Friction Force Changes Research Articles

Preparation of Artificial Skin that Mimics Human Skin Surface and Mechanical Properties.

We have developed an artificial skin that mimics the morphological and mechanical properties of human skin. The artificial skin comprises a polyurethane block possessing a microscopically rough surface. We evaluated the tactile sensations when skin-care cream was applied to the artificial skin. Many subjects perceived smooth, moist, and soft feels during the application process. Cluster analysis showed that these characteristic tactile feels are similar to those when skin-care cream is applied to real human skin. Contact angle analysis showed that an oil droplet spread smoothly on the artificial skin surface, which occurred because there were many grooves several hundred micrometers in width on the skin surface. In addition, when the skin-care cream was applied, the change in frictional force during the dynamic friction process increased. These wetting and frictional properties are important factors controlling the similarity of artificial skin to real human skin.

Research on the Mechanism of In-Plane Vibration on Friction Reduction.

A modified model for predicting the friction force between drill-string and borehole wall under in-plane vibrations was developed. It was found that the frictional coefficient in sliding direction decreased significantly after applying in-plane vibration on the bottom specimen. The friction reduction is due to the direction change of friction force, elastic deformation of surface asperities and the change of frictional coefficient. Normal load, surface topography, vibration direction, velocity ratio and interfacial shear factor are the main influence factors of friction force in sliding direction. Lower driving force can be realized for a pair of determinate rubbing surfaces under constant normal load by setting the driving direction along the minimum arithmetic average attack angle direction, and applying intense longitudinal vibration on the rubbing pair. The modified model can significantly improve the accuracy in predicting frictional coefficient under vibrating conditions, especially under the condition of lower velocity ratio. The results provide a theoretical gist for friction reduction technology by vibrating drill-string, and provide a reference for determination of frictional coefficient during petroleum drilling process, which has great significance for realizing digitized and intelligent drilling.

A Study on Force and Lubrication Characteristics of Ball Piston in Eccentric Ball Piston Pump

Ball piston is an essential design element in eccentric ball piston pump. The objective of this paper is to investigate the dynamic force and lubrication characteristics of the ball piston. In this study, a tribodynamic model of the ball piston is proposed. The model couples the elastohydrodynamic lubrication model of ball–ring pair and the elastohydrodynamic model of ball–cylinder pair with the dynamic model of the ball piston. The interaction between tribological behavior and dynamic performance and the effects of centrifugation and structural deformation of the ball piston are considered. The pressure distributions and film profiles of the ball–ring pair and ball–cylinder pair are calculated. The dynamic normal contact forces and friction forces are analyzed. The friction torque loss and mechanical efficiency of the whole pump are obtained by combing the tribodynamic model of the ball piston with a simplified friction torque model of cylinder-valve shaft pair. A test bench is established for validating the simulation results. The results show that the normal contact force of the ball–ring pair waves in each stroke, and in discharge stroke, the contact force is much bigger than that in suction stoke because of loading force, while the friction force changes very little for the ball sliding in the outer ring. Comparing with the average friction force of the ball–ring pair, the average friction force of the ball–cylinder pair is small, which reflects that the ball–ring pair is more prone to wear. For the ball–ring friction pair, when the load increases, the secondary contact pressure peak appears, the profile of film presents a horseshoe shape, and the classical shrinkage appears at the outlet of contact region. For the ball–cylinder pair, the film pits and the contact pressure jumps at the entrance of contact region for the heavy load and the high shear stain of film. In addition, the friction torque presents a nonlinear growth trend with the increasing working pressure

Modeling Friction Performance of Drill String Torsional Oscillation Using Dynamic Friction Model

Drill string torsional and longitudinal oscillation can significantly reduce axial drag in horizontal drilling. An improved theoretical model for the analysis of the frictional force was proposed based on microscopic contact deformation theory and a bristle model. The established model, an improved dynamic friction model established for drill strings in a wellbore, was used to determine the relationship of friction force changes and the drill string torsional vibration. The model results were in good agreement with the experimental data, verifying the accuracy of the established model. The analysis of the influence of drilling mud properties indicated that there is an approximately linear relationship between the axial friction force and dynamic shear and viscosity. The influence of drill string torsional oscillation on the axial friction force is discussed. The results indicated that the drill string transverse velocity is a prerequisite for reducing axial friction. In addition, low amplitude of torsional vibration speed can significantly reduce axial friction. Then, increasing the amplitude of transverse vibration speed, the effect of axial reduction is not significant. In addition, by involving general field drilling parameters, this model can accurately describe the friction behavior and quantitatively predict the frictional resistance in horizontal drilling.

