Upon the relationship between rolling friction and sliding friction

New micro tribometer for rolling friction

The paper proposes a device for finding the coefficient of rolling friction using a sphere in contact with the inner surface of a ring that rotates about a horizontal axis. The motion of the ball is characterized by the fact that for a stipulated rotation speed of the ring the centre of the ball executes a damped oscillatory motion and at equilibrium the centre of the ball is situated on different vertical than the one the centre of the ring is positioned. It is assumed that this feature is produced by the rolling friction torque that is proportional with the normal pressing force and the nonlinear differential equation of motion is obtained for the intended dynamic model. By the integration of the equation of motion there are confirmed the oscillatory motion of the ball and the eccentric equilibrium position and it is found a dependency of equilibrium position on the coefficient of rolling friction.

A major objective of tribological researches is characterisation of rolling friction, due to various cases encountered in classical engineering applications, like gear transmissions and cam mechanisms or more recent examples met in bioengineering and biomedical devices. A characteristic of these examples consists in reduced dimensions of the contact zones, theoretically zero, the relative motion occurring between the contact points being either sliding or rolling. A characteristic parameter for the rolling motion is the coefficient of rolling friction. The paper proposes a method for estimation of coefficient of rolling friction by studying the motion of a body of revolution on an inclined plane. Assuming the hypothesis that moment of rolling friction is proportional to the normal reaction force, the law of motion for the body on the inclined plane is found under the premise of pure rolling. It is reached the conclusion that there is an uniformly accelerated motion, and thus for a known plane slope, it is sufficient to find the time during which the body runs a certain distance, starting from motionless situation. To obtain accurate results assumes finding precisely the time of motion. The coefficient of rolling friction was estimated for several slopes of the inclined plane and it is concluded that with increased slope, the values of coefficient of rolling friction increase, fact that suggest that the proportionality between the rolling torque and normal load is valid only for domains of limited variations of normal load.

Three-axis tactile sensing has advantages for grasping an object of unknown mass and hardness. We developed a new three-axis tactile sensor that possesses a simple structure to endure a large applied force from a powerful grasp. Normal force distribution is measured based on grayscale values obtained by image data processing, as with previous three-axis tactile sensors. Tangential force distribution is determined by the linear movement of image data calculated by optical flow. The sensing characteristics of this sensor are dominated by the configuration and material of fine conical feelers formed on a silicon rubber sheet. By UV-LIGA, we obtain a fine mold of a silicon rubber sheet. In evaluation experiments, we applied both normal and tangential force to the sensor and confirmed this tactile sensor's ability to acquire normal and tangential forces. In its design, we utilize a USB microscope that has a CMOS camera and a light source. In a series of experiments, we performed normal and tangential force tests to obtain its basic characteristics. The linear relationship between the grayscale value and the normal force is obtained from the normal force test. If the average optical flow is under 0.2 mm, the tangential force is proportional to the average optical flow. The slope of the relationship between the tangential force and the average optical flow increases with additional normal force. Finally, we derive a series of equations for three-axis force calculation.

Previous studies on adaptation of fingertip forces to local friction at individual digit-object interfaces largely focused on static phases of manipulative tasks in which humans could rely on anticipatory control based on the friction in previous trials. Here we instead analyze mechanisms underlying this adaptation after unpredictable changes in local friction between consecutive trials. With the tips of the right index and middle fingers or the right and left index fingers, subjects restrained a manipulandum whose horizontal contact surfaces were located side by side. At unpredictable moments a tangential force was applied to the contact surfaces in the distal direction at 16 N/s to a plateau at 4 N. The subjects were free to use any combination of normal and tangential forces at the two fingers, but the sum of the tangential forces had to counterbalance the imposed load. The contact surface of the right index finger was fine-grained sandpaper, whereas that of the cooperating finger was changed between sandpaper and the more slippery rayon. The load increase automatically triggered normal force responses at both fingers. When a finger contacted rayon, subjects allowed slips to occur at this finger during the load force increase instead of elevating the normal force. These slips accounted for a partitioning of the load force between the digits that resulted in an adequate adjustment of the normal:tangential force ratios to the local friction at each digit. This mechanism required a fine control of the normal forces. Although the normal force at the more slippery surface had to be comparatively low to allow slippage, the normal forces applied by the nonslipping digit at the same time had to be high enough to prevent loss of the manipulandum. The frictional changes influenced the normal forces applied before the load ramp as well as the size of the triggered normal force responses similarly at both fingers, that is, with rayon at one contact surface the normal forces increased at both fingers. Thus to independently adapt fingertip forces to the local friction the normal forces were controlled at an interdigital level by using sensory information from both engaged digits. Furthermore, subjects used both short- and long-term anticipatory mechanisms in a manner consistent with the notion that the central nervous system (CNS) entertains internal models of relevant object and task properties during manipulation.

