界面滑移流体动压膜承载能力的形成

运用界面滑移可在两平行平板表面间形成具有承载能力的流体动压膜．在流体入口区,静止平板表面上流体-接触表面的界面剪切强度具有较低值,以在该界面处产生界面滑移,而在流体出口区,静止平板表面上流体-接触表面的界面剪切强度具有足够高的值,以避免在该界面处出现界面滑移．整个运动平板表面上流体-接触表面的界面剪切强度具有足够高的值,以避免在运动平板表面上出现界面滑移．分析表明,这种流体动压接触区具有显著承载能力．使整个接触区具有最大承载能力的流体出口区宽度与入口区宽度的比值为0.5．     

各向异性压电介质摩擦接触界面波动特性分析

应用Fourier(傅立叶)分析及奇异积分方程技术研究了弹性波与一般压电介质单侧接触界面的相互作用问题.以界面只产生滑移不分离的情况为例,分析了问题的求解思路和过程,给出了弹性波引起界面滑移或分离的条件.以六角晶系极化碳酸钡陶瓷材料和三角晶系石英材料为例,分析了不同材料摩擦接触界面对弹性波入射的不同反应,给出了不同的入射角及不同的外加压力和电场对界面的影响特性.界面产生滑移和分离时,问题的边界条件具有非线性,导致高频谐波出现,以石英材料为例分析了高频成分随外加条件的变化特性.     

基于表面阻抗张量的界面滑移波动态失稳分析

基于Stroh公式和表面阻抗张量理论,提出了研究界面滑移波动态失稳问题的一种新的方法．该方法将表面阻抗张量概念推广到复波速域,并将摩擦接触界面上的边界条件以表面阻抗张量表示．最终将边值问题化归为求解一个复多项式在单位圆内的根．以弹性半空间与刚体平面相对稳态摩擦滑移为例进行了详细的分析,导出了一个4次复特征方程并讨论了方程在单位圆内解的特性,给出了滑移界面波失稳条件的显式解析表达式．     

温差影响下的局部滑移接触行为的研究

针对不同温度装配件间接触界面的局部滑移问题,建立了三维稳态热弹性局部滑移接触的半解析求解模型.基于热弹性理论与热传导方程,构建了半空间受热流载荷和力载荷作用下的频响函数并建立了相应的影响系数矩阵.借助离散卷积-快速Fourier变换等数学工具,实现了针对高温压头与热弹性半空间局部滑移接触问题的高效求解.接触界面间的热量传递满足Fourier热传导定律,并且黏/滑状态由Coulomb定律确定.基于该半解析模型分析了不同荷载及温差对表面法向压力分布、摩擦力分布、刚体位移及接触区黏/滑演化行为的影响.研究结果表明,当法向荷载和切向荷载一定时,温差的上升会导致接触区域的减小,引起接触面法向压力及摩擦力的峰值增大,并且会显著影响黏着区与滑移区的分布情况.     

压电体光滑接触界面有局部分离时的滑移脉冲波传播

应用关于压电材料的Stroh方法以及Fourier分析和奇异积分方程技术,研究了压电体光滑接触界面有局部分离时的滑移脉冲波传播问题,分析了其存在的判据．压电体由单向压应力作用而光滑接触并处于一定强度的电场中．待求问题最终转化为含Cauchy核的奇异积分方程组,并给出其解析解．数值计算结果表明:光滑接触界面上有局部分离的滑移脉冲波普遍存在,且界面法向面力和法向电位移在局部分离区两端有奇异性;对某些特殊的材料组合,外载荷不影响滑移脉冲波的存在性．     

纳米摩擦学的分子动力学模拟研究

用分子动力学模拟研究了纳米级润滑薄膜的固液相变和界面滑移现象以及固体接触和黏着的微观机制.结果表明：纳米薄膜中液体的固化相变压力随膜厚减薄而下降,说明润滑剂可能处于类固态状态.薄膜中的界面滑移现象可能在较低的剪切速率下发生,并与液体的固化程度有较好的对应关系.光滑晶体表面在相互接近或分离过程中可能因部分原子突然跃迁而发生微观黏着,这对于理解界面摩擦的起源具有重要意义.     

