Force of friction between fractal rough surface and elastomer

The force of friction between a fractal rough surface and a model elastomer has been numerically simulated using the method of dimensionality reduction. For elastomers, in which the imaginary part of the complex shear modulus is much greater than the real part, the friction coefficient is proportional to the mean square gradient of the solid surface profile. The empirical value of the proportionality coefficient is close to unity.     

Shearing of fibrillar adhesive microstructure: friction and shear-related changes in pull-off force.

To characterize the effect of shearing on function of fibrillar adhesive microstructure, friction and shear-related changes in pull-off force of a biomimetic polyvinylsiloxane mushroom-shaped fibrillar adhesive microstructure were studied. In contrast to a control flat surface, which exhibited pronounced stick-slip motion accompanied with high friction, the fibrillar microstructure demonstrated a stable and smooth sliding with a friction coefficient approximately four times lower. The structured contact also manifested zero pull-off force in a sheared state, while the flat surface exhibited highly scattered and unreliable pull-off force when affected by contact shearing. It appears that the fibrillar microstructure can be used in applications where a total attachment force should be generated in a binary on/off state and, most surprisingly, is suitable to stabilize and minimize elastomer friction.     

复合纳米有机硅材料处理花岗岩的性能测定及相互影响

通过电渗的方法探讨一种复合纳米有机硅材料对固体表面电性质的改变作用 ,研究固体表面电性质与摩擦力的相依性。结果表明 ,经该材料处理的固体表面 (花岗岩 ) ,其表面电负性随处理液浓度的增大而减小 ,摩擦力则随着表面电性质的改变而改变。     

Calculations of the coefficient of friction under elastic contact conditions

Expressions for the friction coefficient were derived for the case of elastic contact between rough materials. The computation was based on the assumption that the friction force in the case under consideration is due to hysteresis losses during the deformation of a thin surface layer of one friction pair component by protuberances on the counterpart surface and due to molecular interaction at the solid/solid interface in the contact zones. The minimum value of the friction coefficient was calculated, and it was shown that it depends on the degree of surface roughness, physicomechanical properties of friction pair materials and the magnitude of tangential stresses ₀ at the solid/solid interface.     

Fluctuational electromagnetic interaction between a moving particle and a flat surface covered with a thin adsorbed film

The effect of a thin adsorbed film on the fluctuational electromagnetic tangential force of interaction between a moving nanoparticle and a flat solid surface was theoretically studied for the first time in a nonrelativistic approximation. Particular calculations were performed for a metal film on a dielectric and for a dielectric film on a metal. In both cases, the nanoparticle is assumed to be made of a nonmagnetic metal. It is shown that, at a normal temperature, the presence of an adsorbed film may lead to an increase in the tangential friction force by one or two orders of magnitude for a certain relation between the particle distance from the surface and the film thickness. In the case of a dielectric film on a metal substrate, a decrease in the temperature is accompanied by exponential decrease in the viscous friction. For a metal film on a dielectric substrate, the tangential force exhibits a quadratic dependence on the temperature.     

石墨烯基薄膜作为固体润滑材料的研究现状及展望

近年来,微型机械系统对摩擦接触表面和界面性能的要求越来越高,表界面设计与改性问题亟待解决.石墨烯自发现以来,由于具有高机械强度、超薄的厚度、原子级光滑表面及低的层间剪切力和高的化学稳定性,作为表面固体润滑材料在摩擦学领域成为研究热点.本文主要介绍了石墨烯及其衍生物薄膜材料的制备方法,作为固体润滑材料在摩擦学方面的研究现...     

Solid lubricants: a review

The fundamental mechanisms of solid lubrication are reviewed with examples from well-known solid lubricants like the transition metal dichalcogenides and diamond-like carbon families of coatings. Solid lubricants are applied either as surface coatings or as fillers in self-lubricating composites. Tribological (friction and wear) contacts with solid lubricant coatings typically result in transfer of a thin layer of material from the surface of the coating to the counterface, commonly known as a transfer film or tribofilm. The wear surfaces can exhibit different chemistry, microstructure, and crystallographic texture from those of the bulk coating due to surface chemical reactions with the surrounding environment. As a result, solid lubricant coatings that give extremely low friction and long wear life in one environment can fail to do so in a different environment. Most solid lubricants exhibit non-Amontonian friction behavior with friction coefficients decreasing with increasing contact stress. The main mechanism responsible for low friction is typically governed by interfacial sliding between the worn coating and the transfer film. Strategies are discussed for the design of novel coating architectures to adapt to varying environments.     

