同轴静电雾化切削雾化研究

同轴静电雾化对于实际切削加工具有重要影响,通过搭建同轴静电雾化切削平台,利用显微成像系统进行植物性润滑油LB2000和去离子水两种互不相溶液体介质的同轴静电雾化切削雾化试验,研究了电极电压以及内外流量对雾化形态的影响,并将同轴静电雾化切削三维模型导入Ansoft Maxwell有限元仿真软件中,研究电压对喷嘴、刀具和工件之间静电场强度的影响。结果表明:同轴静电雾化切削中出现"滴状"模式、"脉动"模式、"锥射流"模式以及"不稳定"模式;与其他模式相比,稳定的锥射流是适合用于切削加工冷却润滑的同轴静电雾化模式。分析研究了稳定锥射流形成机理,获得了形成该模式的雾化参数范围,结合同轴静电喷雾切削静电场仿真结果,揭示了电极电压对同轴静电雾化切削的雾化形态影响机理,为同轴静电雾化切削的实际应用提供依据。     

电场参数对雾化特性及微量润滑磨削性能影响的实验研究

为了探究针-板电极电场参数对雾化特性微量润滑磨削性能的影响,通过调节电压幅值和电极间距进行微量润滑平面磨削实验,根据所得雾化锥角、雾滴粒径算术平均值、磨削力及表面粗糙度Ra值进行机理分析。实验结果表明静电雾化微量润滑在高压静电场的参与下,液滴荷电后会发生二次甚至多次雾化。随着电压幅值的升高,雾化锥角增大,雾滴的平均粒径减小并扩散均匀,同时润滑液的润滑性能也有所提高。在电压幅值一定,电极间距为160 mm时,获得最优的润滑性能;在电极间距一定,电压幅值为50 k V时,相比于无静电微量润滑,比切向磨削力Ft'、比法向磨削力Fn'及表面粗糙度R_a值,分别减小25.01%、15.08%、22.18%,获得最优的润滑性能。     

静电涂油机中新型油液荷电装置的试验研究及仿真分析

分析了静电涂油机中防锈油液的荷电雾化机理,研制了一种降低静电涂油机油液雾化电压的荷电装置,对该装置进行了试验研究和仿真分析.研究表明,新型的荷电装置可以在较低的工作电压下达到较好的雾化效果,显著提高静电涂油机的涂油质量.     

自激振荡脉冲射流雾化的机理分析

建立了自激振荡雾化喷嘴的物理模型以及数学模型,通过Fluent软件对自激振荡腔室内部流场进行模拟,分析了自激振荡射流扰动波频率与喷嘴固有频率之间的关系、振荡腔室脉冲发生原因,以及射流脉冲特性其对雾化的影响,解释了自激振荡脉冲射流的雾化机理,说明了自激振荡喷嘴能明显提高射流的雾化效果。数值模拟了不同腔长配比和不同出流扩张锥角.结果表明,在其它条件一定的情况下最佳腔长配比值为腔长与上喷嘴直径之比为2.4,最佳出流扩张锥角为(60~65)°。     

乙醇圆柱射流雾化破碎过程的PIV试验研究

在喷雾容弹上利用PIV激光测试系统,研究了容弹背压、容弹温度和喷射脉宽对乙醇圆柱射流破碎雾化的影响。试验结果表明：容弹背压升高,乙醇圆柱射流贯穿距离减小,射流锥角变大;温度由20℃变为60℃时,乙醇运动黏度变小,射流贯穿距离增大,射流锥角略有增加;喷射脉宽的改变对乙醇圆柱射流贯穿距离和射流锥角影响很小,然而大脉宽的乙醇射流雾化困难。     

