Non-Contact Eddy Current Excitation Method for Vibration Testing

When a conductive material is subjected to a time changing magnetic field, eddy currents are induced in that structure. The eddy currents circulate inside the conductor resulting in a magnetic field that interacts with the applied field. The eddy current field is such that it opposes the change in flux resulting in a force between the source and conductor. The time changing magnetic field necessary to induce an electrometric force in the materials can be generated through a variety of different ways. In the present study, a permanent magnet will be mounted to the tip of an electromagnetic shaker such that the motion of the magnet relative to the structure will cause a time changing field and the formation of eddy currents. The actuator will be demonstrated to be beneficial due to its ability to apply actuation forces without contacting the structure. This study will show that the non-contact nature of the system eliminates mass loading and added stiffness which are downfalls of traditional excitation techniques. Additionally, it will be shown that the use of a non-contact device preserves the mode shapes of the structure, whereas a stinger results in distortions due to the added constraint. Using this concept, a model of the actuation system will be developed, allowing the beams response to be simulated. The actuation system will then be used to excite a cantilever beam to obtain the modal parameters without contacting the structure. The novel non-contact actuation system developed in this paper provides a new method performing vibration testing of on lightweight or flexible structures while preserving their dynamics.     

Magnetic filtration of an iron oxide aerosol by means of magnetizable grates

The cleaning of gases with low concentrations of small ferromagnetic or paramagnetic particles is a difficult task for conventional filtration. A new alternative procedure, magnetic filtration, is used in this work. Iron oxide aerosol was generated by elutriation of iron oxide particles from a fluidized bed consisting of a mixture of Geldart-C iron oxide powder and large spherical Geldart-B sand particles. The aerosol was filtered by means of a magnetic filter which consisted of one, two or three iron grates staggered to each other. The experimental installation contained also an isokinetic sampling system and a Microtrac SRA 150 Particle Analyser. A theoretical expression for filtration efficiency was deduced from a previous model taking into account the different forces acting on the iron oxide particles. Experimental filtration efficiency matches quite well calculated theoretical efficiency. It was found that an increase in particle size, in thee number of grates or in the applied magnetic field produced higher filtration efficiencies up to 100% in some cases. In all filtration experiments pressure drop through the magnetic filter was very small.     

内爆磁压缩准等熵加载过程分析与实验验证

利用磁流体力学程序SSS-MHD模拟了炸药柱面内爆磁通量压缩发生器CJ-100装置的加载过程,讨论了各项装置参数的影响,结果表明装置可达到的峰值磁场值与初始磁场值成反比关系。设计了铁/铜夹层结构的样品靶,在该型装置上开展纯铁的准等熵加载实验。利用光子多普勒测速探头测量到6.43 km/s的样品靶自由面速度,在DT4铁中获得206 GPa的准等熵加载压力。铁材料的压力-比容曲线与理论等熵线基本重合,表明内爆磁压缩加载过程具有较高的等熵程度。     

加载速率和几何尺寸对国产A508-III钢断裂行为影响的实验研究

由加载速率和几何约束改变而引起的压力容器钢韧脆转变问题是核能安全领域亟待解决的关键问题. 为了准确分析国产A508-III钢的动态断裂行为, 借助INSTRON VHS高速材料试验机, 开展了不同加载速率和几何尺寸条件下的国产A508-III钢的断裂韧性试验, 研究了加载速率和几何尺寸等因素对国产A508-III钢动态断裂韧性的影响. 研究表明, A508-III钢具有良好的抗冲击韧性, 随着加载速率的提高, 试样的总冲击吸收能基本保持恒定, 裂纹萌生吸收能量不断上升, 而裂纹扩展吸收能量呈下降趋势. J-Δa阻力曲线和条件起裂韧性J_Q随着几何约束的增加而降低, 随加载速率的增加而升高. 当达到某一临界速率时, 条件起裂韧性J_Q基本恒定, 试样断裂方式也由韧性断裂转变为韧?脆?韧混合断裂. 由于出现混合断裂模式, 发生脆性断裂时的最大J积分值J_max更适于描述国产A508-III钢的断裂韧性演化规律. 随着试样面外几何约束的降低, J_max随Δa_m的增加而线性增大. 试样面内几何约束越高, J_max与Δa_m之间的线性关系斜率越大. 随着试样几何约束的增加, 材料的韧脆转变速率增加, J_max值下降. 改变几何约束只能在有限的加载速率范围内改变材料的断裂方式, 当加载速率超过某个临界值时, 加载速率成为影响材料断裂方式的主要因素.      

