Microtribological Studies of Different Nanocomposite TiC/a-C:H Coatings Using a Modified Nanoindentation Setup

The microtribological behavior of different nanocomposite TiC/a-C:H coatings against 100Cr6 (AISI 52100) balls with 250 m radius has been studied using a modified nanoindentation setup and was compared to the results of macroscopic pin-on-disc (POD) experiments. First results reveal significant differences between macroscopic friction coefficients _POD determined using POD tests and microscopic friction coefficients _micro. On the macroscopic scale low friction coefficients can be obtained for high hardness coatings. On the microscopic scale the high hardness samples induce considerable wear on the steel counterbody leading to high microscopic friction coefficients of around 0.3. For samples with lower hardness no wear has been observed and low microscopic friction coefficients (< 0.2) can be acheieved.     

Microtribological studies of unlubricated sliding Si/Si contact in air using AFM/FFM

Tribological properties of Si/Si contacts were measured on a microscale by using an atomic force/friction force microscope. Friction forces and pull-off forces between a Si tip and a polished surface of a Si(100) wafer were studied as a function of applied normal load and relative humidity of the surrounding air. The results show that pull-off forces and friction coefficients increased and were strongly influenced by capillary forces with increasing humidity. Tribological interactions during 20 passes of overlapping sliding contact at 50% relative humidity and very small loads of 70 nN were confined to the layer of adsorbates and chemical reactions, without measurable solid damage on the Si(100) wafer.     

Stick‐slip in the presence of a normal vibration

This paper presents a dynamic analysis of a contact system subjected to an applied normal vibration. The tangential motion of the system is found to exhibit stick‐slip behaviour dependent on the applied vibration, even in the absence of a difference in static and kinetic friction or a negative gradient in the friction‐velocity relation. The analysis leads to the development of a criterion for stick‐slip in the form of an equation defined in terms of the system and input parameters. This criterion is also presented graphically and is assessed through a series of experiments. The analysis and measurements show that stick‐slip occurs for a significantly wider drive velocity range when the normal vibration applied is near the natural frequency of the drive system. In addition, when stick‐slip occurs in the presence of a normal vibration, the frequency of stick‐slip is found to lock in to the frequency of the applied vibration.     

Nano/microtribology Stick-Slip Number Under an Atomic Force Microscope and Its Characteristics

The atomic force microscope (AFM) has become a main instrument in observing nano/microtribological characteristics of sample surfaces. In this paper, we investigated the micro-scale adhesive contact between the AFM tip and the sample surface based on the Maugis–Dugdale contact model, and analyzed the energy conversion and dissipation process during the AFM scanning process. A dimensionless stick-slip number = 8U₁h²/(kR_s ²) was defined, which can serve as a characteristic index for the appearance of nano/microtribology stick-slip behavior. If the stick-slip number is less than one, i.e., <1, the AFM tip slides on the sample surface and no stick-slip behavior occurs in the AFM lateral force signal. When the stick-slip number equals one, i.e., = 1, the tip jumps on the sample surface and the AFM lateral force signal begins to exhibit a stick-slip behavior but without energy dissipation. Only in the case of >1 does the stick-slip behavior appear in the AFM lateral force signal accompanied by an obvious energy dissipation. The defined stick-slip number demonstrates that the nano/microtribological stick-slip behavior is due to the adhesive hysteresis as well as the instability motion of the AFM tip during the scanning process. Finally, the influence on nano/microtribology stick-slip behavior of sample surface energy, surface topography, scanning velocity, spring constant of AFM cantilever probe, etc. are investigated theoretically and experimentally. Various experimental results of nano/microtribology stick-slip behavior under AFM are successfully interpreted according to the stick-slip number.     

