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.     

不同摩擦状态下滑动轴承与转子碰撞振动提取研究

为了研究滑动轴承在不同摩擦状态下碰撞振动的特征,在滑动轴承试验台上进行滑动轴承不同摩擦状态试验,应用谐波小波包变换提取滑动轴承碰撞振动信号,探讨碰撞振动信号在滑动轴承同摩擦状态下的变化。结果表明:当滑动轴承处于边界摩擦状态时,碰撞振动信号的均方根值大,并随着主轴转速的增加而增大;当滑动轴承处于混合摩擦状态时,碰撞振动信号的均方根值随着主轴转速的增加显著下降;当滑动轴承处于液体摩擦状态时,碰撞振动信号的均方根值小,并随着主轴转速的增加呈平稳上升趋势。因此,通过谐波小波包变换提取的滑动轴承碰撞振动信号反映了滑动轴承摩擦状态的变化,可用于滑动轴承摩擦状态的监测。     

金属摩擦副干滑动摩擦噪声机理研究

以销-盘磨损试验机配合振动加速度传感器和精密声级计为试验设备，研究了TiNi合金／GCr15轴承钢摩擦副干滑动摩擦噪声的特点和产生机理。结果表明：由于磨损造成摩擦表面形貌恶化，使摩擦力值增大，且波动剧烈，急剧变化的摩擦力对摩擦系统不断输入能量，引起系统产生自激振动，向环境中辐射噪声。TiNi合金的耐磨性能优于淬火45^#钢，所以在相同的试验条件下，TiNi合金／GCr15钢配副的滑动摩擦噪声比淬火45^#钢／GCr15钢配副的低，尤其在载荷较大时，TiNi合金可以降低摩擦噪声3～5dB。     

盘-销系统摩擦尖叫的时变性:发生机理与关键影响因素

为解释摩擦尖叫时变性的基本机制,建立盘-销系统并完成摩擦尖叫台架试验,成功反复再现间歇性和持续性尖叫。试验时,记录不同速度和法向力载荷工况下的摩擦噪声、动态接触作用力和销端部振动加速度信号。通过试验信号的小波分解、时频分析和馈入能量的计算,系统分析盘-销系统发生时变性摩擦尖叫的机理与因素。研究发现,摩擦尖叫的间歇性或持续性取决于摩擦接触法向力准静态分量的大小。当法向力准静态分量较小时,系统发生间歇性尖叫,反之则发生持续性尖叫。制动盘和销的模态耦合导致摩擦尖叫,尖叫频率会随着法向力准静态分量的变化成比例变化,且与摩擦接触力之间存在显著的滞环效应;能量馈入是产生摩擦尖叫的重要前提,而且馈入能量的变化导致摩擦尖叫声压幅值变化。     

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。     

往复滑动频率和法向力对摩擦噪声强度影响的实验研究

本文在作摩擦噪声试验时，对摩擦噪声的声压级和加速度进行了测量。测量结果表明，往复滑动频率和法向力对摩擦噪声的强度有比较大的影响。     

基于LabVlEW的摩擦噪声测试系统

虚拟仪器(Vinual Instrument，简称VI)是现代计算机软件技术、通信技术和测量技术相结合的产物。LabVIEW语言是美国NI公司推出的一款功能强大的虚拟仪器开发平台。小波变换的主要特点是通过变换能够充分突出某些方面的特征，它是研究信号时一频分析的重要方法。设计和实现了基于LabVIEW、利用小波变换的噪声测试系统；通过该测试系统可以对摩擦噪声进行测量和分析，有利于深入了解摩擦机理，改善摩擦条件，促进环保事业。     

摩擦系数影响摩擦噪声发生的机理研究

结合摩擦系数测量和磨痕表面形貌的观察，认为摩擦力的波动成分是引发摩擦噪声的主要机理。对于往复滑动过程，在摩擦系数一往复循环次数的关系图上一般有一个驼峰状的变化。应用Suh的理论，说明了在摩擦系数的驼峰状上升沿靠顶部的地方既是摩擦力接近最大值，又是摩擦力波动最激烈的地方，因而在这地方很容易出现摩擦噪声。     

在往复滑动条件下摩擦噪声发生时磨痕形貌的观察

为了进一步认识在有摩擦噪声期间磨痕形貌与噪声之间的关系，采用两种常用的铁路车辆制动闸瓦材料进行摩擦噪声试验。试验中测取了不同循环次数时摩擦振动三维加速度、噪声声压等动态信号，并提取了相应的磨痕形貌。通过对磨痕形貌的激光共焦扫描显微镜(OLS)、SEM及光学显微镜观察，研究了噪声出现区域的形貌变化。研究结果显示磨痕上有摩擦噪声区域的形貌与无摩擦噪声区域的形貌有一定差别。     

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 — 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.     

