考虑端面变形微孔表面无压动压润滑比较分析

表面微孔结构在剪切作用下诱发流体产生附加动压效应,提升流体膜承载能力,促使摩擦配合端面间维持流体润滑,改善摩擦性能。以6种不同微孔表面为研究对象,考虑端面弹性变形影响,开展无压工况下动压润滑特性的比较研究,数值分析平衡基础膜厚、流体流量、摩擦转矩、摩擦系数等性能参数随操作条件与孔型参数变化规律,并以最优动压特性与摩擦性能为目标,给定不同孔型参数的优化范围。结果表明:弹性变形与流体膜厚度相对应,轴向压缩变形越大,润滑间隙尺寸越大,膜厚越厚。相比于平衡基础膜厚,端面变形对膜厚分布影响微弱。在微孔倾斜角0～20°范围内,椭圆微孔与矩形微孔动压效应最为显著,且摩擦系数、摩擦转矩较小,优势较为明显。在孔深为4～6μm、方向因子为2时,不同形状孔型结构润滑性能均可达到最佳效果。     

线接触滚/滑状态下表面形貌的弹性变形研究

结合基于表面形貌频谱分析的预测方法和润滑理论对线接触弹流状态下表面形貌的弹性变形进行了研究。制造了4种表面形貌高度算术平均值S_a相同但结构不同的织构表面形貌,通过对表面形貌的频率分量进行降幅处理,并结合弹流润滑模型建立相应的算法,获得了不同载荷和转速工况下接触界面的表面形貌弹性变形结果。在此基础上,选用ISO 25178中的三维形貌高度参数S_a、功能参数V_(vv)和特征参数S_(ds)对弹性变形前后的表面形貌进行了表征和分析,并通过计算膜厚比对比了4种织构表面在考虑弹性变形前后的润滑特性。结果表明,弹流接触过程中表面形貌发生明显的弹性变形,且随着载荷和转速变化呈现不同的规律;不同结构的表面形貌弹性变形程度不同,弹性变形导致的表面形貌的变化对接触表面间润滑性能有明显影响。     

点接触弹流润滑条件下表面弹性变形研究

为研究弹流润滑条件下点接触表面变形及其对表面性能的影响,采用激光微织构法制备了一组不同形貌参数的滚动轴承滚道表面试件,基于表面频谱分析和弹流润滑快速算法（幅值缩减法）分析了试件在不同工况参数下的弹性变形。使用ISO 25178三维形貌参数体系对变形前后表面进行表征,研究了点接触弹流润滑状态下表面形貌的弹性变形与载荷、转速的关系。研究结果表明,弹流接触使表面形貌发生显著的弹性变形,载荷、转速等工况参数对变形量影响较大,表面弹性变形使得形貌参数发生显著变化。     

浅拱形薄壳在流体作用下的变形与应力分析

应用弹性薄壳的基本理论和流体弹性力学基本方程,结合相容拉格朗日-欧拉法,建立接触面处流体与固体相互作用的运动学方程和动力学方程,深入研究浅拱形薄壳在流体作用下的弯曲变形;给出在倾斜流动和对称流动状态下,法向位移系数的线性方程表达式;结合边界条件求解得到浅拱形壳的变形、压力及应力的算式。并通过具体算例,绘出挠度随壳体材料、壳体厚度、壳体弧长、迎角和流体速度等参数变化的关系曲线,给出发生最大变形、最大应力所在的位置及数值;分析相关参数变化对浅拱形壳体变形和应力状态的影响。其分析结果可供流体作用下浅拱形薄壳的强度与刚度设计参考。     

