不同加载条件下50W800G硅钢板的拉伸性能

对50W800G硅钢板采用十字形试样进行了不同加载条件下的单向拉伸试验和双向拉伸试验,并运用ANSYS软件对试验结果进行了有限元模拟。结果表明:50W800G硅钢板双向等比拉伸时的应力-应变曲线位于双向非等比拉伸和单向拉伸时的应力-应变曲线之上;50W800G硅钢没有明显的各向异性行为,双向等比拉伸时轧制方向的应力-应变曲线稍高于垂直于轧制方向的,而双向非等比拉伸时垂直于轧制方向的应力-应变曲线稍高于轧制方向的;ANSYS有限元数值模拟的结果可用来预测双向拉伸过程中的应力-应变关系。     

Effect of gravity field,initial stress and rotation on the S-waves propagation in a non-homogeneous anisotropic medium with magnetic field

In this paper, we investigated the propagation of shear wave under the influences of the magnetic field, gravitational field, rotation and initially stressed in anisotropic non-homogeneous incompressible elastic medium. It is well known in the literature that the earth medium is not at all initial stress free and homogeneous throughout, but it is initially stressed and non-homogeneous. The frequency equation that determines the velocity of the shear waves has been obtained. Keeping these things in mind, we have discussed the frequency equation in an initially stressed, non-homogeneous medium with gravity field, magnetic field, and rotation. It has been observed that the inhomogeneity parameter, gravity field, magnetic field, and the initial stress play an important role in the propagation of S-waves propagation. The numerical values on the dimensionless phase velocities are calculated and presented graphically to illustrate the dependences upon gravity field, initial stress, magnetic field, anisotropy and rotation comparatively. The results indicate that the effects of gravity field, initial stress, magnetic field, anisotropy, and rotation are very pronounced.     

Modeling of a scan type magnetic camera image using the improved dipole model

The scan type magnetic camera is proposed to improve the limited spatial resolution due to the size of the packaged magnetic sensor. An image of the scan type magnetic camera, ∂B/∂x image, is useful for extracting the crack information of a specimen under a large inclined magnetic field distribution due to the poles of magnetizer. The ∂B/ ∂x images of the cracks of different shapes and sizes are calculated by using the improved dipole model proposed in this paper. The improved dipole model uses small divided dipole models, the rotation and relocation of each dipole model and the principle of superposition. Also for a low carbon steel specimen, the experimental results of nondestructive testing obtained by using multiple cracks are compared with the modeling results to verify the effectiveness of ∂B/∂x modeling. The improved dipole model can be used to simulate the LMF and ∂B/∂x image of a specimen with complex cracks, and to evaluate the cracks quantitatively using magnetic flux leakage testing.     

Development of a new precision internal machining process using an alternating magnetic field

Imparting compressive residual stress to a surface improves the fatigue structural integrity of components, which is particularly important for components used in such critical applications as high-pressure gas or liquid piping systems. This paper proposes a new precision internal machining process that controls the surface integrity of internal surface of these components. This process utilizes an alternating magnetic field to control the force and dynamic motion of the tools needed for machining. An experimental set-up was developed to test the processing principle. This study characterizes the in-process tool behavior—that is, the relationships between the magnetic field, the tool properties, and the tool behavior—and reveals the properties of the tools required to achieve the desired results: magnetic anisotropy and a specific geometric restriction. The surface roughness, hardness, and residual stress measurements following machining experiments demonstrate the effects of the tool behavior on the machining characteristics. This paper also proposes methods to obtain desired surface characteristics.     

Measuring magnetic anisotropy with a rotatable ac electromagnet

Magnetic anisotropy of magnetic thin films was determined from a series of hysteresis loops measured via a rotatable alternate current (ac) electromagnet, the rotation angle of which could be continuously tuned at 360° with a high resolution. Co₂FeAl Heusler alloy films grown by molecular beam epitaxy were used to show the benefits of the method for measuring magnetic anisotropy.     

