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。     

NONLINER VIBRATION ANALYSIS OF THE PLATE WITH DRY FRICTION SUPPORT CONDITION

The rigid-interface friction model is usually used in the nonlinear vibration of the rectangular plate with dry friction support edges. The present study provides an extension by using a hysteretic spring friction model and taking account of the stick-slip motion of the plate. Results for a range of problem parameters have been obtained. The results show that the nonlinear frequency response behavior of the system can be quite different from the rigid-interface friction model. The effects of the stiffness at friction interfaces and the stick-slip motion on the nonlinear vibration of the plate are significant and hence cannot be neglected.     

A Note on the Two-Spring Tomlinson Model

In this note, quasistatic solutions of a two-mass-two-spring Tomlinson model for atomic force microscopy are derived, and are compared with the corresponding results of the single-spring Tomlinson model. It is clarified that the solutions of the two models are equivalent provided that the effective spring constant is correctly defined. It is also shown that modeling the onset of stick-slip motion in terms of the criteria defined by explicit tip and cantilever stiffness is the most convenient to investigate the effects of the tip-flexibility on the stick-slip motion.     

Numerical analysis of stick-slip instability by a rate-dependent elastoplastic formulation for friction

In various fields of engineering, it is important to clarify friction-induced vibration, such as stick-slip motion, for a wide range of scales from microscopic elements to continental plates. In the present study, we apply a rate- and state-dependent friction model [30] (Hashiguchi and Ozaki, 2008), which can rationally describe the reciprocal transition between the static friction and the kinetic friction by a unified formulation, to the simulation of stick-slip instability for a one-degree-of-freedom spring-mass system under various conditions. It is verified that the various basic experimental findings on stick-slip motion can be pertinently described by the present approach. Moreover, the effect of the dynamic characteristics of the system, such as the mass, stiffness and driving velocity, is discussed, and parameters prescribing the rate of reciprocal transition of static-kinetic frictions and the preliminary microscopic sliding on the instability of the stick-slip motion are also discussed.     

基于非连续能量耗散的界面摩擦黏滑行为动力学研究

建立界面摩擦过程黏滑行为动力学模型,仿真分析摩擦系统内外因素对黏滑行为的影响规律.结果表明:界面摩擦过程中,黏滑行为不仅与材料本身如晶格常数、原子质量、原子间横向刚度系数有关,而且与系统外界参数如滑动速度及滑动部件的质量有关;材料的原子间横向刚度、晶格常数、原子质量、滑动机构质量愈小,黏滑行为愈显著,而相对滑动速度愈大,黏滑行为愈显著.     

The effect of variable amplitude loading on stress distribution within a cylindrical contact subjected to fretting fatigue

A finite element model of a cylindrical Hertzian contact on a test sample subjected to alternating shear loading has been developed. The model has been used to investigate shear stress distributions at the contact during variable amplitude fretting fatigue for a load configuration in which the sample cyclic stress is applied in phase with shear force on the cylindrical contact. It has been found that during constant amplitude cyclic loading, shear stress distributions and positions of the stick-slip boundary at load maxima and minima remain fixed. Application of overloads changes the stress distribution and the position of the stick-slip boundary attained by loading of subsequent cycles. The largest cycle maximum stress determines the position of the stick-slip boundary adopted by subsequent smaller amplitude cycles. In general variable amplitude fretting fatigue the position of the stick-slip boundary will be changing with each load cycle. Hence fatigue initiation processes will occur at locations dispersed over an extended region over the contact. The implications of this behaviour for models for fretting fatigue life calculation are explored.     

Effects of weight on bit on torsional stick-slip vibration of oilwell drill string

The stick-slip phenomenon is a type of dysfunction detrimental to the drilling operation. Field application shows that stick-slip phenomenon is inclined to appear when using a large Weight on bit (WOB). In this paper, effects of the WOB on the stick-slip vibration are investigated. Based on a lumped torsional pendulum model of the drilling system, equation of motion of the drill bit is obtained. By using parameters commonly used in field applications, the bit dynamics are analyzed and the stick-slip vibrations are discussed. During the stick-slip motions, the negative damping effect occurs in the transition from the stick phase to the slip phase. With the increasing WOB, the bit behavior may change from the stable motion to the stick-slip vibration once the WOB reaches the critical value. In case of stick-slip vibration, the phase trajectory ultimately converges to a limit cycle which represents periodical bit motion. With increases in the WOB, the limit cycle enlarges. For cases without stick-slip vibrations, the drill bit vibrates damply and finally converges to a state of uniform motion. The results presented in this paper can be applied to interpret some of the field phenomena related to WOB.     

