The Influence of Normal Load and Sliding Speed on Frictional Properties of Skin

The study of frictional properties of human skin is important for medical research, skin care products and textile exploi- tation. In order to investigate the influence of normal load and sliding speed on the frictional properties of skin and its possible mechanism, tests were carded out on a multi-specimen friction tester. When the normal load increases from 0.1 N to 0.9 N, normal displacement and the friction coefficient of skin increase. The friction coefficient is dependent on the load, indicating that both adhesion and deformation contribute to the friction behaviour. The deformation friction was interpreted using the plough model of friction. When sliding speed increases from 0.5 mm·s^-1 to 4 mm·s^-1, the friction coefficient increases and ＂stick-slip＂ phenomena increase, indicating that hysteretic friction contributes to the friction. The hysteretic friction was in- terpreted using schematic of energy translation during the rigid spherical probe sliding on the soft skin surface, which provides an explanation for the influence of the sliding speed on the frictional characteristics of the skin.

A Dynamical Model to Analyze the Influence of Sliding Friction on Motion on a Curve—An Analytical Method

To demonstrate the influence of sliding friction of motion on a curve, a circular path is considered for simplicity on which a person slides from the highest point to the lowest point. A slide which represents a quadrant of radius 5 m and a person of mass 60 kg are considered for comparison in this paper. A Differential equation for motion considering the fact that the normal force depends both on the sin component of weight and also on the tangential velocity, is established and is solved using integrating factor method, and the motion is analysed for different surface roughness of the slide and is compared using superimposed graphs, also the limiting value of friction coefficient at which the person just exits the slide is determined. The correction factor for exit velocity with friction as compared with the exit velocity for zero friction is determined. The fraction of energy lost to friction at the exit is evaluated. The Variation of normal force with the position of the person on the slide is plotted for different surface roughness of the slide, and the position on the slide where the normal force or the force experienced by the person is maximum, is determined and hence its maximum value is evaluated for different surface roughness. For simplicity, a point contact between the body and the slide is considered.

Determination of the Friction Coefficient in the Flat Strip Drawing Test

Current work is focused on the influence of friction in deep drawing process. Friction measurements were also conducted using a modified tribotester based on strip sliding between tools. Four different tool surfaces were tested under similar contact conditions regarding contact area, normal pressure, sliding speed, lubricant and surface characteristics to calculate the friction coefficient between the tool surface and a high strength low alloy steel sheet HSLA 380. The results showed that friction coefficient varies over a wide range with different lubricating conditions and different sliding velocities. For some sliding velocities, the coefficient of friction is stable and low, while for others it is unstable and higher. Results of the experiments reveal that this novel tribotester is a very useful tool to evaluate and compare the friction between steel sheet and tool surfaces in alloyed steel for cold working applications. The outcomes have only small dispersion within the different test series, which indicates a stable process with good repeatability. The test method enables comparison of different surface finishes and treatments, lubricants and coatings in terms of friction and galling under conditions similar to those found in sheet metal forming processes. The four different types of surfaces considered for this study were grinded, polished, nitrided and quenched/tempered. The main difference among the tested tools in this work was the surface roughness, which was found to have a strong influence on friction.

Friction and wear properties of in-situ synthesized Al_2O_3 reinforced aluminum composites

Al-5%Si-AI2O3 composites were prepared by powder metallurgy and in-situ reactive synthesis technology. Friction and wear properties of Al-5%Si-Al2O3 composites were studied using an M-2000 wear tester. The effects of load, sliding speed and long time continuous friction on friction and wear properties of Al-5%Si-Al2O3 composites were investigated, respectively. Wear surface and wear mechanism of Al-5%Si-Al2O3 composites were studied by Quanta 200 FE-SEM. Results showed that with load increasing, wear loss and coefficient of friction increased. With sliding speed going up, the surface temperature of sample made the rate of the producing of oxidation layer increase, while wear loss and coefficient of friction decreased. With the sliding distance increasing, coefficient of friction increased because the adhesive wear mechanism occurred in the initial stage, then formation and destruction of the oxide layer on the surface of the sample tended to a dynamic equilibrium, the surface state of the sample was relatively stable and so did the coefficient of friction. The experiment shows that the main wear mechanism of Al-5%Si-Al2O3 composites includes abrasive wear, adhesive wear and oxidation wear.

