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本文阐述时变力学这一新的研究方向,对其基本课题、特征及力学、数学方法与进展作了较为系统概述,并结合工程实践说明时变固体力学方向研究的重要性与发展前景．     

高瞻远瞩加强力学基础研究

本文简要回顾了力学学科的性质与作用;近代力学的发展与现状;我国力学研究的概况;对发展力学学科提出了若干建议。      

固体力学与材料科学交缘的几个新课题

固体力学与材料科学的交缘是当今力学学科发展的一种新趋势．先进材料的研制与发展,引发了固体力学家对丰富多采的材料的微结构变形与损伤过程进行定量力学描述的浓厚兴趣．本文综述了下列三个固体力学与材料科学交缘的新课题:①微电子材料与组件力学;②材料强韧化力学,③多相介质的界面力学．并对这一交缘学科的发展趋势进行了简要的评介与展望．      

贯穿力学史主线的经典力学教学探讨

经典力学主要涵盖牛顿力学、拉格朗日力学及哈密顿力学等三大部分内容。现行高校教育体系下所开设的理论力学课程,承担了经典力学基础知识普及的教学重担。历经数百年发展所臻于完善的经典力学体系,对于绝大数理工科学生来说不啻为一大挑战。在教学中,融入并贯彻力学史主线的经典力学教学,可带来意想不到的良好效果。     

基础力学课程教学改革初探

0 引言 时代已步入世纪之交,面临当今世界科学技术日新月异飞速发展的局面,对如何培养能适应二十一世纪竞争的高质量人才已成为高等教育界议题的热点。 高等教育锐意改革已势在必行,其中高等工程教学的改革至关重要。我从事工科院校力学课程的教学工作已有卅余年,对力学课程体系、教学内容和教学方法如何着手改革颇为关切。1997年初,建设部关于普通高等学校面向二十一世纪高等工程教育教学内容和课程体系改革研究正式立项,根据中国建设教育协会普通高等教育委员会的精神,由大连理工大学牵头,与同济大学、哈尔滨建筑大学、重庆建筑大学、扬州大学等院校组成了建筑力学系列     

力学几落几起,源于生活之树长青

力学是以宏观世界为主要对象,研究力和运动的关系的一门学问．从古至今,不断有人深入钻研力学,成就大事业,如牛顿,拉格朗日,冯．卡门,钱学森等．可能是因为这些对象和现象大多是普通人都能看得见,摸得着的．所以,也不断有人否认,抹杀力学,甚至扼杀力学,使力学的发展受阻．但是,生活这棵常青之树,催生了力学,更繁荣着力学． 聪明的阿基米德（公元前２８７～公元前２１２）奠定了静力学的基础,堪称力学的先驱．他在洗澡盆里洗澡时悟出了浮力的原理,并用来为叙拉古的亥厄洛王测量黄金王冠真伪的故事,脍炙人口．但是,他竟然…     

力学史杂谈(一)—(三)

力学史杂谈（一）—（三）武际可（北京大学力学与工程科学系，１００８７１）（一）汉语中“力学”一词考源摘要本文通过历史回顾，说明汉语中“力学”一词的来源．关键词力学，重学将西文Ｍｅｃｈａｎｉｃｓ一词译为“力学”是何人开始的呢？这人不是力学家，也不是自然...     

力学实验与实验力学

阐述了在实验在力学发展中的作用与实验力学学科产生过程,介绍了力学中的实验与实验力学之间的区别。力学中的实验与力学问题研究紧密相连。而实验力学包括了力学中的实验,但又不局限于此,它与其它学科交叉广泛,与工程应用结合紧密,是一门技术性科学。     

