Stick‐slip with the slip phase as the starting point

In the literature, the stick‐slip phenomenon is always explained and modelled as starting from an initial stick phase. However, stick‐slip can also occur after a decrease in the imposed velocity, commencing above the critical (stick‐slip‐free) velocity. In this paper, it will be shown how stick‐slip can originate from a situation of pure sliding (without stick phases), if the slope of the friction force‐relative sliding velocity relation (F‐v_rel gradient) is negative. The F‐v_rel gradient used to study stick‐slip must, because of the interaction between the friction force and the dynamic behaviour of the mechanical system, be derived from velocity changes with the same time‐constant as the mechanical system of which the friction interface is part. It will also be shown that steady‐state friction data, and dynamic (non‐stationary) friction results obtained for relatively large (but fast) velocity variations, can lead to completely false conclusions related to stick‐slip.     

Modified Burridge-Knopoff model with state dependent friction

A modified version of the Burridge-Knopoff model including a simple model for state dependent friction force was derived. The friction model describes a velocity weakening of friction between moving blocks and an increase of static friction during stick periods. It provides a simplified but qualitatively correct stability diagram for the transition from smooth sliding to stick-slip behavior as observed in various tribological systems. Attractor properties of the model dynamic equations were studied under a broad range of parameters for 1- and 2-dimensional systems.     

Pre-sliding friction control using the sliding mode controller with hysteresis friction compensator

Friction phenomenon can be described as two parts, which are the pre-sliding and sliding regions. In the motion of the sliding region, the friction force depends on the velocity of the system and consists of the Coulomb, stick-slip, Streibeck effect and viscous frictions. The friction force in the pre-sliding region, which occurs before the breakaway, depends on the position of the system. In the case of the motion of the friction in the sliding region, the LuGre model describes well the friction phenomenon and is used widely to identify the friction model, but the motion of the friction in the pre-sliding such as hysteresis phenomenon cannot be expressed well. In this paper, a modified friction model for the motion of the friction in the pre-sliding region is suggested which can consider the hysteresis phenomenon as the Preisach model. In order to show the effectiveness of the proposed friction model, the sliding mode controller (SMC) with hysteresis friction compensator is synthesized for a ball-screw servo system.     

On the motion of the structure varying multibody systems with two-dimensional dry friction

In the present paper the dynamics of the structure varying multibody systems caused by stick-slip motion with two-dimensional dry friction are analyzed. The methods to determine friction force both in stick and slip states are described. The direct method of considering the wagon bogie system as a structure varying system was used to consider two dimensional friction at the wheelset-side frame connection. The concept of friction direction angle used to determine the friction force components of two-dimensional dry friction both in the stick and slip motion states was used. A speed depended friction coefficient was used and described approximately by hyperbolic secant function. All switch conditions were derived and friction forces both for stick and slip states. Some simulation results are provided.     

考虑摩擦影响的重型车床横向进给伺服系统建模与分析

进给伺服系统的性能对数控(Computer numerical control,CNC)机床的跟踪及定位精度、零件加工表面质量等有着重要的影响。摩擦的非线性还会导致系统产生爬行行为。结合Karnopp摩擦模型的建模思想,对导轨接触面建立一种改进的Stribeck摩擦模型,针对闭环控制的某重型车床的横向进给系统,建立综合考虑轴的扭转刚度、齿轮的啮合刚度、丝杠螺母副接触刚度、丝杠轴和轴承轴向刚度、导轨接触面摩擦的进给伺服系统的多自由度力学模型和数学模型,研究低速进给下各个刚度变化对工作台输出的影响,找出机械传动系统中的刚度薄弱环节。现场试验测试工作台不同进给位置下的临界爬行速度,得出临界爬行速度与丝杠的轴向刚度的关系,理论分析与试验结果相吻合。所得结论可为该重型车床横向进给伺服系统的优化设计和性能预测提供理论支持。     

Tribological behavior of reciprocating friction drive system under lubricated contact

The dynamic friction and wear behaviors are investigated in reciprocating friction drive system using a 0.45% carbon steel pair. The effects of various operating parameters on the traction force, stick and slip time, and friction modes are examined under the lubricated contacts. Moreover, the critical operating conditions in classifying three friction modes are also established. Results show that the fluid friction induced by the shearing of lubricant dominates the variation of traction force and produces the positive slope γ at the first period of slip in the traction force–relative sliding velocity curve. The γ value decreases at higher driver speed during stick-slip motion due to the thicker fluid film and shear thinning effect. The γ value increases due to the asperity interactions as the friction region is transferred from stick-slip to sticking with normal load from 196 to 980 N. Furthermore, it is also found that the static friction force is independent of stick time for the tangential loading rate ranged from 1.12 to 16.8 s⁻¹. The transition region produces the severest wear under the different driver speeds, but the wear is insensitive to the friction regions and the severe wear only occurs at higher normal load due to the action of Hertzian contact.     

