凸轮与平底从动件的接触变形与接触刚度计算

将凸轮与平底从动件接触视为二维线性接触,基于无限大半空间模型对从动件的变形量进行了分析,利用圆柱体二维线接触变形的计算方法对凸轮接触变形进行了计算,从而得到了凸轮与平底从动件的接触变形量与接触刚度理论计算公式。利用Palmgren公式和有限元方法对计算公式进行了验证,并分析了接触刚度与凸轮曲率半径、接触力之间的关系,结果表明:接触应力、接触半宽、凸轮接触变形量的理论计算值与有限元计算结果几乎相等,凸轮与从动件的接触变形量之和的理论计算值与有限元计算值相差小于5%;凸轮与平底从动件的接触变形之和、接触刚度都与接触处凸轮的曲率半径无关,而与凸轮与平底从动件间的接触力大小有关。     

磨损数值仿真技术的研究进展

综述了近年来国内外磨损数值仿真技术研究进展和现状，重点评述了数值仿真方法在磨粒磨损、疲劳磨损、磨损表面形貌模拟和实际摩擦副磨损研究方面的应用．指出磨粒磨损仿真主要集中于二体磨损的磨损表面形貌分析和磨损预测;疲劳磨损仿真主要集中基于断裂力学方法的建模以及基于有限元方法的参数定量计算和疲劳裂纹行为数值模拟；实际摩擦副磨损仿真主要侧重于齿轮、凸轮和缸套-活塞环等典型摩擦副的磨损研究．就当前磨损数值仿真研究的主要问题和发展方向提出了建议。     

调整凸轮机构尺寸以减小摆动从动件名义推力的计算方法

本文通过对厚度方向尺度相同的二维相似摆动从动件盘形凸轮机构进行力学分析及数学计算,导出了合理调整凸轮机构尺度的计算公式.按该公式提供的二维相似系数对凸轮机构进行改进设计,可有效地减小摆动从动件的名义推力.本文介绍的方法对摆动从动件盘形凸轮改进设计有参考价值.     

复杂轮廓曲线的凸轮机构运动

<正> T 形平底从动件凸轮机构,当凸轮的轮廓曲线是圆形时的运动学问题,一般的理论力学教材中都能找到.但当凸轮的轮廓曲线是椭圆或其它复杂曲线时,教材中还没有这类问题出现,这时,由于选取形心为动点,其相对于平底从动件的相对运动已不再清楚,故必需另寻它法.本文应用双动系法对这类问题进行了分析,指出:当两构件依赖于其轮     

铰接副磨损与系统动力学行为耦合的数值分析

建立了机械系统的摩擦磨损与动力学行为的耦合分析模型和数值计算框架,以间隙铰接副为对象分析其磨损和动力学行为的交互影响机制.磨损通过有限元理论及ANSYS软件开发的通用程序来计算,其中通过移动边界节点的方法来描述磨损过程,利用结构优化算法中的边界位移法解决了边界节点变动导致的内部网格畸变问题.应用将位移约束转化为接触力约束的方法建立含间隙铰碰撞的多体动力学模型.通过序贯耦合的模式计算出不同寿命时段的磨损间隙和性能特性.结果表明:磨损与动力学行为耦合数值分析可对整个寿命周期内磨损和性能做出预测,可显著提高摩擦学设计的效率和准确性.     

凸轮挺杆摩擦副磨屑的分析研究

本文用多种方法收集和制备了凸轮挺杆磨损过程中的磨屑样品,对磨屑的大小,几何形状及形貌特征进行了系统的扫描电镜观察分析,为不同形式磨损的形成机理提供了直接的证据。并表明磨屑的分析研究对监测磨损过程及研究磨损机理是一个十分重要的手段。     