高速膜盘式太阳轮轴的疲劳强度分析

膜盘联轴器依靠圆盘几何型面的弹性变形补偿输入和输出端的微量位移和角度偏差,且有效地承受离心力、轴向变形作用和传递转矩载荷,主要应用于航空、燃气轮机等高精度和高参数的领域范畴。建立了膜盘和太阳轮轴耦合结构的膜盘式太阳轮轴强度分析计算离散模型,依据旋转机械强度理论,对单一载荷和多耦合载荷作用下太阳轮轴的静强度和疲劳强度展开研究分析,并采用两种疲劳强度评定准则进行强度校核。结果显示,在使用条件参数范围内,单一或多耦合载荷作用下轮轴设计结构强度均满足使用要求;转速与应力呈现非线性关系,造成齿根处发生较大应力,且与耦合载荷引起应力占据比重交替增加;提出高速旋转机械部件进行结构设计时,应充分考虑其离心力和科氏力引起的结构应力作用。同时,在单轴和多轴两种疲劳强度评判准则下,结构设计安全,且具有较大的安全裕量。最大剪切应力主要集中在膜盘轴肩圆角过渡区域,节点最大应力为137. 3 MPa。     

浮动球球阀疲劳寿命分析

介绍了流体供应系统用浮动球球阀结构和性能,以及故障阀门失效产生的原因和机理。基于ANSYS Workbench平台建立模型,依据阀门的工作特性,对球体和左阀体分别在不同载荷下的阀门疲劳寿命情况进行仿真和分析,获得阀门球体和左阀体变形量、应力集中和疲劳损伤大小及位置,并与阀门实际使用情况进行对比验证。提出了改进措施和延长阀门寿命的方法。     

机械结合面接触刚度建模新方法

建立精确、有效的结合面接触刚度模型是进一步开展机床整机动力学建模与分析的基础。提出了一种新的弹性接触刚度模型,该模型考虑基体变形的同时,对GREENWOOD和WILLIAMSON提出的粗糙表面微观接触模型(GW模型)进行了修正。为分析基体对接触变形的影响,首先建立含有基体的单个微凸体接触模型,并基于HERTZ接触理论,获得结合面的接触参数;然后,通过引入三角分布函数和解决GW模型在模拟微观接触行为中存在的问题,建立了新的弹性接触刚度模型,并揭示了分布函数、基体变形以及表面粗糙度对结合面接触特性的影响规律。研究表明:三角分布函数能有效地表征表面微凸体高度分布;基体变形的影响是由基体和微凸体相互作用引起,随着法向载荷的增大而明显;表面粗糙度是影响接触刚度的主要因素,相同载荷下,表面粗糙度越大,接触变形越大,接触刚度越小。     

考虑热弹性变形和表面粗糙度的圆柱滚子轴承热弹流润滑分析

运用线接触热弹性流体动压润滑理论,考虑了润滑油膜温升变化引起的圆柱滚子轴承中滚子和内圈接触表面的径向热弹性变形和表面粗糙度的影响,提出了一种计入热弹性变形和粗糙度影响的圆柱滚子轴承线接触热弹性流体动压润滑分析方法。该方法通过将热弹性变形进行热力转换,得到了滚子和内圈接触表面的材料线热膨胀系数,计算修正了滚子和轴承内圈因油膜温度场变化引起的径向热弹性变形,求得了计入热弹性变形和表面粗糙度后的油膜压力、油膜厚度、油膜温升以及径向热弹性变形量等主要润滑特性,研究了载荷、卷吸速度和滑滚比的变化对最小油膜厚度、最大油膜压力和最大油膜温升的影响规律,结果表明,热弹性变形量与最小油膜厚度处在同一量级,热弹性变形和粗糙度会对润滑特性产生明显的影响。     

多层交替膜界限载荷研究

为了研究软硬交替多层表面膜在磨粒作用下的应力应变响应、膜层界面剥离和裂纹的产生及扩展的影响,采用大变形接触弹塑性有限元法对刚性基体上的TiN/Ti多层交替膜在法向压痕作用下的力学行为进行了模拟和分析,研究不同软硬膜层厚度比下,不同膜层的变形、界面切应力分布和表面张应力分布,分析得出界限载荷变化规律及参数分布对其影响情况.结果表明:当软层厚度小于或等于硬层厚度时,增加膜层总厚度可以明显增大多层膜层体系的界限载荷,而软层厚度大于硬层厚度时,增加膜层总厚度不但不能明显增加界限载荷,反而会因增大最大弯曲应力而使界限载荷变小;软硬层厚度比大,而膜层总厚度小的多层膜体系,具有相对较小的最大弯曲应力,因而能承受最大的界限载荷.     

