Limitation induced by electrical charges effects on micromechanisms

Electrical charges generation occurring during contact, friction or fracture of insulating materials (ceramics, polymers) has been identified for a long time. But the contribution of these electrical charges to the friction and wear behaviour is usually neglected in the energetical balance. Based on published results and on our own experimental results on the ability of the insulating material on trapping charges, we show in this study that the interaction energy during friction depends markedly on these trapped charges which induce moreover long distance effects. Consequently, on the particular case of microdevices for which the surface area to volume ratio is large and the external pressure is low, such effects can act markedly upon both friction coefficient evolution and wear resistance by storage and release of polarisation energy in the whole tribosystem.     

微型机械设计基础研究

针对微型机电系统发展过程中存在的问题 ,论述了开展微型机械设计基础研究的意义和必要性 ,并且总结出微型机械研究中关于微机械设计基础研究的范畴和特点 ,提出了目前迫切需要开展的一些主要研究方向     

Effect of martensite phase volume fraction on acoustic emission signals using wavelet packet analysis during tensile loading of dual phase steels

This paper will investigate the application of wavelet-based Acoustic Emission (AE) signal processing on micromechanisms to identify failure in dual phase steels (DPS)s. The AE signals from a tensile test using a range of DPS with different volume fractions of martensite (VM)s, in the range of 11–65% VM, were obtained and their waveforms were decomposed into various wavelet levels, each of which was related to a specific frequency range. Each level includes precise details, or approximations, of the so-called components. The energy percentage of each component was obtained by comparing it with the total energy of the AE signal. The energy distribution criterion in each component indicates that the energy in the AE signals is essentially concentrated on two or three components within a distinct frequency range. Each frequency range is related to a separate micromechanism, identifying failure. The results found for low VM in the contribution of ferrite/martensite interface decohesion figure prominently because 48% of their total energy was related to this micromechanism for a sample with 11% VM. The contribution of martensite phase fracture increased from 12% to 48.3% of total energy with an increase of VM in the range of 11% to 65% VM. The results were verified with microscopic observations and they indicate that wavelet-based signal processing is an efficient tool in the analysis of AE signals to detect micromechanisms identifying failure in DPS.     

平面双稳态柔性微机构的优化设计

讨论了一种平面双稳态柔性微机构的设计问题。首先给出了机构稳定平衡位置的物理含义 ,建立了两种类型平面双稳态柔性微机构的伪刚体模型。提出了一种允许设计者随意指定稳定平衡位置点的具有较大自由度的优化设计方法 ,建立了优化数学模型及相应的约束准则 ,采用一种改进的遗传进化算法获得了全局最优解。根据所得的最优解对双稳态柔性微机构进行了分析 ,结果表明该设计方法是有效的     

国外微型机械及微执行器的研究

由于高新技术的迅速发展,微型机械包括各种微传感器、微执行器和微控制器的研究和为一些尖端技术发展过程中的重要手段越来越受到国际科技界的重视。微型机械多种多样。如可在狭小的空间和危险场所进行维护检查的自行式微型机械、可进入管道、人体腔体甚至血管进行检查和手术的微型机械、扫描隧道显微镜(STM)和原子力显微镜上的分辨力以纳米计的微动机构、半导体领域和分子机械领域都出现了很精密的微型机械。国外为了提高微型机械的研究水平,最近还定期举办微型机构和微型机器人的比赛,包括爬山、爬崖和自我表演等项目,由于微型机械都必须有所动作,因此其中的微执行器(micro-actuator)最为重要,其工作原理多种多样。本文将就微型机械、微执行器的原理和国外的微型机构比赛作一综述。     

Micromechanism fabrication using silicon fusion bonding

Silicon fusion bonding is studied as an enabling technology for the fabrication of microrobotic mechanisms. The effects of both surface activation technique and annealing temperature on bond strength are considered using a crack-opening technique. As part of the study, the relationship between patterned silicon feature size and the resulting bond strength is explored. Based on the experimental results, recommendations for an optimal silicon fusion bonding process for micromechanism fabrication are presented. The experimental results indicate that bulk silicon bonding strength can be achieved independent of feature size at temperatures as low as 300°C, with positive implications for micromechanism fabrication.     

Micromechanisms of fatigue crack growth in a forged Inconel 718 nickel-based superalloy

The micromechanisms of fatigue crack propagation in a forged, polycrystalline IN 718 nickel-based superalloy are evaluated. Fracture modes under cyclic loading were established by scanning electron microscopy analysis. The results of the fractographic analysis are presented on a fracture mechanism map that shows the dependence of fracture modes on the maximum stress intensity factor, K_max, and the stress intensity factor range, ΔK. Plastic deformation associated with fatigue crack growth was studied using transmission electron microscopy. The effects of ΔK and K_max on the mechanisms of fatigue crack growth in this alloy are discussed within the context of a two-parameter crack growth law. Possible extensions to the Paris law are also proposed for crack growth in the near-threshold and high ΔK regimes.