环境湿度下硅材料表面的粘滑行为及其抑制

通过自行开发的微摩擦测试仪,分别研究了小载荷湿度环境下光洁硅片、物理形貌修饰表面和OTS膜修饰表面的微摩擦行为。实验结果表明,OTS膜表面和凹坑形貌修饰表面在高湿度环境下可以有效地抑制粘滑现象的发生。通过对湿度环境下液桥作用机制的研究,初步认为摩擦力来自于工作间隙的固固、固液和液液3个接触面间相互作用,并且高湿度下是否出现粘滑现象取决于这3种界面间力的竞争关系。     

Suggestion of MSTV (Modified-Stick-Transition-Velocity) model for hysteretic damping mechanism

To decrease vibration and noise in washing machines, lubricated friction dampers were installed. Although the structure of the friction damper is simple, it was not easy to develop a mathematical model for the dynamic behavior of the lubrication damper. To see the dynamic behavior of a friction damper, physical tests were carried out via a material testing machine by changing exciting amplitudes and frequencies. Complicated curves of spring characteristics and damping showed a hysteretic behavior. In this paper, a reasonable model for a friction damper is suggested. To model the hysteretic behavior of a friction damper, a Coulomb friction model was first applied. To get a refined model for stick and transition, an STV (stick transition velocity) model was analyzed. To develop a more accurate mathematical model, an MSTV (modified stick transition velocity) model was proposed. In the MSTV model, the friction force could be changed due to the velocity of the damper, and the damping force was calculated according to the relative velocity between the external displacement and the deformation of the sponge in the friction damper. The MSTV model was in a good agreement with the experimental results.     

Elimination of Stick-Slip Motion in Sliding of Split or Rough Surface

Here, we present a mass-less quasi-static model of stick-slip phenomenon built exclusively on the difference between higher static and lower kinetic friction force. The model allows explaining the disappearance of stick-slip motion when elastic surface slid in contact with rigid counter-face bears large amount of small outgrowths. Adjusting the model parameters, it is also possible simulating systems with different transient responses. The results obtained may also be helpful in understanding the variety of sliding behavior of different materials.     

机械密封的黏滑分析

机械密封副磨损与黏滑引起的振动有关。以密封副动静环为摩擦副进行摩擦磨损试验,通过分析摩擦因数曲线的变化趋势以及机械密封副的磨损形貌,提出在动环与静环相对运动的过程中发生了黏滑振动。考虑动环刚度,构建密封副黏滑模型,通过仿真分析黏滑对密封副表面形貌的影响以及密封副的黏滑磨损机制。结果表明:动环在摩擦扭矩的作用下扭转导致黏滑;动环的最大转速在黏滑过程中达到转轴转速的2倍;黏滑在快速启动阶段并没有发生,仅在速度波动阶段出现,而当速度恢复稳定上升阶段,黏滑现象消失;黏滑最终造成密封副表面严重的黏着磨损。     

Stick-Slip Motions in the Friction Force Microscope: Effects of Tip Compliance

When a microcantilever with a nanoscale tip is scanned laterally over a surface to measure the nanoscale frictional forces, the onset of stick-slip tip motions is an extremely important phenomenon that signals the onset of lateral friction forces. In this article, we investigate theoretically the influence of tip and microcantilever compliance on this phenomenon. We show that static considerations alone cannot predict uniquely the onset of single or multiple atom slip events. Instead, the nonlinear dynamics of the tip during a slip event need to be carefully investigated to determine if the tip evolves to a single or multiple atom stick-slip motions. The results suggest that the relative compliances of the tip and microcantilever can be engineered to induce single or multiple atom stick-slip events and thus control lateral friction forces at the nanoscale.     

Stress drop and contact stiffness measured from stick-slip experiments on PMMA-PMMA friction

We present results from an extensive stick-slip study on PMMA-PMMA dry friction, where we studied the influence of a wide range of normal stresses, loading velocities and roughnesses of the sliding surfaces. In this paper we focus (a) on the analysis of a residual coefficient of friction, i.e., shear stress measured at the end of the slip phase divided by the corresponding normal stress, and (b) on the contact stiffness measured by plotting the relative displacement between sample against the shear stress during the stick phase. It is shown that the residual coefficient of friction (i) decreases as normal stress increases, (ii) shows a slight increase when the roughness of the sliding surfaces increases and (iii) does not vary according to the loading velocity. The contact stiffness proved independent of loading conditions and of the roughness of the sliding surfaces. These results are interpreted in terms of asperity interlocking. This revised version was published online in July 2006 with corrections to the Cover Date.     

Stick-Slip Motion in Boundary Lubrication

Using dynamical analysis for a pin-on-disk sliding system and the consideration of meniscus formation at the sliding interface, a wide range of experimental observations on stick-slip motion can be explained. It is shown that when the initial growth rate of the static friction force is larger than about half the product of the substrate speed and the spring constant, slick-slip motion occurs in that sliding system. The critical substrate speed or the critical spring constant, above which stick-slip motion ceases, can thus be determined. It is also shown that the saturation substrate speed, below which stick-slip motion retains its maximum stick-slip amplitude, is inversely proportional to the total growth time of the static friction force. The maximum stick-slip amplitude is proportional to the final difference between the static and kinetic friction force. For a thicker surface liquid-film, the initial growth rate and the final static friction force are larger but the total growth time is shorter, resulting in a larger critical speed, a larger stick-slip amplitude, and a larger saturation speed. For rougher contact surfaces, the initial growth rate is larger but the final static friction force and the total growth lime are smaller, resulting in a larger critical speed, a smaller stick-slip amplitude, and a larger saturation speed.     