Role of nanometer roughness on the adhesion and friction of a rough polymer surface and a molecularly smooth mica surface

Friction and adhesion measurements between surfaces of cross-linked, stiff polymers of varying roughness against smooth, bare mica surfaces were carried out in dry air as well as in the presence of lubricating oil. The nominal (macroscopic) contact area varies with the applied load according to the Johnson, Kendall and Roberts (JKR) theory, yet shows significant hysteresis due to the irreversibility arising from the loading/unloading curves of multiple asperities. Upon introducing the oil between the surfaces, the critical shear stress is reduced to zero due to the elimination of the adhesion force. However, the effect is less noticeable on the friction coefficient. Lastly, the effect of increasing the (RMS) roughness was greatest over the first few nanometers due to the diminution of the adhesion-controlled contribution to the friction, after which a further increase in roughness had less dramatic effects. A model is presented to account for the observed adhesion hysteresis during repeated loading/unloading cycles of purely elastically deforming rough surfaces. Bruno Zappone and Kenneth J. Rosenberg made equal contributions.     

The effect of slip amplitude and test time on fretting wear in metal-metal contact

A study was conducted to determine the effect of amplitude and test time on surface damage in metal-to-metal contact under lubricated conditions. The test set up consisted of a ball loaded against a flat disc, with an external drive imparting a linear oscillatory motion to the ball on the flat. The materials were steel AISI 52100/AISI 52100, and the lubricant was ISO VG 220. Damage characteristics were defined for amplitudes in the range of 5 to 50 microns and for test times of 10 to 360 min.     

Rolling cylinder on an elastic half-plane with harmonic oscillations in normal force and rotational speed. Part I: Solution of the partial slip contact problem

We study the effect of harmonic oscillations during the steady rolling of a cylinder on a plane in partial slip contact conditions in the limit of small oscillations. The solution is an extension of that given in Barber et al. [1] for infinitely large coefficient of friction. Here, the effect of varying normal load and hence contact area is investigated in detail by analyzing the first order variation of the tangential force and the corresponding relative displacements.In particular, the solution is given in terms of an explicit length scale d in the Flamant solution used as a Green function. Appropriate choice of values of d allows to treat both two-dimensional problems and three-dimensional ones having elliptical contact area sufficiently elongated in the direction of the rotation axis.Also, this analysis can be used as starting point for corrugation calculations in railway tracks, where oscillations in time of the normal forces can result in non-uniform wear and hence in amplification of the corrugation.     

基于Labview虚拟仪器的导电滑环检测系统设计与研究

针对目前导电滑环在模拟空间环境试验过程中,关键技术指标难以进行有效检测的问题,基于Labview虚拟仪器设计了一种可用于模拟空间环境试验的检测装置,该装置可准确模拟导电滑环在空间环境条件下的真实工况,通过对导电滑环的接触电阻变化值、摩擦力矩性能指标进行检测,并对检测结果进行分析研究,可验证导电滑环在模拟空间环境下的各性能指标,从而保证导电滑环的产品质量,对导电滑环的生产与使用具有重要意义。     

Friction and slip of a simple liquid at a solid surface

We report a novel experimental technique using total internal reflection – fluorescence recovery after photobleaching (TIR‐FRAP) to probe the velocity of a liquid near a wall with a resolution of the order of 100 nm. As an example of use, we have investigated the boundary condition of the liquid velocity during lubricated friction and studied the influence of a classical additive (stearic acid) in a base oil (hexadecane), and demonstrate that simple Newtonian fluids can develop slip at the wall. This revised version was published online in September 2006 with corrections to the Cover Date.     

The study of the adhesion of a TiN coating on steel and titanium alloy substrates using a multi-mode scratch tester

A titanium nitride (TiN) coating was deposited by magnetron sputter ion plating onto steel and titanium alloy polished substrates. The adhesion of the coating on each substrate material was investigated using a newly developed multimode scratch tester. Progressive loading scratch tests, constant load scratch tests, multiple scratch tests in the same track and indentation tests were all performed. It was shown that the modified scratch tester can be used to identify not only coating detachment during progressive load scratch tests, but also other failure events such as cracking and cohesive damage to the coatings. By using the additional modes of operation, it was possible to study the fracture mechanisms in more detail i.e. chipping in the scratch track was cohesive for the TiN coated steel and adhesive for the TiN coated Ti alloy.     