Thermo-structural analysis on evaluating effects of friction and transient heat transfer on performance of gears in high-precision assemblies

The high precision assemblies with considerable radial interference should be accompanied by heating and cooling processes.However,the mechanical properties of metals are greatly affected by thermal operations.So,for evaluating the stress distribution and distortion of teeth profiles in a gear/shaft assembly,a transient thermal analysis is necessary for finding the change in mechanical properties.The friction on the contact surface is another important parameter in interaction of the gear with the shaft.Evaluating the gear stress and deformation fields for several modes of heat transfer and friction coefficients showed that the maximum radial or tangential stresses on contact surface of the joint may have more than 8%increase by increasing friction coefficient;while the intensity of heat transfer at cooling stage has lower effect on stress distribution.

Driving force coordinated control of an 8x8 in-wheel motor drive vehicle with tire-road friction coefficient identification

Because of the complexities of tire-road interaction,the wheels of a multi-wheel distributed electricdrive vehicle can easily slip under certain working conditions.As wheel slip affects the dynamic per-formance and stability of the vehicle,it is crucial to control it and coordinate the driving force.With this aim,this paper presents a driving force coordination control strategy with road identification for eight-wheeled electric vehicles equipped with an in-wheel motor for each wheel.In the proposed control strategy,the road identification module estimates tire-road forces using an unscented Kalman filter al-gorithm and recognizes the road adhesion coefficient by employing the recursive least-square method According to road identification,the optimal sip ratio under the current driving condition is obtainedand a controller based on sliding mode control with a conditional integrator uses this value for accel-eration slip regulation.The anti-slip controller obtains the adjusting torque,which is integrated with the driver-command-based feedforward control torque to implement driving force coordination control.The results of hardware-in-loop simulation show that this control strategy can accurately estimate tire-roadrces as well as the friction coefficient,and thus,can effectively fulfill the purpose of driving force coordinated control under different driving conditions.

Friction Characteristics of Space Lubricating Oil No.4129 in Rolling and Sliding Contact

The friction coefficients between the surfaces of a ball and a disc lubricated by a space lubricating oil No.4129 were measured at various operating conditions on a ball-disc friction test rig. Friction characteristic curves were obtained under sliding and rolling movements at point contact. A new model for calculation of the friction coefficient was presented. The results show that the bigger the load is, the larger the friction coefficient becomes. The rolling speed ranging from 1 m/s to10 m/s has an important effect on the friction coefficient. The friction coefficient increases with the increase in sliding speed and the decrease in rolling speed. The linear variation region of the friction coefficient versus the sliding speed at high rolling speed is wider than that at low rolling speed. The model for calculation of the friction coefficient is accurate for engineering use.

Road Friction Coefficient Real-Time Identification Based on the Tire Dynamic Friction Model

Road friction coefficient real-time estimation methods is an important issue and problem in automotive active safety con- trol system development. First a fixed feedback gain sliding mode observer of road adhesion coefficient is designed through the es-tablishment of tire/road dynamic friction model in this article. The simulation results shows that the observer can well real-time iden-tify the current road adhesion characteristics. And more importantly, the observer only need wheel speed signal and the braking torque （brake pressure） signal, so the system is low cost, and its adaptability is good. There is no doubt this estimation method has a good application prospect.

