滑动速度与高频摩擦噪声关系的试验研究

为研究高频摩擦噪声的产生机制,在Plint 92摩擦磨损试验机上采用平面-平面接触的旋转滑动摩擦副系统,研究摩擦副间相对滑动速度与高频摩擦噪声的相关性,测得摩擦过程中摩擦因数的变化情况和产生的高频噪声信号及其声压值,提出基于滑动速度变化的摩擦因数和高频噪声声压值的预测方程。结果表明:滑动速度对摩擦因数和高频噪声的产生和演变有重要的影响,摩擦因数对滑动速度的变化呈现一定的阀值性,且大的摩擦因数更易产生高频噪声。对高频噪声信号进行分析,发现高频噪声具有间歇性出现的特点。摩擦因数和高频噪声声压值随滑动速度变化规律具有一致性。     

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。     

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。     

沟槽织构化表面影响摩擦振动噪声机理

在列车制动盘蠕墨铸铁材料表面上制备出平行间隔分布的沟槽表面织构,将其和光滑表面进行摩擦噪声对比试验,并利用有限元软件ABAQUS/Explicit(显式动态求解器)对试验进行数值模拟分析,研究沟槽织构化表面影响摩擦振动噪声的机理。结果表明,本试验条件下的光滑表面会产生较高强度的噪声而沟槽表面几乎不产生噪声,利用有限元软件ABAQUS/Explicit可以很好地模拟试验现象并揭示沟槽表面织构影响界面摩擦振动噪声的机理,即沟槽织构表面在对磨球滑过并碰击沟槽时引起的摩擦力波动能有效的打断摩擦界面的连续接触,作为不连续激励扰乱系统的自激振动,抑制界面摩擦力和振动加速度高频成分的形成并最终降低摩擦噪声。     

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。     

摩擦力-相对滑动速度关系的实验研究

对金属往复滑动摩擦力-相对滑动速度的关系进行了试验研究，通过设计相对滑动速度曲线实现了无摩擦振动工况下的摩擦力-相对滑动速度关系的测量。文中还对摩擦振动工况下的摩擦力的测量作了探讨。本文的试验数据可作为摩擦振动和摩擦噪声理论研究的基础数据。     

沟槽形表面织构对摩擦噪声的影响

用电加工方法在制动盘蠕墨铸铁材料表面加工出沟槽形表面织构(沟槽深度为30μm、宽度为150μm、间距为500μm),采用球—平面接触方式,选取直径为10mm的Si3N4球为对磨副,对沟槽形织构表面和光滑表面进行了摩擦噪声对比试验,研究了沟槽形表面织构对界面摩擦振动噪声的影响。试验结果表明(以下结论只针对本试验选定尺寸规格的沟槽形表面织构):法向载荷对织构表面产生摩擦噪声强度的影响较小,而对光滑表面产生摩擦噪声的水平具有重要影响;沟槽形织构表面在低法向载荷下较光滑表面更易产生摩擦噪声,但随着法向载荷从5N增大到10N,光滑表面产生的摩擦噪声强度迅速增大并与织构表面的接近;沟槽形表面织构使摩擦系统更易产生多频率的摩擦振动,较早地产生摩擦噪声且其主频率成分较复杂;沟槽形织构表面比光滑表面具有较高的摩擦因数和耐磨性,沟槽形织构的存在明显地改变了接触界面摩擦磨损行为和摩擦噪声特性,但其对应关系需要进一步深入研究。     

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。     

高温氧气条件下CrNiMo钢的摩擦磨损特性研究

以CrNiMo钢和H96黄铜组成配副,利用QG-700型高温气氛摩擦磨损试验机,研究了高温氧气气氛环境中滑动速度、接触压力等对CrNiMo钢摩擦学特性的影响.采用扫描电子显微镜(SEM)和能谱仪(EDS)对磨损表面进行表征.结果表明:在高温氧气气氛中,随着滑动速度和接触压力的增大,摩擦因数逐渐减小,磨损率逐渐增大.在滑动速度和接触压力逐渐增大的过程中,CrNiMo钢的主要磨损机制由粘着磨损转变为氧化磨损.     

