The effects of friction-induced vibration on friction and wear

Friction tests were carried out with an elastic system where the specimen was supported by the elastic plate spring with strain gauges and with a rigid system where the vibration of the specimen was restricted. The coefficient of friction was obtained by two different methods: a deflection method with an assembly that consisted of a spring and strain gauges and an inertia method with a flywheel. The friction and wear properties of steel-steel, white metal-steel, phosphor bronze-steel and bronze-steel pairs were examined. When the frictional operation was conducted in the elastic system accompanied by frictional vibration, the coefficient of friction measured by the deflection method was generally larger than by the inertia method. The relationships between the coefficient of friction and the driving velocity for steel-steel and white metal-steel pairs obtained by the inertia method in the rigid system were significantly different from those obtained by the same method in the elastic system. Frictional vibration increased the wear of white metal-steel, phosphor bronze-steel and bronze-steel pairs but decreased that of a steel-steel pair. Wear measurements from the elastic system exhibited more scatter than from the rigid system.     

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.     

Duffing振子的Lyapunov指数与Floquet指数研究

针对现有基于Duffing振子的信号检测与估计方法在确定振子相变临界阈值和Floquet指数曲线的临界分岔处位置两方面所存在的问题,本文在更大范围上对Duffing振子的Lyapunov指数曲线进行了研究,提出了振子相变临界阈值的改进判定方法和利用Lyapunov指数曲线来获得Floquet指数曲线临界分岔处的方法.理论分析和仿真结果表明,上述改进在不增加系统误报率的前提下,能有效降低系统的漏报率.     

Stability analysis of running-in system based on Nyquist curve of friction vibration

This paper examines the stability of the running-in process using a Nyquist curve analysis of the vibration due to friction. The Nyquist stability criterion uses the frequency characteristic to assess the stability of systems; so when the (−1, j0) point is enclosed by Nyquist curve, the closed-loop system is unstable. Running-in and wear tests of a piston ring against a diesel engine cylinder were conducted on a pin-on-disc tester. The analysis showed when the running-in is confined to the surface layers, the point (−1, j0) is not enclosed by the Nyquist plot and the process is stable; When the running-in is in the severe wear stage, the point (−1, j0) is enclosed by the Nyquist plot, the system is unstable; When running-in is in the stable wear stage, the point (−1, j0) is not enclosed by the Nyquist plot and the process is stable. This method could be used to predict the progress of the running-in process and identify the run-in state.     

Static friction processes under dynamic loads and vibration

The influence of external vibration on friction phenomena was investigated. The influence of vibration on the primary displacement was assessed. The influence of the normal pressure and the amplitude of external vibration on the static friction was also investigated. Non-linear relations between the coefficient of static friction and the external vibration and between the coefficient of static friction and the normal pressure where vibration occurs were established. Static and dynamic loads on the same friction pair were studied. Sinusoidal vibration in the contact area caused a decrease in the coefficient of static friction of about 60% which is important practically, especially in this design of machine connections where vibration occurs.     

Numerical study of friction-induced vibration and noise on groove-textured surface

A numerical study was performed to predict the squeal instability when a sphere sliding on a groove-textured surface through complex eigenvalue analysis, which was discussed with the experimental results. It is shown that the friction system had a propensity to cause squeal instability. Mode coupling was found when squeal occurred. The calculated dominant frequency of squeal was close to the experimental measured one. The numerical model created can be used to predict the squeal instability of the friction system. Sphere sliding along groove showed potential in reducing squeal instability compared to the case of sphere sliding across groove.     

Application of impulse damper in control of a chaotic friction-induced vibration

Friction-induced vibration is an important phenomenon with adverse effects on many dynamic systems involving friction. In this study, a very simple and well-known one-dimensional friction-induced dynamic system is considered in which the novel PZT stack impulse damper is incorporated into the system. It has been shown that by appropriately tuning the damping parameters, the chaotic behavior is removed quickly and efficiently. It has also been demonstrated that the system is sensitive to parameter change, and minimal modification of these parameters can revert the chaotic or periodic motion.     

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指数算法在应答器信号混沌振子检测中的应用

针对为提高在强噪声环境下应答器上行链路传输信号的检测精度,利用混沌系统对初始条件敏感以及对噪声免疫的特性,将混沌振子应用到应答器上行链路信号检测解调中.结合微弱信号Duffing振子检测原理和应答器上行链路信号特征,给出了使用Duffing振子检测应答器信号的方法和步骤,并使用Lyapunov指数算法计算Duffing振子检测系统的临界阈值,定量判断系统的输出状态,实现应答器信号的解调.在理论分析的基础上,进行了实验仿真验证.仿真结果表明,基于Lyapunov指数算法的应答器信号混沌振子检测方法提高了阈值设置的准确性和效率,并确保了应答器信号检测的可靠性.     