基于粘滑驱动的球基微操作器动力学建模与分析

球基微操作器是一种广泛应用于微纳米精密作业的微机器人系统,由基座、微操作球和顶端嵌有红宝石球的3根四分压电陶瓷管组成.基于此,通过驱动压电陶瓷管弯曲或摆动,依靠红宝石球与微操作球间惯性摩擦形成的相对位移实现微操作球3自由度的运动.这种摩擦运动中存在粘滑现象,粘滑驱动带来的非线性导致球基微操作器动力学性能复杂.在简化球面高副连接的条件下,建立具有粘滑特性的微操作器系统动力学模型.基于动态摩擦模型,运用数值方法分析多个参数对微操作器运动性能的影响,通过仿真手段完成模型验证.进行微操作器运动测试试验,进一步验证所建立的动力学模型的正确性和有效性.     

Dynamic behaviour of geared systems with backlash due to stick-slip vibratory motion

Stick-slip phenomena occur with low speed rotors in fluid bearings. A typical case is the turning gear mechanism of large turbomachinery which becomes vulnerable to damage. In other cases such as rolling mills or textile machinery the stick-slip phenomenon influences product quality.An analytical investigation of a linear rotor with a complex turning gear system of many degrees of freedom is presented. Gearing backlash was included in the model. The mechanism of backlash was found to be of considerable importance for the appearance of instability. Velocity and damping were the most influential factors on the amplitude of stick-slip motion and instability.In highly unstable areas of system operation, stick-slip is not present owing to the violent nature of the unstable motion. At the onset of instability and during the transients of stable systems, stick-slip is present. Fatigue damage may result from gear backlash, even in stable systems.     

A Study of the Effect of Normal Stiffness on Kinetic Friction Forces Between Two Bodies in Sliding Contact

This work determined what effect stiffness in the direction normal to the plane of contact between surfaces in sliding contact had on the phenomenon of stick-slip.

The results showed that the amplitude if stick-slip vibrations could be reduced by increasing the normal stiffness with contacting surfaces of mild steel.

It was also observed that with the above mentioned surfaces some wear had to take place before stick-slip would occur. This was attributed to the initial presence of oxide on the surfaces.     

Research and experimental analysis of drill string dynamics characteristics and stick-slip reduction mechanism

Stick-slip of the drill string, as one of the critical factors affecting drilling efficiency, has always been a hot topic for experts and scholars in related fields. Serious stick-slip vibration affects the well construction efficiency, drilling cost and even lead to a downhole accident. Therefore, based on the current research, this paper takes a new type of composite vibration tool as the research object, studies the working mechanism of the tool and analyzes the effect of stick-slip reduction. After establishing the multi-degree-of-freedom torsional dynamics model, we obtained the results of torsional vibration dynamics by cases analysis based on working conditions and related mechanical parameters. In addition, the results of the examples, compared with the field experimental data, verify that the vibration shock generated by the new composite tool can effectively reduce the torque fluctuation range of the system, avoid the occurrence of stick-slip phenomenon, improve the ROP (rate of penetration), and make drilling process more stable. This paper can provide reference for the optimization and development of stick-slip technology in drilling engineering, and the theoretical methods can also be developed to study the dynamics of drill string.     

Effect of stick-slip on the scratch performance of polypropylene

For the scratch process of polypropylene (PP), the stick-slip phenomenon always exists and contributes to the observed periodic surface damage patterns. The stick-slip, one main cause for scratch visibility, alters the surface characteristics of substrate and eventually induces scratch visibility. Both ASTM/ISO and Erichsen scratch test methods are employed to study the stick-slip phenomenon and its effects on scratch behavior of PP. Image analysis shows that the stick-slip phenomenon was responsible for material removal and severe surface damage. Possible solutions to improve the scratch performance of polymeric materials are also discussed in this paper.     

