Fabrication of Cu/graphite film/Cu sandwich composites with ultrahigh thermal conductivity for thermal management applications

Effective thermal management of electronic integrated devices with high powder density has become a serious issue, which requires materials with high thermal conductivity (TC). In order to solve the problem of weak bonding between graphite and Cu, a novel Cu/graphite film/Cu sandwich composite (Cu/GF/Cu composite) with ultrahigh TC was fabricated by electro-deposition. The micro-riveting structure was introduced to enhance the bonding strength between graphite film and deposited Cu layers by preparing a rectangular array of micro-holes on the graphite film before electro-deposition. TC and mechanical properties of the composites with different graphite volume fractions and current densities were investigated. The results showed that the TC enhancement generated by the micro-riveting structure for Cu/GF/Cu composites at low graphite content was more effective than that at high graphite content, and the strong texture orientation of deposited Cu resulted in high TC. Under the optimizing preparing condition, the highest in-plane TC reached 824.3 W·m⁻¹·K⁻¹, while the ultimate tensile strength of this composite was about four times higher than that of the graphite film.     

超精密气体静压系统节流器法向随机微振动研究

以无气腔平面节流器为研究对象,对节流器流固耦合法向随机微振动进行了理论仿真和实验研究。受限于节流器厚度与气膜厚度尺寸的差异和输入初始边界条件,建立了节流器的COMSOL仿真简化模型,对节流器-气膜微流场进行双向流固耦合数值模拟。仿真结果表明,节流器的法向随机微振动幅值关于节流器中心对称,且由中心向边缘逐渐增大;微振动幅值随气体入口流速的增大而增大。实验采用纳米级激光测振仪,依次测量供气压力为0.1,0.2,…,0.5 MPa时尺寸为75 mm×50 mm×14 mm的HEXAGON双环联结型节流器多个不同位置的法向振动,实验结果表明,法向随机微振动幅值分布特性与仿真结果一致,关于节流器中心对称,且由中心向边缘逐渐增大,验证了节流器法向微振动的"跷跷板"振动形式;在0.5 MPa供气压力下,边缘振动幅值超过1 nm。对实验数据进行功率谱密度分析,结果表明不同供气压力下法向随机微振动均在9.4 kHz和10.6 kHz处产生较大功率,可认为与节流器-气膜流固耦合系统的固有频率有关。研究结果有效地揭示了节流器法向随机微振动的特性,为气体静压系统避开随机共振区、优化气体静压系统的设计提供了理论指导。     

基于RGV轨导柔性线环境离散型零件生产过程管理与实践

为满足航空中小型结构件快速交付的需要,以提升航空中小型结构件制造高精度、自动化和高效率为目标,通过对航空中小型结构件加工现状进行梳理分析,搭建柔性生产线自动排程与调度平台,实现柔性生产线工艺设计与准备过程管理,简化工艺准备流程,推进快换工装的应用并进行自动化程序管理;在柔性生产线加工运行过程中采用可视化管理方法,推动自动化环境下加工过程资源保障集中化管理。最终使该管理方法在某项目中进行成功实践,取得了良好的经济效益。     

Unusual Two-Step Assembly of a Minimalistic Dipeptide-Based Functional Hypergelator

Self-assembled peptide hydrogels represent the realization of peptide nanotechnology into biomedical products. There is a continuous quest to identify the simplest building blocks and optimize their critical gelation concentration (CGC). Herein, a minimalistic, de novo dipeptide, Fmoc-Lys(Fmoc)-Asp, as an hydrogelator with the lowest CGC ever reported, almost fourfold lower as compared to that of a large hexadecapeptide previously described, is reported. The dipeptide self-assembles through an unusual and unprecedented two-step process as elucidated by solid-state NMR and molecular dynamics simulation. The hydrogel is cytocompatible and supports 2D/3D cell growth. Conductive composite gels composed of Fmoc-Lys(Fmoc)-Asp and a conductive polymer exhibit excellent DNA binding. Fmoc-Lys(Fmoc)-Asp exhibits the lowest CGC and highest mechanical properties when compared to a library of dipeptide analogues, thus validating the uniqueness of the molecular design which confers useful properties for various potential applications.     

Inhibition of stress corrosion cracking in 304 stainless steel through titanium ion implantation

The effects of titanium ion implantation on the stress corrosion cracking (SCC) behaviour of 304 austenitic stainless steel were studied. Slow strain rate tests (SSRTs) were conducted on 304 steel in air and in 5?wt-% NaCl solution. The microscopic effects of ion implantation were evaluated by Stopping and Range of Ions in Matter Procedures (SRIM). Fracture morphologies and microstructures were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The fracture surfaces illustrate that ion implantation significantly inhibits the corrosion pits that initiate SCC. A dense passive film, which inhibits SCC, was formed during the ion implantation process. SCC initiation was restrained due to the dense dislocation nets that were generated by titanium ion implantation.

Highlights

• Ion implantation inhibits SCC susceptibility.