一对钢－钢摩擦副摩擦磨损的原位动态研究

摩擦磨损的扫描电子显微镜原位动态研究，可以跟踪观察磨屑形成和磨痕演变的全过程，以及材料表面在摩擦磨损中变化的真实情况．在由国产台式扫描电子显微镜改装成的滑动摩擦磨损试验装置上，对１５＃钢－４５＃钢摩擦磨损过程所作的原位动态研究表明：１５＃钢在对摩过程中始终存在粘－滑现象，微切削是其主要磨损机理；１５＃钢磨痕形貌变化可分５个阶段——第１阶段出现与滑动方向垂直的横向裂纹，第２阶段产生大片状剥离，第３阶段产生小片状疲劳剥离，第４阶段产生块状磨屑并形成表面凹坑，第５阶段磨痕趋于平坦．这种滑动摩擦磨损试验装置不仅具有对摩擦磨损过程作动态跟踪观察的功能，而且可用于对摩擦学过程作准动态观察，这两种观察方法对研究摩擦磨损过程同等重要     

高韧性管道动态断裂的气体减压模式和材料韧性研究

天然气管道上动态裂纹扩展包含气体、结构和断裂的相互作用．因此，分析射流场分布特性及其与管壁开裂变形的相互作用是数值模拟过程的关键问题．随着钢管韧性等级的迅速提升和气体压力的不断提高，原有的经验公式乃至算法多数不再适用，亟需通过理论、试验和数值模拟给出新的扩展与止裂判据，以控制裂纹在管道上扩展的速度和距离．本文通过一系列的韧性试验校正了现行的管材韧性判定办法，并对不同工况下的裂纹动态扩展以及超声速射流场进行了数值仿真，以建立一套工程适用的评价体系。     

牙齿表面微观磨损形貌的数值化分析研究

牙齿表面磨损一般通过显微镜进行形貌图像表征分析，而数值化分析牙齿表面磨损形貌的工作相对较少. 本研究中通过白光共聚焦显微镜，Solarmap Universal 软件和Tooth-Frax软件对牙齿咬合前后表面磨损形貌进行数值化分析，建立磨损前后表面尺度敏感曲线. 结果显示:牙齿表面磨损形貌可以通过轮廓分形分析法建立相应的表面尺度敏感曲线，形成表面磨损尺度敏感数字信号. 本工作的主要目的是寻求通过表面磨损数值化分析为研发牙齿磨损动态监测设备提供理论基础和技术支撑.      

结构疲劳寿命的区间估计

对材料性质和载荷具有不确定性的结构进行了疲劳寿命估计．结构的疲劳寿命往往是这些不确定性因素的函数．以区间数学为基础，将这些不确定性因素用区间进行定量化，借助一阶Taylor级数，提出了近似估计结构疲劳寿命的区间分析方法．区间分析方法克服了概率分析方法需要预先知道大量统计数据的缺点，且计算量小．通过典型数值算例将区间分析方法和概率分析方法进行了比较，结果表明了区间分析方法对线性和非线性形式的结构寿命估计在小不确定度情况下均能提供足够的精度．     

Experimental and numerical verification of bifurcations and chaos in cam-follower impacting systems

In this paper, we present the design, modelling and experimental validation of a novel experimental cam-follower rig for the analysis of bifurcations and chaos in piecewise-smooth dynamical systems with impacts. Experimental results are presented for a cam-follower system characterized by a radial cam and a flat-faced follower. Under variation of the cam rotational speed, the follower is observed to detach from the cam and then show the emergence of periodic impacting behaviour characterized by many impacts and chattering. Further variations of the cam speed cause the sudden transition to seemingly aperiodic behaviour. These results are compared with the numerical simulation of a mathematical model of the system which shows the same qualitative behaviour. Excellent quantitative agreement is found between the numerical and experimental results.     

