粗糙表面上微织构对流量因子的影响

为研究混合润滑条件下粗糙表面上微织构对流量因子的影响,在不同表面纹理方向的高斯随机粗糙表面的基础上,建立不同织构参数的几何模型,通过数值求解雷诺方程,研究织构的面密度及深宽比对压力流量因子、剪切流量因子的影响。结果表明:压力流量因子和剪切流量因子随着表面织构面密度和深宽比的增大而增大,且随着深宽比的增加,压力流量因子增大的幅度逐渐减小;在各向同性、横向纹理及纵向纹理表面下,表面织构的面密度和深宽比对压力流量因子和剪切流量因子的影响大致相同。     

粗糙表面上微凸体间气穴对流量因子的影响

研究了粗糙表面上微凸体间气穴对用于混合润滑分析的流量因子的影响.在利用自编程序产生了具有不同纹理方向的随机粗糙表面的基础上,使用扩展的气穴方程分析了微凸体间气穴对压力流量因子、剪切流量因子的影响.计算结果表明:气穴的存在,在小膜厚比范围内会使压力流量因子有所增加,而使剪切流量因子减小;在大膜厚比范围内,气穴对流量因子的影响可以忽略不计;而且气穴对流量因子的影响与粗糙表面的纹理方向有关.因此,微凸体间气穴对流量因子的影响应加以考虑.     

线接触弹流问题弹性变形方程的数字信号解法

根据数字信号系统的分析方法,提出了与弹性体受力变形对应的信号系统模型,在时域和频域内对该系统加以描述。利用信号分析的快速傅里叶变换及其卷积性质,实现了线接触弹流问题弹性变形方程的快速计算,其计算工作量为O（Nlog2N）。对Hertz压力分布接触区弹性变形的计算表明,弹性变形方程数字信号解法的精度与变形矩阵法相当,而计算量及存储空间的开销则大大低于变形矩阵法。因而,弹性变形方程的数字信号解法在弹流计算中具有实用价值。     

弹性变形对锥形配流副润滑特性的影响

考虑到锥形配流副在高压条件下的弹性变形量已与油膜厚度同一数量级,应用弹性流体动力润滑理论,建立了其弹性变形条件下锥形配流副的润滑数学模型,采用有限差分法求解了模型的控制方程,进行了弹性变形对锥形配流副润滑特性的影响研究.结果表明,锥形配流副的弹性变形对其润滑特性有较大的影响,它增大了泄漏量,降低了摩擦转矩; 工作压力对摩擦转矩的影响程度要大于偏心率.     

随机型条纹粗糙表面的弹流润滑

本文在不同的工况及形貌参数下，用Ｎｅｗ－ｔｏｎ—Ｒａｐｈｓｏｎ完全数值解法，对任意条纹方向两维粗糙度的随机雷诺方程进行了数值求解，讨论了表面粗糙度及其纹路方向对机械零件润滑状态的影响。     

计及轴受载变形的粗糙表面轴承热弹性流体动力润滑分析

同时计及表面形貌、热效应和轴承表面(热和弹性)变形等,对轴受到载荷作用产生变形,导致轴颈在轴承中倾斜时滑动轴承的热弹性流体动力润滑性能进行研究,主要分析讨论表面热变形等对粗糙表面倾斜轴颈轴承热弹性流体动力润滑性能的影响.计算中,采用基于平均流量模型的广义Reynolds方程进行轴承的润滑分析,采用变形矩阵方法计算轴承表面(热和弹性)变形,采用能量方程和热传导方程计算润滑油和轴承的温度分布.结果表明,计及表面热变形时,半径间隙对轴承最大油膜压力、最小油膜厚度、油膜压力和油膜厚度的分布有较大影响;轴承载荷越大,表面热变形对轴承性能的影响越显著;表面热变形对轴承性能的影响程度与转速高低有直接关系,转速越高,表面热变形的影响越大;相比于表面弹性变形,表面热变形对轴承性能的影响较大;表面形貌是否影响轴承性能以及影响程度与轴承表面变形情况有较大关系,仅考虑热变形时,表面形貌有一定影响,同时考虑热变形和弹性变形时,表面形貌的影响非常小.     