真空感应气体雾化技术中紧耦合环缝喷嘴雾化过程的仿真

采用流体体积方法耦合雷诺应力模型与离散相模型结合泰勒类比不稳定性破碎模型，利用计算流体力学软件Fluent19.2,对紧耦合环缝喷嘴初次雾化与二次雾化进行全流程仿真，并进行了试验验证。结果表明：初次雾化过程使导流管底部形成环形液膜结构，液膜前端的初次雾化主要是气体射流自由边界湍流剪切的结果，并且初次雾化形成的液滴直径满足正态分布；随着分散的液滴群外侧接触气体射流，从液滴群的外侧开始向心部发生二次雾化过程，但是未接触气体射流的液滴仍保持较高的过热度。仿真得到紧耦合环缝喷嘴二次雾化后粉末的直径与试验结果吻合较好，相对误差小于5%,验证了仿真的准确性。     

近场电流体动力锥射流微图案化打印方法研究综述

电流体动力打印技术是实现柔性电子器件高分辨率微图案化直写打印的重要技术和方法,目前还面临着锥射流形成和空间运动不稳定性等诸多挑战。总结了电流体动力锥射流打印技术实现高分辨率微图案化稳定打印的研究进展,综述了电流体动力形成细小而稳定的泰勒锥射流,以及射流在空间运动稳定性的影响因素。影响锥射流的稳定性的因素众多,采用响应面法分析工艺参数和打印质量之间的关系,进行参数优化,是实现电流体动力微图案化稳定打印的常用方法。     

自激振荡脉冲雾化喷嘴的空化特性研究

基于自激振荡脉冲喷嘴结构及其射流空化特性,建立了射流雾化过程中的液滴高密度区域和低密度区域破碎模型,分析了空化特性对自激振荡射流液滴破碎的影响,得到了影响自激振荡脉冲喷嘴空化特性的主要因素。研究结果表明:自激振荡脉冲射流呈周期性变化的空化特性使喷嘴出口形成超空化,出口处射流低密度区域形成一次雾化,而高密度区域则以液滴二次雾化形式破碎,增强喷嘴空化强度有利于射流雾化;自激振荡脉冲射流系统频率、喷嘴出口锥角以及射流进口压力都影响喷嘴的空化效果。     

电压对电喷印影响的数值模拟及实验研究

电喷印技术是基于电流体动力学(electrohydrodynamic,EHD)原理的一种沉积技术,可以得到比喷头尺寸小一个数量级的喷印精度。在电喷印过程中,电压是影响喷印的核心因素,对于泰勒锥的形成和稳定性起着重要作用。文中通过数值模拟和实验研究得出:随着外加电压的增加,泰勒锥逐渐形成,同时液滴的锥角也在减小;当达到一定的电压(2000V)时,得到的锥形最稳定且锥角最小;而当电压继续增加,泰勒锥锥形开始缩短最终失稳。因此,电压为2000V是实验条件下的最优参数。     

同轴电射流打印实验研究

分别以光刻胶和硅油作为内、外液进行了同轴电射流打印实验,研究了关键工作参数对电射流形态及打印结果的影响,包括外液粘度、溶液流量以及施加在喷针上的电压。实验结果表明,同轴电射流形态受外液粘度影响较大,粘度越大,射流的聚焦效果越好;打印结果尺寸随着溶液流量的增大而增大;电压过小,液体无法形成射流,电压过大,液体会形成多股射流的不稳定状态。     

A lead-free piezoelectric transformer in radial vibration modes

In this study, a disk-shaped piezoelectric transformer was fabricated using lead-free (K,Na)NbO(3)-based ceramics with high mechanical quality factor. The transformer can operate in the fundamental or the third radial vibration mode. The transformer is poled along the thickness direction. The top surface is covered by ring/dot silver electrodes separated by an annular gap which serve as the input and output parts of the transformer, respectively. The bottom surface, fully covered with a silver electrode, is grounded as a common electrode. The dimensions of the top ring/dot electrodes are designed such that the third radial vibration mode can be strongly excited. The electrical properties of the transformer with diameter of 34.2 mm and thickness of 1.9 mm were measured. For a temperature rise of 35 degrees C, the transformer has a maximum output power of 12 W. With the matching load, its maximum efficiency is >95%, and maximum voltage gains are 6.5 and 3.9 for the fundamental and the third radial vibration modes, respectively. It has potential to be used in power supply units and other electronic circuits.     