Characterization of friction-induced local convex topography under dual-rotary fretting

Dual-rotary fretting (DRF) is a complex fretting wear mode combining torsional fretting with rotational fretting. Two different typical friction-induced convex topographies (Type I and Type II) in contact area were showed, which are under the control of torsional and rotational fretting components, respectively. To investigate their evolution characteristics and formation mechanism, the convex topographies were analyzed by SEM, XPS, a nano-hardness tester and surface profilometry, etc. The results show that the convex topographies significantly depended on the test parameters and environmental conditions. The initiation and propagation of fretting fatigue cracks were found related with the convex topography under the fretting wear.     

Relief-face friction in vibration tapping

One of the key problems in the tapping process for difficult-to-cut materials such as titanium alloys is that the relief-face friction of the tap is very large. In this paper, the vibration tapping process, in which the spring-back of the machined surface can be removed, has been analyzed with elasto-plasticity. Thus the reason why vibration tapping can reduce the tapping torque has been explained qualitatively, and a theoretical basis for choosing reasonable values for the cutting parameters for vibration tapping has been provided. The theoretical analysis shows good agreement with the experimental results obtained when tapping a titanium alloy.     

Rubber friction on rough and smooth surfaces

Some rigorous contact mechanics is used in a dynamic stiffness approach to generate a new theory for hysteresis sliding friction on some ideal peak shapes. These were the two- and three-dimensional projections: cylinder, wedge, sphere and cone, configured singly or as a periodic array. The theory is then extended for a ‘single roughness order’ i.e. identical peaks arranged with a randomly distributed envelope. A simple algebraic expression is obtained that is closely linked to the rubber complex modulus, with friction bandwidths extending over several decades. Several other secondary effects are introduced: multiple roughness orders, adhesion, stick-slip behaviour, friction magnification from either moments or atmospheric pressure, as these influence the observed friction bandwidth and amplitude. The sliding friction theory and secondary effects are compared to the measurements of Grosch [K.A. Grosch, The relation between the friction and the visco-elastic properties of rubber, Proc. Roy. Soc. Lond. A 274 (1963) 21–39] and Barquins et al. [M. Barquins, A.D. Roberts, Rubber friction variation with rate and temperature: some new observations, J. Phys. D: Appl. Phys. 19 (1986) 547–563], and are able to account for the friction amplitude and bandwidth for both gum and carbon loaded rubbers.     

Rolling friction and adhesion between smooth solids

Rolling friction has been explained in terms of crack propagation through an adhesive joint. The contact between a smooth cylinder and flat has been regarded as an adhesive junction bounded by two cracks moving in the same direction at the same speed, one crack continually opening and one closing. Propagation of these cracks requires a force which is calculated from crack theory and shown to be equal to the friction.The theory has been verified experimentally using glass cylinders rolling on smooth rubber. Results show that rolling friction is closely connected with peel adhesion. Moreover, this adhesion interpretation of rolling friction between smooth surfaces explains several observations: (a) the existence of a static rolling friction, (b) the unusually high value of friction and its independence from load and roller radius, (c) the marked effect of lubricant or dust.     

The adhesion and friction of smooth rubber surfaces

In an earlier study of adhesion between smooth rubber and rigid surfaces time effects were apparent. It now appears that under non-equilibrium conditions these effects largely determine the magnitude of the force required to separate adhering surfaces. This paper presents an optical study of contact area time effects between such surfaces and shows in a simple way how these optical observations may be used to predict the rate of rolling of a ball bearing on smooth rubber, the time taken to detach itself under gravity and its resilience when bouncing on smooth rubber. The friction when a rigid surface slides over smooth rubber under conditions where Schallamach waves are generated is also shown to be quantitatively related to their mutual adhesion.     

An arc stability evaluation approach for SW AC SAW based on Lyapunov exponent of welding current

Based on the experimental non-linear time series of welding current produced by Square Wave Alternating Current Submerged Arc Welding (SW AC SAW) at different frequency and duty cycle, the largest Lyapunov exponents of the welding system are numerically evaluated by the phase space reconstruction technique and the improved small-data method algorithm. The experimental and calculated results show that the largest Lyapunov exponent can describe the arc stability as a quantitative indicators at the process of Square Wave AC SAW. Further analysis proves that when the duty cycle of welding current is 0.5, the largest Lyapunov exponent reaches small values and the welding processes approach high steady states. When the welding current frequency is larger, the largest Lyapunov exponent reaches small values and the welding processes approach high steady states. When the welding current frequency is smaller, the system is at the unsteady mode and the largest Lyapunov exponent attains large values. Therefore, the welding current frequency is negatively correlated with the welding process stability.     

