旋转端面系统摩擦振动机理的实验研究与分析

旋转摩擦副不稳定现象是工程中常见的摩擦问题。在摩擦试验平台上进行旋转端面摩擦试验研究,测量了摩擦过程中的摩擦振动响应,分析了相对滑动速度和接触载荷对摩擦响应的影响。研究结果表明:摩擦振动具有随机性,在摩擦过程中系统出现碰撞现象;系统振动集中在4个频率附近,提高相对滑动速度和接触载荷使高频振动更突出;试验模态说明摩擦引起了系统的共振并产生振动耦合。该研究成果可为轴系类旋转部件的端面摩擦现象研究提供参考。     

基于小波变换的摩擦噪声激励源的研究

在往复滑动试验机上作了金属摩擦噪声试验,试验期间同时测量了摩擦噪声、摩擦振动三维加速度和名义摩擦力等动态信号,这些信号含有与摩擦振动激励源有关的信息。应用小波变换技术对这些信号进行了分解,在对应摩擦振动主频的小波分解细节分量中,可以清楚地看出激励摩擦振动的摩擦力动态分量,从而说明了摩擦噪声是由波动变化的摩擦力所引发。     

摩擦振动引起的波状磨耗的试验研究

采用销-盘摩擦试验装置模拟轮轨之间的接触应力,研究轮轨间的波状磨耗(简称波磨)问题.通过测量试验过程中摩擦振动信号及试验后的摩擦表面轮廓,研究摩擦振动和摩擦表面波磨间的关系.结果显示,摩擦振动容易引起摩擦表面波磨,且波磨的波长大致等于滑动速度和摩擦振动周期的乘积.     

基于活塞—缸套组件的振动减摩可行性研究

深入进行活塞-缸套组件的减摩研究,对于提高和改善内燃机机械效率与整机性能具有重要意义.为了研究振动减摩在活塞-缸套组件上的可行性,通过引入缸套表面振动变形,构建了活塞-缸套组件的改进润滑模型,对附加振动引起的缸套减摩现象进行了仿真分析,并基于摩擦测量试验机和高频激振设备搭建了内燃机摩擦测量试验台架,对不同超声激振工况下活塞-缸套组件的减摩情况进行了试验研究.研究结果表明:施加参数合理的超声激振能够有效降低活塞-缸套组件间摩擦力.     

气缸套活塞环摩擦副上止点附近的低速润滑特性

针对柴油机气缸套-活塞环摩擦副在上止点附近的低速润滑问题,采用往复摩擦磨损试验方法,获得不同载荷、不同润滑介质条件下,速度对润滑特性的影响规律。试验结果表明:低速区域滑动速度的微小变化带来了上止点附近润滑特性的明显改变。当载荷为10 MPa,滑动速度小于0.4 mm/s时,润滑油中的添加剂ZDDP会显著减小摩擦力;滑动速度大于0.4 mm/s时,添加剂ZDDP对减小摩擦力的影响减弱。当载荷为20 MPa时,添加剂ZDDP在试验速度范围内会一直减小摩擦力。     

金属滑动干摩擦条件下高频噪声的测试与分析

基于面-面接触旋转式滑动干摩擦系统,选用A3&45#钢为摩擦副材料,研究相对滑动速度,表面压力对高频摩擦噪声的影响和规律。运用ABAQUS有限元模态分析高频摩擦噪声产生的原因与机理。通过实验与模态分析发现,摩擦高频噪声易于发生在相对滑动速度较低处。A3&45#摩擦副,在面-面接触旋转式滑动干摩擦条件下,产生的高频摩擦噪声能量集中分布在7950 Hz,9200 Hz。验证了干摩擦条件下,摩擦高频噪声是由于摩擦界面形成类似"锤击效应"的微凸体之间的运动,使得摩擦力高频成分和系统固有频率耦合引起的系统不稳定现象。     

高速、高精度数控伺服工作台摩擦误差的研究

建立了一种考虑摩擦影响的PID控制下的高速、高精度进给伺服工作台的数学模型。伺服机构中的摩擦力是采用一种“两维混合摩擦模型”来描述的。该模型可以根据滑动速度、表面接触物体的油膜厚度等计算摩擦力。通过数值仿真与实际测量 ,在大范围的工况下 ,研究了圆运动过象限时出现凸起的误差现象。通过计算与试验结果的比较 ,证明了提出的考虑摩擦影响的数学模型能够精确地模拟PID控制下的高速、高精度进给伺服工作台的动力学过程 ,能够正确地预测进给运动过程中摩擦误差大小及特征。     

电梯滑动导向系统的摩擦及能耗测量

提出了一套原位测量电梯滑动导靴和导轨间摩擦力及摩擦能耗的装置和方法,并在检修速度下对实际电梯系统进行了摩擦力及其能耗的实验研究。研究表明,实际电梯的各钢丝绳受力不均匀;电梯运行过程中钢丝绳固定端和运动端的受力情况不同;上行的摩擦力和摩擦损耗比下行的摩擦力和摩擦损耗大。     

模拟空间环境摩擦试验技术

将空间环境模拟技术和摩擦试验技术组合,实现了超高真空、交变温度和原子氧、紫外、质子和电子等多种辐照环境摩擦试验功能.该摩擦试验采用球-盘滑动摩擦试验技术,采用重力法施加法向载荷,通过计算机采集摩擦力数据并控制滑动速度,摩擦力数据经计算机处理后实时显示摩擦系数-时间曲线.采用该技术试验了溅射沉积Ag膜在真空和原子氧辐照前后的摩擦性能,发现该膜具有较好的真空润滑性能,而在大气环境和原子氧辐照后的真空中摩擦系数均明最增大,润滑性能显著退化.结果表明.该摩擦试验技术可以获得模拟空问环境下的摩擦试验数据,适用于研究材料的空间环境摩擦学性能.     

