超声振动辅助激光熔覆IN718-Hf涂层的抗高温氧化性能

目的 基于航天航空领域对IN718合金的抗高温氧化性能需求,通过活性元素(RE)掺杂与物理场辅助,提升IN718合金的抗高温氧化性能。方法 采用超声振动辅助激光熔覆工艺,在IN718合金表面制备IN718-Hf熔覆层,研究涂层的微观结构演变,以及在800℃下长达100h的氧化行为。利用扫描电子显微镜(SEM)、电子探针显微分析仪(EPMA)研究涂层的显微组织、氧化膜结构和元素分布。通过X射线衍射仪(XRD)分析物相。结果 在不同Hf含量(均以质量分数表示)的涂层中,IN718-Hf(0.3%)涂层中的氧化层最薄、最均匀。Hf的高化学活性使得它很容易与其他元素发生反应,增加了成核粒子数量,使涂层中的微观结构细化。超声振动的施加提升了熔池的过冷程度,同时打碎了熔池中粗大的柱状枝晶,从而达到了细化晶粒的目的。晶粒细化有利于形成致密均匀的氧化层,从而增强材料的抗高温氧化性。氧化层具有双层结构,外层为Mn Cr₂O₄尖晶石,内层为Cr₂O₃。Hf的掺杂和超声振动的施加促进了Mn Cr₂O...     

Experimental and numerical study of a horizontal-vertical gas-solid two-phase system with self-excited oscillatory flow

To better explore the energy-saving mechanism and flow characteristics of the self-excited oscillatory flow, the experiment is performed by a new self-excited oscillatory flow generator that the 45° oblique sheet is mounted through the pipe axis in a horizontal-vertical closed pneumatic conveying system. The experimental study focuses on the optimum air-velocity and power consumption, and results shows the maximum reduction of the optimum air-velocity and the coefficient of power consumption are approximately 8.2% and 16.4%, respectively. In addition, the CFD-DEM coupled approach is first developed to investigate the interaction of gas-solid flow in terms of the gas turbulent kinetic energy and spatial particle flow characteristics. Compared with the conventional pneumatic conveying, it is found that the optimum air-velocity and power consumption are reduced by the new self-excited oscillatory flow at lower air-velocities. The numerical results show that the approximately symmetric distribution of axial velocity and the intensive tangential velocity is emerged in the self-excited oscillatory flow at upstream. Particles is efficiently dispersed and suspended by the self-exited oscillatory flow reflecting in the smaller particle variation coefficient and the lager particle suspension coefficient. And since the airflow kinetic energy is utilized more fully to promote particles flowing, the spatial particle axial velocity is accelerated and reached early steady state. As a result, the developed numerical model is further explained the mechanism of energy saving with the self-excited oscillatory flow.     

小孔流道内容积交变空化流场特性分析

目的 基于容积交变空化原理,研究小孔流道内容积交变空化流场的演变规律,以及容积交变频率和容积变化量等关键工艺参数对流场特性的影响,为容积交变空化抛光小孔内表面提供指导。方法 首先,建立小孔流道内容积交变空化流场的三维瞬态仿真模型。其次,采用标准k-epsilon模型、Zwart-Gerber-Belamri模型模拟不同容积交变频率和容积变化量下容积交变空化流场含气率和湍流强度,并与高速摄像结果进行比较分析。最后,对机械加工的Al 1060和T2 Cu小孔内表面进行抛光,验证容积交变空化抛光小孔内表面的可行性。结果 在一个周期内,当容积变化量为20 mm,容积交变频率分别为90、100、110、120 Hz时,小孔流道内容积交变空化流场含气率和湍流强度均随容积交变频率的增大而增大,含气率最高可达0.664 8;当容积交变频率为120 Hz,容积变化量分别为10、15、20、25 mm时,小孔流道内容积交变空化流场含气率和湍流强度均随容积变化量的增大而增大,含气率最高可达0.706 8。随着活塞的拉伸和压缩,湍流强度也由两边强、中间弱逐渐转变为两边弱、中间强,并在周期末达到最大。实验研究表明,经过容积交变空化抛光后,Al 1060小孔内表面的粗糙度由0.704 4 μm降低到0.324 7 μm,T2 Cu小孔内表面的粗糙度由0.721 4 μm降低到0.357 3 μm,小孔内表面粗糙度明显降低。结论 容积交变空化抛光小孔内表面具有可行性。可通过提高容积交变频率和容积变化量来提高小孔流道内容积交变空化流场含气率和湍流强度,进而提高容积交变空化抛光小孔内表面的抛光效率。     