Effect of Magnetic Oxidation and Surface Carbon Distribution on Friction and Wear Characteristics of 45 Steel under the DC Magnetic Field

Abstract

The sliding dry friction behaviors and wear properties of normalized 45 steel and annealed 45 steel under different magnetic field intensities were experimentally studied using a self-made HY-100 pin–disc friction and wear tester. The influence of a magnetic field on the friction and wear of 45 steel were also investigated by analyzing the microscopic friction surface and subsurface using a 3D shape analyzer and metallographic microscope. The experimental results show that the friction coefficient of the normalized 45 steel was greater than that of the annealed 45 steel under magnetic field. In addition, the results illustrate that the external magnetic field can effectively improve the wear performance of carbon steel. The wear rate of normalized 45 steel was lower than that of annealed 45 steel. The wear performance of normalized 45 steel was more significantly improved compared to annealed 45 steel with a magnetic field. Energy spectrum analysis indicated that the effect of the magnetic field on the degree of friction and oxidative wear of the normalized 45 steel was weaker than that of the annealed 45 steel, and the ratio of oxygen to iron and the oxidation area on the friction surface of the normalized 45 steel were smaller. It is believed that as an oxidation protectant, carbon reduces the oxidation wear of 45 steel. The carbon on the normalized 45 steel surface was uniformly distributed and the protective effect of friction surface was better. Therefore, the oxidation wear and oxide shedding were reduced and the wear performance was improved.     

Production of centrifugal fields greater than 100 million times gravity

A high-speed rotation instrument to produce centrifugal fields greater than 100 million times gravity has been constructed. Small, solid, spherical high-carbon chromium steel rotors are suspended magnetically in high vacuum and spun by a rotating magnetic field. It is found that the spinning rotor explodes when the calculated average value of stress in the meridian plane reaches about 1.2 times the tensile strength of the material. The maximum speed of rotation so far achieved for more than a few days without bursting was obtained with a rotor of 1.50 mm diameter. The speed of 2.11 x 10(5) rev/s corresponded to a centrifugal field of 1.34 x 10(8) times gravity. Our instrument will find application in the study of nuclear atomic phenomena.     

Parametric study on mechanical clinching process for joining aluminum alloy and high-strength steel sheets

The purpose of this study is to investigate the effects of process parameters on the joint characteristics of advanced high-strength steel DP780 and Al5052 alloy sheet in mechanical clinching process. The defects in the clinching joint, such as necking of the upper sheet, cracks in the lower sheet, and no interlocking, occur because of the different ductility between advanced high-strength steel and aluminum alloy. In this study, the effect of the process parameters of the clinching process on the joinability of advanced high-strength steel with Al5052 alloy was investigated using finite element (FE) analysis. From the result, the die radius, die depth, and die groove shape were mainly affected by the joinability of advanced high-strength steel with Al5052 alloy. H-type tension test was performed under the same condition as the FE analysis. In addition, the joint strength was determined by interlocking length as well as neck thickness.     

旁路励磁的钢缆索索力传感器磁路分析

基于钢缆索逆磁致伸缩索力测量原理,讨论了一种旁路励磁的索力传感器。用磁导分析法对磁路做了详细的推导,结果表明可通过检测感应线圈的感应电压反映材料所受的外力,传感器输出与外力信号本身的变化、感应线圈的匝数、材料截面积、外激励磁化场及该磁场下的材料磁导率有关。在外力是缓慢变化情况下,可通过求感应积分电压得到外力;从激励磁化方式、参考工作点的选取,传感器的尺寸设计原则等三个方面做了讨论,确定传感器的参数。最后,利用万能拉力机对该种结构的传感器做了拉力模拟实验,实验结果表明旁路励磁的传感器磁路分析与参数设计比较合理,可用于钢缆索的索力测量。     

Note: A time-resolved Kerr rotation system with a rotatable in-plane magnetic field

A time-resolved Kerr rotation system with a rotatable in-plane magnetic field has been constructed to study anisotropic spin relaxation of electrons in semiconductors. A permanent magnet magic ring is placed on top of a motor-driven rotation stage (RS) to create the rotatable in-plane magnetic field. The RS is placed on a second translation stage to vary the local magnetic field around a sample. The in-plane magnetic field in such a system varies from 0.05 to 0.95 T, with full-round 360° rotatablity, thus offering a convenient and low-cost way to study the anisotropy of spin dynamics in semiconductors. Its performance was demonstrated via measurement of the anisotropy of the spin dephasing time (SDT) of electrons in a two-dimensional electron system embedded in a GaAs/Al(0.35)Ga(0.65)As heterostructure. The SDT with B∥[110] was observed to be 10% larger than that with B∥[110], consistent with the results of others, which was measured via rotating sample.     