基于LuGre模型的转子压缩机滑片-滑槽运动副摩擦力测试

为研究转子压缩机滑片-滑槽运动副的摩擦特性,根据LuGre摩擦模型的建模方法和该运动副的运行特点及工况特点,设计并搭建了滑片-滑槽等效摩擦力测试系统,分析了该系统的摩擦力跃动现象、数据采集区域和摩擦力测量的重复性问题,并进行了摩擦力测试实验。结果表明：该摩擦力测试系统可以根据压缩机的实际工况,对滑片均匀加载相应的正压力FH,并能实现不同匀速直线运动下的摩擦力测量;可以有效消除低速润滑不均匀导致的摩擦力跃动现象;通过润滑初始化可以较准确地获得基于滑片速度变化的摩擦力表达曲线。实验结果与数值计算结果吻合,从而为正确辨识LuGre摩擦模型的参数提供了实验依据。     

Stochastic modeling of friction force and vibration analysis of a mechanical system using the model

The squeal noise generated from a disk brake or chatter occurred in a machine tool primarily results from friction-induced vibration. Since friction-induced vibration is usually accompanied by abrasion and lifespan reduction of mechanical parts, it is necessary to develop a reliable analysis model by which friction-induced vibration phenomena can be accurately analyzed. The original Coulomb’s friction model or the modified Coulomb friction model employed in most commercial programs employs deterministic friction coefficients. However, observing friction phenomena between two contact surfaces, one may observe that friction coefficients keep changing due to the unevenness of contact surface, temperature, lubrication and humidity. Therefore, in this study, friction coefficients are modeled as random parameters that keep changing during the motion of a mechanical system undergoing friction force. The integrity of the proposed stochastic friction model was validated by comparing the analysis results obtained by the proposed model with experimental results.     

滑动摩擦振动噪声的非线性显式动力学分析

利用有限元软件ABAQUS/Explicit(显式动态求解器)对球-平面接触条件下的滑动摩擦振动噪声进行了数值模拟分析。对比试验结果,探讨了摩擦噪声的发生机制,并分析了摩擦噪声发生时接触界面的运动特性。结果表明,摩擦噪声主要是由摩擦系统的自激振动引起的,法向振动与切向振动的耦合是系统产生自激振动和摩擦噪声的一个重要因素。当摩擦系统发生自激振动时,从面节点与主面的接触并不是连续不变的,两者在相对运动的过程中具有黏着-滑动-分离-黏着的特性。     

Friction-induced vibration of oscillating multi-degree of freedom polymeric sliding systems

The purpose of this study is to investigate friction-induced vibration of oscillating systems. Special attention is focused on modeling polymer-on-metal systems. Past experimental and analytical friction results from non-oscillating or unidirectional translational sliding modes are extended into the oscillating sliding mode. Specifically, this refers to the incorporation of a representative functional shape of the friction–velocity relationships estimated from experimental results. Dependent on the relative sliding velocity between the frictionally coupled subsystems, the modeled system exhibits behavior such as a single stick–slip at the beginning of oscillatory motion, a single stick–slip at each motion reversal, or multiple stick-slip events during each half cycle of motion. Additionally, the boundary of incipient friction-induced vibration was identified via a rigorous definition of friction-induced vibration.     

旋转滑动摩擦高频噪声产生机理的实验研究

为了深入研究金属旋转滑动摩擦高频噪声的产生机理,以多功能摩擦磨损试验机为平台,采用单因素实验法来研究相对滑动速度、接触压力、表面形貌等影响因素对摩擦高频噪声的影响规律。实验发现：金属旋转滑动高频摩擦噪声多发生在相对滑动速度低、接触压力较大以及摩擦因数-速度负斜率处;摩擦副间相对滑动速度、接触压力和表面粗糙度的变化几乎不会对高频噪声的频率产生影响,但高频噪声声压级随表面粗糙度的增大呈现明显减小趋势。对摩擦噪声声压信号和法向、切向振动加速度信号进行互相关分析,结果表明,法向振动加速度信号和摩擦噪声声压信号之间具有更高的相关性,从而为进一步理解摩擦高频噪声的产生机理和预测模型的建立提供了参考。     

Lowering friction coefficient under low loads by minimizing effects of adhesion force and viscous resistance