Magnetic field-induced martensitic phase transformation in magnetic shape memory alloys: Modeling and experiments

In this work, a continuum based model of the magnetic field induced phase transformation (FIPT) for magnetic shape memory alloys (MSMA) is developed. Hysteretic material behaviors are considered through the introduction of internal state variables. A Gibbs free energy is proposed using group invariant theory and the coupled constitutive equations are derived in a thermodynamically consistent way. An experimental procedure of FIPT in NiMnCoIn MSMA single crystals, which can operate under high blocking stress, is described. The model is then reduced to a 1-D form and the material parameter identification from the experimental results is discussed. Model predictions of magneto-thermo-mechanical loading conditions are presented and compared to experiments.     

Magnetically modified microbial cells： A new type of magnetic adsorbents

Microbial cells, either in free or immobilized form, can be used for the preconcentration or removal of metal ions, organic and inorganic xenobiotics or biologically active compounds. Magnetic modification of these cells enables to prepare magnetic adsorbents that can be easily manipulated in difficult-to-handle samples, such as suspensions, in the presence of external magnetic field. In this review, typical examples of magnetic modifications of microbial cells are presented, as well as their possible applications for the separation of organic xenobiotics and heavy metal ions.     

层状磁电复合材料界面共线裂纹平面问题分析

本文研究了面内电磁势载荷作用下双层压电压磁复合材料中共线界面裂纹问题．考虑了压电材料的导磁性质和压磁材料的介电性质,引入了界面电位移和磁感强度的连续性条件．利用Fourier 变换得到一组第二类Cauchy 型奇异积分方程．进一步导出了相应问题的应力强度因子、电位移强度因子和磁感强度强度因子的表达式,给出了应力强度因子的数值结果．结果表明电磁载荷会导致界面裂纹尖端I、II 混合型应力奇异性,同时还伴随着电位移和磁感强度的奇异性．比较了双裂纹左右端的应力强度因子,发现在面内极化方向上施加面内磁势载荷时共线裂纹内侧尖端区域的两个法向应力场发生互相干涉增强．     

Loading effect on ACPD of a crack in ferromagnetic material

The loading effect on alternating current potential drop (ACPD) for a ferromagnetic material containing a two-dimensional surface crack was investigated under opening mode loading without shear (mode I). The change in potential drop due to load was obtained with and without a magnetic field around the specimen. To remove the magnetic field from the circumference of the specimen, a new measuring system using the characteristic of coaxial transmission line was made. When the magnetic field does not exist around the specimen, the change in potential drop with load is governed by the change in electromagnetic properties near the crack tip. The results obtained by using the new measuring system are the basis for an application of the ACPD technique to the experimental determination of the stress intensity factor, since they are independent of the arrangement of the measuring probe lines and the current supply lines. The relationship between the change in potential drop and the change in load is linearized by demagnetization. The change in potential drop per unit change in the stress intensity factor is independent of the crack length.     

应力调整对石英玻璃珠低速冲击破碎行为的影响

结合高速摄影技术,应用SHPB加载装置,分别使用钢制、铝制和有机玻璃制3种透射杆,对直径约7.90、11.80、15.61 mm 3种尺寸的石英玻璃珠进行了低速冲击实验。根据不同透射杆条件下的玻璃珠破碎过程中的载荷-位移曲线,结合有限元软件计算玻璃珠在冲击作用下载荷的变化情况以及实验过程中玻璃珠的应变,探讨了应力调整对玻璃珠破碎过程的影响。结果表明:相同冲击条件作用下,改变透射杆的材料,会改变玻璃珠破碎过程中的载荷分布,即透射端边界波阻抗的改变会导致反射波发生改变,从而导致玻璃珠内部载荷发生变化;透射杆为铝材和有机玻璃材质时,玻璃珠在破碎过程中的载荷明显下降,在加载过程中伴随着垫块的变形,玻璃珠内部的应力调整时间变长;透射杆为钢杆时,玻璃珠的应变主要表现为两端最大,越靠近中间应变越小,对于透射杆为铝杆和有机玻璃杆的玻璃珠,透射端局部出现了卸载行为。采用有机玻璃透射杆之后,局部应力和变形降低的结果使得玻璃珠在经受较大的变形之后发生破碎,表明玻璃珠的破碎行为由局部变形和局部变形梯度共同控制。     