磁表面张力--磁流体密封机理研究的新思路

本语文从液体与固体界面之间的关系,以及它们之间存在的表面张力入手,从另一个角度探讨了磁流体密封的机理。通过分析和试验,得出了磁流体密封能力与表面张力间的定必顷把磁性力作为附加的范德瓦引力的新思路基础上,提出了磁表面张力新概念,为研究磁流体密封能力作限一些基础性的工作。     

Design of a vector magnet for the measurements of anisotropic magnetoresistance and rotational magneto-optic Kerr effect

A vector magnet is designed and assembled with two electromagnets to produce a rotational magnetic field in any direction within a plane. This design allows a rotation of the magnetic field without a mechanical rotation of the magnets. The fast speed of the field rotation (~10 s for a complete 360° rotation) and the stability against mechanical vibration easily overcome the slow drifting effect in anisotropic magnetoresistance (AMR) and rotational magneto-optic Kerr effect (ROTMOKE) measurements. As an example we applied this vector magnet to carry out AMR and ROTMOKE measurements on epitaxial growth of Fe(10 nm)∕MgO(001) films. The result demonstrates the stability and high quality of the vector magnet in determining the magnetic anisotropy of magnetic thin films using AMR and ROTMOKE techniques.     

静载拉伸下磁记忆信号变化特征分析

通过对带中心圆孔缺陷的20#钢平板试件做静拉伸试验,研究在不同载荷作用下,铁磁材料的表面磁场强度垂直分量的变化.试验研究表明:磁场强度垂直分量过零点不能完全表征应力集中位置,磁场强度梯度的变化与应力集中程度有关,随着载荷的增加,沿试件轴线方向磁场强度发现一定规律的变化,且集中系数m=Kmax/Kau≥2.6,试件处于危险状态.     

Analysis and visualization of rotation searching efficiency in two-round rotation based magnetic tracking

A magnetic sensor attaching on the moving object will have a maximum intensity measurement when the rotating magnetic field is pointing at it. Before solving the position and orientation, the magnetic field could be rotated in two orthogonal planes to find the maximal pointing direction. In order to realize a real-time tracking, efficient searching strategies for this maximum-oriented magnetic field rotation must be provided. This paper sets up a novel rotation searching efficiency model to quantitatively evaluate the relationship between the rotation searching time and the rotation axis in the two-round rotation based magnetic field measurement. Based on this model, two searching strategies are proposed. Simulation results suggest that both searching strategies can realize full space tracking without any latency larger than 30 ms. Corresponding system platform is under development.     

Development of an optimised magnetic field source for flowmeter applications

Sensitivity of a magnetic flowmeter relies on many factors like magnetic field strength, gap between electrodes, material properties, magnet temperature etc. For a given measuring conditions, a strong magnetic field source can produce highest sensitivity for the flowmeter. An economic design of magnetic field source would be to produce the strongest magnetic field from a given amount of magnetic material. In this paper, various magnet configurations are analyzed using FEM and the flowmeter sensitivity using such magnet configurations are compared. It is observed that magnets arranged in a Halbach fashion produce the highest sensitivity for the flowmeter using a given amount of magnetic material. The major challenge for the development of such a magnetic field source is its fabrication from its constituent magnets, combatting their huge attractive/repulsive forces (∼2500 N for our case). Therefore, a specific mechanical tool has been designed for assembling the magnetic field source and a robust assembly technique has been devised using numerical computations. The designed magnetic field source produces a peak magnetic field of 0.78 T in the pole cross section of 50 mm × 50 mm.     

Finite-element simulation of hole-flanging process of circular sheets of anisotropic materials

A hole-flanging operation on a flat circular sheet with a hole in the center is simulated by an incremental elasto-plastic finite-element method, which incorporates strain-hardening and anisotropy in the direction normal to the sheet, with care taken to describe the boundary conditions of penetration, separation and the alternation of the sliding—sticking state of friction. The simulation clearly demonstrates the processes of generation of deformation shape until unloading. The calculated sheet geometries and the relationship of punch load to punch stroke are in good agreement with the experimental data.The stress at the hole periphery in the flange is assumed to a state of circumferential uniaxial tension, in order to simplify the fracture mode as a simple tension test. By making use of the instability of uniaxial tension, an approximate relationship to determine the onset of necking of the hole periphery in the hole-flanging process is derived and it is found to be influenced by the process geometry and the plastic properties of the material, such as the stress-concentration factor K, strain-hardening n and normal anisotropy R, and the estimated value, being obtained by the derived equation, agrees well with the experimental data.It is noted that the derived relationship for estimating the instability of the hole-flanging process can be combined into the developed finite-element model to simulate the critical condition of the limiting deformation of the hole-flanging process. This combined method could possibly be applied towards improving both the manufacturing process and the design of tools for the hole-flanging operation.     

