焊接微缺陷磁光成像检测有限元分析

目的 研究铁磁材料焊接微缺陷的磁光成像规律.方法 运用漏磁检测原理和法拉第磁致旋光效应,建立微缺陷三维有限元模型,分析微缺陷磁光成像过程与磁场之间的关联,研究不同提离值、励磁电流、缺陷宽度、缺陷深度下的磁光成像,以及探索这些因素对磁光图像特征的影响.在此基础上,对最小宽度为0.05 mm的微缺陷进行磁光成像检测实验,并...     

Pr2/3Sr1/3MnO3薄膜外场诱导自旋输运特性

采用脉冲激光沉积法制备了稀土掺杂钙钛矿锰氧化物Pr2/3Sr1/3MnO3(PSMO)外延薄膜,研究了薄膜在磁场、激光和电流作用下的自旋输运特性.在低温铁磁金属相,激光作用使薄膜的电阻增大,而磁场和电流则诱导电阻减小;在高温顺磁绝缘态,外场诱导均使电阻减小.在铁磁金属相,外场诱导输运特性的变化可归结于外场对体系电子自旋系统的影响:磁场和电流加强材料中eg电子和t2g局域电子间的自旋平行,增强了双交换作用;激光作用可产生光致退磁效应,减弱双交换作用.在顺磁绝缘态,场致电阻降低源于外场致使小极化子的退局域化效应.     

脉冲磁场激励下铁磁梁式板动力响应特征研究

基于广义变分原理得到磁力计算模型和磁场摄动技术,研究了不可移简支铁磁梁式板在矩形和锯齿形两类典型脉冲磁场作用下的磁弹性动力响应特征及动力失稳现象。数值模拟了铁磁梁式板在稳恒磁场,脉冲磁场下的振幅,频率的变化及其动力失稳特征。揭示了脉冲磁场的形状,脉冲持续时间,脉冲幅值与铁磁梁式板振幅,频率,临界失稳磁场值等特征参量之间的关系,为工程实际中铁磁结构的安全设计和可靠性评估提供依据和参考。     

靶向治疗中水基铁磁流体在磁场作用下的聚集性研究

以水基铁磁流体为载体,研究其在磁场作用下的聚集性.通过体外模拟和动物实验,说明铁磁流体中的10～20nm的磁性颗粒可以在磁场作用下聚集在靶部位.理论分析表明这种聚集是由于铁磁流体在磁场作用下形成了微米级的磁性液珠而产生的.     

铁磁形状记忆合金Ni2MnGa多晶的磁-力学特性

对外加磁场、应力场共同作用下的铁磁形状记忆合金多晶的磁-力学特性进行了实验测试与研究,分别获得了两种组分Ni52Mn27Ga21和Ni54Mn25Ga21多晶样品在不同磁场倾角下、不同预加应力下的磁化曲线和磁滞回线;以及不同外加磁场及磁场倾角下的应力-应变曲线和磁致应变曲线等磁-力学特性曲线.结果表明铁磁形状记忆合金多晶沿样品轴向所测的饱和磁化强度随磁场倾角的增大而减小,施加预应力并不显著影响样品的磁化曲线和磁滞回线;各种角度时不同磁场对两种多晶样品的应力-应变关系影响均很小.     

磁脉冲作用下铁磁梁式板的磁弹塑性动力响应与失稳

基于等效的夹层梁模型和伽辽金方法，首先推导了不可移铁磁简支梁式板的磁弹塑性动力控制方程，在此基础上采用龙格-库塔方法数值模拟了矩形、锯齿形、三角形和正弦形四类横向磁脉冲作用下，铁磁梁式板的动力响应曲线及其动力失稳特征。数值结果表明：在磁脉冲持续时间、磁脉冲峰值相同的情形下，铁磁梁式板发生动力失稳时，矩形磁脉冲对应的临界磁场值最小，依次为锯齿形磁脉冲，三角形磁脉冲，正弦形磁脉冲。数值结果还进一步展示了磁脉冲结束后，铁磁梁式板的残余构形等力学特征。     

磁性流体在交变梯度磁场作用下发生磁致伸缩的实验研究

实验建立一个交变的梯度磁场作用于磁性流体,通过压电陶瓷换能器检测到磁性流体振动而产生的声波,发现磁性流体在交变梯度磁场作用下有磁致伸缩效应.导出了磁性流体振动特性的动力学一般方程,揭示了交变的梯度磁场作用引起了交变的磁性流体的内压强,从而引起磁性流体的体积发生伸缩,产生机械振动,激励空气产生声波的机理.     