Gait control in a soft robot by sensing interactions with the environment using self-deformation.

All animals use mechanosensors to help them move in complex and changing environments. With few exceptions, these sensors are embedded in soft tissues that deform in normal use such that sensory feedback results from the interaction of an animal with its environment. Useful information about the environment is expected to be embedded in the mechanical responses of the tissues during movements. To explore how such sensory information can be used to control movements, we have developed a soft-bodied crawling robot inspired by a highly tractable animal model, the tobacco hornworm Manduca sexta. This robot uses deformations of its body to detect changes in friction force on a substrate. This information is used to provide local sensory feedback for coupled oscillators that control the robot's locomotion. The validity of the control strategy is demonstrated with both simulation and a highly deformable three-dimensionally printed soft robot. The results show that very simple oscillators are able to generate propagating waves and crawling/inching locomotion through the interplay of deformation in different body parts in a fully decentralized manner. Additionally, we confirmed numerically and experimentally that the gait pattern can switch depending on the surface contact points. These results are expected to help in the design of adaptable, robust locomotion control systems for soft robots and also suggest testable hypotheses about how soft animals use sensory feedback.

Modeling friction-reducing performance of an axial oscillation tool using dynamic friction model

An axial oscillation tool (AOT) is an effective means to solve the problem of high friction observed in structurally complex wells during sliding drilling. However, the classical Coulomb model does not explain the mechanism of friction reduction caused by the AOT. To solve this problem, a theoretical model for the analysis of frictional force is proposed based on the dynamic friction model and microscopic contact deformation theory. The Dahl model, an innovative dynamic friction model, is used in this model to determine the friction force changes during slide drilling with an imposed axial vibration. A computational program is developed in the Matlab/Simulink environment. The results indicate that the calculation results using the present model and the experimental results are in good agreement (the average error is only 5.09%), verifying the accuracy of the present model and method. The reduction of friction increases with the vibration frequency and tangential contact stiffness coefficient; it first increases with vibration amplitude and then tends to decrease before reaching the optimal amplitude, but it decreases with increasing relative sliding velocity. The instantaneous frictional force does not exhibit an abrupt phenomenon. The prerequisites for reducing friction caused by the AOT are that the relative sliding velocity should be less than the maximum velocity of the axial vibration. The present model can quantitatively characterize the axial vibration and the relationship between the frictional force and asperity deformation during sliding drilling, and it also can be utilized to analyze the variations of frictional force in real-time. In addition, this model can provide a quantitative calculation to predict the frictional resistance in horizontal drilling.

Dynamic Friction Performance of a Pneumatic Cylinder with Al2O3 Film on Cylinder Surface.

A friction force system is proposed for accurately measuring friction force and motion properties produced by reciprocating motion of piston in a pneumatic cylinder. In this study, the proposed system is used to measure the effects of lubricating greases of different viscosities on the friction properties of pneumatic cylinder, and improvement of stick-slip motion for the cylinder bore by anodizing processes. A servo motor-driven ball screw is used to drive the pneumatic cylinder to be tested and to measure the change in friction force of the pneumatic cylinder. Experimental results show, that under similar test conditions, the lubricating grease with viscosity VG100 is best suited for measuring reciprocating motion of the piston of pneumatic cylinder. The wear experiment showed that, in the Al2O3 film obtained at a preset voltage 40 V in the anodic process, the friction coefficient and hardness decreased by 55% and increased by 274% respectively, thus achieving a good tribology and wear resistance. Additionally, the amplitude variation in the friction force of the pneumatic cylinder wall that received the anodizing treatment was substantially reduced. Additionally, the stick-slip motion of the pneumatic cylinder during low-speed motion was substantially improved.