Experimental and numerical study on the horizontal-vertical pneumatic conveying system with pulse excitation flow based on POD and recursive analysis

To solve the problem of energy loss during pneumatic conveying, a new energy-saving method of pneumatic transportation, pulse excitation flow, is proposed and applied to the transportation of petroleum coke. Firstly, the minimum pressure drop velocity of petroleum coke transported by pulse excitation flow is obtained through experimental research, and then the energy-saving mechanism of pulse excitation flow is explored through CFD-EDM coupling. The experimental results show that the energy loss coefficient of pulse excitation flow is reduced by 12.6% compared with axial flow. The numerical results show that the pulse excitation flow will produce alternating positive and negative vortices, and using the pulse excited flow conveying can make the particles enter the suspension region 6D earlier and reduce the energy loss, which further indicates that the gas–solid coupling effect of the pulsed excitation flow is more conducive to the dispersion and acceleration of the particles compared with axial flow.     

高效求解三维装箱问题的剩余空间最优化算法

为实现三维装箱问题的高效求解，提出了一个三维的剩余空间最优化算法（Three-Dimensional Residual-Space-Optimized Algorithm，3D-RSO）。在满足3个著名约束的条件下，该算法将三维问题转化为带有高度约束的二维问题，通过对箱子放置后的剩余空间状态分析，提出了基于概率较优的空间分割方法和箱子布置规则。相比于传统算法，3D-RSO在求解过程中不需要任何的预处理和搜索操作，是一种最坏计算复杂度为[O(2n2)]的直接求解算法。针对强异构体的实验表明，该算法能够在极短的时间内对算例进行高效求解，适合应用在大规模或者需要被快速求解的三维装箱问题中。     

Evaluation of the impact of the physical dimensions and material of the semiconductor chip on the reliability of Sn3.5Ag solder interconnect in power electronic module: A finite element analysis perspective

This paper primarily focuses on an evaluation study for the temperature cycling capability of tin silver solder interconnect in power electronic applications by the impact of die dimensions and die material properties. The study was investigated on finite element analysis perspective on chip/solder/substrate structure. A commercially available chip was chosen in the finite element analysis (FEA) as the nominal base die. Two thermal cycle profiles were utilised. The effect of die area, die thickness and material properties (Si and SiC) on the thermal cycling capability of the solder layer was investigated from FEA perspective. From the FEA, it was concluded that decrease in die thickness resulting in increment of thermal cycling capability of solder layer for both material (Si and SiC). Increase in die area increases the thermal cycling capability of solder. For higher ΔT thermal cycle, solder under SiC die perform better than solder under Si die in terms of thermal cycling capability. When the die thickness become smaller than a threshold value of the thermal cycle regime, solder under Si die have better thermal cycling capability than solder under SiC die. Additionally a parametric study was undertaken for a SiC chip/substrate structure under high ∆ T temperature cycling profile for solder layer geometric parameter (wetting angle, titling angle and thickness). From the parametric study which utilised design of experiments (DoE), a wavelet radial basis surrogate model was generated. A sensitivity analysis was performed on surrogate model in order to identify the most influencing parameter. From the sensitivity analysis, it was concluded that wetting angle and solder layer thickness of solder layer have significant impact on the thermal cycling capability of the solder layer.     