• The lack of Cr at the grain boundary leads to the expansion of SCC along the grain boundary.

• Implantation-induced damage leads to high-density dislocations.

• The surface was amorphised due to high-density dislocations.

     

太赫兹可调谐滤波器设计

为了实现太赫兹信号的可调谐滤波，设计了一种基于柔性材料的太赫兹可调谐滤波器。通过扭曲特氟龙（Teflon）波导形成环型谐振器，实现了160～200 GHz频段的带阻滤波功能。改变谐振腔长可实现自由频谱范围（FSR）和滤波频点的调谐，实验测试了自由频谱范围在1.9 GHz和2.8 GHz间切换以及相应的滤波特性。研究表明，谐振腔长一定时，改变弯曲半径可实现滤波阻带抑制度的调节，柔性材料太赫兹环型谐振器可用于可调谐滤波，且具有较高的自由度。     

A Smart Flexible Solid State Photovoltaic Device with Interfacial Cooling Recovery Feature through Thermoreversible Polymer Gel Electrolyte

Quasi‐solid‐state dye‐sensitized solar cells (DSSCs) fabricated with lightweight flexible substrates have a great potential in wearable electronic devices for in situ powering. However, the poor lifespan of these DSSCs limits their practical application. Strong mechanical stresses involved in practical applications cause breakage of the electrode/electrolyte interface in the DSSCs greatly affecting their performance and lifetime. Here, a mechanically robust, low‐cost, long‐lasting, and environment‐friendly quasi‐solid‐state DSSC using a smart thermoreversible water‐based polymer gel electrolyte with self‐healing characteristics at a low temperature (below 0 °C) is demonstrated. When the performance of the flexible DSSC is hindered by strong mechanical stresses (i.e., from multiple bending/twisting/shrinking actions), a simple cooling treatment can regenerate the electrode/electrolyte interface and recover the performance close to the initial level. A performance recovery as high as 94% is proven possible even after 300 cycles of 90° bending. To the best of our knowledge, this is the first aqueous DSSC device with self‐healing behavior, using a smart thermoreversible polymer gel electrolyte, which provides a new perspective in flexible wearable solid‐state photovoltaic devices.     

织物表面导电线路喷射打印起始端凸起形成过程研究

为提高织物表面微滴喷射打印导电线路的成形质量,针对导电线路喷射打印过程中线路沉积形貌的起始端凸起现象,利用高速相机对线路成形过程进行采集,研究微滴间融合振荡过程中左右接触角的动态变化,微滴与线路融合以及液体向线路起始端的输送过程,提出线路起始端凸起的消除方案并进行实验。结果表明:在融合振荡过程中,微滴向起始端的振荡趋势始终大于向另一侧的振荡趋势,导致打印线路起始端的织物基板润湿区域不断扩大;微滴与线路接触后,其中一部分液体润湿织物基板拓展线路长度,一部分通过线路以恒定速度输送至起始端,在线路起始端形成凸起;利用抗坏血酸溶液润湿织物表面后,成形线路起始端凸起现象得到消除,整体线路路径均匀,沉积形貌良好。     

微观表面形貌对螺旋槽液膜密封空化发生的影响

为探索微观表面形貌对液膜密封空化的影响,基于满足质量守恒的JFO空化模型及坐标变换,建立考虑微观表面形貌的双坝区螺旋槽液膜密封数学模型;采用有限体积法离散求解控制方程,综合分析表面粗糙度、周向波度和径向锥度对螺旋槽液膜密封空化发生的影响规律。结果表明:相比而言,密封面计入微观表面形貌后,摩擦副液膜中空穴区发生位置分散且形状不规则;以空化面积比为判据,较大表面粗糙度对液膜空化促生虽起到积极作用,但数据较小,可忽略不计;锥度对液膜中空穴促生和抑制影响有限,波幅的增加显著促进液膜中空穴的发生;高频波数时,正锥度有利于降低液膜空化面积比,抑制空穴。     

自旋对角接触球轴承弹流润滑与油膜刚度的影响

根据角接触球轴承自旋运动特征，同时考虑弹流润滑效应，建立角接触球轴承考虑自旋运动的弹流润滑模型；采用多重网格法求解弹性变形，利用有限差分法迭代求解雷诺方程，得到较为精确的数值解；分析不同赫兹接触压力、滚道表面粗糙度下自旋对角接触球轴承弹流润滑和油膜刚度的影响。结果表明：考虑自旋时随着Hertz接触压力、自旋角速度增大，油膜厚度减小，油膜压力增大，油膜承压区域呈细长状，并向接触中心靠近；随着滚道表面粗糙度幅值增大，油膜压力和膜厚均出现了波动，且考虑自旋运动时，轴承油膜厚度明显减小，油膜局部压力峰值更大；随着卷吸速度、润滑油黏度增大，油膜刚度减小，而考虑自旋运动时油膜刚度值更大；随着自旋角速度增大，油膜刚度逐渐增大。