一种新型平面研磨机的研制与实验

根据研磨最佳运动学条件,结合现有研磨机,研制了新型行星轮式恒速率变向平面研磨机.研磨机具有被研磨表面各点研磨轨迹相同、速度相同,研磨运动方向恒速率变向的运动特性.利用研磨实验机进行了大量研磨实验,取得了很好的研磨效果,研磨表面Ra可至纳米级.     

Monitoring of neuronal and glial calcium activity using a novel direct-contact probe

In vivo neuronal and glial calcium activity was monitored using a novel direct‐contact probe that was designed for fluorescence detection deep within biological tissue. A small diameter fibre bundle direct‐contact probe was employed with a laser scanning confocal microscope to detect evoked neuronal and glial activity in the posteromedial barrel subfield of the rat somatosensory cortex in vivo. Resolution of the probe allowed discrimination of single cells, and calcium dynamics spanning milliseconds to several seconds were observed. Initial results indicate that the probe has useful practical applications in the imaging of individual cells and monitoring rapid calcium fluctuations within their cell body and large processes.     

Dynamics and Wheel’s Slip Ratio of a Wheel-legged Robot in Wheeled Motion Considering the Change of Height

The existing research on dynamics and slip ratio of wheeled mobile robot (WMR) are derived without considering the effect of height, and the existing models can not be used to analyze the dynamics performance of the robot with variable height while moving such as NOROS-Ⅱ. The existing method of dynamics modeling is improved by adding the constraint equation between perpendicular displacement of body and horizontal displacement of wheel into the constraint conditions. The dynamic model of NOROS-Ⅱ in wheel motion is built by the Lagrange method under nonholonomic constraints. The inverse dynamics is calculated in three different paths based on this model, and the results demonstrate that torques of hip pitching joints are inversely proportional to the height of robot. The relative error of calculated torques is less than 2% compared with that of ADAMS simulation, by which the validity of dynamic model is verified. Moreover, the relative horizontal motion between fore?hind wheels and body is produced when the height is changed, and thus the accurate slip ratio can not be obtained by the traditional equation. The improved slip ratio equations with the parameter of the vertical velocity of body are introduced for fore wheels and hind wheels respectively. Numerical simulations of slip ratios are conducted to reveal the effect of varied height on slip ratios of different wheels. The result shows that the slip ratios of fore?hind wheels become larger?smaller respectively as the height increases, and as the height is reduced, the reverse applies. The proposed research of dynamic model and slip ratio based on the robot height provides the effective method to analyze the dynamics of WMRs with varying height.     

A review of railway sanding system research: adhesion restoration and leaf layer removal

ABSTRACT

This paper aims to provide a comprehensive review into academic and industrial research concerning the use of particles as a means of recovering adhesion when low adhesion conditions exist within the wheel/rail contact. The most common particle used is sand, generally possessing a high silica content, usually between 0.85 and 1.4?mm in size. Sand is currently being applied in low adhesion conditions in two ways: firing the sand into the wheel/rail contact by means of a train-borne sanding system, or by suspending it in a gel and applying it to the rail head with either a train-borne system or using a wayside applicator. Sanding has been used for a long time, but little research has been conducted on the sanding system, with research shortfalls surrounding particle properties and models of the mechanical behaviour of the particles’ effect in the wheel/rail contact. This paper includes a gap analysis method whereby previous research has been categorised based on seven criteria, designed to help assess the papers. The research was then graded as either ‘A’, ‘B’ or ‘C’ with ‘A’ grade research representing peer-reviewed work conducted across a range of scales or with an aspect of modelling. Most academic research was of ‘B’ grade due to the lack of multiple scales or modelling, which was also lacking in industrial research, but due to the lack of peer review most industrial research received a ‘C’ grade. The review also found there was evidence to suggest a lack of linkage between academia and industry with regards to taking sanding research findings forward. Additionally, this review helps clarify what future work is needed to optimise the sanding system to best recover adhesion and remove lubricating layers in the wheel/rail contact.     