Development of tribophysical foundations of lubricity of liquid-crystal additives to base oils

The model of the tribological system using liquid crystals as anti-friction and anti-wear additives in the base oil was presented in the paper. The model takes into account functional dependences between input and output characteristics of the system through the functional dependence between input characteristics and characteristics of the internal state of the system. Further research in the paper is aimed at establishing the patterns that describe the impact of the internal state of the tribosystem on the main output characteristics - friction force and wear rate under various contact conditions. Dependence for determining the total specific friction force in tribosystems considering the molecular component of the specific friction force in boundary films of liquid crystals and mechanical friction component was given. Dependences for determining the linear wear rate at elastic and elastic-plastic contact in tribosystems were also presented. Such dependences were obtained taking into account the properties of liquid-crystal boundary film. The results of experimental studies of sliding tribosystems on friction machines using liquid crystals as additives to base oils were shown. In studies, the patterns of changes in specific friction force and wear rate in tribosystems depending on the main characteristics of the phase state of liquid-crystal additive were obtained.

Dynamic characteristics of helical gears under sliding friction with spalling defect

The change of friction force on both sides of the pitch plane and the change of contact stiffness induced by tooth spalling defect cause the change of the dynamic characteristics of helical gears. However, there is no good solution for the modeling and calculation of the internal excitation in helical gears with spalling defect to reveal the change of the dynamic characteristics. In this study, the calculation methods of friction excitations and contact stiffness are proposed based on the time-varying length of contact line in helical gears. By considering the change of the mesh position and the loss of length of contact line induced by tooth spalling defect, the time-varying friction force is obtained by subtracting the length of spalling defect at the mesh position from the length of the normal contact line, and the time-varying contact stiffness is obtained by Hertz contact algorithm. A six-degree-of-freedom analytical helical gear pair model is developed by incorporating the time-varying sliding friction and mesh stiffness based on the changes of friction force and mesh stiffness. Dynamic characteristics are simulated via helical gear pair examples with spalling defects. The results show that the oscillations of the dynamic responses become more significant at both the beginning and the end of the spalling area, especially with the growth of the spalling size. The developed analytical model provides a new method for the study of excitation characteristics in helical gears with tooth spalling defect.

Nonlinear vibration and dynamics of ceramic on ceramic artificial hip joints: a spatial multibody modelling

The present study investigates nonlinear vibration and dynamic behaviour of a ceramic-on-ceramic hip implant. The aim of this research is to firstly gain a better understanding of hip squeaking and vibration and secondly to investigate the effect of friction on contact point path during normal gait. For this purpose, a spatial multibody dynamic hip model was developed, using a friction-velocity constitutive law combined with a Hertzian contact model. Furthermore, the physiological three-dimensional rotation angles and forces are taken into account to calculate tangential and normal contact forces, respectively. Comparing the outcomes with that available in the literature allowed for the validation of our approach. It was shown that the cause of hip squeaking is friction-induced vibration owing to different phenomena such as stick–slip friction, negative-sloping friction and contact force changes. Moreover, friction-induced vibration does significantly change contact point path during the gait when compared to non-friction analysis.

제동시 발생하는 리어 드럼브레이크 Grunt(stick-slip) Noise 개선

Grunt(stick-slip) noise happens between rear lining and drum on braking condition while vehicle is returning to steady position after nose-dive. The study presents a new testing and analysis methods for improving brake grunt noise on vehicle. Grunt noise is called a kind of stick slip noise with below 1 kHz frequency that is caused by the surfaces alternating between sticking to each other and sliding over each other with a corresponding change in friction force. This noise is typically come from that the static friction coefficient of surfaces is much higher than the kinetic friction coefficient. For the identification of the excitation mechanism and improvement of grunt noise, it is necessary to study variable parameters of rear drum brake systems on vehicle and to implement CAE analysis with stick slip model of drum brake. The aim of this study has been to find solution parameters throughout test result on vehicle and dynamo test. As a result of this study, it is generated from stick slip between rear lining and rear drum and it can be solved to reduce contact angle of lining with asymmetric and is effected not only brake drum strength but also rear brake size and brake factor.