Amontonian friction induced by flexible surface features on microstructured silicon

Friction between nonadhering sliding surfaces are normally described by Amontons' law, which states that there exists a linear relationship between the friction force and the normal applied load and that the friction force is independent of the macroscopic contact area between the surfaces and the sliding velocity. In this study we have measured friction as a function of applied load between a spherical silica particle and a microstructured silicon surface consisting of arrays of vertical microneedles, and we have challenged Amontons' law by changing the size of the silica particle and the sliding velocity. First, when looking at the friction as a function of time for a given applied load, the friction force was observed to oscillate with a period related to the spacing between the microneedles when using a small silica particle, whereas the friction force exhibited a more random variation when a larger silica particle was used. The oscillation in the friction force is a direct evidence for bending and release of individual microneedles and the observation illustrates that the energy dissipating mechanism becomes hidden in the friction data when the dimensions of the sliding body becomes much larger than the length scale of the surface features causing the friction. Second, when looking at the average friction force as a function of applied load we find, in accordance with Amontons' law, a linear relationship between the friction force and the applied load and the friction force is independent of both the size of the sliding silica particle and of the sliding velocity. One exception from this, however, was observed when sliding a small silica particle at low velocity, where a deviation from Amontons' law was noticed. The deviation from Amontons' law is suggested to be attributed to a change in the energy dissipating mechanism giving rise to the friction force. In light of that it is suggested that Amontons' law only is valid as long as the main energy dissipating mechanism does not change with the applied load. To get a better understanding of the general validity of Amontons' law, our results were evaluated against different microscopic models.     

芯轴摩擦系数对推压-拉拔复合缩径的影响

推压-拉拔复合缩径工艺是管坯减径的新方法,芯轴外表面与管坯内表面之间摩擦系数对工艺有重要的影响。通过建立推压-拉拔复合缩径变形过程中变形管坯的力学模型,分析了芯轴外表面与管坯内表面之间摩擦系数对成形的影响规律。针对某载重6.5 t胀压成形汽车桥壳管件的第一道次推压-拉拔复合缩径,设定不同的芯轴摩擦系数,进行了有限元仿真,得到了芯轴摩擦系数对管坯变形的影响规律,并基于管坯传力区不失稳以及变形所需凹模推力和芯轴拉拔力较小,给出了芯轴摩擦系数的设定范围。进行了缩径实验,实验和有限元模拟的结果接近。较小的芯轴摩擦系数可能造成管坯起皱失稳,而较大的芯轴摩擦系数,有利于降低管坯轴向压应力、凹模推力和芯轴拉拔力,但可能造成管坯表面划伤。     

Measurement of interfiber friction force for pulp fibers by atomic force microscopy

Interfiber friction in paper exists in fiber suspensions, fiber flocs, and fiber networks. The interfiber friction force is, therefore, important both in papermaking and in the use of paper. The objective of this research is to develop a methodology using atomic force microscopy (AFM) for the direct measurement of the friction force between pulp fibers. Different factors such as AFM scanning velocity, contact area, and fiber surface roughness were investigated. The results show that AFM is an effective tool for measuring micro-scale interfiber friction forces. Both AFM scanning velocity and fiber surface roughness affect the measured results. The coefficient of friction increases, but the initial adhesion force decreases, with increasing fiber surface roughness.     

The study of an interaction of solid particles with various surfaces using TSM sensors

The interaction of solid particles with various surfaces has been experiencing growing interest in many areas of nanotechnology, colloidal science, and biology. In this paper the interactions of solid particles with the surface of piezoelectric thickness shear mode (TSM) sensors have been studied. A mechanical model has been presented to evaluate the effect of particle loading on the behavior of a TSM sensor. The main sources contributing to the interaction, such as Van der Waals force, friction force, and electrostatic force, are discussed. Experiments have been designed for 10-100 microm particles on the 5-MHz and 10-MHz TSM sensors. It has been shown that the resonant frequencies of the TSM sensors might increase or decrease depending on the interaction conditions. The results have shown that the TSM sensor technique could provide the information on the mass/size of a particle and the binding energy between a particle and the sensor surface. This technique may find its applications in characterizing the properties of an interaction between particles and various surfaces.     

