磁弹性、热磁弹性理论及其应用

介绍了磁弹性、热磁弹性的基本内容,发展简史,基本方程,理论研究,实际应用研究及其未来应用前景．      

磁弹性簿板屈曲的研究进展和存在的若干问题

着重评述了近２０年来有关铁磁材料弹性薄板处在均匀横向外加磁场中发生屈曲这一新的磁－力耦合问题的理论与实验研究进展,在此基础上,介绍了笔者近年来围绕这一问题所开展的工作以及尚需进一步研究的几个问题。      

磁弹性簿板屈曲的研究进展和存在的若干问题

着重评述了近２０年来有关铁磁材料弹性薄板处在均匀横向外加磁场中发生屈曲这一新的磁－力耦合问题的理论与实验研究进展，在此基础上，介绍了笔者近年来围绕这一问题所开展的工作以及尚需进一步研究的几个问题。     

磁敏智能软材料及磁流变机理

磁敏智能软材料是一类将微米或纳米尺度的磁性颗粒分散在不同基体中制备而成的多功能复合材料.由于其流变性能在外磁场的调控下可以实现连续、快速、可逆的改变,因此在建筑、振动控制和汽车工业等领域得到了广泛地应用.本文首先介绍了磁敏智能软材料发展历史及分类,分析了不同种类的磁敏智能软材料的特点和存在的科学问题;然后从实验和理论两个方面讨论了磁流变机理的研究现状;最后从实际应用的角度对这类材料未来的发展方向进行了展望.      

天然橡胶基磁流变弹性体的研制与表征

磁流变弹性体又称磁敏高弹体,是一种由高分子聚合物和磁性颗粒构成的新型智能材料,它的力学、电学、磁学等诸性能可以由外加磁场来控制,因此磁流变弹性体在舰船、振动控制等领域具有广泛的应用前景.但目前国际上研制的磁流变弹性体存在机械性能不够好和磁致效应不够强的问题,这制约了基于磁流变弹性体器件的设计和应用.为了制备出实用型磁流变弹性体,本文对其制备条件进行了研究,包括基体类型、预结构化时磁场强度和温度、增塑剂和磁性颗粒含量对磁流变弹性体磁致效应的影响.结果表明,以天然橡胶为基体的磁流变弹性体,在高于600mT外加磁感应强度下,当磁性颗粒含量为80%(质量比)时,剪切模量的相对增量达133%;而当磁性颗粒含量为90%时,剪切模量的绝对增量达4.5MPa.本文还对磁流变弹性体应用环境进行了实验研究,结果表明磁流变弹性体在小应变下显示出更强的磁致效应,而激励频率不改变材料的磁致模量.     

天然橡胶基磁流变弹性体的研制与表征

磁流变弹性体又称磁敏高弹体，是一种由高分子聚合物和磁性颗粒构成的新型智能材料，它的力学、电学、磁学等诸性能可以由外加磁场来控制，因此磁流变弹性体在舰船、振动控制等领域具有广泛的应用前景。但目前国际上研制的磁流变弹性体存在机械性能不够好和磁致效应不够强的问题，这制约了基于磁流变弹性体器件的设计和应用。为了制备出实用型磁流变弹性体，本文对其制备条件进行了研究，包括基体类型、预结构化时磁场强度和温度、增塑剂和磁性颗粒含量对磁流变弹性体磁致效应的影响。结果表明，以天然橡胶为基体的磁流变弹性体，在高于600mT外加磁感应强度下，当磁性颗粒含量为80％（质量比）时，剪切模量的相对增量达133％；而当磁性颗粒含量为90％时，剪切模量的绝对增量达4．5MPa。本文还对磁流变弹性体应用环境进行了实验研究，结果表明磁流变弹性体在小应变下显示出更强的磁致效应，而激励频率不改变材料的磁致模量。     

矩形夹层板的非线性磁弹性随机振动

以表层较薄、夹心较软的四边简支矩形夹层板为研究对象,分析其在磁场环境中的非线性磁弹性随机振动问题。根据板壳磁弹性基本理论、夹层板的弯曲振动理论、连续体的随机振动理论,利用伽辽金积分法得到了在电磁场中受横向随机载荷作用时四边简支矩形夹层板的非线性磁弹性随机振动方程;并利用FPK方程法解出了四边简支矩形夹层板非线性随机振动位移响应和速度响应的方差、位移响应和速度响应的概率密度等多个数字特征。最后针对具体算例,通过数值模拟讨论了电磁参数、功率谱密度参数、板的几何尺寸的变化对各数字特征的影响。由数值模拟结果可知,调节随机激励、磁场强度、板的几何尺寸的大小能有效地控制结构随机振动产生振动位移的概率。     

一种测量纯摩擦力的柔性传感器及应变敏感条的研制

研制了一种可以测量纯摩擦力的柔性力学量传感器,作用在传感器上的正压力对摩擦力测量的影响不超过满量程的1.8％.传感器灵敏度高(186με/N),测量范围在几个牛顿(N)的量级.传感器的敏感元件为柔性敏感条,由电阻应变片和超弹性硅橡胶组成,其继承了超弹性材料的柔软性与电阻应变片技术成熟的特点.实验证明,柔性敏感条具有输入...     