Pulsed Flame for Syngas Production via Partial Methane Oxidation

The behavior of pulsed flame (PF) and its potential application as a source for syngas production was investigated. Methane/oxygen mixtures of different compositions with and without nitrogen dilution in the temperature range of 278-673 K were studied. This allowed to study the influence of operating temperature, equivalence ratio and dilution on the PF behavior and syngas production efficiency. The PF exhibits two different modes of flame propagation: one relatively slow (several m/s) observed for CH₄/O₂ mixtures diluted by nitrogen and another, very fast, with flame speed of ～1300 m/s, observed for the mixtures containing only CH₄ and O₂ without nitrogen dilution. The exhaust gases emerging from the PF were analyzed by Gas Chromatography (GC) and Fiber Laser Absorption Spectroscopy (FLICAS) for CO:CO₂ ratio. The CO:CO₂ ratio observed in the PF exhaust was found to be higher than that observed in continuous flame, suggesting additional advantages for employing PF for syngas production.     

Inelastic behavior of an AS4/PEEK composite under combined transverse compression and shear. Part I: experiments

The nonlinear behavior in shear and transverse compression of unidirectional AS4/PEEK and their interaction are investigated experimentally. The composite is rate dependent even at room temperature and its rate exponent is similar to that of neat PEEK. The material is tested under pure shear, pure compression and under biaxial loading histories. The biaxial tests are performed in a custom facility on thin strips of the material. The facility allows freedom to choose the loading path in the biaxial stress and strain spaces of interest. Tests are performed for three biaxial loading paths. In the first, the specimen is sheared then compressed while the shear stress is held constant; in the second, the specimen is compressed then sheared while the compressive stress is held constant; and in the third, the specimen is loaded simultaneously by proportional amounts of compression and shear. It was found that the induced deformation is influenced significantly by the loading history followed. Also, initial loading in shear or compression has only a modest effect on subsequent loading of the other type. An unorthodox yielding behavior for the composite results from this lack of interaction. Finally, the stresses at failure are found to trace an elliptical path in the shear–transverse compression plane, but the failure stress state is not significantly affected by the loading path followed.     

A parametric study of the head-on collision of normal shock waves in dusty gases

The effect of the various flow parameters, namely: the diameter of the solid particles, the material density of the solid particles, and the loading ratio of the solid particles on the flow field which is obtained when two normal shock waves collide head-on in a two phase dust-gas suspension has been investigated numerically, using the modified random choice method (RCM). The results were compared with those appropriate to the dust physical parameters used recently by Elperin, Ben-Dor and Igra in their study of the head-on collision of normal shock waves in dusty gases.     

磁驱动准等熵加载装置CQ-4的加载能力及主要应用

利用脉冲大电流与其自身磁场相互作用产生磁压实现对样品平面等熵压缩,是国外新发展起来的动高压加载技术。CQ-4装置是在自然科学基金仪器专项资助下,建立的国内首套可实现110GPa等熵压缩,宏观金属飞片发射达15km/s的紧凑型脉冲功率装置。本文重点介绍该装置的主要性能和加载能力,以及基于其上开展的材料高压本构、相变、未反应炸药等力学行为等应用研究情况。     

Preliminary thermodynamic study for an efficient turbo-blower external combustion Rankine cycle

This research paper presents a preliminary thermodynamic study of an innovative power plant operating under a Rankine cycle fed by an external combustion system with turbo-blower (TB). The power plant comprises an external combustion system for natural gas, where the combustion gases yield their thermal energy, through a heat exchanger, to a carbon dioxide Rankine cycle operating under supercritical conditions and with quasi-critical condensation. The TB exploits the energy from the pressurised exhaust gases for compressing the combustion air. The study is focused on the comparison of the combustion system’s conventional technology with that of the proposed. An energy analysis is carried out and the effect of the flue gas pressure on the efficiency and on the heat transfer in the heat exchanger is studied. The coupling of the TB results in an increase in efficiency and of the convection coefficient of the flue gas with pressure, favouring a reduced volume of the heat exchanger. The proposed innovative system achieves increases in efficiency of around 12 % as well as a decrease in the heat exchanger volume of 3/5 compared with the conventional technology without TB.     

Magnetic modification of diamagnetic agglomerate forming powder materials

A simple method for the magnetic modification of various types of powdered agglomerate forming diamagnetic materials was developed. Magnetic iron oxide particles were prepared from ferrous sulfate by microwave assisted synthesis. A suspension of the magnetic particles in water soluble organic solvent (methanol, ethanol, propanol, isopropyl alcohol, or acetone) was mixed with the material to be modified and then completely dried at elevated temperature. The magnetically modified materials were found to be stable in water suspension at least for 2 months.     

