气体静压轴承与主动磁轴承混合支撑轴系结构设计及静态性能研究

针对由气体静压轴承作为支撑的气浮精密主轴存在承载力相对较小及可控性不高的问题,结合带有周向微通槽的气体静压轴承与基于增量式PID控制的主动磁轴承,设计一款气磁混合支撑主轴。为提高小孔节流气体静压轴承的承载力,将气体静压轴承内表面的稳压室用矩形、三角形、半圆形截面动压微通槽相连通,通过FLUENT仿真分析3种截面动压微通槽对轴承承载能力的影响;以主轴的回转精度为衡量标准,在Matlab Simulink中仿真分析增量式PID控制的主动磁轴承的性能。结果表明:3种截面动压微通槽能有效提高气体静压轴承的承载能力,其中同等条件下矩形截面效果最好,可使轴承的承载力提高54%;基于增量式PID控制的主动磁轴承能够有效提高主轴的稳态响应速度及回转精度,使其在启动40 s后保持0.2μm的回转精度。     

Photophoretic Levitation of Macroscopic Nanocardboard Plates

Scaling down miniature rotorcraft and flapping-wing flyers to sub-centimeter dimensions is challenging due to complex electronics requirements, manufacturing limitations, and the increase in viscous damping at low Reynolds numbers. Photophoresis, or light-driven fluid flow, was previously used to levitate solid particles without any moving parts, but only with sizes of 1–20 µm. Here, architected metamaterial plates with 50 nm thickness are leveraged to realize photophoretic levitation at the millimeter to centimeter scales. Instead of creating lift through conventional rotors or wings, the nanocardboard plates levitate due to light-induced thermal transpiration through microchannels within the plates, enabled by their extremely low mass and thermal conductivity. At atmospheric pressure, the plates hover above a solid substrate at heights of ≈0.5 mm by creating an air cushion beneath the plate. Moreover, at reduced pressures (10–200 Pa), the increased speed of thermal transpiration through the plate's channels creates an air jet that enables mid-air levitation and allows the plates to carry small payloads heavier than the plates themselves. The macroscopic metamaterial structures demonstrate the potential of this new mechanism of flight to realize nanotechnology-enabled flying vehicles without any moving parts in the Earth's upper atmosphere and at the surface of other planets.     

BHA轴向磁干扰对方位测量误差的影响——基于人工磁场模拟方法

井下钻具组合（BHA）磁化形成的轴向磁场干扰是定向组件磁方位测量的一个重要的误差因素。为了对该误差因素进行独立分析，建立了大型三轴亥姆霍兹线圈人工磁场系统作为研究环境，使用不同磁通量的多个磁化组件作为干扰源研究在理想环境中轴向干扰磁场对定向组件的影响，并在此基础上提出了一种估算磁化组件磁极强度和校正轴向干扰的方法，通过改变空间姿态和三轴亥姆霍兹线圈磁场强度，分析了在不同井斜角、方位角和磁倾角的井眼轨迹中，轴向磁干扰对定向组件方位测量误差的影响，最后证明了校正磁性组件的轴向干扰方法，可以有效地提升BHA定向组件的方位测量精度。     

Effects of isothermal treatment parameters on the microstructure of semisolid alloys

Cold-rolled 6061 aluminium alloys are used to prepare semisolid billets by recrystallisation and partial melting. The effects of isothermal treatment parameters on the microstructures were investigated. The results indicated that the high isothermal holding temperature increases the experimental liquid fraction, average grain size and shape factor. A long isothermal holding time also increases the experimental liquid fraction and improves the spheroidisation degree of solid grains, but the average grain size also increases. Moreover, when the isothermal holding time at high temperature is increased, the size of intragranular liquid droplets increases, but their quantity decreases. The optimal isothermal holding temperature and time during semisolid isothermal treatment were 635°C and 5?–?10?min, respectively.     

电永磁吸盘在石油套管接箍切断机下料工序中的应用

针对石油套管生产过程中接箍切断岗位人员搬运接箍劳动强度大、存在安全隐患的问题，对生产工艺过程、电磁吸盘的原理和性能进行分析，采用电永磁吸盘设计了一种接箍自动下料装置。该装置可以根据设定进行电磁吸盘的充/退磁，实现整层接箍的抓取和卸料，整个过程实现一键自动下料，全程不需人工干预。现场生产应用表明，使用电永磁吸盘进行整层接箍下料，能大幅降低岗位员工的劳动强度，生产效率提高5%以上，减少了安全隐患，达到了预期目的。     

Deformation and fracture mechanisms of in situ synthesized TiC reinforced TC4 matrix composites produced by selective laser melting