The discrete element method (DEM) is an effective tool for obtaining qualitative and quantitative information on particle motion, which aids in the design and optimization of agricultural equipment structures. The accuracy of the DEM simulation parameters significantly impacts the simulation results. This study employed a combination of high-speed camera measurement, DEM simulation, and validation tests to determine the material and interaction property parameters for fertilizer particles. The basic parameters (triaxial size, bulk density, density, and coefficient of static friction) and coefficients of restitution between fertilizer and material were measured for three fertilizer varieties. There was a significant difference in the angle of repose between various material plates and fertilizer particles. The calibration values of coefficients of restitution and coefficients of rolling friction between fertilizer particles were optimized using the Box–Behnken method. The angle of repose was significantly affected by the coefficient of static friction and the coefficient of rolling friction between the fertilizer particles. The determined values for the coefficient of restitution, coefficient of static friction, and coefficient of rolling friction between the fertilizer particles were 0.323, 0.381, and 0.173, respectively. The error in the angle of the repose test was less than 3.0%, and the variation coefficient for each row consistency was less than 1.68 percentage points under the optimal simulation parameters. DEM simulations of the angle of repose and each row consistency variation coefficient test using the measured parameters can accurately predict the experimental results. The findings of this paper provide a theoretical basis for the DEM study of fertilizer particles.

PurposePipeline maintenance technology using smart isolation tool is becoming more widely used in the global scope. This paper aims to investigate the effects of parameters on the frictional resistance between the slip and pipeline and the frictional characteristics under different lubrication films.Design/methodology/approachAn experimental platform consisting of slip, pipeline and data acquisition system was developed, wherein the slip slips on the pipeline under different normal forces and velocities. In addition, three lubrication conditions, namely, dry wall, oil liquid and black powder on the wall, were investigated to study the effects of lubrications on the frictional coefficient and characteristics.FindingsResearch results indicate that the frictional force and coefficient were sensitive to normal force. The crude oil affected the frictional coefficient within a certain range of normal force, and the black powder enhanced the surface roughness in the natural gas pipeline. However, velocity had no effect on them. In addition, different contact behaviors could be observed from the frictional coefficient curves.Originality/valueIn this paper, the effects of normal force and velocity on frictional resistance of sliding slip during decelerating process in pipeline were investigated, and the effects of lubrication films on frictional characteristics were also revealed. The research results are of great value to improve the prediction accuracy of smart isolation tool, and also provide a guiding significance for the development of maintenance operation in pipelines.

Purpose. The value of drive resistance to its movement is the main parameter at calculating the drive power of bridge crane. The value of the wheel rolling friction on the rails is one of the important parts of the resistance to movement. It is necessary to determine the dependence of static (dynamic) quantities of resistance to the bridge crane movement on a straight section of the track from the position of the bogie in the span, and explore the influence of the wheel flanges resistance for wear. Methodology. Using the analytical dependences for determining the rolling friction coefficient, that depends on the size of the half-width of the contact between the wheel and rail, the improved method for calculating the required drive power of the crane was proposed. Findings. With the proposed method of power calculation the characteristic curve of the crane wheel loads, the coefficient of rolling friction of the wheels and the crane resistance to movement from the position of the bogie on span were built. In the result of graphs analysis it was found that the engine power, obtained by the proposed method is higher than the recommended by the existing standards. The more precise formula for determining the total coefficient of sliding friction that takes into account the friction of wheel flanges on the rail is given. The characteristic curves of such coefficient of friction and the total resistance to movement of the position of the crane bogie were built. Originality. The scientists proposed an improved method of determining the required engine power of bridge crane, which takes into account the effect of rolling friction of the wheels on the rails and the bogie in the span. The improved formula for determining the coefficient of friction that takes into account the friction wheel flanges of the rail was given. The characteristic curve of this coefficient of friction and the total resistance movement of crane from the position of the crane bogie were built. Practical value. The application of the proposed method of determining the driving power of the crane allows determining its value more precisely, taking into account the impedance of the rolling friction of the wheels on the rails with a flanged on the rails. This approach enables better selection of elements of the mechanism of the bridge crane movement.

In present paper, a semi-empirical grinding force model is developed combined with the achievements of previous researchers by composing effects of normal and tangential grinding forces in two main parts respectively: cutting force and sliding force. Final equations for the total normal and tangential force components is established. This model is used to predict the total normal and tangential force in the surface grinding. These force components were expressed in terms of the grinding process parameters. There are four unknown coefficients in each equation which can be determined by experiment results at specific conditions with the variations of grinding process parameters. An equation for sliding force is established with the effect of specific sliding energy in terms of the experimental parameters. The average contact pressure and friction coefficient are taken into account. Four different water-based grinding fluids were tested for different specific grinding conditions. Low viscosity grinding fluid can have better performance than the high viscosity one due to the higher useful flow in the grinding contact area. The calculated normal and tangential grinding results are compared with the experimental ones. The verifications show that deviations can be affected by the performance of the fluid at heavy grinding conditions due to the sliding friction inside of rolling friction. To have a better agreement with experiment data. Shallow grinding condition is chosen to obtain the modified model.