超磁致伸缩材料ΔE效应理论建模与试验研究

为研究超磁致伸缩材料的ΔE效应,采用Jiles-Atherton模型和磁弹性效应相结合的方法,提出了一种考虑动态应力影响及系数变化的磁化模型。分别对磁场和应力作用下超磁致伸缩材料的磁场-磁化关系和应力-磁化关系进行建模,并根据胡克定律以及二次畴转模型计算出材料在应力和磁场综合作用下的总应变,得到不同外加磁场下材料的应变-应力环。通过对应变-应力曲线斜率的计算,得到超磁致伸缩材料在不同外加磁场下,弹性模量随应力变化规律。搭建了应力测试装置,对不同磁场作用下Terfenol-D的磁化-应力响应和应变-应力响应测试,试验结果与模型计算结果基本一致,结果表明,ΔE效应是磁场能量和应力各向异性平衡的结果,Terfenol-D最大弹性模量变化达到513%。研究成果为新型机电系统变刚度设计提供了理论基础和调控手段。     

低频脉冲磁场处理Co_(60.15)Fe_(4.35)Si_(12.5)B_(15)非晶合金薄带巨磁阻抗效应的研究

对Co60.15Fe4.35Si12.5B15非晶合金薄带进行了低频脉冲磁场处理,M ssbauer谱分析及透射电镜观察表明样品发生了纳米晶化,处理过程样品温升ΔT≤5℃,在直流磁场Hex为0.296kA/m、交变驱动电流频率为2MHz时,磁阻抗比值达255%。实验表明,材料的巨磁阻抗效应与低频脉冲磁场的频率、强度有关,同时低频脉冲磁场处理致非晶合金纳米晶化创新了一种获得巨磁阻抗效应新的处理工艺。     

超磁致伸缩薄膜难磁化轴方向动态特性研究

磁场驱动频率高是限制超磁致伸缩薄膜器件推广应用的关键因素之一,研究如何降低超磁致伸缩薄膜器件的磁场驱动频率对超磁致伸缩薄膜器件的推广应用将具有重要意义。在深入分析超磁致伸缩薄膜存在各向异性根本原因的基础上,结合薄膜磁致伸缩过程中磁畴的运动机理,提出只要能够克服超磁致伸缩薄膜中存在的退磁场,低磁场驱动频率下就可在难磁化轴方向获得更为优良动态特性的新思路。通过建立超磁致伸缩薄膜难磁化轴实验系统进行实验研究,结果表明通过施加合适的偏置磁场克服退磁场,可以使薄膜在难磁化轴方向产生响应优良的超谐共振,为低频驱动GMF器件的研制提供了一种新的思路。     

Magnetic field and concentration dependence of light scattering from a ferrofluid

Measurements of light scattering from a ferrofluid were undertaken as functions of both magnetic field and particle concentration. The results show that the distribution pattern of light intensity in space is a continuous banding perpendicular to the field direction. The light intensity weakens with increasing scattering angle. The experiments also indicate that the scattering coefficient increases both with the magnetic field and with the particle concentration and tends to saturate at higher field strengths. Finally, the experimental results are discussed in terms of an expanded theory of light scattering established by considering the widths of the chains formed in the ferrofluid as functions of both the magnetic field and the particle concentration.     

磁流体薄片中聚焦激光束对交流磁场的相位独立响应

报导了磁流体薄片中聚焦激光束在探测50Hz交流磁场时产生与磁场相位无关响应的效应。聚焦于并通过磁流体薄片的633nm激光束的偏转角仅与交流磁场的幅度相关。为了探寻其机理，还研究了磁流体中聚焦激光束对开／关磁场或激光的瞬态响应。提出了基于磁熵守恒的磁流体中磁性粒子密度再分布正反馈模型来解释这一效应。这一模型也可以预 磁流体中一种磁－热失稳现象。     

Rotation of the magnetization vector of a monodomain particle under the action of a high-frequency field pulse

We obtained a numerical solution of the modified Hilbert equation describing rotation of the magnetization vector in a high-frequency field of large amplitude. Based on this solution, we have studied rotation of the magnetization vector of a spherical ferromagnetic monodomain particle, possessing a cubic anisotropy, from the direction parallel to an easy magnetization axis to the perpendicular direction under the action of a high-frequency magnetic field pulse. The amplitudes and the interval of frequencies of the magnetic field capable of rotating the particle magnetization vector are determined.     

Effect of aggregates on the magnetization property of ferrofluids: A model of gaslike compression

The effect of field-induced aggregation of particles on the magnetization property of ferrofluids is investigated. From the viewpoint of energy, magnetizability of ferrofluids is more complicated than predicted by Langevin theory because the aggregation, i.e., the transition of ferrofluid microstructure, would consume the energy of the applied magnetic field. For calculating the effect of aggregates on the magnetization of ferrofluids, a model of gaslike compression (MGC) is proposed to simulate the evolution of the aggregate structure. In this model, the field-induced colloidal particles aggregating in ferrofluids is equivalent to the “gas of the particles” being compressed by the applied magnetic field. The entropy change of the ferrofluid microstructure is proportional to the particle volume fraction in field-induced aggregates ø_H. On the basis of the known behavior of ferrofluid magnetization and the aggregate structure determined from the present experiments, ø_H is obtained and found to depend on the aggregating characteristic parameter of ferrofluid particles γ in addition to the particle volume fraction in ferrofluids ø and the strength of applied magnetic field H. The effect of the nonmagnetic surface layer of ferrofluid particles is also studied. The theory of MGC conforms to our experimental results better than Langevin theory.     

