摩擦振动的时频特性

采用短时傅里叶变换(Short-time Fourier transform,STFT)和Zhao-Atlas-Marks分布(ZAMD)这两种时频分析技术对往复滑动条件下的摩擦振动时频特性进行研究。用例子探讨了这两种时频分析技术的特点,联合采用STFT 和ZAMD方法可得到较高的时频分辨率。对摩擦振动信号的时频特性研究表明,摩擦振动的频率从其初始形成到消失的全过程中基本没有发生变化,这个特性显示在摩擦振动的形成和消失过程中没有遇到结构非线性因素。还讨论了时频不变特性的物理意义,指出用模态耦合理论不能满意地解释摩擦振动有限和消失现象。     

Time–frequency analysis of friction-induced vibration under reciprocating sliding conditions

A time–frequency analysis can give an overall view of the behaviour of friction-induced vibration. In this paper, short-time Fourier transform (STFT), Wigner–Ville distribution (WVD), Choi–Williams distribution (CWD) and Zhao–Atlas–Marks distribution (ZAMD) are applied to analyze time–frequency characteristics of friction-induced vibration. The result shows that there is always a frequency change in the time–frequency presentation of vibration in the location where the vibration is bounded. The frequency changes in time–frequency presentations are associated with nonlinearity of vibration systems. The nonlinearity may be counted as the evidence to support the consideration that friction-induced vibrations are bounded by limit cycles due to the system nonlinearity. Based on the time–frequency presentations of vibrations, it may be concluded that the friction vibration system is generally a linear system in the phase of vibration initiation but is a nonlinear system in the phases of vibration being bounded and disappearance.     

Effect of a dynamic absorber on friction-induced vibration of a rectangular plate

When a plate-like object is rubbed by rubber, friction-induced vibration is generated. To reduce the friction-induced vibration, we experimentally investigate the characteristics of the vibration of a rectangular glass plate. The results show that the frequency of the friction-induced vibration is almost the same as the natural frequency of a glass plate. The vibration is generated when the natural frequency of a rubbing system is close to that of a glass plate. We then examine the effect of a dynamic absorber mounted on the glass plate. The results demonstrate that the damping of a dynamic absorber is effective for suppressing the friction-induced vibration. Numerical simulation is also performed using a simplified analytical model. The calculated results agree qualitatively with the experimental ones.     

Lyapunov exponent of friction-induced vibration under smooth friction curve

This paper studies the nonlinear behavior of the friction-induced vibration by using spring-mass model subject to the smooth frictionvelocity curve. The nonlinearity and instability of the friction may produce the chaotic vibration depending on the friction curve. In order to show this, the Lyapunov exponents are calculated for a variety of the slope and magnitude in the smooth friction curve. In turn, the dependency of the friction curve on the chaotic attractor is illustrated.     

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.     

Comparison of the tribological behavior of columnar-grained polycrystalline copper with vertical/horizontal orientation sliding against AISI 1045 steel

The unlubricated tribological behavior of columnar-grained polycrystalline copper with vertical orientation (VO) and horizontal orientation (HO) in sliding against AISI 1045 steel is investigated in room air. The friction coefficient and wear rate of HO Cu in sliding against AISI 1045 steel are lower than that of the VO Cu. The friction-induced layers are distinct. The friction-induced layer on HO Cu is composed of metallic Cu, Fe₂O₃, and Fe₃O₄. The wear debris is agglomerated fine particles. The friction-induced layer on VO Cu presents characteristics of plastic deformation and flow. The wear debris is plate-like. The grain orientations and boundaries of VO/HO Cu sample are contributed to the different friction-induced layer and wear mechanism. For VO Cu, the grain boundary perpendicular to the sliding direction makes the slip motion activate difficultly. For HO Cu, the grain boundary parallel to the sliding direction makes the slip motion activate easily.     