Conditions (normal load, sliding speed, ambient conditions, and material) to obtain the lower friction coefficient were studied by measuring the friction and pull-off forces between a metal pin (copper or gold) and a plate (steel or single crystal silicon). First, a pin was rubbed against a plate under a normal load between −12 and 870 μN at a sliding speed between 0.012 and 9.6 μm/s. The friction force was measured during reciprocating sliding motion. The pull-off force was measured before and after each friction force measurement. All the force measurements were taken in high vacuum at 10⁻⁵ Pa, dry argon at 1 atm, and ambient humid air of 38 and 60% relative humidity. Then, the friction coefficient was calculated by dividing friction force by the sum of normal load and pull-off force. In high vacuum, when a copper pin was rubbed against either a silicon or steel plate, the friction coefficient decreased to less than 0.05 with decreasing sliding speed. The effect of sliding speed on the friction coefficient suggests that under a low normal load the viscous resistance of liquid contributed to the friction force. When a gold pin was rubbed against a silicon plate, the friction coefficient was not affected by sliding speed.     

往复运动机构的摩擦过渡

往复运动机构在运动速度较高时能够保持流体润滑状态,但当速度降低到一定程度,运动副间的润滑形态则由流体润滑状态过渡到边界润滑状态,其摩擦系数陡增,振动和噪音加大。当在润滑剂中加入抗磨添加剂时,这种现象立即消逝。此实验提示：抗磨添加剂对于发动机润滑油是必不可缺的,对于解决往复运动机构的爬行是行之有效的。     

Friction-induced vibration — with and without external disturbance

The dynamics of friction-induced vibration resulting from a velocity-dependent friction characteristic is studied theoretically and experimentally. The frictional system is further studied in the presence of an external dynamic force. The amplitude of quasi-harmonic vibration is shown to increase with sliding velocity until oscillation ceases at some upper velocity boundary depending on the friction characteristic. The vibration, which can exist at high sliding velocities, may influence the operation of automatic transmissions, brakes and clutches. Introduction of strong damping to the system can reduce or eliminate the induced-vibration. Similar results could be achieved by modifying the friction-velocity characteristic of the fluid and materials at the interface. An external excitation in the transverse direction, with properly chosen frequency and force ratios, can also reduce the amplitude of the friction-induced vibration. The theoretical and experimental results are in good agreement.     

Contact of a Finger on Rigid Surfaces and Textiles: Friction Coefficient and Induced Vibrations

The tactile information about object surfaces is obtained through perceived contact stresses and friction-induced vibrations generated by the relative motion between the fingertip and the touched object. The friction forces affect the skin stress-state distribution during surface scanning, while the sliding contact generates vibrations that propagate in the finger skin activating the receptors (mechanoreceptors) and allowing the brain to identify objects and perceive information about their properties. In this article, the friction coefficient between a real human finger and both rigid surfaces and fabrics is retrieved as a function of the contact parameters (load and scanning speed). Then, the analysis of the vibration spectra is carried out to investigate the features of the induced vibrations, measured on the fingernail, as a function of surface textures and contact parameters. While the friction coefficient measurements on rigid surfaces agree with empirical laws found in literature, the behaviour of the friction coefficient when touching a fabric is more complex, and is mainly the function of the textile constructional properties. Results show that frequency spectrum distribution, when touching a rigid surface, is mainly determined by the relative geometry of the two contact surfaces and by the contact parameters. On the contrary, when scanning a fabric, the structure and the deformation of the textile itself largely affect the spectrum of the induced vibration. Finally, some major features of the measured vibrations (frequency distribution and amplitude) are found to be representative of tactile perception compared to psychophysical and neurophysiologic works in literature.     

摩擦噪声有限元预测

发展一种利用商业有限元软件进行摩擦系统全模型摩擦噪声预测的方法,可以对包括摩擦力和真实边界条件下的摩擦系统的复特征值进行分析,提出进行摩擦噪声预测的主要步骤.该方法能够大大提高摩擦噪声预测分析的精度和效率.利用该方法分析往复滑动摩擦系统的噪声发生趋势,获得系统特征方程的特征根及其变化特性,据此可判断摩擦系统自然频率和可能发生摩擦噪声的频率.计算结果表明,摩擦因数和滑动方向对系统摩擦噪声的形成有重要影响,摩擦噪声发生时摩擦系统具有振动模态重合的特点.将计算得到的系统可能发生摩擦噪声的频率与系统的试验噪声频率进行比较,发现有比较好的一致性.     

矩形密封圈的增效运行参数研究

建立矩形密封圈的混合润滑模型,分析工作压力、活塞杆运行速度和密封件粗糙度对轴向往复用矩形密封圈的摩擦力矩、泄漏量的影响。结果表明:过大的密封压力会对密封件造成损坏,使得摩擦力和净泄漏量极速增大;往复速度的增加会使摩擦力线性增大,直线往复密封的净泄漏量随着表面粗糙度的增大表现为越来越大的增量。利用田口实验设计方法对矩形密封圈操作压力、运行速度和密封件粗糙度进行正交试验,分析得到最优参数组合,并得到各影响因素对密封性能的影响程度由大到小依次为往复速度、粗糙度、密封压力。