Sliding friction of wiper blade: Measurement, FE modeling and mixed friction simulation

In this paper, the dry and wet friction of a commercial wiper blade is investigated. The effect of load and velocity on sliding friction is studied at specimen-level experimentally, the material response is characterized by DMA tests, while the contact behavior is analyzed by plain strain FE models. Holding the normal force constant the numerical analysis makes it possible to follow the variation of interference between the wiper blade and glass surface, the change of friction force and contact pressure distribution, as well as the variation of nominal contact area during the transition from wet to dry friction. As a last step, the steady-state elastohydrodynamic lubrication problem of wiper blade/glass contact is solved by using a recent mixed friction model.

Effect of Three Types of Driving Modes of Rolling Mill with Six Rolls on the Friction Force between Rolls

Three-dimensional finite element model of rolling mill with six rolls in a factory is modeled by nonlinear FEM software called ABAQUS. It is a three-dimensional elastic-plastic rolling model. It includes not only elastic-plastic deformation of strip but also the bending of roll system and flattening of rolls. It can describe the changes in friction force between rolls better. Conclusions are as follows. When the driving roll is the backup roll, friction force between the backup roll and the intermediate roll is easy to reach the maximum value, slipping phenomenon is easy to appear. When the driving roll is the intermediate roll, friction force between the intermediate roll and the work roll is easy to reach the maximum value, slipping phenomenon is easy to appear. When the driving roll is the work roll, the changes in frictional force between the rolls is smooth. Slipping phenomenon is not easy to appear.

Controlling Nanoscale Friction through the Competition between Capillary Adsorption and Thermally Activated Sliding

We demonstrate measurement and control of nanoscale single-asperity friction by using cantilever probes featuring an in situ solid-state heater in contact with silicon oxide substrates. The heater temperature was varied between 25 and 790 °C. By using a low thermal conductivity sample, silicon oxide, we are able to vary tip temperatures over a broad range from 25 ± 2 to 255 ± 25 °C. In ambient atmosphere with ∼30% relative humidity, the control of friction forces was achieved through the formation of a capillary bridge whose characteristics exhibit a strong dependence on temperature and sliding speed. The capillary condensation is observed to be a thermally activated process, such that heating in ambient air caused friction to increase due to the capillary bridge nucleating and growing. Above tip temperatures of ∼100 ± 10 °C, friction decreased drastically, which we attribute to controllably evaporating water from the contact at the nanoscale. In contrast, in a dry nitrogen atmosphere, friction was not affected appreciably by temperature changes. In the presence of a capillary, friction decreases at higher sliding speeds due to disruption of the capillary; otherwise, friction increases in accordance with the predictions of a thermally assisted sliding model. In ambient atmospheres, the rate of increase of friction with sliding speed at room temperature is sufficiently strong that the friction force changes from being smaller than the response at 76 ± 8 °C to being larger. Thus, an appropriate change in temperature can cause friction to increase at one sliding speed, while it decreases at another speed.

Thermo-mechanical properties of the cell surface assessed by atomic force microscopy

Atomic force microscopy (AFM) in lateral force mode was applied to assess the microscale thermo-mechanical (frictional) properties of the air-dried cell surface in the wide temperature range (288–363K/15–90°C). AFM-investigated cell surface layer can be represented as a biocomposite composed of several layers including the glycocalyx, the membrane and the intercellular layer containing membrane (cortical) cytoskeleton. The cells with two different cytoskeleton structures, erythrocytes and thymocytes, were studied. Above a certain temperature (Tg), the significant change in friction force with temperature was revealed for the both cell types whereas there was no similar change in their topography parameters. The experimentally determined value Tg for erythrocyte samples was lower than that for thymocyte ones. Treating living cells with the cross-linking agent, glutaraldehyde, led to the weakening of the temperature dependence of air-dried cell surface frictional properties in the studied temperature range. Addition of oxidizing agent, peroxynitrite, to living cell suspensions changed the temperature dependence of air-dried cell surface frictional properties depending on cell type and peroxynitrite concentration. The obtained data indicate that the study of thermo-mechanical properties of air-dried cells with AFM in lateral force mode provides expanded information on the structural characteristics of the living cell surface layer, and sets the stage for the development of AFM-based method (with using a lateral force mode) for the cell pathology diagnostics.