弹性-幂硬化蠕变性材料Ⅱ型界面裂纹准静态扩展的渐近分析

建立了弹性-幂硬化蠕变性材料Ⅱ型界面裂纹准静态扩展的力学模型,求得了在裂纹表面自由和裂纹面有摩擦接触两种情况下,裂纹尖端应力场分离变量形式的渐近解．求解结果表明:Ⅱ型界面裂纹问题的应力、应变具有相同的奇异性;Ⅱ型界面裂纹尖端场不存在振荡奇异性;材料的幂硬化指数n和弹性模量比对裂纹尖端应力场幂硬化蠕变性材料区有着显著的影响,而弹性区仅受幂硬化指数n的影响,当n很大时,蠕变变形占主导地位,应力场趋于稳定,不随n的变化而变化;泊松比对裂纹尖端应力场的影响不明显．     

界面性能对陶瓷基复合材料桥联增韧的影响

对单向纤维增强陶瓷基复合材料内垂直于纤维的基体裂纹扩展和偏转条件进行研究,侧重于界面性能对裂纹尾区桥联力学分析的影响。结果表明:在界面相脱粘摩擦区和弹性滑移区共同影响下,界面韧性g_i与增强纤维相关联参量(σ_cr²r/E_f)比值是界面脱粘的重要控制条件,并决定主裂纹是否转向,脱粘发生后脱粘摩擦区的长度取决于摩擦力τ₀并与其成反比.此外,界面厚度、剪切模量等也对桥联断裂分析产生重要影响.     

DTM-BF方法和可渗透收缩壁面上带滑移速度的非稳态磁流体力学流动

研究了运动的粘性导电流体中可渗透收缩壁面上非稳态磁流体边界层流动,利用解析和数值方法对问题进行了研究,并考虑了壁面速度滑移的影响．提出了一个新的解析方法（DTM-BF）,并将其应用于求解带有无穷远边界条件的非线性控制方程的近似解析解．对所有的解析结果和数值结果进行了对比,结果显示两者非常吻合,从而证明了DTM-BF方法的有效性．另外,对不同的参数,得到了控制方程双解和单解的存在范围．最后,分别讨论了滑移参数、非稳态参数、磁场参数、抽吸/喷注参数和速度比例参数对壁面摩擦、唯一解速度分布和双解速度分布的影响．     

7050铝合金扭动微动磨损特性的研究

在CETR UMT-2型多功能摩擦磨损实验机上对7050铝合金进行扭动微动磨损实验,主要研究当法向载荷一定时,角位移幅值、循环次数等参数对该材料扭动微动磨损特性的影响。结果表明,随着角位移幅值的增加,材料接触表面依次运行于3个区域;结合光镜下的磨斑形貌分析,3个区域材料表面的损伤情况各不相同,部分滑移区损伤轻微,混合区和完全滑移区的磨损机制为剥层、磨粒磨损和氧化磨损。     

箱式约束变分不等式的一类新光滑gap函数

针对箱式约束变分不等式问题,利用一类积分型全局最优性条件,提出了一个新光滑gap函数．该光滑gap函数形式简单且具有较好的性质．利用该gap函数,箱式约束变分不等式可转化为等价光滑优化问题进行求解．进一步地,讨论了可保证等价光滑优化问题的任意聚点为箱式约束变分不等式问题解的条件．以一个简单的摩擦接触问题为例阐释了该方法的应用．最后,利用标准的变分不等式考题验证了方法的有效性．     

Modeling of the Wear Particle Flow in Tribological Contacts

The dynamics of tribological systems with pronounced memory effects are characterized by the complex coupling of mechanical, thermal, and chemical processes. At the Institute of Dynamics and Vibrations in Braunschweig, Cellular Automata have been developed that facilitate the evaluation of dynamics in technically relevant systems within a reasonable time. The flow of wear material is decisive for the formation, localization, and reconstitution of load-bearing structures or films. In this paper, two opposed frictional contacts are chosen exemplarily for the investigation of the wear particle flow: a vehicle brake system and the sanding of wood. For this purpose, a modeling technique is proposed that is based on established force laws for micro particles and differentiates mechanisms of transport for different phases of the particle movement. The resulting transport of a single particle interacting with the topology of the frictional gap is analyzed for varying particle properties and process parameters. In a second step the insights are transferred to a set of rules for a Cellular Automaton which allows for quick evaluation and the incorporation of coupled effects. The validity and quality of the model transfer are discussed. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dynamic responses to sinusoidal excitations of beams with frictional joints

We consider the dynamic responses of a beam with a frictional joint. The frictional force at the joint is modeled using the Coulomb friction model. The frictional force at the joint makes the nature of the boundary conditions at the joint uncertain. Therefore, this problem represents a type of nonlinear problems where the boundary conditions are coupled to the solutions. Using numerical integration of the resulting differential equations obtained by combining the finite element method and the Lagrange equations, we study the steady-state solutions of the system to sinusoidal excitations. We explore the dependence of the system responses to various parameters including the frictional force, the forcing frequency and the forcing amplitude. A result of special interest is the existence of an optimum friction force if the frictional joint is used to control the system response amplitude. We also examine the ways that friction affects the resonance frequency of the structure. Experiments are carried out, which agree qualitatively with the numerical results.     