轮轨滑动摩擦生热分析

利用ANSYS有限元软件建立轮轨滑动摩擦热-结构耦合简化模型,针对特定载荷、摩擦因数和相对滑动速度工况进行了轮轨的温度场和应力场研究.结果表明:轮轨处在滑动摩擦状态时,需考虑材料参数随温度变化的影响;热影响区分布于轮轨表面很薄层,并在此薄层产生很高的热应力;随着轴重力、摩擦因数和相对滑动速度的增大,轮轨的热效应越明显.轮轨滑动过程的热效应问题研究将有助于揭示接触过程中的表面磨损机理.     

Friction-Induced Vibration by Stribeck’s Law: Application to Wiper Blade Squeal Noise

This paper is concerned with the squeal noise of a wiper/windscreen contact. It is shown that squeal noise stems from friction-induced self-excited vibrations in the context of Stribeck’s law for friction coefficient. The study is specifically focussed on the instability range of velocities and not on the amplitude of limit cycles. The studied dynamic system consists of a single degree-of-freedom mass-spring-damper oscillator submitted to a velocity-dependent frictional force which follows the Stribeck law. The local stability is analyzed by the first Lyapunov method and results in a stability criterion. Experiments have been performed on a glass/elastomer contact lubricated with water. The tribometer ‘LUG’ provides measurements of the vibrational velocity and friction force versus sliding speed. It is found that the instability appears during the transition between boundary and elastohydrodynamic regimes where the negative gradient of the friction versus velocity curve is steep. The apparition and vanishing of instability are correctly predicted by the steady-state stability criterion.     

Effect of the Abrasive Size on the Friction Effectiveness and Instability of Brake Friction Materials: A Case Study with Zircon

The friction-induced vibration triggered at the sliding interface between the gray iron disk and brake friction material was studied by changing the size of the zircon particles in the friction material. The friction tests were performed using a reduced brake dynamometer and the friction characteristics of the friction materials containing zircon particles with sizes of 3, 50, and 100 μm were analyzed. Our results show that the properties of the sliding surface were strongly affected by the entrenchment of the abrasive particles in the friction layers during sliding. The friction effectiveness was inversely proportional to the size of the abrasive, while friction instability was pronounced when smaller zircon particles were used. The smaller zircon particles produced larger plateaus on the sliding surface with low contact stiffness. However, the contact plateaus with the low contact stiffness showed higher amplitudes of the friction oscillations, suggesting a surface with low stiffness also can produce high propensity of friction instability during sliding. Based on the friction stability diagram and surface properties, such as contact stiffness and surface roughness, it was suggested that the static coefficient of friction, which was changed as a function of dwell time, was crucial to understand the cause of friction-induced force oscillations and propensity of friction instability of brake friction materials.     

Experimental investigation into squeal under reciprocating sliding

Experiments on squeal under reciprocating sliding were performed by means of a ball against a block. Vibration accelerations, sound pressure level of squeal and tangential force were measured simultaneously. Under certain test conditions, the reciprocating sliding can create a whole process from squeal generation to disappearance. Based on power spectral density (PSD) and short-time Fourier transform (STFT) analyses on the vibration accelerations in that process, it was found that the dominant frequencies of the friction-induced vibrations associated with squeal is not varied. Examination of the friction–velocity slope shows that there is no invariable correlation between the negative friction–velocity slope and occurrence of squeal. Squeal can occur in regions with both negative and positive friction–velocity slopes.     

The mechanism of dry friction of polyoxymethylene against steel

The mechanism of friction between polyoxymethylene and steel was investigated. The coefficient of friction was determined, and the effects of the hardness of the steel, the roughness of the sliding surface, the temperature, the relative sliding velocity and the contact pressure were examined. Additional investigations were carried out to explain the mechanism of friction between the polymer and steel. Structural changes in the friction surfaces were investigated by microscope examination. Five fundamental types of friction were identified and are discussed.     