原子力显微镜研究材料光滑表面的微摩擦性能

用原子力显微镜研究了单晶硅、云母表面的微摩擦性能,通过选择扫描角度及对分长度的方法,研究了一种有效的测试光滑材料表面微观静摩擦力的方法.结果表明,新解理云母与探针间的微观静摩擦系数和动摩擦系数均低于单晶硅的表面,但粘附力要大于单晶硅,这可能是由于新解理云母表面带有的电荷易吸收水分造成的.     

Highly Transparent and Integrable Surface Texture Change Device for Localized Tactile Feedback

Human–machine haptic interaction is typically detected by variations in friction, roughness, hardness, and temperature, which combines to create sensation of surface texture change. Most of the current technologies work to simulate changes in tactile perception (via electrostatic, lateral force fields, vibration motors, etc.) without creating actual topographical transformations. This makes it challenging to provide localized feedback. Here, a new concept for on‐demand surface texture augmentation that is capable of physically forming local topographic features in any predesigned pattern is demonstrated. The transparent, flexible, integrable device comprises of a hybrid electrode system with conductive hydrogel, silver nanowires, and conductive polymers with acrylic elastomer as the dielectric layer. Desired surface textures can be controlled by a predesigned pattern of electrodes, which operates as independent or interconnected actuators. Surface features with up to a height of 0.155 mm can be achieved with a transformation time of less than a second for a device area of 18 cm². High transparency levels of 76% are achieved due to the judicious choice of the electrode and the active elastomer layer. The capability of localized and controlled deformations makes this system highly useful for applications such as display touchscreens, touchpads, braille displays, on‐demand buttons, and microfluidic devices.     

Mathematical modelling of an experimental‐analytical method for friction coefficient determination in deep drawing

The main aim of this paper is to determine the friction coefficient μ and maximum drawing force in deep drawing process of aluminum alloy EN AW 1050 utilizing strip drawing method. Influence and interaction between lubrication condition, blank holder force and strip surface roughness on maximum drawing force and friction coefficient are investigated. Response surface methodology and D‐Optimal design are utilized in order to create an experimental plan. According to the design, 23 strip drawings experiments are performed and statistical analysis was done. The regression and variance analysis results with 18 significant mathematical models which are derived in order to describe influence of mentioned parameters on friction coefficient and maximum drawing force. Results are discussed according to previous research. Finally, the optimization of processing parameters is performed aiming for lower friction coefficient and maximal drawing force.     

考虑离心作用的螺杆挤出机固体输送理论模型

在固体输送段,物料由散粒体逐渐被压缩,形成压力梯度。离心力对固体输送有较大的影响,由于离心力的作用,物料与机筒之间的径向作用力大于物料与螺杆之间的径向作用力。在固体输送段压力沿螺杆轴向逐渐增大,输送角逐渐减小。文中根据实验现象,考虑离心力,建立了可压缩体的固体输送物理模型,并求出数学模型的解析解。理论计算表明,即使机筒与固相的摩擦系数小于螺杆与固相的摩擦系数,仍会有固体输送。     

膨胀管塑性膨胀过程摩擦问题研究

关于膨胀管膨胀过程中的摩擦问题,目前还没有文献考虑各因素对摩擦因素的影响,而摩擦因素对膨胀管的膨胀过程有直接的影响.根据膨胀管膨胀过程塑性成形特点,分析了膨胀管膨胀过程摩擦力的构成,讨论了管材材料、膨胀速度、膨胀锥表面状态、膨胀率等因素对摩擦因素的影响.在此基础上建立了膨胀过程摩擦力学模型,并用有限元建立了一个N80实体膨胀管模型验证膨胀管膨胀过程中摩擦因素对套管膨胀过程的影响,给出了摩擦因数分别为0.1,0.15,0.2,0.25,0.3时的等效应力云图.通过对等效应力云图分析发现,摩擦因数大于0.25时膨胀管内出现了明显的犁沟,而摩擦因数小于0.25时膨胀管内不会出现犁沟.有限元计算结果与膨胀管实际膨胀过程特点相吻合,在摩擦因素较大时很容易出现犁沟而使摩擦力增加.因此,在设计膨胀工艺时,应综合考虑各种情况,降低摩擦因素,以满足实际的工程需求.     