Estimation of dry road braking distance considering frictional energy of patterned tires

This paper is concerned with the braking distance estimation of tire controlled by anti-lock brake system (ABS) according to a numerical–analytical method. While the frictional heat dissipation at disc pad is derived analytically, the tire frictional energy loss is computed by the 3D dynamic rolling analysis of patterned tire. Since the tire rolling analysis to obtain the time history of the frictional energy rate for the entire braking period is impractical, we alternatively seek the tire frictional energy rate curve versus the lapse of time by interpolating the discretized frictional energy rates computed at intervals of 10 km/h. The effect of ABS is numerically implemented by specifying the corresponding tire angular velocity to the dynamic rolling analysis. Applying the energy conservation law to each speed interval determines the interval-wise braking times and distances from which the total braking time and distance are predicted. Illustrative numerical experiment is presented together with the comparison with the experimental estimation.     

橡皮环大变形接触问题

本文借助于子结构技术解决了大变形橡皮环和弹性薄极具有摩擦的接触问题,研究了摩擦系数、极厚对橡皮环变形的影响。     

Dynamic modeling of a high-precision self-moving stage with various frictional models

The piezoelectric actuator (PA) has been used for precision positioning from micro-meter down to nano-meter scale. In this paper, the frictional force is first described by the LuGre model and Leuven model, which allow accurate dynamic modeling both in the sliding and the presliding regimes without using switching functions. The hysteresis frictional parameters controlling the restoring force amplitude and the shape of hysteresis loop are investigated. Sequentially, the two frictional models are employed in the self-moving stage for high-precision positioning under different applied voltages. From the numerical results in the pre-sliding regime, it is shown that the hysteresis frictional force has critical influence on the final position of the micro- and nano-meter positioning.     

层流边界层方程的近似分析解

献[1]引用压力梯度作为新的自变量以代替通常的纵坐标x，从而将经典的边界层方程变为新的形式。在些基础上，献[1]用图解法求定作地一截面处的摩探应力因子。本仍然采用献[1]的变量置换，但用级数法求得了层边界层方程的一级近似分析 解；并得到了计算摩擦应力因子的公式（4.13）对于主函数中不含常数项的一类流动说，本求得的摩擦应力因子和献[1]的结果十分符合；对于主函数中含有常数项的另一类流动，中作了更进一步的简化，求得的摩控应力因子和献[1]的结果相比较，误差也低于10％。     

Modeling of large deformation frictional contact in powder compaction processes

In this paper, the computational aspects of large deformation frictional contact are presented in powder forming processes. The influence of powder–tool friction on the mechanical properties of the final product is investigated in pressing metal powders. A general formulation of continuum model is developed for frictional contact and the computational algorithm is presented for analyzing the phenomena. It is particularly concerned with the numerical modeling of frictional contact between a rigid tool and a deformable material. The finite element approach adopted is characterized by the use of penalty approach in which a plasticity theory of friction is incorporated to simulate sliding resistance at the powder–tool interface. The constitutive relations for friction are derived from a Coulomb friction law. The frictional contact formulation is performed within the framework of large FE deformation in order to predict the non-uniform relative density distribution during large deformation of powder die pressing. A double-surface cap plasticity model is employed together with the nonlinear contact friction behavior in numerical simulation of powder material. Finally, the numerical schemes are examined for efficiency and accuracy in modeling of several powder compaction processes.     

三维弹塑性有摩擦接触问题求解的一个新算法

空间弹塑性有摩擦问题是两种非线性相互耦合的边值待定问题,由于涉及到空间接触问题,切向滑动状态的确定就成为一个重要的方面,为获得高精度的结果,大量的计算工作是难免的.规划法与迭代法是处理这类问题的两种重要的方法.作者提出了将这两种方法相结合的规划-迭代算法,充分利用两种方法各自的长处来处理空间弹塑性接触问题.数值结果表明了所提出算法的良好性态.