基于盘／销装置的摩擦尖叫噪声研究

为了研究摩擦尖叫的产生机理,利用汽车制动盘、摩擦材料及铝合金圆销设计了一种长度可调的盘／销摩擦试验装置,进行了不同销长的摩擦尖叫试验。基于盘／销零件的约束模态试验结果,建立了装置的有限元模型。利用复特征值分析方法研究了销长、摩擦因数、载荷、速度和材料特性等因素对摩擦尖叫噪声的影响。结果表明：当圆销和制动盘间弯曲模态频率相近时会形成模态耦合,系统不稳定,产生摩擦尖叫噪声;通过改进系统结构、适当降低摩擦因数和调整材料特性可以减轻或消除摩擦尖叫。     

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.     

表面粗糙度对滑动电接触磨损率的影响

在电气化铁路弓网系统中,磨损率是衡量列车运行状态与接触导线使用状态的重要指标。为了充分模拟弓网系统中磨损率情况,利用自行搭建的滑动电接触摩擦磨损试验机对滑板和接触导线进行摩擦磨损试验,分析滑板表面粗糙度、法向压力、接触电流与运行速度对磨损率的影响。得出结论:滑板磨损率随滑板初始表面粗糙度、接触电流、法向压力、运行速度的增加而增加,而高载荷下粗糙度对于磨损率的影响降低;滑板摩擦从磨合期进入稳定摩擦期存在一个临界表面粗糙度,当滑板初始表面粗糙度值等于临界粗糙度值时,其磨损率最低;不同初始表面粗糙度的滑板在跑合期内磨损过程不同,在稳定摩擦期内磨损过程趋于一致,且摩擦试验后滑板表面粗糙度也接近。     

Friction characteristics of a ferritic-austenitic stainless steel during lubricated reciprocating motion

This report describes friction measurements of stainless steel against stainless steel during lubricated, small-amplitude reciprocating motion. The experimental investigation was divided into two parts. First, four different lubricants were evaluated using a response surface design, during which the average contact pressure and the sliding velocity were varied. Secondly, a 2⁴ factorial design with three replicate runs was performed. Here, the coefficient of friction in the initial stage and the duration of that stage were studied. The independent variables were the average contact pressure, sliding velocity, surface roughness and type of lubricant. In the early state (stage I), the value of the frictional force is controlled by plowing of the surfaces by asperities. In many lubricated contacts, this is the practically useful stage. The experimental results from the response surface design show that the duration of stage I depends on the type of lubricant. Adhesive wear can take place before 100 cycles. The factorial design indicates that the coefficient of friction in the initial stage is affected by the type of lubricant, surface roughness and the simultaneous change of the surface roughness and type of lubricant. The duration of the initial stage is affected by a change in the surface roughness, average contact pressure and a simultaneous change in average contact pressure and surface roughness. A two-parameter Weibull analysis was performed on the data from the factorial design. For the tests where lubricant no. 3 was used, a mixed distribution was indicated for the duration of stage I. This mixed distribution indicates that a weakest-link process as well as a healing process were involved.     

Effects of Contact Pressure and Sliding Speed on the Unlubricated Friction and Wear Properties of Zn-15Al-3Cu-1Si Alloy

The unlubricated friction and wear properties of Zn-15Al-3Cu-1Si alloy were studied over a range of contact pressure (1–5 MPa) and sliding speed (0.5–2.5 ms^?1) for a sliding distance of 2,500 m using a block-on-disc type test machine. It was observed that as the contact pressure increased, the friction coefficient of the alloy decreased but its working temperature, surface roughness, and wear volume increased. Sliding speed had no significant effect on the friction coefficient of the alloy but increased its working temperature, surface roughness, and wear volume. It was also observed that the formation of a hard and brittle surface layer had a great influence on the wear behavior of the experimental alloy. The hardness and thickness of this layer increased with increasing contact pressure and sliding speed. However, contact pressure was found to be much more effective on the hardness of the surface layer of this alloy. Both adhesion and abrasion were observed to be the dominant wear mechanisms for the alloy under the given sliding conditions. The results obtained from the friction and wear tests are discussed in terms of the test conditions and microstructural changes that take place during sliding.