基于ANSYS多物理场的水润滑轴承的数值分析

借助ANSYS多物理场求解器的流固耦合功能对六沟槽水润滑橡胶合金轴承进行2D数值模拟,得到了水润滑橡胶合金轴承润滑膜内的压力分布、速度分布及橡胶轴瓦的弹性变形状况,进而分析了水润滑橡胶合金轴承的润滑性能.结果表明:在载荷较大及中高速工况下,橡胶轴瓦的弹性变形会显著影响水膜膜厚分布及水润滑轴承的润滑性能.     

A System-Approach to the Elastohydrodynamic Lubrication Point-Contact Problem

The classical EHL point contact problem is solved using a new “system-approach,” similar to that introduced by Houpert and Ham-rock for the line-contact problem. Introducing a body-fitted coordinate system, the troublesome free-boundary is transformed to the fixed domain. The Newton-Raphson method can then be used to determine the pressure distribution and the cavitation boundary subject to the Reynolds boundary condition. This method provides an efficient and rigorous way of solving the EHL point contact problem with the aid of a supercomputer and a promising method to deal with the transient EHL point contact problem. A typical pressure distribution and film thickness profile are presented and the minimum film thicknesses are compared with the solution of Hamrock and Dowson. The details of the cavitation boundaries for various operating parameters are discussed.     

多圆弧凸轮接触点位置的计算机辅助求解

提出了一种简单有效的多圆弧凸轮机构瞬时接触点位置的计算机辅助求解方法,它通过分析凸轮与从动件的瞬时接触公法线与圆弧区域界线之间的相对关系来判断任一瞬时凸轮与从动件的接触点的位置、接触点处的曲率半径和曲率中心的位置,据此,可对凸轮机构进行高副低代和运动分析。该方法对于直动、摆动、尖顶、滚子、平底从动件凸轮机构均适用。应用被建议的方法对含平底摆动从动件圆弧凸轮的多功能家用缝纫机送料机构进行了运动分析及动态仿真,验证了该方法的有效性。     

表面粗糙度对点接触弹流润滑性能的影响

本文应用多重网格法对椭圆接触的部分膜弹流问题进行了完全数值求解，计算中采用了Ｐａｔｉｒ－ｃｈｅｎｇ的平均流量模型及Ｇｅｅｎｗｏｏｄ和Ｔｒｉｐｐ的表面微峰弹性接触模型。在大量数值计算结果的基础上分析了表面粗糙度大小及纹理方向对点弹流的油膜厚度及微峰接触载荷的影响。     

Influence of a surface irregularity on the rigidity of a lubricated contact

A technique is presented for numerical solution of the problem of the elastohydrodynamic point contact characteristic of antifriction bearings and tooth gears, taking into account that on the surface in the contact area there is an irregularity in the form of a hill or a dimple. Distributions of pressure and thickness of the lubricant film in the contact area are obtained. The influence of the type of irregularity on the elastic characteristics and rigidity of the elastohydrodynamic point contact is shown. The presented results may be used in calculations of concentrated lubricated contacts. The mathematical model of the elastohydrodynamic contact is described by a system of nonlinear integrodifferential equations with a free boundary (the outflow boundary of the contact area). The computational algorithm is based on the Newton method.     

Jumping mode AFM imaging of biomolecules in the repulsive electrical double layer

We present a method to image single biomolecules in aqueous media by atomic force microscope (AFM) without establishing any mechanical contact between the tip and the sample. It works by placing the feedback set point in the repulsive electrical double-layer curve just before the mechanical instability occurs. We use the jumping operation mode, where the set point is controlled at every image point and a stable imaging is achieved for several hours. This is a necessary condition for this method to be operative, otherwise the tip can fall in contact in a short time. The method is applied to image single-avidin protein molecules deposited on cleaved mica. In addition, the dependence of the height of avidin molecules as a function of ion concentration, due to differences in surface charge density of mica and avidin, is tentatively used to deduce relative values of these quantities.     

Effect of the cut-off frequency on rough-point and flat-surface contacts?