Friction coefficient and microhardness of anodized aluminum alloys under different elaboration conditions

The effects of anodizing conditions （electrolyte, current density and temperature） on the friction coefficient and Vickers mierohardness of anodic oxide layers formed on A1 5754 and A1 1050A substrates were investigated. The studied properties were examined using DELTALAB HVS-1000 Vickers mierohardness tester and rotating pin on disc tribometer. It was established that the highest microhardness （〉HV 400） and the lowest friction coefficient （〈0.4） were obtained with the oxalic acid addition of 10 g/L at high current density of 3 A/dm2 and low temperature of 5 ~C. The presence of oxidized Mg through the anodic oxide layer formed on A1 5754 was examined using glow-discharge optical emission spectroscopy （GDOES）. The MgO was found to act negatively on the mechanical property of the layer. Finally, the scanning electron microscopy （SEM）, energy dispersive X-ray spectroscopy （EDS）, and atomic force microscopy （AFM） were used to characterize the anodic layer before and after friction tests. It is found that the wear mechanism is related to many aspects of the initial morphology, chemical composition of the layer （C, S and Mg）, porosity and internal stress.

Dry sliding wear behavior of Al_2O_3 fiber and SiC particle reinforced aluminium based MMCs fabricated by squeeze casting method

Al2O3 fiber （Al2O3f） and SiC particle （SiCp） hybrid metal matrix composites （MMCs） were fabricated by squeeze casting method.The tests were carried out using a pin-on-disk friction and wear tester by sliding these pin specimens at a constant speed of 0.36 m/s （570 r/min） against a steel counter disk at room temperature,100 C and 150 C,respectively.To observe the wear characteristics and investigate the wear mechanism,the morphologies of the worn surfaces and specific wear rate were analyzed by using scanning electron microscope （SEM） and Arrhenius plots.Moreover,the effects of fiber orientation and hybrid ratio were discussed.

Sliding wear behavior of magnetorheological fluid for brass with and without magnetic field

A pin-on-disc wear apparatus was used to carry out the tribological experiment of brass to investigate the effect of a magnetorheological （MR） fluid on the interfacial surface with and without magnetic field. A series of tests were performed at the loads of 20-100 N and rotating speeds of 127-425 r/min for 2 h. The friction coefficient and wear rate were monitored by the wear apparatus, while the microstructures of the worn surfaces were observed by scanning electron microscope （SEM）. In addition, the chemical composition of worn surfaces was analyzed by energy dispersive X-ray spectroscopy （EDS）. Test results show different friction and wear performance of the MR fluid with and without magnetic field. At the same time, the effects of various normal loads and rotating speeds on the tribological behavior were investigated. Through the investigation of the morphologies of the wom surfaces under the magnetic field, it is found that the MR particles are clearly evident on the wom surface and the plastic flow of ridges causes the lateral extrusion. This directly indicates that abrasive wear is the predominant wear mechanism observed with MR fluid.

Reciprocating sliding tribology of brake oil treated carbon fiber reinforced ceramic matrix composites

The effect of brake oil on sliding behavior of carbon/carbon(C/C) and carbon/carbon-silicon carbide(C/C-SiC) composites was investigated with the variation of laminate orientation and surface conformity. The partial and low conformity contacts with the normal and parallel orientations of laminates were considered. The normal load was varied from 50 to 90 N in a step of 10 N. The friction and wear behavior was investigated under reciprocating sliding conditions. The results showed that friction coefficient and wear loss of composites with normal orientation of laminates were larger as compared to those of composites with parallel orientation of laminates. C/C composites with normal orientation of laminates yielded the highest value of friction coefficient. Wear loss decreased by a maximum of 78%, and friction coefficient decreased by a maximum of 49% in low conformity contacts as compared to partial conformity contacts. The presence of brake oil reduced the adhesion tendency of compacted wear debris because the formation of friction film was difficult, and thus, friction behavior was affected. The wear debris retention between the contact surfaces due to confined area motion in reciprocating sliding depicted the tribological behavior.

COMPOSITION EFFECT ON DRY SLIDING WEAR BEHAVIORS OF Ti-B-N THIN FILMS

Friction and sliding wear behaviour of Ti-B-N coatings against AISI440C steel ba ll and WC-6wt%Co ball were studied by using pin-on-disk tribometer along with mi crostructure characterization using optical microscopy (OM), scanning electron m icroscopy (SEM) and X-ray photoelectron spectroscopy (XPS). It is shown that the wear resistance of film depended on the wear mechanism. In the case of AISI440C steel, adhesive wear were pre-dominant and the wear rate increased sharply to a maximum when N content reach ~38at.%. This might be related to the change of fi lm microstructure and phase configuration, so the least adhesive transfer of tri bo-film was observed. If WC-6wt%Co ball was used, less deformation wear debris w as observed, this was responsible for the rise of wear rate. Despite of differen t wear modes, friction coefficients in both cases were found to depend mainly on the formation and the amount of h-BN phase. Elemental analysis by energy disper sive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) revealed that oxygen participated in the wear behavior by reacting with films to form the deb ris comprised of various types of Ti oxide including TiO, TiO2 and Ti2O3 , which increased wear resistance.