In this study, TiC/TC4 composites were fabricated using selective laser melting (SLM), and the deformation mechanism and fracture characteristics of the composites with nano-sized TiC particles formed in situ were studied. The experimental results showed that the rapid melting and solidification characteristics of SLM and the Marangoni effect of the liquid pool promoted a considerably homogeneous dispersion of the in situ-formed nanoscale-TiC reinforcement in the TiC/TC4 composites. In particular, an enhanced compressive strength of 1490.2 MPa and a considerable fracture elongation of 21.5% were simultaneously achieved for the TiC/TC4 composites, which could be attributed to the load transfer effect and the formation of denser and more uniformly distributed dimples. Combined with the finite element (FE) analysis, the uneven stress distribution in the shear band of the TiC/TC4 composites led to the fracture. Further, the fracture surface analysis showed that the in situ nanoscale TiC reinforcement promoted the fracture of microbubbles from the α/β interface with the concentrated distribution of the V element to the interface between TiC and the Ti matrix because of the load transfer, which promoted the uniform distribution of the V element in the dimple.     

Process parameter dependencies of continuous and pulsed laser modes on surface polishing of additive manufactured aluminium AlSi10Mg parts

Laser powder bed fusion is a well-established 3D printing technique for metal alloys, but exhibits a poor surface quality. Laser polishing provides the possibility of a fast contact-free and fully-automatable surface treatment. This paper deals with the experimental investigation of laser polishing of laser powder bed fusion parts made of aluminium AlSi10Mg. Laser polishing is done with a 4 kW solid state disc laser in combination with a multi-axis system and a one dimensional scanner optic. The laser is operated at continuous and pulsed operation mode. The parameter study reveals a high dependency of the achievable roughness on the laser beam intensity, the track and pulse overlap, the energy density and the number of polishing passes and polishing directions. Pulsed laser polishing mode with up to four passes from different directions revealed the lowest surface roughness of 0.14 μm Ra. With respect to the initial average surface roughness of Ra = 8.03 μm a reduction of the surface roughness of greater than 98 % could be achieved. Polishing with continuous laser radiation at one polishing pass resulted in Ra = 0.23 μm at an area rate of 20 cm²/min. Laser polishing using four passes achieved a further improvement up to Ra = 0.14 μm.     

Characterisation and in vitro cytotoxicity of toxic and degradation compounds in bamboo shoots (Dendrocalamus Sinicus) during traditional fermentation

Fermentation has been historically applied to reduce bamboo shoot (BS) toxicity. However, the underlying degradation pathway of the toxic compounds remains unknown. In this work, the cytotoxicity of BS against the BRL-3A cells was evaluated, and the changes in chemical constituents were determined to reveal the influence of fermentation on BS. The in vitro toxic evaluation revealed fermentation time was crucial in decreasing the toxicity. The main compounds in fresh and fermented were qualitatively and quantitatively determined and were further targeted isolated and identified. A mathematical model to describe the change rate as a function of fermentation time was formulated. Dynamic profiling revealed that taxiphyllin 1 , p-hydroxybenzaldehyde 2 and methyl-p-hydroxybenzoate 3 decreased and transformed into intermediate compounds (p-hydroxybenzoic acid 4 and p-hydroxybenzyl alcohol 5 ), finally converting into p-hydroxytoluene 6 during fermentation. The results provided basis on the chemical components for practical fermentation and the quality control of BS products.     

磁絮凝强化技术处理厌氧消化污泥脱水液

为满足后续生物处理单元对固体悬浮物（SS）和铁浓度的进水要求，采用磁絮凝强化技术对厌氧消化污泥脱水液进行预处理。通过正交试验和单因素试验，本文考察了混凝水力条件、聚合氯化铝（PAC）投加量、聚丙烯酰胺（PAM）投加量、磁粉投加量及药剂投加顺序对磁絮凝效果的影响。试验结果表明：磁絮凝强化技术在快搅300r/min（2min）、慢搅100r/min（15min）、静置10min时，依次投加磁粉（40mg/L）、PAC（30mg/L）、PAM（4mg/L）时处理效果最好。在此运行条件下，SS和Fe³⁺去除率分别为97.61%、98.24%、絮凝指数（FI值）取得最大值、zeta电位绝对值最小，絮凝效果最佳。与对照相比，磁絮凝强化技术对SS和Fe³⁺去除率分别可提高3.70%和10.82%，同时絮体最大沉降速度可提高33%。磁絮凝技术处理后的出水不仅可以满足后续生物处理单元对SS和铁浓度的要求，还可以有效提高磁絮凝体的沉降速度，减小沉淀时间，具有较好的实用价值。