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。     

基于高阶累积量的齿轮箱故障诊断研究

当齿轮箱发生故障时，实际测得的齿轮振动信号一般是非平稳和非高斯分布的信号，不同故障状态下的振动信号具有不同的高斯性和对称性，通常包含较强的噪声。高阶累积量具有对加性高斯噪声和对称非高斯噪声不敏感的特性，可以应用在齿轮箱的故障诊断中。短时分析方法可以在低信噪比情况下提取周期性冲击故障信号特征。在对振动信号进行短时分析的基础上，计算原始信号及其短时能量函数的高阶累积量。从高阶累积量提取的特征可有效地将正常状态、中度磨损状态、严重磨损状态和断齿状态的齿轮振动信号分离开来，这表明高阶累积量可定量地描述振动信号偏离正态分布的程度，采用样本分割后，还可以定量描述齿轮的磨损程度。     

齿轮点蚀破坏中磨损与振动关系的试验研究

利用铁谱分析技术和振动分析技术中的时频分析方法研究了模拟点蚀故障齿轮磨损与振动的关系。分析结果表明点蚀齿轮磨损和4个时域特征值从一面一点、一面三点到多面多点依次变大,多面多点蚀齿轮磨损严重,磨粒数量最多;点蚀齿轮出现以输入输出端的啮合频率为中心,以转频为调制频率的边频带。齿轮磨损与振动相互关联,磨损量的变化率与振动方差变化率在3种点蚀齿轮中表现明显;但磨损量的增长率不仅与齿面点蚀的程度有关,还与点蚀的齿数有关;而齿轮的振动强度与齿轮齿面点蚀的程度最相关,即齿面点蚀破坏越厉害,振动越剧烈。     

多自由度振动系统非线性动力特性的HHT辨识方法研究

HHT方法(包括EMD方法)已成功地用于线性振动系统的辨识研究。本文针对多自由度非线性振动系统,利用小波分析方法对非线性振动响应进行预处理,把信号分解成一系列的窄带信号,应用EMD方法使得各阶内在模函数(IMF)均为单一成份信号,然后运用HT方法辨识自由振动响应的非线性特征。典型的线性振动系统和非线性振动系统的辨识结果说明了该方法的有效性。     

Improving Dynamic and Tribological Behaviours by Means of a Mn–Cu Damping Alloy with Grooved Surface Features

In this work, the effect of the damping component with/without individual grooved surface features on the friction-induced vibration and noise (FIVN) and surface wear performance is studied experimentally and numerically. The experimental results show that introducing a grooved damping component in the system has a significantly improved capability in suppressing the generation of FIVN. In addition, it is observed that the friction system with a grooved damping component suffers slighter wear. Numerical results show good agreement with the FIVN events observed in the experimental test. Through analysing the deformation behaviour of damping component and the contact behaviour of the friction system during friction process, it is speculated that the deformation behaviour of damping component plays a significant role in affecting the contact pressure and FIVN behaviour. In addition, linking the vibration performance and wear evolution, the connection between damping, and vibration and wear behaviour is discovered, which can further explain why the friction system with a grooved damping component shows improved capability in suppressing the FIVN of friction system.     

异型螺杆铣削过程刀具磨损状态检测研究

针对异型螺杆铣削加工，采用振动信号特征值作为检测刀具磨损的参量。利用小波分析构建滤波器组，对振动信号进行多尺度分解和多分辨率逼近，提取出刀具磨损特征信号。特征信号处理结果反映了刀具磨损变化规律，振动幅值大小反映了刀具磨损状况，从而实现了刀具磨损状态在线实时检测。     

一种基于EMD与多特征支持向量机(SVM)故障诊断方法

针对齿轮箱故障振动信号的不平稳非线性冲击行为,本文提出了一种基于经验模态分解的特征值提取及多特征支持向量机的智能诊断方法。在电机频率分别取30 Hz、35 Hz、40 Hz;载荷分别取0 N∙M、15 N∙M、30 N∙M;采样频率为1500 Hz条件下,进行齿轮正常状态、齿面磨损和齿轮裂痕故障模拟实验。试验结果表明:该创新方法在有限样本数据分析中可以准确、有效地对齿轮箱的工作状态和故障类型进行分类,且支持向量机在故障诊断中使用方便,可以提高诊断的精确性,在齿轮箱故障诊断或类似振动信号的检测应用中具有很强的实用性。     

车轮非圆化磨耗对机车轮轨系统动态响应的影响

对频繁发生振动报警问题和运营正常的某型号电力机车分别进行车轮非圆化磨耗测试,对比分析运营正常和发生异常振动报警车轮的非圆化磨耗特征。测试结果表明:运营正常的机车车轮非圆化磨耗形式主要以低阶为主,而频繁发生振动报警的机车车轮非圆化磨耗除低阶磨耗外,还存在明显的16～25阶非圆化磨耗,这是造成机车异常振动的根本原因。建立机车车辆-有砟轨道耦合动力学模型,研究车轮非圆化磨耗对轮轨动态相互作用的影响,系统地调查分析轮轨动态相互作用随车轮非圆化磨耗特征的变化规律。结果表明:严重的车轮非圆化磨耗会加剧轮轨动态冲击作用,轮轨系统动力学响应随非圆化磨耗幅值的增大而增大,但随非圆化磨耗阶次的增长而呈非线性变化趋势。     