Probing the intriguing frictional behavior of hydrogels during alternative sliding velocity cycles

Understanding the friction behavior of hydrogels is critical for the long-term stability of hydrogelrelated bioengineering applications.Instead of maintaining a constant sliding velocity,the actual motion of bio-components(e.g.,articular cartilage and cornea)often changes abruptly.Therefore,it is important to study the frictional properties of hydrogels serving under various sliding velocities.In this work,an unexpected low friction regime(friction coefficientμ<10^(-4) at 1.05×10^(-3) rad/s)was observed when the polyacrylamide hydrogel was rotated against a glass substrate under alternative sliding velocity cycles.Interestingly,compared with the friction coefficients under constant sliding velocities,the measuredμdecreased significantly when the sliding velocity changed abruptly from high speeds(e.g.,105 rad/s)to low speeds(e.g.,1.05×10^(-3) rad/s).In addition,μexhibited a downswing trend at low speeds after experiencing more alternative sliding velocity cycles:the measuredμat 1.05 rad/s decreased from 2×10^(-2) to 3×10^(-3) after 10 friction cycles.It is found that the combined effect of hydration film and polymer network deformation determines the lubrication and drag reduction of hydrogels when the sliding velocity changes abruptly.The observed extremely low friction during alternative sliding velocity cycles can be applied to reduce friction at contacted interfaces.This work provides new insights into the fundamental understanding of the lubrication behaviors and mechanisms of hydrogels,with useful implications for the hydration lubrication related engineering applications such as artificial cartilage.

深中通道沉管隧道最终接头MGB滑轨摩擦系数试验研究

深中通道沉管隧道最终接头采用了水下推出式对接方式,推出过程中采用MGB滑轨作为底部滑行系统,为分析结构受力,建立了与施工现场荷载相同的试验结构,研究了深中通道沉管隧道最终接头MGB滑轨与防腐涂层在不同施工荷载和润滑状态下的摩擦系数,并与厂家提供的摩擦系数进行了对比。研究结果表明:MGB材料的摩擦系数随着荷载的增大而减小,干摩擦情况下的静摩擦系数范围为0.181~0.266,滑动摩擦系数范围为0.150~0.226,在水润滑条件下摩擦系数小于干摩擦,摩擦系数与接触界面有关,工程中建议根据实际荷载和摩擦界面情况对摩擦系数进行测试。

Ⅱ型截面双层组合梁摩擦型螺栓连接节点弯矩分配系数

为探究Ⅱ型截面双层组合梁摩擦型螺栓连接节点翼缘和腹板的弯矩比,通过对3种腹板螺栓布置形式的Ⅱ型截面双层组合梁连接节点接触面滑移特征和力学传递机理的分析,进行Ⅱ型截面组合梁螺栓连接节点弯矩分配系数研究。结果表明:组合梁摩擦型螺栓连接节点滑移和力学传力过程可分为翼缘外接触面未完全滑移和完全滑移以及翼缘内接触面完全滑移3个阶段;组合梁摩擦型螺栓连接节点接触面承担弯矩与无连接板截面弯矩之和等于该梁截面处的理论弯矩,腹板接触面承担的弯矩主要由其上的水平摩擦力承担;摩擦型螺栓连接节点接触面上的摩擦力随节点滑移而重新分配,腹板螺栓布置形式对连接节点弯矩分配系数影响明显;根据推出的组合梁摩擦型螺栓连接节点的弯矩分配系数计算式所得结果与数值模拟结果吻合良好,最大误差为7.13%,该计算可用于优化螺栓连接设计。