Frictional contact of two rotating elastic disks

We study the problem of constrained uniform rotation of two precompressed elastic disks made of different materials with friction forces in the contact region taken into account. The exact solution of the problem is obtained by the Wiener-Hopf method.An important stage in the study of rolling of elastic bodies is the Hertz theory [1] of contact interaction of elastic bodies with smoothly varying curvature in the contact region under normal compression. Friction in the contact region is assumed to be negligible. If there are tangential forces and the friction in the contact region is taken into account, then the picture of contact interaction of elastic bodies changes significantly. Although the normal contact stress distribution strictly follows the Hertz theory for bodies with identical elastic properties and apparently slightly differs from the Hertz diagram for bodies made of different materials, the presence of tangential stresses results in the splitting of the contact region into the adhesion region and the slip region. This phenomenon was first established by Reynolds [2], who experimentally discovered slip regions near points of material entry in and exit from the contact region under constrained rolling of an aluminum cylinder on a rubber base. The theoretical justification of the partial slip phenomenon in the contact region, discovered by Reynolds [2], can be found in Carter [3] and Fromm [4]. Moreover, Fromm presents a complete solution of the problem of constrained uniform rotation of two identical disks. Apparently, Fromm was the first to consider the so-called “clamped” strain and postulated that slip is absent at the point at which the disk materials enter the contact region.Ishlinskii [5, 6] gave an engineering solution of the problem on slip in the contact region under rolling friction. Considering the problem on a rigid disk rolling on an elastic half-plane, we model this problem by an infinite set of elastic vertical rods using Winkler-Zimmermann type hypotheses. Numerous papers of other authors are surveyed in Johnson’s monograph [7].The exact solution of the problem on the constrained uniform rotation of precompressed rigid and elastic disks under the assumptions of Fromm’s theory is contained in the papers [8, 9]. In the present paper, we generalize the solution obtained in [8, 9] to the case of two elastic disks made of different materials.     

颗粒材料接触特性之接触点的确定

颗粒物质在自然界中普遍存在,如砂砾、谷物、堆石体和碎屑流等,许多自然现象和工业过程都与颗粒物质的运动状态有关。弄清颗粒之间的接触特征是理解颗粒变形与运动规律的关键,与之相关联的接触点确定是获取全场接触力(包括力链)信息的难点。近年来,光弹法逐渐成为这类问题研究的有效手段之一,原因在于该方法具有原理简单、操作方便、图像直观等优点。然而,已有的接触点判定方法主要依赖于圆盘圆心距离的计算,对于小变形圆盘接触特征难以有效识别。为此,本文发展了一种基于去除零级条纹区域及图像矩阵转换的算法,可以有效地确定接触点的位置。主要步骤如下:首先运用主成分分析方法对图像进行分析,提取主成分,并重构原图像;然后利用模板匹配方法提取各个光弹圆盘,接着对提取出来的各个圆盘进行图像矩阵变换;最后对变换后的图像局部进行垂直方向灰度梯度平方计算,描绘梯度变化曲线并提取曲线峰值,从而识别出接触点(位置)。     

Transient squeeze flow of viscoplastic materials

The transient, axisymmetric squeezing of viscoplastic materials under creeping flow conditions is examined. The flow of the material even outside the disks is followed. Both cases of the disks moving with constant velocity or under constant force are studied. This time-dependent simulation of squeeze flow is performed for such materials in order to determine very accurately the evolution of the force or the velocity, respectively, and the distinct differences between these two experiments, the highly deforming shape and position of all the interfaces, the effect of possible slip on the disk surface, especially when the slip coefficient is not constant, and the effect of gravity. All these are impossible under the quasi-steady state condition used up to now. The exponential constitutive model, suggested by Papanastasiou, is employed. The governing equations are solved numerically by coupling the mixed finite element method with a quasi-elliptic mesh generation scheme in order to follow the large deformations of the free surface of the fluid. As the Bingham number increases, large departures from the corresponding Newtonian solution are found. When the disks are moving with constant velocity, unyielded material arises only around the two centers of the disks verifying previous works in which quasi-steady state conditions were assumed. The size of the unyielded region increases with the Bingham number, but decreases as time passes and the two disks approach each other. Their size also decreases as the slip velocity or the slip length along the disk wall increase. The force that must be applied on the disks in order to maintain their constant velocity increases significantly with the Bingham number and time and provides a first method to calculate the yield stress. On the other hand, when a constant force is applied on the disks, they slow down until they finally stop, because all the material between them becomes unyielded. The final location of the disk and the time when it stops provide another, probably easier, method to deduce the yield stress of the fluid.     

