尔文热力学温度的唯一基准点，也是ITS-90国际温标重要的定义固定点。因此，水三相点不确定度分析对整个温标的建立、温度量值传递起着至关重要的作用。近3年来，中国计量科学研究院研制出一系列高质量的水三相点容器，加强了水三相点的研究，为不确定度的分析提供了更为可靠的实验依据。同时，不确定度的分析也是客观评价新研制容器性能的一个重要指标。因此，根据实验结果对新研制容器所复现的水三相点进行了不确定度评定。评定结果表明，其扩展不确定度为0．16mK(k=2．69，P=0．99)。     

心电图机电压测量示值误差测量值的不确定度评定

本文介绍了心电图机电压测量示值误差测量值的不确定度评定与表示方法。     

可燃气体检测报警器测量结果的不确定度评定

本文详细介绍了可燃气体检测报警器示值误差测量结果的不确定度评定方法。