An optimal cam profile design considering dynamic characteristics of a cam-valve system

In this work, an optimal cam profile design method for an OHV-type cam-valve train is studied considering the dynamic characteristics of the valve system. When designing a cam profile for an internal combustion engine, it is desirable to make the valve lift area be as large as possible and the valve peak acceleration and seating velocity be as low as those can be within the cam-event angle. But, as we know, those features conflict with one another. An optimal design must strike a compromise between the two. Another important factor in valve train design is avoiding abnormal valve motions such as jump and bounce. It is known that jump and bounce are closely related to valve train dynamic characteristics.In this paper, a two-step optimization technique to design an optimal cam profile is proposed. In the first step, an attempt was made to maximize valve lift area without causing abnormal valve motions while satisfying all the given constraints such as cam-event angle, maximum valve acceleration, and cam displacements at both ends of the cam-event angle. Then, in the second step, minor modifications of the cam developed in the first step were made in order to reduce the cam acceleration while maintaining the maximized valve lift area and satisfying constrains obtained in the first step.In order to prove the effectiveness of the optimization method, the valve motion driven by the optimized cam was not only simulated with a four degree of freedom model but was also tested experimentally. It was found that the measured valve motions agree quite well with the simulation results. Comparing the valve motions of the optimized cam with those of the original cam, it was found that the optimized cam can increase the valve-lift area by 8.6 percent while reducing the peak cam acceleration by 28.7 percent. Also, it was noted that the optimized cam increases the cam-valve train operating speed at which jump and bounce occur.Paper was presented at the 1988 SEM Spring Conference on Experimental Mechanics held in Portland, OR on June 5–10.     

THE APPLICATION OF DISCRETE ELEMENT METHOD IN SOLVING THREE-DIMENTIONAL IMPACT DYNAMICS PROBLEMS

A three-dimensional discrete element model of the connective type is presented. Moreover, a three- dimensional numerical analysis code, which can carry out the transitional process from connective model (for continuum) to contact model (for non-continuum), is developed for simulating the mechanical process from continuum to non-continuum. The wave propagation process in a concrete block (as continuum) made of cement grout under impact loading is numerically simulated with this code. By comparing its numerical results with those by LS-DYNA, the calculation accuracy of the model and algorithm is proved. Furthermore, the failure process of the concrete block under quasi-static loading is demonstrated, showing the basic dynamic transitional process from continuum to non-continuum. The results of calculation can be displayed by animation. The damage modes are similar to the experimental results. The two numerical examples above prove that our model and its code are powerful and efficient in simulating the dynamic failure problems accompanying the transition from continuum to non-continuum. It also shows that the discrete element method (DEM) will have broad prospects for development and application.     

基于超二次曲面的非球形离散单元模型研究

通过对颗粒体系接触过程的运动学和动力学分析,建立了一种基于超二次曲面的非球形离散单元模型,该模型避免了球形接触模型描述颗粒形状的局限性,使离散单元法更接近物理事实,并在此基础上提出了计算求解模型的数值方法,实现了对复杂形状的颗粒体系的模拟计算。将所建立的数值计算方法进行了编程实现,并对模型和算法进行了算例测试,证实了本文所建立的非球形离散单元模型的可行性和正确性。测试结果表明,本文的模型能够比较准确地模拟复杂颗粒体系的真实运动,可为复杂颗粒体系的模拟研究提供一种新的数值计算方法。     

Electromagnetic Cam Driven Compression Testing Equipment

This paper presents innovative equipment for the compression testing of materials under high rates of loading (above 1,000 s⁻¹). The equipment consists of an electromagnetic actuator, a fixed housing containing two flat compression platens, a translating cam and a follower. The electromagnetic actuator makes possible reaching high strain rates with a very precise control of the impact velocity and of the energy transmitted to the translating cam. The cam profile enables compression testing to be performed under the strain rate vs. strain loading paths that are commonly found in manufacturing in order to meet the machine-tool and process combined specifications. Special emphasis is placed on the adequacy of the proposed electromagnetic cam drive compression testing equipment to characterize material behaviour in orthogonal metal cutting because non-proportional loading paths during metal cutting are known to have significant influence on the material stress response. The flow curves obtained by means of the equipment are implemented in a finite element computer program and applied in the numerical simulation of orthogonal metal cutting under different cutting velocities.     