In the past years, contact between two bodies has been studied from various ways that do not consider the cut-off frequency effect on the contact mechanism. This paper reports the correlation between rough point contact and flat surface contact at different cut-off frequencies of filter. The similarity and difference between the two types of contact mechanisms are presented for materials with linear or elasticperfectly plastic deformation. The conjugate gradient method (CGM) is used for analysing the rough point contact, while the rough flat surface contact is studied with an improved CGM in which the influence coefficient for the elastic deformation of the rough flat surface is obtained with finite element method. Numerical results show that for the above two types of contacts, their von Mises stress and maximum shear stress are greatly affected by the cut-off frequency of a high-pass filter. Moreover, a decrease in the cut-off frequency leads to an increase in the contact area and a decrease in the approach for the rough flat surface contact, while the opposite variations is for the point contact between rough bodies with the small radii.     

Envelope-approximation theory of manufacture technology for point-contact tooth surface on six-axis CNC hypoid generator

A new generation method for point-contact tooth surface is proposed based on the six-axis movement of CNC machine. The new method is derived from the idea of motion of Darboux-Frenet trihedron along a predesigned path of contact on the predesigned (theoretical) tooth surface. The generated tooth surface provided by the new method has tangency of second order with the predesigned (theoretical) surface along the predesigned path of contact and the predesigned (least) warping in regions that differ from the path of contact. This means that the new method can reliably control meshing characteristics at each contact point. In contrast, the previous method can only control meshing characteristics at a mean contact point and make correction by observing the contact-bearing condition to determine meshing characteristics at other contact points. Different from the previous CNC generation method translated from the cradle-style universal hypoid generator, the developed method directly suits the six-axis movement of CNC machine to identify the relative motion between the tool and the workpiece based on the predesigned meshing characteristics of the gear being generated. A numerical example is given to prove that the above-mentioned manufacture method is accurate and feasible.     

克林根贝格螺旋锥齿轮接触区域的二阶修正

基于克林根贝格螺旋锥齿轮的切齿理论,建立了克林根贝格螺旋锥齿轮接触区域的几何修正模型,给出了影响齿长、齿高方向接触位置的因素和产生对角接触原因,推导了调整接触区位置各参数的调整量计算公式,提出了齿长和齿高方向和对角接触的接触区域调整方法。     

A finite element method to generate digitized-die shape from the measured data of desired part

Digitized-die forming (DDF) is a rapid and flexible manufacture technology for sheet metal parts. An integrated method is developed in the paper, through which the digitized-die geometry can be directly generated from the measured data of a desired part. The method involves two steps, in the first step, based on the theory of optimal approximation and energy smoothing principal, a positive definite functional is constructed by introducing a smoothing factor and minimized by use of 18 degree-of-freedoms triangular finite-element, then the optimal solution is obtained and the objective surface of the desired part is represented by FE interpolation. The second step involves a process of digitized-die geometry generation from the FE model of the surface. The geometry of the digitized-die is characterized in terms of an array of punch positions and a punch position is determined by the contact point of the punch with objective surface, an efficient contact point searching and calculation scheme is suggested. The detailed method is presented together with typical application examples.     

基于有限元法的准双曲面齿轮时变啮合特性研究

准确计算准双曲面齿轮的时变啮合参数是其系统动力学分析的基础。基于接触有限元分析原理,应用有限元分析软件ABAQUS对齿轮进行加载接触分析(Loaded tooth contact analysis,LTCA),准确计算准双曲面齿轮时变等效啮合参数,包括时变等效啮合点位置、时变等效啮合力作用方向、等效啮合力作用方向上的线位移传动误差和时变等效啮合刚度,并研究转矩大小对时变啮合参数的影响。对比有限元法与经典齿轮接触分析(Tooth contact analysis,TCA)方法求得的传动误差曲线,并对比有限元法计算与加载啮合试验获得的齿面啮合印迹,验证有限元模型和计算的正确性。该方法求得的时变等效啮合参数能够准确体现准双曲面齿轮的时变啮合特性,为进一步研究准双曲面齿轮系统动力学特性提供依据。