Herschel-type venturimeter discharge coefficients at low Reynolds number

A theoretical equation has been developed in order to estimate the influence of Reynolds number on the discharge coefficients of a venturimeter. It is shown that the factors which influence the coefficient of discharge are the momentum transport coefficient, the semi-cone angle of the convergent section, the rate of contraction (m) and the Reynolds number. Tests performed with three brass-lined venturimeters are in good agreement with the theoretically predicted values.     

Cross-talk effect in electrostatic based capillary array nozzles

Electrohydrodynamic printing is a promising technique for printed electronics application. Most researchers working in this field are using a single nozzle configuration. However, for large area printing a multi-nozzle setup will be required for time and cost effective process. In this paper the influence of electric field and flow-rate on jetting angle on multi-nozzle array has been investigated experimentally. A three nozzle setup has been used in a linear array by using glass capillary as a nozzle with independent voltage applied on each nozzle and independent ink supply. The experiments are performed by changing the nozzle to nozzle gap and the effect on the jetting angle has been investigated. It has been observed that by increasing the applied voltage the jetting angle also increases at fixed flow-rate. In case of increasing the flow-rate, the jetting angle first increases with increase in flow-rate, but as the flow-rate increases at certain level the jetting angle decreases; moreover, at a high flow-rate the cone-jet length starts increasing. Numerical simulation has been performed to have a better understanding of the electric-field with respect to jetting angles. The influence of one nozzle on another nozzle is also investigated by operating the nozzle independently by using different operating cases. The cross-talk effect is also minimized by reducing the nozzle diameter. At 250 μm nozzle diameter the cross-talk effect was negligible for 5 mm nozzle-to-nozzle gap. This study will help in better understanding of the interaction between different nozzles in multi-nozzle cases and better design of the multi-nozzle system by minimizing the effects of adjacent nozzles for multi-nozzle electrohydrodynamic printing system.     

螺旋桨轴毂复合联接结构接触问题的非线性有限元分析及结构尺寸优化

针对航空工业产品使用的情况分析:要求其在保证承载的前提下,在设计中尽可能使其结构紧凑或减重.利用ANSYS软件建立一种新型螺旋桨轴毂复合联接结构的有限元接触模型,并以其复合结构中关键零件弹性环的半锥角及宽度为设计变量、弹性环的最大应力为状态变量,对弹性环的结构尺寸进行优化分析,为设计一种能满足航空行业中使用要求的螺旋桨轴毂复合联接结构提供理论分析基础.     

空间探测小型质谱仪关键技术研究

小型质谱仪的理论和应用研究对于空间探测具有非常重要的意义,针对商用质谱仪存在的缺点,采用静电双平方离子势阱和离子聚焦技术设计了空间有机分子小型质谱探测器。探测器由质谱传感器、分压控制电路及微电流检测放大电路构成。圆柱形传感器腔体内置多个不同电位的环形电极,在腔体轴向上形成双平方离子势阱,离子在势阱中可形成稳定振荡,振动频率与离子质量成一定的反比关系。通过测量法拉第杯产生的电信号,经FFT提取振动频率,从而探测有机分子质量。在理论上,其主要技术指标为：质量扫描范围 m/z 1~2 000,分辨率>400,灵敏度>100 cps/ppb,总质量<4.5 kg,功耗<5 W,码速率>1.5 kbps。初步调试结果验证了该技术具有一定的可行性,后期可通过对离子源及其与质谱传感器配合的研究来完成整机的具体性能指标测试。     

半导体硅电极多通道放电机理研究

为了实现电火花加工同一时刻形成多个放电通道蚀除工件,克服现有放电加工理论中同一时刻仅有一个放电通道蚀除工件的限制,提出了采用半导体材料作为电极进行放电加工的新方法。首先,通过试验证明以半导体硅为电极加工金属可以形成多通道放电;其次,建立了半导体电极单通道放电等效电路模型,发现半导体电极在放电加工时不是一个等势体,并进行了电势差分布试验,验证了多通道放电形成的原因是远离放电点处的电势较高,可以同时形成击穿产生放电;最后,进行了半导体硅电极单脉冲放电试验及成型加工试验。试验结果显示,半导体硅电极通过1次脉冲放电同时形成多个放电通道,有效地分散放电能量,相较于金属电极,每个放电坑的直径和深度都显著减小。在相同放电参数下,对比钢电极,用硅电极进行电火花加工的表面粗糙度值下降71.7%。     