基于力信号的低频振动制孔刀具磨损状态分析

为分析碳纤维增强树脂基复合材料(CFRP)/钛合金(TC4)叠层材料低频振动制孔工艺下刀具磨损状态,开展基于切削力信号的制孔刀具磨损状态研究.通过采集CFRP/TC4叠层材料低频振动制孔过程中的切削力信号,进行时域和频域分析,探讨各信号特征量与刀具磨损状态之间的联系.研究结果表明:CFRP/TC4叠层材料低频振动制孔轴...     

内燃机气阀漏气故障的高阶谱分析

将高阶谱理论引入内燃机的振动诊断中,分析了不同状态时缸盖表面振动信号的三阶谱特性,并计算出三阶谱的峰值,用于刻划各状态时缸盖系统的非线性行为。结果表明:正常状态时缸盖表面振动信号的三阶谱接近为零,可以认为缸盖系统是线性系统;当气阀发生漏气故障时,缸盖表面振动信号的三阶谱就会出现较大的峰值,而且不同状态时所对应的峰值也存在着较大差别,说明不同气阀漏气状态时缸盖系统表现出不同程度的非线性。可以将三阶谱的峰值作为判断气阀是否漏气的一个诊断特征量,同时也为诊断内燃机气阀的早期漏气故障提供了依据。     

基于长短时记忆卷积神经网络的刀具磨损在线监测模型

为了提高机械加工过程中刀具磨损在线监测的准确性,提出了一种基于长短时记忆卷积神经网络（LSTM-CNN）的刀具磨损在线监测模型。在该监测模型中,通过振动、力、声发射传感器对刀具切削过程中的振动、力和声发射信号进行采集,采集的数据其本质为时间序列数据。考虑采集数据的序列和多维度特性,采用LSTM-CNN网络对采集的数据进行序列和多维度特征提取,利用线性回归实现特征到刀具磨损值的映射。通过实验验证了该模型的有效性和可行性,模型的精度较其他几种方法有了较大的提高。     

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.     

Catalytic effect during friction

The possibility of influencing friction-induced processes and friction parameters through catalytic phenomena is discussed. A catalytic effect is shown using examples of material treatment and friction with the collection of electric current. The friction-induced catalytic effect is described based on nonequilibrium thermodynamics and the theory of self-organization. Addition of a catalyst into rubbing materials can help increase the wear rate of the materials under mechanical treatment or decrease the wear rate of wear-resistant materials by accelerating spontaneous or nonspontaneous physicochemical processes, respectively.     

A new way to feed nanoparticles to friction interfaces

Fullerene-like WS₂ (MoS₂) nanoparticles (IF) have been studied in the past. Their efficacy as additives for lubrication fluids has been demonstrated. It was shown that the IF nanoparticles are usually delaminated in the inlet of the smooth contact. Thin sheets of broken IF nanoparticles can be entrapped between the rubbed surfaces and thus favorably affect the friction and the wear. Friction pairs at real mechanical macrosystems are often subjected to friction-induced vibrations. It was shown that the mechanical excitations can improve the supplying and preservation of fluid lubricant film in the interface. It can be hypothesized that under vibrations in a definite range of frequencies and amplitudes, the probability for small IF aggregates to be entrapped into the interface is increased. The main goal of this work was to study the effect of artificial mechanical excitations on the friction and wear of contact pairs rubbed with nanoparticles. In order to avoid friction-induced excitations, a new ball-on-flat friction device was developed. The frequency and the amplitude of the ball were varied using a motion of miniature micromotor attached to the ball holder. The behavior of IF nanoparticles in friction tests with and without external mechanical excitations was compared with the tribological behavior of the contact pair lubricated with pure paraffin oil. It was found that the external mechanical excitation of the mechanical parts rubbed with nanoparticles allows a penetration of these nanoparticles into interface. This effect leads to a remarkable shortening of the run-in period and improves the tribological properties of contact pairs. From the present results it may be anticipated that the accidental friction-induced vibrations, which are determined by the stiffness and damping force of the device, lead to preferential penetration of the IF nanoparticles into the contact area, affecting thereby the tribological behavior of the interface.