On rubber disks under rotation or axisymmetric stretching

The governing equations for a class of axisymmetric problems under large elastic deformation, concerned with a circular rubber disk with body force as well as non-uniform initial thickness, are formulated in terms of two coupled first-order ordinary differential equations with explicit derivatives. The following two problems subjected to different boundary conditions are solved: (a) Rotating disks with uniform initial thickness (b) Circular disks with non-uniform initial thickness under axisymmetric stretching at the outer boundary. In problem (b), the rubber disk whose initial thickness contour is h₀ = crⁿ (where c and n are any constants), or whose final thickness is a constant, is considered. Highly elastic materials with a Mooney strain-energy function are used for numerical calculations.     

Bonded contact of a flexible elliptical disk with a transversely isotropic half-space

The article concerns the problem of bonded contact of a thin, flexible elliptical disk with a transversely isotropic half-space. Three different cases of loading have been considered: (a) the disk is loaded by a transverse force, whose line of action passes through the center of the disk and lies in the plane of the disk; (b) the disk is subjected to a rotation by a torque, whose axis is perpendicular to the surface of the half-space; (c) the half-space with the bonded disk is under uniform stress field at infinity. The problem corresponding to all three cases is reduced, in a unified manner, to a set of coupled two-dimensional integral equations. Closed-form solutions for these equations have been obtained by using Galins theorem.     

复合材料层压板低速冲击响应尺度效应数值模拟研究

为了研究尺度效应对于复合材料层压板在低速冲击作用下的动态响应和冲击损伤的影响,基于相似理论,建立了三种不同尺寸的层压板受冲击的三维有限元模型。在该模型中,针对层压板的面内损伤,采用改进的Chang-Chang准则进行预测;针对层压板内层间分层损伤,则使用Cohesive界面单元进行模拟。一旦复合材料层压板在低速冲击作用下产生损伤,则对出现损伤的区域进行材料参数退化。采用该模型对三种不同尺寸的层压板的冲击过程进行有限元分析,并将不同冲击速度下的冲击响应进行比较,得出了如下结论：在层压板内未发生冲击损伤时,冲击产生的挠度和冲击力与相似理论解十分吻合,一旦出现冲击损伤,则冲击力的变化与相似理论解有所差别;如果两个缩放模型的冲击速度之比等于缩放比例的平方根,则两个模型中的相对分层尺寸基本是相同的,这个结果与已有的实验结果吻合;而对冲击后面内损伤的分析表明,其损伤尺寸不符合这一相似规律。     

纯铁在球/面接触下的冲击微动磨损行为研究

在自制的新型试验机上,以纯铁为考察对象开展了球/平面接触模式下的冲击微动磨损试验.在改变冲击能量、冲击质量的情况下,研究了材料的冲击力学响应和磨损机制.结果表明:在增大冲击能量的条件下,试样受到的冲击力和能量吸收率相应增加,磨损体积、磨损率也随之提高.冲击动能相同时,增大冲击质量(降低冲击速度),冲击力峰值和能量吸收率进一步提高,磨损程度减轻.纯铁的冲击磨损机制主要表现为剥层磨损,且磨痕区域发生了氧化行为,越靠近边缘,氧化程度越高.     

磁头/磁盘滑动接触下磁盘温度及热退磁临界条件的研究

采用二维轴对称有限元模型计算磁头/磁盘滑动接触下,铝质磁盘的稳态温度和热应力场以及热退磁临界条件.结果表明:磁盘温度在极短时间内升至摩擦稳态值,然后缓慢线性升高到最终稳态值;经过充分热传导和热交换后磁盘的温度梯度较小,此时磁层内的热应力集中分布于磁盘固定端边缘附近;磁盘的稳态温度和热应力均随速度增大而增大,且载荷越大其值增大越快;热应力小于1.2 GPa时所对应的速度和载荷为安全工况;温升大于373 K时所对应的工况将导致磁盘退磁.