微造型形状对滑动轴承摩擦特性的影响

利用激光微造型技术在滑动轴承轴颈表面加工出三角形、圆形和正方形微造型,分析不同形状微造型化滑动轴承的摩擦特性,并表征表面形貌,研究表征参数和摩擦特性的关系。结果表明:与未造型的滑动轴承相比,随着载荷增加,微造型后滑动轴承的摩擦系数逐渐减小,三角形微造型的滑动轴承摩擦系数最小,其次是圆形,最后是正方形。当表面偏态增加,摩擦系数升高,而表面峰态增加时,摩擦系数变化正好相反;当表面谷处和中心处平均空体体积增加时,摩擦系数先降低后升高,表面谷处及中心处平均空体体积分别为6.148×10^(-4)mm^(3)和5.418×10^(-3)mm^(3)时,摩擦系数最低;当表面峰和谷平均体积增加时,摩擦系数降低。在载荷3200 N及600 r/min时,微造型后滑动轴承的摩擦系数随着连通性系数的增加而降低。

自然老化服役后板式橡胶支座摩擦滑移性能试验研究

为了解自然老化服役后板式橡胶支座的摩擦滑移性能,取实际桥梁中服役10年的7个板式橡胶支座进行摩擦滑移试验,分析不同竖向压应力下支座摩擦滑移规律,研究自然老化板式橡胶支座的水平弹性刚度、摩擦系数及耗能能力等,并对比人工热老化支座的相关性能。结果表明:相同服役年限的自然老化板式橡胶支座老化程度并不相同;自然老化板式橡胶支座摩擦系数随着竖向压应力的增大而减小,水平弹性刚度随着竖向压应力的增大而增大;压剪作用对老化板式橡胶支座的耗能能力影响较小,但需要注意累积的摩擦滑移会使支座耗能能力降低。自然老化板式橡胶支座(试验值)相较于未老化支座(理论值)的表面摩擦系数有所降低,但水平弹性刚度明显增大;自然老化板式橡胶支座水平弹性刚度增大幅度远高于人工热老化的板式橡胶支座,人工热老化研究严重低估了自然老化对板式橡胶支座的危害。

弹性滑板支座不同摩擦系数对楼层反应谱的影响

采用课题组建立的楼层反应谱Benchmark模型,研究弹性滑板支座不同摩擦系数对楼层反应谱的影响.使用ETABS软件建立隔震结构有限元模型,在底层柱底和基础之间布置弹性滑板支座,为了使楼层反应谱具有实用性和代表性,输入FEMA P695中推荐的22条远场地震动,分别对4个摩擦系数的基础隔震结构进行非线性时程分析,研究弹性滑板支座摩擦系数对楼层反应谱的影响,且与铅芯橡胶支座隔震结构楼层反应谱进行比较.结果表明:摩擦系数影响楼层反应谱的谱值,但不改变楼层反应谱峰值出现的周期,不影响楼层反应谱的频谱特征;在周期0~6 s内,文中4种摩擦系数的弹性滑板支座结构的楼层反应谱谱值均小于铅芯橡胶支座的谱值,说明该结构弹性滑板支座的隔震性能优于铅芯橡胶支座.

自复位刚性滑板隔震支座水平力学性能研究

介绍了自复位刚性滑板隔震支座的基本构成和隔震原理,基于力学平衡原理,对自复位刚性滑板隔震支座进行了理论分析,推导了支座的等效刚度,构造了支座的滞回模型,探讨了支座的回复特性。使用电液伺服压剪试验机测试了支座在低周往复荷载作用下的滞回特性及回复能力。采用ABAQUS软件模拟支座在水平位移激励作用下的滞回特性及回复能力。结果表明:数值模拟结果和试验结果较吻合;自复位刚性滑板隔震支座的滞回性能良好,压力越大,滞回曲线越饱满;该支座往复加载过程的最大应力位于刚性滑块的中心位置,处于弹性范围内;该支座的自复位能力与滑动面摩擦系数呈反相关,与回复橡胶的剪切模量呈正相关。