求解非线性方程组的混沌分形方法

混沌分形是动力系统普遍出现的一种现象,牛顿-拉夫森NR(Newton-Raphson)方法是重要的一维及多维迭代技术,其迭代本身对初始点非常敏感,该敏感区是牛顿-拉夫森法所构成的非线性离散动力系统Julia集,在Julia集中迭代函数会呈现出混沌分形现象,提出了一种寻找牛顿-拉夫森函数的Julia点的求解方法,利用非线性离散动力系统在其Julia集出现混沌分形现象的特点,提出了一种基于牛顿-拉夫森法的非线性方程组求解的新方法,计算实例表明了该方法的有效性和正确性.     

聚合物/金属摩擦界面迁移过程的数值模拟

聚合物材料在与金属对偶件滑动接触时,会在摩擦界面上发生界面迁移,导致在金属对偶件表面形成一层转移膜.转移膜的存在能够有效地降低聚合物材料的磨损.本文基于离散单元法,利用二维颗粒流程序(PFC2D),对PTFE/45钢界面迁移过程进行数值模拟分析.模拟结果表明:PTFE与45钢组成摩擦副时,会在45钢表面形成一层转移颗粒层.一开始转移颗粒数逐渐增大,一段时间后随着转移颗粒层的形成与完整,转移颗粒数趋于一个定值且保持动态平衡,磨损颗粒增加速率显著下降,并维持在一个稳定的值.     

考虑空化影响的水润滑橡胶合金轴承冲蚀磨损研究

用计算流体力学方法,数值模拟水润滑轴承空化-冲蚀交互作用时气液固三相流场的动力学特性(压力场、速度场、气含率分布),然后在水润滑轴承摩擦磨损装置上,进行试件磨损试验,并观察试件表面形貌.结果表明:考虑空化影响后,水润滑轴承整个流场压力分布更接近实际;数值模拟所得的流场压力、速度、气含率最大值,均出现在发生空化的位置附近,其余位置基本不变,说明交互磨损比单一磨损严重.观察试件表面磨痕,存在短程犁沟、空蚀针孔、麻点状气蚀坑和蚀坑,磨痕呈现规律性,磨痕与轴转速的方向基本一致.试验结果和数值计算吻合较好,证明了理论分析的正确与合理.上述仿真与试验初步探讨了水润滑轴承空化与冲蚀交互作用的磨损机理与影响因素.     

Transient analysis of multipass crossflow heat exchangers

By means of both the discrete and continuous approaches, this paper proposes dynamic simulation algorithm of multipass crossflow heat exchangers with arbitrary rows per pass. Heat capacities of both fluids and of the core wall as well as conduction resistance of the wall are taken into account. Effect of the possible tubeside flow maldistribution is described with the dispersed plug-flow model. Furthermore, the simulation solution based on the conventional plug-flow model is developed. Transient temperature profiles are obtained by numerical inversion of the Laplace transform. Some examples are calculated and discussions are made.     

Stabilitätsverhalten der Stösselstange in geradgeführten Kurvengetrieben

Übersicht In diesem Beitrag wird die Stößelstange in geradgeführten Kurvengetrieben als ein gedämpfter Euler-Bernoulli-Stab aufgefaßt. Nach dem Aufstellen der Differentialgleichung für die Querschwingungen mittels des Hamiltonschen Prinzips wird diese mit Hilfe des Galerkinschen Verfahrens auf ein System von Hillschen Differentialgleichungen reduziert. Dann werden für ein allgemeines Kurvenbewegungsgesetz Näherungsformeln für die Grenzkurven der Instabilitätsbereiche hergeleitet, wobei der (bezogene) Stößelhub in Abhängigkeit der Kurvenwinkelgeschwindigkeit dargestellt wird. Die Ergebnisse werden durch ein Beispiel veranschaulicht.

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On the stability behaviour of the reciprocating follower in cam mechanisms

Summary This paper is concerned with the simulation of the reciprocating follower in cam mechanisms as a damped Euler-Bernoulli beam. The governing partial differential equation of the transversal vibrations of the follower is derived, using Hamilton's principle. Then it is reduced to a system of Hill-equations by the Galerkin method. For the case of a general motion of the follower the approximate formulas of the boundaries between the stable and unstable regions are derived, represented in the plane of strok depending on the angular velocity. The obtained results are illustrated by an example.