摩擦离合器黏滑振动特性的显式动力学分析

针对摩擦离合器在接合过程中出现的黏滑振动问题,建立了某车型离合器三维有限元模型,通过采用有限元软件ABAQUS内嵌的显式动力学分析算法,对离合器系统在接合过程中产生的黏滑振动特性进行研究,通过改变法向载荷和摩擦片厚度,探讨了两者对离合器系统黏滑振动行为的影响.研究结果表明,利用ABAQUS显式动力学分析能有效地模拟出离合器接合过程中产生的黏滑振动现象.黏滑振动发生过程中,系统位移信号呈现出明显的锯齿状波动,飞轮盘和摩擦片会在一定时刻形成相互咬合的状态.离合器黏滑振动的频率和系统的自然频率非常接近,受到系统结构的影响.当法向载荷从1.0 MPa增大到1.5 MPa时,系统振动位移信号的波动幅值增大,黏滑振动周期减小,系统颤振现象更加明显.但当法向载荷进一步增大到3.0 MPa时,黏滑振动逐渐演变为持续的摩擦自激振动现象.通过合理地调控离合器接合的法向载荷,有利于改善黏滑振动现象.摩擦片厚度对系统黏滑振动特性的影响显著,当摩擦片厚度从2 mm逐渐增加为4 mm时,系统的结构频率发生变化,从而使得系统黏滑振动的频率发生变化.此外,增大摩擦片厚度能够改善系统黏滑振动行为,降低系统黏滑振动强度,因此适当地增大摩擦片厚度,是改善黏滑振动强度的有效手段.     

摩擦离合器黏滑振动特性的显式动力学分析

针对摩擦离合器在接合过程中出现的黏滑振动问题,建立了某车型离合器三维有限元模型,通过采用有限元软件ABAQUS内嵌的显式动力学分析算法,对离合器系统在接合过程中产生的黏滑振动特性进行研究,通过改变法向载荷和摩擦片厚度,探讨了两者对离合器系统黏滑振动行为的影响.研究结果表明,利用ABAQUS显式动力学分析能有效地模拟出离合器接合过程中产生的黏滑振动现象.黏滑振动发生过程中,系统位移信号呈现出明显的锯齿状波动,飞轮盘和摩擦片会在一定时刻形成相互咬合的状态.离合器黏滑振动的频率和系统的自然频率非常接近,受到系统结构的影响.当法向载荷从1.0 MPa增大到1.5 MPa时,系统振动位移信号的波动幅值增大,黏滑振动周期减小,系统颤振现象更加明显.但当法向载荷进一步增大到3.0 MPa时,黏滑振动逐渐演变为持续的摩擦自激振动现象.通过合理地调控离合器接合的法向载荷,有利于改善黏滑振动现象.摩擦片厚度对系统黏滑振动特性的影响显著,当摩擦片厚度从2 mm逐渐增加为4 mm时,系统的结构频率发生变化,从而使得系统黏滑振动的频率发生变化.此外,增大摩擦片厚度能够改善系统黏滑振动行为,降低系统黏滑振动强度,因此适当地增大摩擦片厚度,是改善黏滑振动强度的有效手段.     

摩擦离合器黏滑振动特性的显式动力学分析

针对摩擦离合器在接合过程中出现的黏滑振动问题,建立了某车型离合器三维有限元模型,通过采用有限元软件ABAQUS内嵌的显式动力学分析算法,对离合器系统在接合过程中产生的黏滑振动特性进行研究,通过改变法向载荷和摩擦片厚度,探讨了两者对离合器系统黏滑振动行为的影响.研究结果表明,利用ABAQUS显式动力学分析能有效地模拟出离合器接合过程中产生的黏滑振动现象.黏滑振动发生过程中,系统位移信号呈现出明显的锯齿状波动,飞轮盘和摩擦片会在一定时刻形成相互咬合的状态.离合器黏滑振动的频率和系统的自然频率非常接近,受到系统结构的影响.当法向载荷从1.0 MPa增大到1.5 MPa时,系统振动位移信号的波动幅值增大,黏滑振动周期减小,系统颤振现象更加明显.但当法向载荷进一步增大到3.0 MPa时,黏滑振动逐渐演变为持续的摩擦自激振动现象.通过合理地调控离合器接合的法向载荷,有利于改善黏滑振动现象.摩擦片厚度对系统黏滑振动特性的影响显著,当摩擦片厚度从2 mm逐渐增加为4 mm时,系统的结构频率发生变化,从而使得系统黏滑振动的频率发生变化.此外,增大摩擦片厚度能够改善系统黏滑振动行为,降低系统黏滑振动强度,因此适当地增大摩擦片厚度,是改善黏滑振动强度的有效手段.     

Some considerations of slideway friction characteristics by observing stick-slip vibration

It is important to clarify the frictional characteristics of a slideway and to prevent unstable vibration, such as stick-slip vibration, for the improvement of kinematic performance and for precise positioning. In this research, the relations among the dynamic friction characteristics, the pitching motion or the floating up of the slider, the surface roughness of a slideway, and the lubricant property are investigated experimentally. As a result, some points necessary for the kinematic performance improvement of the slider are clarified.     

Effects of surface texturing on friction and vibration behaviors of sliding lubricated concentrated point contacts under linear reciprocating motion

Friction and vibration behaviors of lubricated concentrated point contacts with surface texturing have been experimentally investigated under reciprocating motions. Ground, lapped and textured lapped flat surfaces are tested against polished ball surfaces. Coefficient of friction, surface temperature, electrical resistance and vibrations at the lubricated contacts have been measured and analyzed. In the presence of surface texture, the coefficient of friction reduces by 30% in some of the cases. Surface temperature distributions on reciprocating tracks have also been measured and compared. Vibrations associated with lubricated point contacts formed between textured surfaces/balls reduce significantly at resonance frequency in comparison to polished surfaces/balls.