大塑性变形工艺制备纳米晶过饱和固溶体的研究进展

合金在大塑性变形过程中能够形成纳米晶过饱和固溶体,呈现出不同于传统粗晶材料的微观结构和独特性能。近年来,纳米晶过饱和固溶体的形成机制及其热稳定性已成为国内外的一个研究热点。综述了大塑性变形工艺(如机械合金化法、高压扭转法等)制备纳米晶过饱和固溶体的研究概况,着重讨论分析了大塑性变形诱导纳米晶形成和固溶度扩展的几种机制及其局限性,简要介绍了纳米晶过饱和固溶体的热稳定性及其影响因素,最后对该领域今后的研究方向做出了分析和展望。     

Investigation of TiAlN coated roller burnishing on Al-(B4C)p MMC workpiece material

Burnishing avoids the need for super finishing operations after the conventional turning process, to enhance the surface quality. This paper deals with the surface modifications of Al(B₄C)_p Metal Matrix Composites (MMC) workpiece material after burnishing with a TiAlN coated WC roller. The burnishing speed, lubrication type, burnishing passes, and coating were the input parameters. Surface hardness and roughness after the burnishing were studied. It was found that the coating on the WC roller had enhanced the hardness in the workpiece after burnishing in the case of Al-5?wt.% (B₄C)_p, under all conditions. The effect of the coating on the work piece surface hardness was not significant with Al-10?wt.% (B₄C)_p. While burnishing Al-5?wt.% (B₄C)_p, the minimum surface roughness combined with maximum surface hardness was obtained, during the third pass under dry condition using uncoated rollers. The number of passes to achieve the desired surface conditions reduced, on using coated rollers with kerosene as the lubricant.     

Natural Plant Materials as Dielectric Layer for Highly Sensitive Flexible Electronic Skin

Nature has long offered human beings with useful materials. Herein, plant materials including flowers and leaves have been directly used as the dielectric material in flexible capacitive electronic skin (e‐skin), which simply consists of a dried flower petal or leaf sandwiched by two flexible electrodes. The plant material is a 3D cell wall network which plays like a compressible metamaterial that elastically collapses upon pressing plus some specific surface structures, and thus the device can sensitively respond to pressure. The device works over a broad‐pressure range from 0.6 Pa to 115 kPa with a maximum sensitivity of 1.54 kPa^?1, and shows high stability over 5000 cyclic pressings or bends. The natural‐material‐based e‐skin has been applied in touch sensing, motion monitoring, gas flow detection, and the spatial distribution of pressure. As the foam‐like structure is ubiquitous in plants, a general strategy for a green, cost‐effective, and scalable approach to make flexible e‐skins is offered here.     

钛合金双态组织高温拉伸行为的晶体塑性有限元研究

创建一个包含多变体结构特征的双态组织几何模型,提出一种变形协调性的评估方法,采用以率相关滑移为主的晶体塑性有限元本构关系,研究了具有不同组织特征的Ti-6Al-4V合金双态组织的高温拉伸行为。结果表明：在多晶变形过程中,α_p相承载了更多的应变;在变形后的样品中,出现了大致对称分布于拉伸方向两侧的高应变交叉条带;存在于α_p与β_T之间的包围结构特征,可加剧局域应变分配的差异;随着α_p相体积分数的升高应变量降低,整体应变协调性先较快降低而后平稳;随着α_s片层厚度的增加高应变条带特征弱化,整体应变协调系数升高;含双变体α_s片层团簇结构的β_T组织,其应变协调性低于含单变体和三变体的组织。     

微观组织演变对细晶Mg-Y-Nd合金超塑性性能的影响

在初始应变速率为2×10^-2~4×10^-4 s^-1,温度为683~758 K的条件下,对用水下搅拌摩擦加工制备的细晶Mg-Y-Nd合金进行高温拉伸实验,研究了微观组织演变对其超塑性性能的影响。结果表明:因为具有细小均匀的微观组织和良好的热稳定性,Mg-Y-Nd合金在733 K和3×10^-3 s^-1初始应变速率下表现出最大的伸长率(967%),在758 K和2×10^-2 s^-1条件下表现出最优的高应变速率超塑性(900%)。在高温下暴露时间过长导致α-Mg晶粒和第二相颗粒显著长大,使试样的伸长率明显降低;因为第二相颗粒与镁基体之间有良好的变形协调性,在相界处不会产生明显的应力集中,裂纹主要在晶界生成。     

Bionic autonomous learning control of a two-wheeled self-balancing flexible robot

This paper presents an OCPA (operant conditioning probabilistic automaton) bionic autonomous learning system based on Skinner’s operant conditioning theory for solving the balance control problem of a two-wheeled flexible robot. The OCPA learning system consists of two stages: in the first stage, an operant action is selected stochastically from a set of operant actions and then used as the input of the control system; in the second stage, the learning system gathers the orientation information of the system and uses it for optimization until achieves control target. At the same time, the size of the operant action set can be automatically reduced during the learning process for avoiding little probability event. Theory analysis is made for the designed OCPA learning system in the paper, which theoretically proves the convergence of operant conditioning learning mechanism in OCPA learning system, namely the operant action entropy will converge to minimum with the learning process. And then OCPA learning system is applied to posture balanced control of two-wheeled flexible self-balanced robots. Robot does not have posutre balanced skill in initial state and the selecting probability of each operant in operant sets is equal. With the learning proceeding, the selected probabilities of optimal operant gradually tend to one and the operant action entropy gradually tends to minimum, and so robot gradually learned the posture balanced skill.     

基坑开挖对邻近建筑物影响的数值模拟

基坑开挖引起的近邻建筑物沉降变形是多种因素耦合作用的结果,现有的计算理论很难考虑这种多因素的耦合作用。针对这一问题,采用大型工程软件ADINA对锚杆支护形式下基坑开挖引起的近邻建筑物沉降问题进行了数值模拟分析,得出了一些基本结论:建筑物的沉降在宽度方向变化显著,在长度和高度方向变化不明显;建筑物的水平位移在高度方向变化显著,在长度和宽度方向变化不明显,基础埋得越深对沉降的影响越小,在开挖到基础标高之前,建筑物沉降不大,当开挖到标高以后,沉降发展很快,因此在实际施工时,基础标高以上可以加快开挖速度,标高以下需要放慢开挖速度。对于结构设计而言,应该在基础以下进行加固处理,以减小由基底附加应力产生的较大沉降。     

基于FLAC~(3D)的引水隧洞主、支洞交叉部位的围岩变形分析

圆形洞室开挖后,岩体中形成一个自由空间,使原来处于挤压状态的围岩,由于失去了支撑而发生向洞内松动变形;如果这种变形超过了围岩本身所能承受的能力,则围岩就会发生破坏。本文应用有限差分法数值模拟软件FLAC3D对主、支洞交叉部位的隧洞围岩变形进行模拟分析。模拟结果表明,隧洞开挖后,围岩各部分的位移量较大,围岩应力集中在主、支洞交叉部位。     

AC powder electroluminescent displays

Abstract— The current status of AC powder electroluminescent (ACPEL) displays is reviewed with particular emphasis given to color and lifetime. The printing of the displays in forward and reverse architectures is also discussed, in addition to the fabrication of ACPEL displays with interdigitated electrodes, and different types of ACPEL phosphors and materials for back electrodes, transparent conducting electrodes, binders, and dielectrics are considered. Furthermore, shape conformable and highly flexible ACPEL displays are surveyed.