斜磁场中矩形铁磁薄板的几何非线性磁弹性行为分析

基于复杂磁场中铁磁介质磁弹性广义变分原理,给出了包含磁场、铁磁薄板几何非线性的一组基本方程,并对斜磁场中铁磁薄板的磁弹性弯曲问题进行了分析.根据铁磁板内磁场分布特点定性分析了铁磁薄板所受磁力的特征,建立了考虑铁磁板磁场端部效应以及耦合非线性、几何非线性的磁弹性有限元模型,数值模拟了铁磁薄板的磁弹性耦合弯曲特性并给出铁磁悬臂、简支薄板随磁场倾角变化的磁弹性弯曲变形特征等,数值结果与定性分析结果吻合良好.     

四边固定载流矩形薄板的磁弹性稳定性分析

本文针对四边固定载流矩形薄板,利用Mathieu方程解的稳定性,研究其在电磁场与机械荷载共同作用下的磁弹性稳定性问题。首先在载流薄板的磁弹性非线性运动方程、物理方程、几何方程、洛仑兹力表达式及电动力学方程的基础上,导出了载流薄板在电磁场与机械荷载共同作用下的磁弹性动力稳定方程,然后应用Galer-kin方法将稳定方程整理为Mathieu方程的标准形式,并将薄板的动力稳定性问题归结为对Mathieu方程的求解。利用Mathieu方程的稳定解区域与非稳定解区域的分界,即方程系数λ和η的本征值关系,得出了磁弹性问题失稳临界状态的判别方程。通过具体算例,给出了四边固定载流矩形薄板的磁弹性动力失稳临界状态与相关参量之间的关系曲线,并对计算结果及其变化规律进行了分析讨论。     

无网格法研究进展及其应用

从加权残量法的角度出发，系统地总结了现有各种无网格法的基本格式，阐明了无网格法的特点，论述了无网格法的研究进展，给出了无网格法在碰撞、动态裂纹扩展、金属加工成型、流体力学以及其它领域中的应用。     

Experimental characterization of thin films,droplets and rivulets using LED fluorescence

Imaging based on fluorescence has been used in the past to investigate, mostly in a qualitative manner, liquid films occurring in various applications. In the present paper, a simple quantitative experimental setup and the associated calibration procedure are detailed for a configuration involving Rhodamin B or Rhodamin 101 excited with light-emitting diodes (LEDs). The measurement procedure has been first validated for an open-channel flow considering different Reynolds numbers around 550 and has then been applied to the characterization of thin films, isolated droplets and rivulets. Using this technique the film thickness, film velocity and contact angle have been evaluated accurately for a variety of flow conditions.     

空腔膨胀理论靶体阻力模型及其应用研究进展

从静/动态空腔膨胀模型的理论体系出发,介绍了空腔膨胀模型在不同方向上取得的成果,主要涉及理想侵彻条件的空腔膨胀压力计算模型及数值模拟方法和空腔膨胀模型在典型侵彻问题及复杂弹靶条件下的应用。在理想侵彻条件下的空腔膨胀压力计算模型中,主要讨论了靶体材料、屈服准则和状态方程对空腔边界应力的影响规律及空腔膨胀模型的适用性问题;根据数值模拟中初始条件的不同,介绍了空腔表面恒定速度/恒定压力两种数值模拟方法,证明了数值模拟方法的可靠性;整理了空腔膨胀模型的基本假设、适用范围、工程应用特点,列举了其在典型侵彻问题及多层复合靶板、约束靶体、弹体刻槽和异形截面形状弹体等复杂弹靶条件下的应用。针对空腔膨胀模型的研究现状,总结了目前空腔膨胀模型在冲击动力学领域的应用方向,归纳了空腔膨胀模型应用中尚存在的问题,展望了空腔膨胀模型下一步的重点发展方向。     

Research progress on bulk nanobubbles

There are still fundamental problems lying in the basic research of bulk nanobubbles. Are the bulk nanobubbles reported in the literature nano scale bubbles or contaminants in fact? At present, there is not yet sufficient experimental evidence to show that the bulk nanoparticles are only gas bubbles but not other nano scale contaminants. If they are indeed nanobubbles, what causes the bulk nanobubbles observed in the literature to be much more stable than being predicted by the Epstein-Plesset theory?This paper firstly discusses the contradiction between the traditional theory prediction and the observed lifetime of the bulk nanobubbles, and then discusses whether the so-called nanobubbles are gas aggregates. We review the existing typical models, and the influence of different conditions on the stability of bulk nanobubbles, for paving the road to a clear understanding of the stability mechanism of bulk nanobubbles. In addition, the representative production methods and characterization methods of bulk nanobubbles are discussed in order to offer some guidance to their wide range of commercial applications.     