磨损轮廓与弹性变形对滑靴动态特性的影响

考虑滑靴的倾斜与底面实际磨损轮廓,结合滑靴实际受力状况,建立描述滑靴微观运动的动力学方程,对滑靴的刚度分布特性进行研究从而引入底面流体压力所导致的结构弹性变形所带来的影响.联立动力学方程、瞬态二维雷诺方程、油膜描述方程,弹性变形方程,油室压力控制方程,实现滑靴动力学特性与摩擦特性的耦合求解,获得整个工作周期内滑靴的微观运动状态,实现滑靴副润滑特性的精确计算.探讨微观磨损几何、滑靴底面的流固耦合效应对滑靴动态油膜特性的影响.分析结果表明,一定的磨损轮廓与弹性变形均可以保证滑靴承载特性的稳定性,较大的磨损轮廓会降低滑靴的承载力并使滑靴最小膜厚降低;当滑靴位于低压吸入区时,具有表面磨损轮廓的滑靴会出现很大的倾斜现象;磨损轮廓与弹性变形对滑靴的摩擦转矩特性也存在一定的影响.     

浮环弹性变形对浮环动静压轴承润滑特性的影响

浮环轴承在高速工况下运行时,浮环表面在油膜压力作用下会发生弹性变形,影响轴承润滑性能。针对带有深浅腔的浮环动静压轴承,采用有限元法和有限差分法耦合求解油膜Reynolds方程、能量方程和温黏关系式,采用变形矩阵法求解弹性变形方程,计算浮环弹性变形分布;在浮环平衡的基础上,分析浮环变形对环速比、油膜承载力、端泄流量等润滑特性参数的影响。结果表明：浮环弹性变形分布与油膜压力分布呈现一致性,转速越高,偏心越大,变形越明显;考虑浮环弹性变形,浮环达到平衡状态时,内膜偏心率增加,环速比减小,轴承承载力与摩擦力矩均有所增加;由于浮环变形对内、外膜间隙及流动液阻的不同影响,使得内膜端泄流量增加,外膜端泄流量减少。     

弹性材料表面织构对摩擦副润滑性能的影响

为了研究弹性材料表面微织构对摩擦副空化现象和润滑特性的影响,建立考虑空化效应的二维弹性织构计算模型,采用流固耦合方法计算润滑流场与材料变形之间的相互作用。对比刚性材料表面微织构,从弹性模量、滑动速度、微织构深度以及织构间距等方面分析弹性材料表面织构对摩擦副润滑性能的影响,通过实验验证模拟结果的准确性。结果表明：弹性织构摩擦副比刚性织构摩擦副摩擦因数更小,润滑性能更好;存在最优织构深度,使得弹性织构摩擦副的摩擦力最小且承载力最大;适当增大滑动速度以及织构间距可以提高弹性摩擦副的润滑性能;随着弹性模量的降低,弹性变形和油膜厚度增加,空化现象更为显著,摩擦副的润滑性能得到提升。     

浮环弹性变形对浮环轴承润滑特性的影响

采用有限差分法联立求解内、外油膜的Reynolds方程、膜厚方程和浮环弹性变形方程,到在不同转速和偏心率下浮环的弹性变形量,研究浮环弹性变形对浮环轴承润滑特性的影响。结果表明:随着转速和偏心率的增加,浮环弹性变形量逐渐增加;浮环弹性变形降低了内油膜的承载力、端泄流量和摩擦功耗,增加了外油膜的承载力、端泄流量,但对外油膜摩擦功耗影响较小。     

On the Modeling of Elastic Contact between Rough Surfaces

The contact force and the real contact area between rough surfaces are important in the prediction of friction, wear, adhesion, and electrical and thermal contact resistance. Over the last four decades various mathematical models have been developed. Built on very different assumptions and underlying mathematical frameworks, model agreement or effectiveness has never been thoroughly investigated. This work uses several measured profiles of real surfaces having vastly different roughness characteristics to predict contact areas and forces from various elastic contact models and contrast them to a deterministic fast Fourier transform (FFT)-based contact model. The latter is considered “exact” because surfaces are analyzed as they are measured, accounting for all peaks and valleys without compromise. Though measurement uncertainties and resolution issues prevail, the same surfaces are kept constant (i.e., are identical) for all models considered. Nonetheless, the effect of the data resolution of measured surface profiles will be investigated as well. An exact closed-form solution is offered for the widely used Greenwood and Williamson (GW) model (Greenwood and Williamson, Proceedings of the Royal Society of London A, vol. 295, pp. 300–319), along with an alternative definition of the plasticity index that is based on a multiscale approach. The results reveal that several of the theoretical models show good quantitative and qualitative agreement among themselves, but though most models produce a nominally linear relationship between the real contact area and load, the deterministic model suggests otherwise in some cases. Regardless, all of the said models reduce the complicated surface profiles to only a few key parameters and it is therefore unrealistic to expect them to make precise predictions for all cases.     