纳米碳酸钙与液晶添加剂的摩擦磨损分析

在15^#机械油中添加纳米碳酸钙或纳米液晶，用标准的立式万能摩擦磨损实验台实验分析了15^#机械油、15^#机械油＋纳米碳酸钙、15^#机械油＋5CB液晶的摩擦磨损性能。针对磨合阶段、稳定磨损阶段、胶合失效与摩擦噪声进行分析。结果表明，在磨合阶段摩擦因数有较大变化，随后的稳定磨损阶段中摩擦因数变化减小，在摩擦副出现胶合失效前，摩擦副的摩擦因数急剧上升；在摩擦因数变化幅度达到5％左右时出现嗡嗡声，在摩擦因数变化幅度达到10％左右时，在摩擦因数上升阶段出现摩擦啸叫声，而在摩擦因数下降阶段不出现摩擦噪声。提出了用能量耗散原理来解释上述现象。     

Experimental Study on Corrugation of a Sliding Surface Caused by Frictional Self-Excited Vibration

A series of tests is conducted on a pin-on-disc tester to study the effect of frictional self-excited vibration on evolution of the scar profiles. A laser displacement sensor is used to measure the profile size of the worn scars. An accelerometer is used to measure vibration of the pin specimen. The test results show that a sustained frictional self-excited vibration easily occurs under dry friction. When the vibration lasts for a long enough time, corrugation is generated on the sliding surface of the disc specimen. The wavelength of corrugation is approximately equal to the sliding speed multiplied by the period time of the friction-induced vibration.     

基于SOM神经网络的摩擦状态识别研究

为提取摩擦振动的特征和实现摩擦副摩擦状态的识别,在往复摩擦磨损试验机进行摩擦副混合摩擦和干摩擦状态的摩擦磨损试验。应用谱减法对试验采集的摩擦振动信号进行降噪,计算降噪后的摩擦振动15个特征参数。应用自组织映射(Self-organizing map, SOM)神经网络对摩擦副不同摩擦状态的摩擦振动特征参数进行分析,得到摩擦振动的SOM神经网络神经元分类。研究结果表明,谱减法能消除摩擦磨损试验机的背景噪声,SOM神经网络算法能够有效分析摩擦振动信号的特征,实现摩擦副摩擦状态的识别。     

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.     

胆甾醇润滑添加剂的摩擦噪声与胶合分析

在N15机械油中添加胆甾醇,用标准的立式万能摩擦磨损试验台实验分析了N15机械油、N15油机械 胆甾醇的摩擦磨损性能。针对磨合阶段、稳定磨损阶段、胶合失效与摩擦噪声进行分析。结果表明,在磨合阶段摩擦因数有较大变化,随后的稳定磨损阶段中摩擦因数变化减小;在摩擦副出现胶合失效前,摩擦副的摩擦因数急剧上升;N15机械油 1.7%胆甾醇的抗胶合性能较好,但N15机械油 0.106%胆甾醇的摩擦噪声特性较好;胆甾醇添加剂可以显著改善N15号机械油的抗胶合能力。     

Analysis of Friction-Induced Vibration Leading to Brake Squeal Using a Three Degree-of-Freedom Model

Friction-induced vibration is a common phenomenon in nature and thus has attracted many researchers’ attention. Many of the mathematical models that have been proposed on the basis of mode coupling principle, however, cannot be utilized directly to analyse the generation of friction-induced vibration that occurs between two bodies because of a difficulty relating model parameters to definite physical meaning for real friction pairs. In this paper, a brake squeal experiment is firstly carried out by using a simple beam-on-disc laboratory apparatus. Experimental results show that brake squeal correlates with the bending mode of the beam and the nodal diameter out-of-plane mode of the disc as well as the cantilever length of the beam. Then, a specific three degree-of-freedom dynamic model is developed of the beam-on-disc system and the vibration behaviour is simulated by using the complex eigenvalue analysis method and a transient response analysis. Numerical simulation shows that the bending mode frequency of the beam a little greater than the frequency of the nodal diameter out-of-plane mode and a specific incline angle of the leading area to the normal line of the disc as well as a certain friction coefficient, are necessary conditions for the mode coupling of a frictional system. Results also show that when the frictional system is transited from a steady state to an unstable state for the variation of parameters, its kinetic and potential energy increase with time due to continuous feed-in energy from the friction force while the dynamic responses of the system change from the beating oscillation to the divergent, which leads to the friction-induced vibration and squeal noise.     

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.