Stick-slip algorithm in a tangential contact force model for multi-body system dynamics

Contact force of Multi-body dynamics (MBD) system can be classified two parts. First is a normal force and the other is a tangential force called friction force. And the friction force can be represented by two states such as stick and slip. The stick-slip phenomenon is simply described as a simple contact model which is a rigid body contacted on a sloped surface. If the calculated friction coefficient between the body and sloped surface is less than the static friction coefficient, the body should be stuck. If the calculated friction coefficient is greater than the static friction coefficient, the body will be sliding along the surface. The phenomenon is called as stick and slip state of friction, respectively. Usually many researchers and commercial MBD software used a coulomb friction force model which is defined with an only function of relative velocity. This kind of friction force model will be called a conventional friction force model in this paper. A big problem of the conventional model can not describe a stick state of friction phenomenon. In the case of conventional friction force model, the body will be sliding even though friction state is stick. Because, the relative velocity must have a non-zero value in order to generate the friction force. To solve this kind of problem, we propose a stick-slip friction force model including a spring like force. In the case of stick-slip friction force model, the body can be stuck on the sloped surface because the friction force will be a non-zero value, even though the relative velocity approaches zero. We defined a relative displacement variable called stiction deformation. In this paper, the stick-slip friction model is proposed and applied in the contact algorithm of MBD system. And then two friction models are compared with numerical examples. With the proposed stick-slip friction model, more realistic results are achieved.     

爬行物理模型的建立与仿真分析

建立了爬行的物理模型(2自由度质量—弹簧—阻尼系统),根据模型所描述的动力学系统建立了状态参量的数学表达式,仿真分析了系统的刚度(水平、垂直方向)、阻尼比、质量和静动摩擦因数的差值对爬行评价指标的影响,从而得出：增大水平方向的刚度,减小阻尼比、系统的质量和静动摩擦因数的差值,增大驱动速度,适当地提高垂直方向的刚度,控制系统垂直方向的振幅可明显地减小爬行,并给出了表明仿真结果正确性的试验例证。     

载荷对径向微动磨损的影响

为了研究在实际工况中较为常见的圆柱/平面接触副的径向微动磨损特性,分析载荷对径向微动磨损影响,本文通过ANSYS建立圆柱/平面的径向微动磨损模型,分析施加载荷过程,不同时间点的载荷对径向微动磨损的影响,并通过接触切应力和X方向应力的分析,提出径向微动磨损在粘滑过渡点以及X方向应力为零的点为裂纹萌生点.     

基于黏滑运动原理的单自由度纳米定位台设计与动力学分析

为解决基于扫描电镜纳米操作系统定位驱动方面的关键技术,分别研制能够实现水平定位和垂直定位的单自由度纳米定位台。定位台采用黏滑驱动原理,驱动机构采用柔性铰链设计,O形调节圈的引入既实现摩擦力的精密调节又保证整体结构的紧凑。为研究黏滑驱动原理和辅助纳米定位台设计,建立单自由度纳米定位台的动力学模型。考虑压电陶瓷的动态特性和摩擦力的非线性变化,对压电驱动模型进行线性化处理,引入LuGre模型实现对摩擦力的表达。试验结果表明该动力学模型能够有效地描述黏滑定位台的运动状态。单自由度水平和垂直纳米定位台的最大外形尺寸分别为24 mm×24 mm×17 mm和24 mm×24 mm×34 mm,均具有8 nm定位分辨率和50 mm行程,最大负载质量可达66 g。利用所设计的两种纳米定位台搭建基于SEM的双探针纳米操作系统,纳米线双探针操作试验表明该两种纳米定位台完全满足SEM下进行纳米操作的要求。     

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。     

Comparison of two stick-slip testers and recommendations for repeatable and significant stick-slip testing

Because of the interaction of the large number of parameters influencing stick-slip, it is very difficult to perform repeatable and reproducible tests that define the anti-stick-slip properties of lubricants. In order better to understand the difficulties encountered in stick-slip testing, an overview of the influencing parameters, with a discussion of each parameter, is given in this paper. Some modifications of the reciprocating stick-slip tester that was used in the ASTM test procedure before the latter was withdrawn, in order to improve the repeatability of its test results, are discussed. The significance of the results is checked by comparison with a rotary stick-slip tester. Finally, recommendations for correct stick-slip testing and interpretation of stick-slip results are presented.     

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.