Inertial Piezoelectric Micro Rotary Actuator

A newly inertial piezoelectric rotary actuator is proposed based on controlling the orderly changes of friction force between the rotator and supporting faces in mechanical way. The dynamic simulation model of the actuator is derived. A prototype small inertial rotary actuator characterized by two symmetric piezoelectric stacks has been fabricated based on the proposed method. The actuator can rotate when it is powered with a square-wave or sine-wave voltage. The experimental and simulation results show that its angular speed is proportional to both the driving voltage’s amplitude and the frequency. The experimental results also show good agreement with the simulation analysis.

Kinetic Study of PZT Inertial Micro Rotary Actuator

Based by controlling the orderly changes of friction force between the PZT rotary actuator and supporting faces in mechanical way, a novel kind of inertial piezoelectric rotary actuator is proposed. the dynamic simulation model of the actuator based on karnopp friction model is established, by using matlab software, Four ordered Runge-Kutta calculation method is used to carry out kinematics simulation of the actuator, the curve of driving signal frequency、voltage and dynamic characteristics is conducted, the prototype of rotary actuator is designed and manufactured, the performance of the actuator is tested，The experimental results show that the developed actuator is characterized by large travel (360º) , good resolution (15µrad) , high speed (0.26rad/s) , and work stability. The motion theory and dynamic formulation of the actuator are proved through comparing the results of simulation and experiment.

An Innovative Design of a Measuring Equipment and Using TiO<sub>2</sub> Nanogrease to Reduction of Friction Force for Pneumatic Cylinder

The purpose of the study is to measure the maximum static friction and dynamic friction in the actuation process of pneumatic cylinder after TiO2 nanoparticles are added to grease. The study makes an innovative design of a new measuring equipment of friction force, which can measure the friction force between the piston seal in pneumatic cylinder and the cylinder bore. The friction force of pneumatic cylinder bore directly affects the output dynamic property of pneumatic cylinder motion. Friction force measuring system can measure the change of friction force of pneumatic cylinder bore under the condition with different operating speeds, and can analyze the relationship between friction force of pneumatic cylinder and output dynamic property of pneumatic cylinder. Such a friction force measuring equipment takes pneumatic cylinder as an output of motive force to drive the measurement of pneumatic cylinder, and uses load cell and draw-line encoder to measure the friction force of pneumatic cylinder bore and the motion speed. In the experiment, the friction forces of pneumatic cylinder given with oil and without oil are measured respectively, achieving the friction force property of pneumatic cylinder bore when being lubricated by nanogrease added with nanoparticles of different weight percentages (wt.%). The experimental results show that adding TiO2 nanoparticles to grease can effectively decrease the friction force produced in the actuation process of pneumatic cylinder.

Research on CMP Characteristics Attribute to Groove Size

Groove pads are used quite widely in chemical mechanical polishing (CMP), and groove size plays an important role in CMP characteristics. This study focuses on the investigation of the groove size effect using X-Y groove pads which are different with pitch and width. The first experiment shows the size effect on the polishing characteristics including material removal rate (MRR), within wafer non-uniformity (WIWNU) on 4 inch oxide blanket wafers for 60 seconds. The second experiment verifies the reason why MRR and WIWNU are different, by the calculation of slurry duration time (SDT) resulting from the change of friction force. All experimental results indicated that a significant difference of slurry flow attributed to groove width and pitch has an impressive influence on friction force, finally the MRR and WIWNU are affected by the groove size.

2A1-K10 曲管内走行可能な螺旋駆動型管内移動ロボットのための最適なバネ定数の設計(環境適応メカニズムと制御)

To make the inspection robot pass in small pipes or vertical pipes, it is hard to equip several motors and mechanisms. Screw drive mechanisms have been focused because a minimum number of motor is only one. It can achieve downsizing, lightweight and energy-saving. Some existing robots can pass in the curved pipes with large curvature radius. However, it can not pass in the pipes with small curvature radius and mobility analysis and verification have not been conducted. In this paper, we consider the cross-sectional shape of a curved pipe that the in-pipe robot attaches. Necessary spring stiffness of elastic driving arms and motor torques are derived for the robot to pass in the curved pipe and the vertical pipe where the friction force changes.