Research progress on bulk nanobubbles

There are still fundamental problems lying in the basic research of bulk nanobubbles.Are the bulk nanobubbles reported in the literature nano scale bubbles or c...     

高速列车的关键力学问题

在过去10 年时间, 中国和谐号系列高速列车经历了一系列速度上的飞跃. 在最初引进消化吸收基础上, 研制了新一代高速列车并大规模投入运营, 伴随这一过程的大量试验与工程实践, 大大促进了对高速铁路这样一个车- 线- 网- 气流强耦合的复杂大系统中的关键力学问题的深入理解和全面研究. 该文将从6 个方面对高速列车研制和运行过程中的典型力学问题的研究进展以及未来的研究方向做一个梳理. 考虑到这样一个大系统的复杂性,同时也为了使对高速列车感兴趣的技术与科研人员对这些力学问题有一个比较全面的认识, 文中将分别就高速列车的空气动力学、弓网关系、车体振动与车体模态设计、车体运行稳定性、高速轮轨关系、关键结构的运行可靠性和列车噪声等方面的研究进行总结和展望. 同时也对中国及国际高速列车发展趋势及其中的力学问题做了一个简要介绍.      

导电性磁流变弹性体的研究进展

磁流变弹性体(magnetorheological elastomer,MRE)因其独特的场相关性能在工程应用领域引起了广泛关注.论文介绍了MRE的最新发展,重点介绍导电性MRE在材料设计、力学行为和实际应用等方面的研究现状.论文从高性能导电性MRE的研制开始,讨论了材料与结构设计中涉及的关键问题;介绍了导电性MRE材料在磁场作用下的磁、力、电学行为的耦合作用机理和相关物理模型;之后对导电性MRE器件的研究现状进行了总结;最后展望了导电性MRE的发展潜力和面临的挑战.     

Nonlinear friction dynamics on fibrous materials,application to the characterization of surface quality. Part I: global characterization of phase spaces

The diversity and the complexity of fibrous materials (woven fabrics, nonwovens or knitted fabrics) make the control of surface qualities very difficult. The control and the comprehension of the tribological phenomena generated by a dynamic friction are of major importance. Whereas the traditional investigations such as measurements of average parameters like roughness or friction coefficient quickly find their limits on such deformable, heterogeneous and flexible fibrous surfaces with very heterogeneous relief, this series of two publications proposes a new manner of observing the interactions of friction. Our laboratory has developed a patented method of measurements, called MODALSENS, which aims at rubbing a very fine and flexible blade on the analyzed surface. Dynamic friction with the contact generates nonlinear vibrations, and the response of the sensor is analyzed in its phase space using the tools of nonlinear analysis of time series. Then, when the evaluated surfaces change, this first part endeavors to characterize the portraits of phases related to the nonlinear vibrations of MODALSENS in a global way, by quantifying its invariants such as dimensions, Shannon entropies, diameters of attractors and largest Lyapunov exponents. From this first part, a classification of studied fibrous surfaces is built and is expected to give rise to new estimators for the surface quality analysis of fibrous media.     

The characterization of telephone cord buckling of compressed thin films on substrates

The topology of the telephone cord buckling of compressed diamond-like carbon films (DLC) on glass substrates has been characterized with atomic force microscopy (AFM) and with the focused ion beam (FIB) imaging system. The profiles of the several buckles have been measured by AFM to establish the symmetry of each repeat unit, revealing similarity with a circular buckle pinned at its center. By making parallel cuts through the buckle in small, defined locations, straight-sided buckles have been created on the identical films, enabling the residual stress in the film to be determined from the profile.It has been shown that the telephone cord topology can be effectively modeled as a series of pinned circular buckles along its length, with an unpinned circular buckle at its front. The unit segment comprises a section of a full circular buckle, pinned to the substrate at its center. The model is validated by comparing radial profiles measured for the telephone cord with those calculated for the pinned buckle, upon using the residual stress in the film, determined as above. Once validated, the model has been used to determine the energy release rate and mode mixity, G(ψ).The results for G(ψ) indicate that the telephone cord configuration is preferred when the residual stress in the DLC is large, consistent with observations that straight-sided buckles are rarely observed, and, when they occur, are generally narrower than telephone cords. Telephone cords are observed in many systems, and can be regarded as the generic morphology. Nevertheless, they exist subject to a limited set of conditions, residing within the margin between complete adherence and complete delamination, provided that the interface has a mode II toughness low enough to ensure that the buckle crack does not kink into the substrate.     

Research progress on the cleaning and regeneration of PM2.5 filter media

Reusable PM2.5 filter media and their regeneration techniques have attracted widespread attention and shown significant prospect for application in air purifica...