界面温度对摩擦学过程激活机制研究

基于摩擦界面微结构与界面温度的关系,建立界面摩擦过程中界面原子热振动的温升模型,探讨界面温度对摩擦学过程的激活机制。结果表明:考虑原子质量单因素时,原子质量的变化抑制摩擦界面温升,且界面温度愈高抑制作用愈显著;综合考虑原子质量及原子固有频率影响因素时,在相对滑动速度较小且界面温度较低的情况下,原子质量的变化对摩擦学激活作用很小,而在相对滑动速度较高且界面温度较高时,原子质量对摩擦界面温升具有较为明显的正向激活作用;晶格常数随温度变化的特性对摩擦学过程具有反向抑制作用,且摩擦界面晶体热膨胀系数越大,其抑制作用愈强。     

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。     

黏滑振动理论及其在铁路机车中的应用

为研究机车处于黏着极限态时轮对的动态行为,提出平均滑动率和动态滑动率的概念并对黏滑振动稳定性及其振动特点进行分析.黏滑振动是介于黏着和滑动的动态过程,其稳定性取决于轮轨黏着,减小平均滑动率和动态滑动率有利于黏滑振动稳定.当轮对在黏着及滑动状态的往复交替时,轮对旋转与轮对纵向振动通过轮轨纵向切向力耦合,轮对的纵向振动频率为轮对旋转固有振动频率的整数倍.建立机车机电、控制一体化系统动力学模型,再现轨面黏着条件降低时轮对黏滑振动现象,对理论分析结果进行验证.研究结果表明:增大机车一系纵向刚度,电动机吊挂刚度有利于黏滑振动稳定性,提高机车黏着性能,需要合理匹配轮对纵向定位刚度和电动机吊挂刚度,避免机车黏滑振动时引起结构共振.     

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。     

界面黏滑摩擦现象的研究进展

从宏观尺度和微观尺度两个方面介绍了界面黏滑摩擦的研究进展,重点概述了宏观黏滑现象及其摩擦特性、微观黏滑现象及其摩擦特性、黏滑摩擦的建模以及黏滑实验研究进展,分析了现阶段界面黏滑摩擦研究中的重点问题。最后指出,从微观和介观尺度上研究界面摩擦行为是黏滑摩擦的未来发展方向。     

连接界面黏滑摩擦模型参数辨识研究

连接界面的非线性黏滑摩擦行为对结构的动力学响应有重要影响。基于描述界面多尺度黏滑摩擦行为的Iwan模型建模连接刚度和阻尼的非线性特性,利用连接结构的幅变非线性动力响应时程信息,提取响应包络作为特征参量,构造用于模型参数辨识的多层前馈神经网络,并分别以含非线性连接的集总参数系统和螺栓搭接梁结构为对象,进行数值和实验验证。结果表明,该方法所提取的特征量和构造的神经网络能够有效地应用于连接界面非线性黏滑摩擦模型参数的辨识,且具有简单、精度高和对噪声有一定鲁棒性的优点。     

干摩擦下含双侧间隙碰撞振动系统的动力学分析

建立干摩擦下含双侧塑性约束的双自由度碰撞振动系统的动力学模型。分析系统中存在的黏滑、滑动及碰撞等运动,分别给出其运动方程和衔接条件,并利用数值迭代方法求解和分析系统的复杂动力学行为,同时分析了干摩擦和传送带速度对系统动力学行为的影响。     

Ti6Al4V/WC-Co干摩擦性能研究

利用Optimal SRV高温摩擦磨损试验机,研究干摩擦条件下钛合金(Ti6Al4V)对硬质合金(WC-Co)的摩擦学性能.研究了载荷、温度与滑动速度对摩擦过程的影响,通过磨损区微观形貌表征分析了磨损机理.结果表明:Ti6Al4V与WC-Co的摩擦系数波动剧烈,产生了严重的黏滑摩擦,且随着载荷、温度与滑动速度的增加,黏...     

一种考虑粗糙结合面切向黏滑摩擦模型

提出一种描述粗糙结合面的跨尺度黏滑摩擦行为的参数化力学模型。将名义平面的接触问题视作服从随机分布规律的微凸体的接触问题。基于Mindlin弹性接触理论并采用KD(Kragelsky-Demkin)表面粗糙度描述形式,应用概率统计方法导出粗糙表面切向相对位移与作用力、结合面能量耗散之间的关系。将该模型计算结果与光滑表面接触模型结果进行对比,研究模型参数变化对结合面黏滑摩擦行为的影响。结果表明,提出的考虑粗糙表面接触的结合面黏滑摩擦模型能够描述结合界面的跨尺度黏滑摩擦行为;粗糙度参数对切向刚度和振荡激励的能量耗散有很大的影响。     

聚酰亚胺材料自润滑性能研究进展

聚酰亚胺(PI)作为一类优异的自润滑材料近年受到广泛关注.PI的摩擦性能与诸多因素有关,其磨擦因数一摩擦时间(μ-t)曲线一般存在咬合和稳定阶段;不同温度下的摩擦性能与PI分子链的运动有关;不同滑动速度下,PI的摩擦性能取决于摩擦热与载荷;不同载荷下,PI摩擦性能与滑动速度和机械过载有关;纯PI在低湿度下具有更好的自润滑性能;摩擦副对摩擦性能的影响体现在界面粘结力和转移膜形成的难易;适当剂量的离子注入可以制备μ值很低的PI材料;运用材料复合能够有效进行材料增强和润滑改性.     