The influence of rheological properties of mineral oil in the stick-slip phenomenon

Within the range of small and very small sliding velocities that are typical of applications such as clutch mechanisms, guideways of machine-tools, hydraulic or electric drives for robots, and continuous-indexing mechanisms, the phenomenon of ‘stick-slip’ occurs. By taking into consideration the dependence of kinetic friction force on sliding velocity during the slip period, three critical velocities of movement stability are revealed. One of the important ways for reducing the amplitude of the phenomenon is by designing lubricating grooves of optimum geometry brought about by oil viscosity and surface tension.     

界面摩擦过程黏滑行为特征研究

通过建立界面摩擦系统动力学模型,并利用原子力显微镜测试云母、石英以及单晶硅片界面摩擦条件下的黏滑行为特征,探讨摩擦系统内外因素对黏滑频率、幅值的影响。结果表明:同一实验条件下,不同材料的黏滑频率与黏滑波动幅值不同;缓慢滑动时,黏滑的频率主要取决于表面势场的频率,波动幅值取决于表面势场强度,随着滑动速度逐渐增大,黏滑频率同时取决于表面势场频率和探针系统的固有频率,波动幅值取决于表面势场强度和探针系统结构;滑动速度较大时,黏滑频率及波动幅值主要取决于探针系统,且随着滑动速度增大,波动幅值逐渐减小。     

The generation of dislocations in metals under a sliding contact and the dissipation of frictional energy

Observations on static friction behaviour under stick-slip vibration conditions are presented. A static contact-time model of static friction does not adequately describe the observed variation in static friction; the governing variable is the rate of increase of the tangential force coefficient.     

纳观纹理表面相关参数对滑动摩擦过程的影响

采用分子动力学方法研究了半球形刚性压头在单晶铜纹理表面上的纳观黏着滑动摩擦过程。对不同纹理密度下纹理形状和纹理深度对黏滑摩擦性能的影响进行了全面研究,通过对比分析不同纹理参数下的滑动摩擦力和基体变形,揭示了上述参数对纹理表面黏滑摩擦的影响规律。模拟结果表明:在相同的纹理密度下,柱状纹理表面的滑动摩擦力小于矩形纹理表面。相比矩形纹理,柱状纹理表面的结构稳定性较差,但纹理表面的结构稳定性随着纹理密度的增加而加强。在相同的纹理密度下,矩形纹理表面的滑动摩擦力随着纹理深度的增加而减小。     

Kinetic friction characterizations of the tubular rubber seals

In this paper, both the kinetic friction characterizations and the stick–slip motion phenomena for the tubular rubber seals are studied. First, the kinetic friction model of the rubber seal is established to explain the kinetic friction mechanism of the tubular rubber seals. Second, both the measurement principle and the test instrument for the kinetic friction properties of the tubular rubber seals are developed, and then both the normal force curve and the friction force curve are obtained. Finally, the influences of the sliding velocity and the compressive displacement on the kinetic friction properties and the stick–slip motion of the tubular rubber seals are analyzed. The results will play an important role for designing and evaluating advanced rubber seal components.     

Bridging the Gap Between the Atomic-Scale and Macroscopic Modeling of Friction

A short survey of a modern view on the problem of friction from the physical viewpoint is presented. An atomically thin lubricant film confined between two substrates in moving contact has been studied with the help of molecular dynamics (MD) based on Langevin equations with coordinate- and velocity-dependent damping coefficient. Depending on model parameters, the system may exhibit either the liquid sliding regime, when the lubricant film melts during sliding (the “melting-freezing” mechanism of stick-slip motion), the “layer-over-layer” sliding regime, when the film keeps a layered structure at sliding, or the solid sliding regime, which may provide an extremely low friction (“superlubricity”). Atomic-scale MD simulations of friction, however, lead to a “viscosity” of the thin film, as well as to the critical velocity of the transition from stick-slip to smooth sliding, which differ by many orders of magnitude from the values observed in macroscopic experiments. This contradiction can be resolved with the help of the earthquakelike (EQ) model with a continuous distribution of static thresholds. The evolution of the EQ model is reduced to a master equation which can be solved analytically. This approach describes stick-slip and smooth sliding regimes of tribological systems within a framework which separates the calculation of the friction force from the atomic-scale studies of contact properties.     

由振动引起的螺栓连接预紧力松脱的数学模型

引入一种数学模型以研究螺纹连接在横向振动作用下引起的松脱.此横向振动激励会引起螺纹接触面间的滑动以及螺栓头与支撑表面之间的滑动.式中包括剪切力、支撑力以及螺纹摩擦阻力矩,它们均与振动速度相关,当所施加横向振动激励足够大时,螺纹连接会出现松脱现象.本文研究了螺栓预紧力、支撑力及螺纹摩擦系数、横向振动激励以及螺栓头下部弯矩...