Strain gradient plasticity based finite element analysis of ultra-fine wire drawing process

Steady-state rigid-plastic finite element analysis coupled with strain gradient plasticity theory has been performed to examine the size effect of material on its plastic deformation behavior and find an optimal semi-cone angle of die which minimizes the drawing energy in the ultra-fine wire drawing process. A stream-line tracing method was adopted to calculate strain component at each element and a strain surface function was introduced to compute the equivalent strain gradient of each element. Introduction of this function enables us to use an established FE code without renewal of its main structure. Hence, the constitutive equation in FE formulation is changed to couple the strain gradient plasticity. A series of FE simulation reveals that significant differences in drawing stress are observed when material size approaches its intrinsic material length. When the strain gradient plasticity theory is reflected on the steady-state FE analysis, the optimal semi-cone angle of the die is reduced by 30%. The variation of optimal semi-cone angle is attributable to considerable increment of homogeneous deformation when the material size reaches its intrinsic material length.     

Note: Fabrication of tapered fibre tip using mechanical polishing method

Tapered fibre tips fabricated using mechanical polishing method is studied. The fibre tips are formed by sequential polishing flat-ended single mode fibres with decreasing aluminium oxide polishing film grit size. Based on the proposed technique, tapered fibre tips with cone angle ranging from 30° to 130° are fabricated by controlling the polishing angle. Besides the variety of cone angle, considerable smoothness of the fibre tip surface may assist in good metal coating and hence a well-defined aperture can be obtained. In addition, this paper presents a two-step hybrid fabrication method combining the proposed polishing method with chemical etching method to increase the possible fibre tip cone angles achievable by chemical etching method.     

Elastic buckling of ring-stiffened cone–cylinder intersections under internal pressure

Cone–cylinder intersections are commonly found in pressure vessels and piping. Examples include conical end closures to cylindrical vessels and conical reducers between cylinders of different radii. In the case of a cone large end-to-cylinder intersection under internal pressure, the intersection is subject to a large circumferential compressive force. Both the cone and the cylinder may be thickened near the intersection to resist this compression, but it is often convenient and necessary to augment further the strength of the intersection using an annular plate ring stiffener. Under this large circumferential compression, the intersection may fail by elastic buckling, plastic buckling or plastic collapse. This paper describes an investigation of the elastic buckling strength of ring-stiffened cone–cylinder intersections. Two buckling modes are identified: a shell mode for thin intersections with a shallow cone (a cone with its apex half angle approaching 90°) and/or a relatively stocky ring stiffener, and a ring mode for other cases. An existing elastic buckling approximation for annular plate rings in steel silos is found to be applicable to the intersection when it buckles in the ring mode. New approximate design equations are also established for the shell mode. In addition, simple expressions are identified which relate the number of circumferential buckling waves to the geometric parameters of the intersection.     

Plastic flow through conical converging dies, using a viscoplastic constitutive equation

The influence of the working speed in drawing or extrusion processes is shown when a viscoplastic constitutive equation is used and when the yield condition is replaced by a yield inequality. It is shown that the drawing (or extrusion) pressure is increased when the speed of the process or when the viscosity coefficient of the material is increased, or when the diameter of the die is decreased or when the mean yield stress of the billet is reduced. This increase is more significant for higher reduction ratios and semi-cone angles. It is shown that the optimum semi-cone angle is also dependent on the speed of the process as is the critical semi-cone angle, which corresponds to the possible formation of a dead-zone near to the die surface. The pressure on the die surface is variable and depends on the speed of the process also. From the numerical examples given it is evident that in many practical circumstances the influence of speed may be significant even for very low working speeds.