用Pro/Mechanism实现复杂凸轮机构的设计及运动分析

针对复杂平面运动从动件盘形凸轮机构设计的困难,介绍1种利用Pro／Mechanism的强大功能实现复杂凸轮机构的创新设计、运动仿真及运动分析。这种创新方法可以使复杂凸轮机构设计变的快捷、便利。     

曲线半径及轴重对轮轨摩擦功影响的研究

基于非Hertz滚动接触理论利用数值计算方法详细分析了静态接触情况下,轴重和曲线半径对轮轨接触质点间等效应力、接触斑粘滑区的分布、总滑动量和摩擦功的影响。分析计算表明,轴重增加引起轮轨接触质点间等效应力,接触质点间粘滑区的面积以及总滑动量的变化,同时对轮轨接触质点阍的摩擦功的变化有重要影响;小曲线半径处轮轨接触质点间的总滑动量,接触斑滑移区的面积以及摩擦功都明显增大,导致曲线上钢轨磨损加剧。因此曲线半径和轴重是影响轮轨滚动接触磨损的重要因素。     

一种开式或闭式动力变速器性能的预测

本文介绍一种设计具有转差元件和行星齿轮的开环变速箱的车辆的性能预测方法,同时采用数学模型对这种装置的内功率流程图进行理论分析,推荐一种用性能迹线图表示整个装置特性的几何方法有效测定新设计的动力变速箱,它完全一性预测性能和设计因素的影响,这些因素是装置的设计,行星齿轮传动的类型和速比双及转差元件的设计参数,采用测功仪对动力变速器的预测结果进行试验比较。     

Frictional properties of some additives for sliding guide way lubricants in a sliding speed range between 0.002 and 1.5 m/s with a thrust collar friction tester

Frictional properties of some additives used in sliding guide way lubricants were studied for a pair of mild steels under sliding speeds ranging from 0.002 to 1.5 m/s with a thrust collar type friction tester. As the sliding speed was decreased, the coefficient of friction first decreased, then after reaching the minimum value, it increased. The minimum friction coefficient μ_min and the transition sliding speed V_min showing μ_min depended upon the additive. That is, μ_min for the oil containing sulfurized lard was lower than those for the other oils tested and its V_min was as low as 0.005–0.1 m/s compared with the transition speeds of 0.2–0.5 m/s for the other oils tested. Observations of the surface profile and surface analyses of the test specimen after the tests indicated that the unique phenomena for sulfurized lard were due to the formation of a boundary film containing a long carbon chain with a chemical bond between the sulfur and carbon.     

Tribocarbonisation of a synthetic engine oil in lubricated piston ring/cylinder bore sliding contact and its relation to friction and wear

Tribocarbonisation of a fully formulated synthetic engine oil, an API SJ/SAE 5W‐30 containing an organic molybdenum friction modifier, was investigated in an Optimal SRV® tribotester, with a Mo‐coated piston ring and a cast iron cylinder bore tribopair in lubricated sliding contact and under stepwise heating conditions. The friction characteristics were determined by the friction coefficient curve which showed that two local minimum values occurred as the temperature increased stepwise. The local minimum friction coefficient at the lower temperature of 290°C was the result of the formation of MoS₂ and MoO₃, tribochemically generated by MoDTC and ZDTP. For the other local minimum friction coefficient at the higher temperature of 400°C, FT‐IR and Raman spectroscopic examinations of the worn tracks on the cylinder bore samples indicated that tribopyrolysis of the oil components and simultaneous polycondensation into carbonaceous species had occurred. Detailed Raman analyses showed that the carbonaceous species included a disordered phase and an ordered phase characterised, respectively, by the D‐line (1370 cm⁻¹) and G‐line (1580 cm⁻¹). The peak positions and sizes of the graphite crystallites involved varied according to temperature, and were related to the specific points on the friction coefficient versus temperature curve. Tribochemistry could enhance pyrolysis of the oil and facilitate the production of the carbonaceous species and growth of the graphite crystallites.