外加磁场作用方向对焊接残余应力的影响

针对新近发展起来的降低钢铁工件中残余应力的脉冲磁处理方法作用规律较为复杂的现状,研究了磁处理降残余应力效果的外磁场方向这一关键因素。通过盲孔法在16Mn焊接应力试样上进行残余应力的研究,研究脉冲磁处理前后试样中的残余应力分布,并对不同外磁场方向导致的磁处理效果进行对比。试验结果表明,在其他处理参数相同的情形下,不同的外磁场方向可导致不同的磁处理效果：磁场沿最大主应力方向进行处理,残余应力变化不明显;而磁场与最大主应力方向垂直进行处理,可获得较为明显的残余应力降低效果。采用电阻应变片研究不同外磁场方向引起试样中的磁致伸缩,获得不同外磁场方向作用下试样中磁致伸缩的不同特征,分析认为,这与脉冲磁处理效果的方向敏感性密切相关。     

脉冲磁场处理对SKD11模具钢残余拉应力的影响机理分析

为了探究脉冲磁场处理对SKD11钢残余应力的影响机理,设计了单因素试验并得到了磁场强度、磁场频率、磁场方向以及磁处理时间等参数单独变化时试样残余拉应力的变化结果。同时从应力的本质入手,将磁处理过程划分为位错塞积开动和位错增殖两个阶段来分析,对试验现象做出了全面解释,推导出了在第一阶段中使位错塞积群克服点阵阻力所需的临界磁场强度Hp的公式,以及在第二阶段中使单个弗兰克-瑞德位错源增殖所需的临界磁场强度Hc的公式和使单个位错克服点阵阻力所需的临界磁场强度H'-p的公式。最后,以试验结果和理论推导为依据,建立了脉冲磁场处理在冲压模具的应用中需要遵循的原则。     

金属板材成形应力统一解

为了弄清材料拉压强度不相等时板材成形问题的应力解答和最大截面缩减率,根据统一强度理论,对金属板材成形问题进行分析,得出考虑中间主切应力影响和材料拉压比影响的金属板材成形应力统一解,以及反映最大截面缩减率与拉压比和中间主切应力参与系数之间关系的统一解,给出韧性金属板材成形最大截面缩减率可能的取值域.分析过程中引入一个反映金属板材拉制和压制工艺的系数,将金属板材成形问题的拉制解和压制解统一起来.当材料拉压强度相同时,金属板材成形应力统一强度理论解退化为金属板材成形应力统一屈服准则解,金属板材成形应力的Mises解是金属板材成形应力统一屈服准则解的特例.     

Earing predictions for strongly textured aluminum sheets

Metallic alloy sheets develop crystallographic texture and plastic anisotropy during rolling. Deep drawing of a cylindrical cup from a rolled sheet is one of the typical forming operations where the effect of this anisotropy is most evident. Generally, in the finite element analyses of this process, the evolution of anisotropy during forming is neglected. In this paper, results of an experimental program carried out to quantify the anisotropy of aluminum alloy AA5042-H2 are reported. In addition to tensile tests along seven directions in the plane of the sheet, cup-drawing tests were conducted. It was observed that the material displays eight ears. The effects of the evolution in anisotropy and the directionality in hardening on the predictions of the earing profile for this material are investigated using a new methodology that incorporates multiple hardening curves corresponding to uniaxial tension along several orientations with respect to the rolling direction, and to biaxial tension. Yielding is described using the anisotropic yield function Yld2000-2D [1] and a form of CPB06ex2 yield function [2], which is tailored for metals with no tension–compression asymmetry. It is shown that even if distortional hardening is neglected, the latter yield function predicts a cup with eight ears as was observed experimentally. Consideration of distortional only leads to improved accuracy in prediction of the non-uniformity of the cup height profile.