基于LabVIEW的离网型风力发电机风速-功率特性研究

通过对离网型风力发电机实际运行状态及气象情况的监测,绘制了风速-功率散点图.利用最大似然估计法对风机输出功率曲线进行拟合,结果表明:七次多项式拟合结果最逼近实际工况;二次多项式拟合曲线精度稍差,但表达式简单明了,可快速预测风力发电机发电量.此外,通过对风力发电机发电量的实际值、理论功率曲线预测值以及利用最大似然估计法拟合得到的功率曲线的预测值的对比,结果表明:风力发电机生产厂商提供的曲线只能反映其稳态的风速-功率关系,用来预测风力发电机发电量还存在较大误差;利用最大似然估计法拟合得到的功率曲线预测的风力发电机发电量误差明显偏小.     

A two-dimensional optical cross-connect with integrated waveguides and surface micromachined crossbar switches

The design, fabrication and test results of an all-optical cross-connect, which uses electrostatically actuated micromechanical digital mirrors to steer optical signals in a network of planar waveguides, are presented. The substrate consists of a network of spliced planar waveguides on silica substrates. The switches, located at the waveguide intersections, are formed with an electroplated T-structure consisting of a horizontal perforated square plate suspended by four elastic beams. When operated, the horizontal plate is pulled up making the mirror move out of the optical path thus steering the beam. An 8×8 switch array has been fabricated and tested. Actuation and relaxation switching times near 3 ms have been demonstrated with an actuation voltage of 120 V. The optical insertion loss for the array typically varied from 2.3 dB for a single trench in the optical path (shortest optical path) to 8 dB for 15 trenches in the optical path (longest optical path).     

微型胶囊机器人外壳的淹没式空化射流成形质量分析

目的 针对微型胶囊机器人外壳成形的技术难题,提出了一种基于淹没式空化射流冲击箔材的微型机器人外壳成形方法,分析了微型外壳的成形质量。方法 基于微型胶囊机器人外壳的特征尺寸设计模具,利用淹没式空化射流试验装置,完成了对T2铜箔的高能冲击成形试验,分析了淹没式空化射流的成形原理,讨论了微型外壳的成形深度、表面粗糙度、厚度减薄率以及纳米硬度。结果 在空化射流冲击成形过程中,微型外壳成形深度的增长率随成形时间的延长而减小,最大成形深度可达291.4 μm(模具最大深度为300 μm);成形后微型外壳表面粗糙度Ra值由0.789 7 μm逐渐增加至1.057 6 μm,厚度减薄率为10%~25%,纳米硬度提高了21.78%~46.64%,最大硬度增长率出现在刃口处。结论 在淹没式空化射流成形过程中,微型外壳的成形深度与模具的相当,微型外壳表面存在小幅度粗化现象,成形后减薄率降低,纳米硬度大幅提高,抵抗外界破坏能力提高。     

Orientation and strain rate dependent tensile behavior of single crystal titanium nanowires by molecular dynamics simulations

Molecular dynamics simulation was employed to study the tensile behavior of single crystal titanium nanowires(NWs)with1120,1100and[0001]orientations at different strain rates from 10~8s~(-1)to10~(11)s~(-1).When strain rates are above 10~(10)s~(-1),the state transformation from HCP structure to amorphous state leads to super plasticity of Ti NWs,which is similar to FCC NWs.When strain rates are below 10~(10)s~(-1),deformation mechanisms of Ti NWs show strong dependence on orientation.For1120orientated NW,1011compression twins(CTs)and the frequently activated transformation between CTs and deformation faults lead to higher plasticity than the other two orientated NWs.Besides,tensile deformation process along1120orientation is insensitive to strain rate.For 1100orientated NW,prismaticaslip is the main deformation mode at 10~8s~(-1).As the strain rate increases,more types of dislocations are activated during plastic deformation process.For[0001]orientated NW,1012extension twinning is the main deformation mechanism,inducing the yield stress of[0001]orientated NW,which has the highest strain rate sensitivity.The number of initial nucleated twins increases while the saturation twin volume fraction decreases nonlinearly with increasing strain rate.