Drop detachment and motion on fuel cell electrode materials

Liquid water is pushed through flow channels of fuel cells, where one surface is a porous carbon electrode made up of carbon fibers. Water drops grow on the fibrous carbon surface in the gas flow channel. The drops adhere to the superficial fiber surfaces but exhibit little penetration into the voids between the fibers. The fibrous surfaces are hydrophobic, but there is a substantial threshold force necessary to initiate water drop motion. Once the water drops begin to move, however, the adhesive force decreases and drops move with minimal friction, similar to motion on superhydrophobic materials. We report here studies of water wetting and water drop motion on typical porous carbon materials (carbon paper and carbon cloth) employed in fuel cells. The static coefficient of friction on these textured surfaces is comparable to that for smooth Teflon. But the dynamic coefficient of friction is several orders of magnitude smaller on the textured surfaces than on smooth Teflon. Carbon cloth displays a much smaller static contact angle hysteresis than carbon paper due to its two-scale roughness. The dynamic contact angle hysteresis for carbon paper is greatly reduced compared to the static contact angle hysteresis. Enhanced dynamic hydrophobicity is suggested to result from the extent to which a dynamic contact line can track topological heterogeneities of the liquid/solid interface.     

缝针刺入角膜组织的力学模型

首先通过分析缝针刺入角膜组织过程中的力学行为,将缝针与角膜组织之间的相互作用力分解为表面接触力、摩擦力和切割力.根据修正的Karnopp摩擦模型,进行了正弦加载的摩擦力提取实验.根据摩擦力-时间变化曲线,得到了针刺角膜的摩擦力模型.其次,基于针刺角膜过程中表面接触力的实验结果,通过二次曲线拟合方法建立了表面接触力模型.最后,根据针刺角膜的力-位移关系和摩擦力模型,得到了对应的切割力模型.此研究为手术机器人进行角膜缝合精细作业提供了依据.     

The assessment of particle friction of a drug substance and a drug carrier substance

The centrifuge technique, which has been previously used in adhesion experiments, has been modified for use in single particle friction studies. Both flat compacted surfaces and large single particles were used as substrate surfaces to allow assessment of drug-drug, drug-drug carrier and drug carrier-drug carrier friction forces. Particle size, particle shape and surface roughness were identified as main factors influencing the change from a static into a dynamic friction process and the division between friction due to adhesion and ploughing. The forces of adhesion and friction were found to be proportional to the reversible energy of adhesion. The ratio between the force of adhesion and the press-on force applied and the ratio between the force of friction and the press-on force can be related to the yield stress and the reduced Young's modulus of the materials in contact.     

Prediction and optimization of friction welding parameters for super duplex stainless steel (UNS S32760) joints

Friction welding finds widespread industrial use as a mass production process for joining materials. Friction welding process allows welding of several materials that are extremely difficult to fusion weld. Friction welding process parameters play a significant role in making good quality joints. To produce a good quality joint it is important to set up proper welding process parameters. This can be done by employing optimization techniques. This paper presents a multi objective optimization method for optimizing the process parameters during friction welding process. The proposed method combines the response surface methodology (RSM) with an intelligent optimization algorithm, i.e. genetic algorithm (GA). Corrosion resistance and impact strength of friction welded super duplex stainless steel (SDSS) (UNS S32760) joints were investigated considering three process parameters: friction force (F), upset force (U) and burn off length (B). Mathematical models were developed and the responses were adequately predicted. Direct and interaction effects of process parameters on responses were studied by plotting graphs. Burn off length has high significance on corrosion current followed by upset force and friction force. In the case of impact strength, friction force has high significance followed by upset force and burn off length. Multi objective optimization for maximizing the impact strength and minimizing the corrosion current (maximizing corrosion resistance) was carried out using GA with the RSM model. The optimization procedure resulted in the creation of nondominated optimal points which can aid the process operator to fix the input control variables. The selection of a point from the Pareto front will always be a trade-off between the corrosion resistance and impact strength of the weld depending on the application.