Nanomechanical characteristics at an ultra-small particle-surface contact interface

Atomic force microscopy (AFM) measurements have shown that nanoscale interfaces in sliding contact frequently exhibit atomic lattice stick-slip friction. Using various material surfaces and AFM tips, including colloidal probes, and systematically varying applied load and lever stiffness, it is demonstrated that transitions can be repeatedly observed from smooth sliding to single unit-cell slips and then multiple slips. The behavior is dependent on the interplay between the stiffness of the contact zone, the measurement system (i.e., the AFM cantilever), and the interfacial potential. Atomic lattice stick-slip occurs with colloidal particle tip orders of magnitudes larger than those previously used. Stable atomically corrugated sliding in ambient conditions that cannot be seen elsewhere is reported. The generality of these conditions suggests that atomic-scale stick-slip behavior may be far more prevalent than previously appreciated. In addition, the friction-stiffness maps of various material surfaces in contact with a colloidal particle were reported, and the complex effects of system stiffness and pressure were discussed for chemical-mechanical polishing applications.     

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.     

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.     

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。     

Atomic-scale study of friction and energy dissipation

This paper presents an analysis of the interaction energy and various forces between two surfaces, and the microscopic study of friction. Atomic-scale simulations of dry sliding friction and boundary lubrication are based on the classical molecular dynamics (CMD) calculations using realistic empirical potentials. The dry sliding of a single metal asperity on an incommensurate substrate surface exhibits a quasi-periodic variation of the lateral force with two different stick-slip stage involving two structural transformation followed by a wear. The contact area of the asperity increases discontinuously with increasing normal force. Xe atoms placed between two atomically flat Ni surfaces screen the Ni-Ni interaction, decrease the corrugation of the potential energy as well as the friction force at submonolayer coverage. We present a phononic model of energy dissipation from an asperity to the substrates.     

Atomic Friction Modulation on the Reconstructed Au(111) Surface

Friction between a nanoscale tip and a reconstructed Au(111) surface is investigated both by atomic force microscopy (AFM) and molecular statics calculations. Lateral force AFM images exhibit atomic lattice stick–slip behavior with a superstructure corresponding to the herringbone reconstruction pattern. However, the superstructure contrast is not primarily due to variations in the local frictional dissipation (which corresponds to the local width of the friction loop). Rather, the contrast occurs primarily because the local centerline position of the friction loop is periodically shifted from its usual value of zero. Qualitatively, similar behavior is reproduced in atomistic simulations of an AFM tip sliding on the reconstructed Au(111) substrate. In both simulations and experiments, this centerline modulation effect is not observed on unreconstructed surfaces. Similarly, using a topographically flat surface as a hypothetical control system, the simulations show that the centerline modulation is not caused by variations in the reconstructed surface’s topography. Rather, we attribute it to the long-range variation of the local average value of the tip-sample interaction potential that arises from the surface reconstruction. In other words, surface atoms located at unfavorable sites, i.e., in the transition between face-centered-cubic (FCC) and hexagonal-close-packed (HCP) regions, have a higher surface free energy. This leads to a varying conservative force which locally shifts the centerline position of the friction force. This demonstrates that stick–slip behavior in AFM can serve as a rather sensitive probe of the local energetics of surface atoms, with an attainable lateral spatial resolution of a few nanometers.     

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。     

Effect of surface topography on the frictional behavior at the micro/nano-scale

In this paper, the effect of surface topography on the frictional behavior is investigated at micro/nano-scale in order to better understand the influence of asperity contact angle on friction. Experiments were performed to observe the variation in the frictional force as a spherical ball slides across a grooved surface. Specimens with single and multiple grooves of tens of micrometers in width were fabricated on silicon wafers. The frictional behavior between these specimens and steel balls of different diameters were observed with a tribometer built inside a scanning electron microscope (SEM). Normal load in the range of 20 mN and sliding speed of about 1-6 μm/s were applied in the experiments. It was shown that for relative ball/groove dimension that resulted in low contact angle, the overall frictional force was less than that observed for surface without the groove. Also, in situations where there was a great change in the contact angle stick-slip behavior could be observed. This stick-slip behavior is attributed to mechanical interlocking action.In addition to the above experiments, tests were conducted using lateral force microscopy (LFM). Unlike the previous finding that LFM output is dependent on the slope alone, it was found that the signal was more sensitive to the change in slope, especially when the slope was relatively large. Overall, both micro and nano-scale topographic effect on friction was similar. These results will ultimately aid in design of surface topography for micro-systems for best tribological performance.     

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.