A 3D three-equation linear spring-dashpot model considering the normal contact force, the tangential contact force, and the rolling friction torque, and the corresponding programs for granular dynamics were developed. The flow and the segregation of the S-type binary granular mixtures in a thin rotating horizontal drum were simulated by using the new model. The influences of the rotation speed and the load of the drum on the pattern formation were discussed. The simulation results show that the pattern formation of the S-type binary granular mixtures in the rotating drum can be predicted accurately. As the rotation speed is high, the moon pattern appears,in which the small particles concentrate in a central core and the large particles distribute in the periphery. As the rotation speed is lowered, the petal pattern is found in thin drums, and the number of petals increases as the rotation speed decreases. The process of pattern formations was obtained by the simulation. As the petal pattern forms, the wavy flow of granules in the drum appears. Finally, the necessary condition and mechanisms of the pattern formation in the thin drums are discussed in the paper.

Lowering friction coefficient under low loads by minimizing effects of adhesion force and viscous resistance

This paper deals with the problem of static and dynamic (or kinetic) friction, namely the coefficients of friction for the two states. The coefficient of static friction is well known, and its theory and practice are commonly accepted by the academia and the industry. The coefficient of kinetic friction, however, has not fully been understood. The popular theory for the kinetic friction is that the coefficient of dynamic friction is smaller than the coefficient of static friction, by comparison of the forces applied in the two states. After studying the characteristics of the coefficient of friction, it is found that the comparison is not appropriate, because the inertial force was excluded. The new discovery in the paper is that coefficients of static friction and dynamic friction are identical. Wheel “locked” in wheel braking is further used to prove the conclusion. The key to cause confusions between the two coefficients of friction is the inertial force. In the measurement of the coefficient of static friction, the inertial force is initiated as soon as the testing object starts to move. Therefore, there are two forces acting against the movement of the object, the frictional force and the inertial force. But in the measurement of the coefficient of kinetic friction, no inertial force is involved because velocity must be kept constant.

One of the main problems in obtaining long life in telephone switching equipment is the wear caused by large momentary forces. In order to investigate this problem several new techniques have been devised for measuring normal and tangential forces and for producing and controlling normal and tangential motions for wear studies. The forces are measured by inserting small barium titanate ceramics between the points of application of the forces and observing the voltages generated on a cathode ray oscillograph. Barium titanate ceramic is about fifty times as sensitive as quartz and has a high enough dielectric constant so that with conventional amplifiers time intervals as long as a tenth second can be measured. Both normal and tangential forces can be measured by using properly poled ceramics. By using weights on top of the crystals, normal and tangential accelerations can be measured. With these ceramics, forces have been measured for relays and for frictional sliding of a wire over a plastic. By employing a barium titanate transducer capable of a large amplitude at 18,000 cycles it has been shown that no wear occurs for normal forces, and that all the wear observed in a relay is due to tangential sliding. Quantitative measurements of wear have been made for a variety of materials, and it has been shown that materials with a large elastic strain limit will wear better than materials with a small elastic strain limit even though the latter have a higher yield stress; materials such as plastics and rubber will outwear materials such as metals or glasses. As the length of slide is reduced there is a threshold of motion for which there is no gross slide and very little wear. This region is determined by the condition that the tangential force is smaller than the normal force times the coefficient of friction. Theoretical and experimental results are obtained for this region and an equation is derived which determines the possible displacement without gross slide. The stress strain curve occurs in the

Normal and tangential forces coexist between rough surfaces in engineering components under most operating conditions. Accurate measurement of contact forces (both normal and tangential forces) on rough surfaces is critical for the safety and stability of engineering equipment, as interfaces are typically discontinuous regions within mechanical systems. However, existing contact mechanics and electrical contact models mostly neglect tangential force effects, hindering their application to shearing behavior research and precluding the development of a contact force measurement methodology applicable to simultaneous normal and tangential force quantification. Inspired by the yield criterion for material damage, a contact mechanics model was developed that simultaneously accounts for the effects of normal and tangential forces. Then, a new principle of contact forces measurement is developed by correlating the contact resistance with the real contact area, which enables the simultaneous measurement of normal and tangential forces between rough surfaces based on the single contact resistance under steady-state contact conditions. By proposing a “static friction surface”, the static and dynamic friction stage is effectively differentiated, and the reasons for the sudden drop in friction force and the sudden increase in contact resistance during the static and dynamic transition stages are given. This work proposes a novel explanation for the friction mechanism in terms of mechanical deformation and electrical resistance changes.

The tire is a component of the vehicle in direct contact with the pavement surface. The friction coefficient of tire and road surface is inseparable from the driving safety, mobility and economy of the vehicle. This paper presents a method based on code and formula simulation to estimate the effect of friction between each tire and the road and the driving state of the whole vehicle. By classifying different road conditions, different tires and different speeds, using the Magic formula, rolling friction torque and substituting a series of vehicle basic data, the corresponding tire-road friction coefficient is obtained. All basic vehicle parameters and tire parameters are obtained from the manufacturer's official website, instructions and other channels. Then the linear images are processed by Kalman filter. These images show that different tire types, different road conditions and different driving habits will affect the friction coefficient. The feasibility of the conclusion is verified by simulation in Adams car 2020, to put forward suggestions and improved methods for the comprehensive performance of vehicle driving from many aspects.