粗糙表面塑性变形对弹流润滑性能的影响

利用弹塑性动压润滑理论来分析线接触条件下粗糙表面的塑性变形对润滑性能的影响。首先计算总变形量,然后根据弹塑性理论对总变形量进行修正获得弹塑性变形量。计算中采用直接迭代法对雷诺方程进行数值求解,用多重网格法得到弹塑性变形量。为定量分析塑性变形的影响,采用余弦粗糙度来代替实际的粗糙表面,通过改变余弦粗糙度的峰高、波长和相位来表征粗糙度的变化,以此来分析粗糙度对弹塑性流体润滑的影响。计算结果表明:考虑塑性因素后,在接触的高压区膜厚变小,油膜分布曲线变得平坦,同时接触区域的油膜压力也明显变小;此外塑性变形因素的存在使得接触区的压力和油膜分布宽度增加,第二压力峰和最小膜厚点后移。     

Theoretical and Experimental Study of a Thermal Contact Conductance Model for Elastic,Elastoplastic and Plastic Deformation of Rough Surfaces

This study developed a thermal contact conductance model that takes into account surface asperities with elastic, elastoplastic and plastic deformation. The surface asperity model considers the continuity and smoothness of variables across different modes of deformation. Experiments were also conducted to measure thermal contact conductance for samples with different surface roughness when the contact pressure was increased or decreased. The trend of the test data supports the theoretical results.     

Time-Dependent Fluid Squeeze-Out Between Soft Elastic Solids with Randomly Rough Surfaces

We study the time dependency of the interfacial separation and of the area of real contact between a soft elastic cylinder and a rigid solid with a randomly rough surface, squeezed with normal approach in a fluid. This problem is relevant for biological, as well as for bio-medical, seals and tires applications. An ad-hoc numerical scheme is developed to solve the transient mixed-EHD homogenized lubrication problem. We show that, for the soft contact case, the transition from the EHD to the boundary regime can be much more efficiently studied within a simplified (Grubin-like) problem formulation then with the full numerical scheme. This is not only of great conceptional importance, but also of practical importance as the latter calculation is much simpler and faster than the full scheme calculation.     

弹性变形对大型球磨机轴承性能的影响

研究弹性变形对大型球磨机滑履轴承性能的影响。采用有限差分法求解简化形式的N-S方程,得出油膜压力分布和膜厚分布;借助有限元软件ANSYS分析中空轴和轴瓦的弹性变形。将变形作为油膜变化的条件,油膜压力分布作为变形的条件,进行耦合分析,得出润滑油膜厚度及压力分布。结果表明:考虑中弹性变形时计算得到的最小油膜厚度小于未考虑弹性变形时的厚度,且球磨机四块瓦的油膜厚度分布规律不同,表明中空轴和轴瓦的变形对膜厚分布规律、压力分布及最小膜厚有较大影响,设计时必须考虑弹性变形的影响,以防止出现油膜过薄导致轴承失效。     

基于多项式伸缩因子的参数曲面自由变形

为得到理想的参数曲面造型效果,构造了一种新的基于多项式的伸缩因子,它不仅具有已有伸缩因子的特性,还具有区域峰值性;同时,扩展了参数曲面自由变形方法,将变形区域由圆域推广至四边域。在将伸缩因子作用于待变形曲面方程时,通过交互改变控制参数来控制曲面的形状,从而得到变形效果。实验结果表明,该方法计算简单、易于控制,可以得到丰富的变形效果。适用于几何造型、计算机动画、CAD/CAM等领域。     

A Numerical Model for the Dry Sliding Contact of Layered Elastic Bodies with Rough Surfaces

A numerical model for the two-dimensional dry sliding contact of two elastic bodies with real rough surfaces has been developed, where an elastic body contacts with a multi-layer surface under both normal and tangential forces. The model uses surface profile data directly recorded with a stylus measuring instrument and it is suitable for use on a microcomputer. Green's function for a unit normal load and a unit tangential load for the generalized plane strain problem are derived. Verification of the accuracy of the model by reproduction of test case results is presented. Contact pressure distribution for layers of varying coefficient of friction, thickness and elastic modulus is analyzed.