含力磁屈服区的压磁材料硬币型裂纹问题研究

本文利用Hankel 变换及Copson 求解方法,得到了在无穷远处磁荷载以及对称力荷载作用下的无限大压磁材料中,硬币型裂纹在裂纹尖端含有环状力磁双屈服区情况下的相关解析解．本文考虑了磁屈服区尺寸小于、大于、等于力屈服区尺寸的三种情况．结果表明：屈服区尺寸不仅与外荷载及材料常数相关,更与力磁屈服区尺寸的相对大小有关;其中,较大尺寸的屈服区仅受同性质单一荷载影响,与材料常数无关;而较小尺寸屈服区受力磁两荷载与材料常数共同影响;裂纹张开位移、磁势跳变均沿裂纹面径向增大而减小;裂尖张开位移、裂尖磁势跳变与材料常数相关,且随外荷载增大而增大．     

Sedimentation acceleration of remanent iron oxide by magnetic flocculation

Sedimentation based processes are widely used in industry to separate particles from a liquid phase. Since the advent of the ＂Nanoworld＂ the demand for effective separation technologies has rapidly risen, calling for the development of new separation concepts, one of which lies in hybrid separation using the superposition of a magnetic field for magnetic particles. Possible product portfolio of such separation consists of pigment production, nanomagnetics production for electronics and bio separation, A promising step in that direction is magnetic field enhanced cake filtration, which has by now progressed from batch to continuous ooeration. In sedimentation processes in a mass force field the settling behaviour of particles strongly depends on physico-chemical properties, concentration and size distribution of the particles. By adjusting the pH, the interparticle forces, in particular the electrostatic repulsion, can be manipulated. For remanent magnetic particles such as magnetite, pre-treatment in a magnetic field could lead to a change of interparticle interactions. By magnetizing the particles apart from van der Waals attraction and electrostatic repulsion, an additional potential is induced, the magnetic attraction, which could easily dominate the other potentials and result in agglomeration in the primary minimum. By sedimentation analysis, a wide spectrum of parameters like pH, magnetic field strength and concentration have been investigated. The results show a strong increase of sedimentation velocity by magnetic flocculation of the raw suspension. This leads to a rise in throughput due to the acceleration of sedimentation kinetics by imparting a non-chemical interaction to the physico-chemical properties in the feed stream of the separation apparatus.     

Effects of magnetic field on fluidization properties of magnetic pearls

An experimental study of the influence of external magnetic field on the fluidization behavior of magnetic pearls was carried out. Magnetic pearls are a magnetic form of iron oxide that mainly consists of Fe2O3 which are recovered from a high-volume power plant fly ash from pulverized coal combustion. Due to its abundance, low price and particular physical and chemical properties, magnetic pearls can be used as a heavy medium for minerals or solid waste dry separation based on density difference. This paper introduces the properties of magnetic pearls and compares the performance of magnetic pearls fluidised bed operation with or without an external magnetic field. Experimental results show that an external magnetic field significantly improves the fluidization performance of magnetic pearls such as uniformity and stability.     

Experimental study on heat transfer of thermally developing and developed, turbulent, horizontal pipe flow of dilute air-solids suspensions

Heat transfer characteristics of a turbulent, dilute air-solids suspension flow in thermally developing/developed regions were experimentally studied, using a uniformly heated, horizontal 54.5 mm-ID pipe and 43-μm-diameter glass beads. The local heat transfer was measured at 27 locations from the inlet to 120-dia downstream of the heated section over a range of Reynolds numbers 3×10⁴−1.2×10⁵ and solids loading ratio 0–3, and the fully developed profiles of air velocity/temperature and particle mass flux were measured at a location 140-dia downstream of the heated section using specially designed probes, inserted into the suspension flow. The effects of the Reynolds number, solids loading ratio, and azimuthal/longitudinal locations on the heat transfer characteristics and their interactions are discussed through comparison of the present results with the data obtained by other investigators. Received on 14 October 1996     

Weakly magnetic field-assisted synthesis of magnetite nano-particles in oxidative co-precipitation

This paper presents experimental results on weakly magnetic field-assisted synthesis of magnetite （Fe3O4） nano-particles in an oxidative co-precipitation method, in comparison to the case without magnetic induction. The XRD results show that a weakly magnetic induction below 220 Gs could accelerate the phase transformation from goethite （α-FeOOH） to magnetite （Fe3O4）, and affect the crystal structure, the particle size/morphology and magnetic response of the magnetite nano-particles synthesized. In addition, a higher concentration of the FeCl2 solution in the synthesis reaction led to finer particles, both with and without magnetic induction.