Effect of aggregates on the magnetization property of ferrofluids: A model of gaslike compression

The effect of field-induced aggregation of particles on the magnetization property of ferrofluids is investigated. From the viewpoint of energy, magnetizability of ferrofluids is more complicated than predicted by Langevin theory because the aggregation, i.e., the transition of ferrofluid microstructure, would consume the energy of the applied magnetic field. For calculating the effect of aggregates on the magnetization of ferrofluids, a model of gaslike compression (MGC) is proposed to simulate the evolution of the aggregate structure. In this model, the field-induced colloidal particles aggregating in ferrofluids is equivalent to the “gas of the particles” being compressed by the applied magnetic field. The entropy change of the ferrofluid microstructure is proportional to the particle volume fraction in field-induced aggregates φ_H. On the basis of the known behavior of ferrofluid magnetization and the aggregate structure determined from the present experiments, φ_H is obtained and found to depend on the aggregating characteristic parameter of ferrofluid particles γ in addition to the particle volume fraction in ferrofluids φ and the strength of applied magnetic field H. The effect of the nonmagnetic surface layer of ferrofluid particles is also studied. The theory of MGC conforms to our experimental results better than Langevin theory.     

Complex microwave susceptibility of a ferrofluid with Mag-Hematiteparticles: nonreciprocal phenomena in magnetic liquids

We present susceptibility measurements on a ferrofluid in the microwave frequency range with three different measurement cells: a coaxial line, an X-band rectangular waveguide, and an X-band slab-loaded rectangular waveguide. We use the reflection/transmission method to obtain the complex susceptibility χ^*. We have subjected the cells to a constant magnetic field applied parallel or transversal to the propagation direction. We observe an increase of the gyromagnetic resonance phenomenon and some discrepancies between the consequences of a parallel or transverse applied field. Nonreciprocal phenomenon has been observed for the first time in a ferrofluid when a transversal field is applied to an X-band slab-loaded rectangular waveguide     

Numerical calculations for ferrofluid seals

The magnetic field and the seal capacity of ferrofluid seals are calculated and analyzed by numerical methods. Based on the magnetic filed calculations, the isobars in the ferrofluid and the cross sections of the fluid sealing ring are described. The relations of the seal capacity to the ferrofluid amount and the magnetic circuit parameters are analyzed. The action of the centrifugal force on the seal is indicated     

Room temperature magneto-optics of nanostructured ZnO:Mn thin film grown by spray pyrolysis

Undoped ZnO and ZnO:Mn thin films with different amounts of Mn concentration (5, 10 and 15 mol%) were grown on glass substrates by spray pyrolysis technique. X-ray diffraction patterns showed that the undoped ZnO thin film exhibited wurtzite structure preferably oriented in c-axis direction and the doped samples were polycrystalline. The surface morphology and topography of the films were investigated by SEM and STM micrographs. Magneto-optical characterizations of the samples were carried out by using Kerr and Faraday effects spectroscopy. Kerr effect studies showed that all Mn doped thin films exhibited the room temperature ferromagnetism. The magnetic ordering observed in the film with 5 mol% Mn concentration was stronger comparing to the other doped samples. The carrier densities of the samples were calculated by using a method based on the Faraday rotation. A clear relation between sp-d coupling and strength of magnetic ordering with carrier density was observed.     

Forced convection of a temperature-sensitive ferrofluid in presence of magnetic field of electrical current-carrying wire: A two-phase approach

This research examines laminar forced convection of a temperature-sensitive magnetic nanofluid flowing within a horizontal tube through the two-phase mixture model. The ferrofluid flowing in the tube is exposed to the magnetic field generated by electrical current-carrying wire(s) along the tube, and the effect of such magnetic field is studied on heat and mass transfer phenomena. It is observed that due to the dependency of magnetization on temperature, the cold fluid flowing at the central regions of the tube is attracted more significantly towards the source of the magnetic field, which results in creation of secondary flow. Such mixing in the flow, subsequently, disturbs the thermal and hydrodynamic boundary layers, especially at the vicinity of the magnetic field source, leading to better heat transfer rate and also higher pressure drop. Furthermore, increasing the strength of the magnetic field leads to greater enhancement in heat transfer, while increasing the Reynolds number decreases the effectiveness of the magnetic field on the ferrofluid flow and heat transfer. Moreover, placing two wires above and under the tube can enhance the heat transfer even more significantly, such that the average convective heat transfer coefficient in this case is about 34.5% higher than that of the case without magnetic field.     

Anisotropic scattering of polarized light in a ferrofluid layer

Previously unknown effects wherein the scattering of plane-polarized light in a ferrofluid layer depends on the orientation of the electric field of the polarized radiation relative to the direction of the applied magnetic field are found experimentally, and their physical nature is explained. Pis’ma Zh. Tekh. Fiz. 23, 7–10 (September 12, 1997)