Change In Friction Coefficient Research Articles

The friction and wear properties of steel wire rope sliding against itself under impact load

Friction and impact between steel wire rope always exist in multi-layer winding hoist during the winding-in process, in particular for an ultra-deep coal mine. To understand the friction and wear mechanisms of wire rope among the layers in the winding hoist, a series of sliding friction experiments were carried out using a self-made friction test rig. The results show that the coefficient of friction (COF) of the wire rope changes little with increasing load and stabilizes at approximately 0.73, but decreases with the sliding velocity under dry-friction condition. However, under lubrication condition, there is almost no effect of the contact load and sliding velocity on the COF, which stabilizes at approximately 0.35. Additionally, the temperature rise is concentrated at the contact area, and it increases with the load and the sliding velocity. The maximum temperature rise with the lubrication is much lower, approximately 10 °C, than that under the condition of dry-friction, which is approximately 103 °C. Furthermore, the maximum of the COF under the impact load is significantly lower than that for the stable contact friction. With the impact and sliding velocities increase, the maximum COF under the impact load experiences a slight increase and reaches a maximum value of approximately 0.36. As the impact load increases, the COF changes little, but the impact process occurs more than once.

Tactile Texture of Cosmetic Sponges and Their Friction Behavior under Accelerated Movement.

We evaluated the friction properties of five cosmetic sponges on artificial skin using sinusoidal motion-friction evaluation system. No significant difference was observed in the pleasant score of the five sponges when these sponges were rubbed on the skin surface. The sponges were classified into three groups based on their tactile feel. Their characteristic tactile textures were moist-soft-slippery, moist-dry-rough, and moist feels. The slippery feel was found to depend on the thickness of the sponge's cell wall, its surface tension, and the change in friction coefficient in the dynamic friction process. These findings are useful in the design of cosmetic sponges.

Design of Model-based Controller with Disturbance Estimation in Steer-by-wire System

The steer-by-wire system is a next generation steering control technology that has been actively studied because it has many advantages such as fast response, space efficiency due to removal of redundant mechanical elements, and high connectivity with vehicle chassis control, such as active steering. Steer-by-wire system has disturbance composed of tire friction torque and self-aligning torque. These disturbances vary widely due to the weight or friction coefficient change. Therefore, disturbance compensation logic is strongly required to obtain desired performance. This paper proposes model-based controller with disturbance compensation to achieve the robust control performance. Targeted steer-by-wire system is identified through the experiment and system identification method. Moreover, model-based controller is designed using the identified plant model. Disturbance of targeted steer-by-wire is estimated using disturbance observer(DOB), and compensate the estimated disturbance into control input. Experiment of various scenarios are conducted to validate the robust performance of proposed model-based controller.

Friction Characteristics of Synchronization Process Based on Tribo‐Thermodynamics

In order to improve the shift control accuracy and shift quality, the temperature and friction coefficient changing regularities of a friction cone during the synchronization process were investigated. The thermal‐structural coupling model was established through tribo‐thermodynamic analysis. The relevant experiment was carried out as well. The results show that the error between the experimental and simulated results is within 3%. Besides, the maximum temperature of the synchronous ring friction surface increases 1.8°C for every additional 50 N of shift force, while increases 1.1°C for every additional 200 r/min shift speed difference. Moreover, the friction coefficient declines rapidly first and then tends to be stable slowly during the synchronization process. The result of friction coefficient changing regularity lays a good theoretical basis for establishing an effective friction coefficient compensation control strategy.

Study on frictional behavior of carbon nanotube thin films with respect to surface condition

In this work, tribological characteristics of thin films composed of entangled carbon nanotubes (CNTs) were investigated. The surface roughness of CNT thin films fabricated via a dip-coating process was controlled by squeezing during the process with an applied normal force ranging from 0 to 5 kgf. Raman spectra and scanning electron microscopy (SEM) images of the thin films were obtained to estimate the influence of the squeezing process on the crystallinity of the CNTs. The analysis revealed that squeezing could reduce surface roughness, while preserving the crystallinity of the CNTs. Moreover, the surface energy of the cover glass used to press the CNT thin film was found to be the critical factor controlling surface roughness. A micro-tribometer and macro-tribometer were used to assess the tribological characteristics of the CNT thin film. The results of the tribotest exhibited a correlation between the friction coefficient and surface roughness. Dramatic changes in friction coefficient could be observed in the micro-tribotest, while changes in friction coefficient in the macro-tribotest were not significant.

Skin friction coefficient change on cement grouts for micropiles due to sulfate attack

This paper presents a study of skin friction change of cement pastes used for micropiles as a geotechnical foundation when grout surface is affected by sulfate attack. In this research skin friction coefficient between cement paste – cement paste was measured, studying change in friction depending on the initial roughness of samples. Tests were performed after 3 and 6 months of immersion in a 15% Na2SO4 solution. Results show that sulfate attack increases skin friction coefficient for both surface finishes, concluding that this attack does not have a negative effect on friction in the experimental conditions of this work.

Experimental investigation of friction noise on lubricated contact

In order to remove friction noise, a lubricant is normally applied on the friction surface either after cleansing the contact surface or without any surface treatment. As the friction continues, the lubrication performance deteriorates and the friction noise can reoccur in the both cases, but the cause of friction noise may be different. This study originally investigates the mechanism of friction noise under a lubricant on either the clean or contaminated surface. During the friction noise test, the vibration and sound pressure, the changes in friction coefficient and the characteristics of the contact surfaces are measured for the two lubrication scenarios. Particularly, the surface image and chemical state on the contact area are measured by SEM/EDS analysis in sequence. The results show that friction noise under the lubrication on the clean surface is induced by the reduction of the lubricant causing the increase of friction coefficient. For the lubrication on the contaminated surface by wear debris, the lubricant is mixed and contaminated with wear debris, and then friction noise eventually occurs with the negative slope of the friction-velocity curve in the absence of the increase of friction coefficient.

Impact of mechanism vibration characteristics by joint clearance and optimization design of its multi-objective robustness

Joint clearances and friction characteristics significantly influence the mechanism vibration characteristics; for example: as for joint clearances, the shaft and bearing of its clearance joint collide to bring about the dynamic normal contact force and tangential coulomb friction force while the mechanism works; thus, the whole system may vibrate; moreover, the mechanism is under contact-impact with impact force constraint from free movement under action of the above dynamic forces; in addition, the mechanism topology structure also changes. The constraint relationship between joints may be established by a repeated complex nonlinear dynamic process (idle stroke - contact-impact - elastic compression - rebound – impact relief - idle stroke movement - contact-impact). Analysis of vibration characteristics of joint parts is still a challenging open task by far. The dynamic equations for any mechanism with clearance is often a set of strong coupling, high-dimensional and complex time-varying nonlinear differential equations which are solved very difficultly. Moreover, complicated chaotic motions very sensitive to initial values in impact and vibration due to clearance let high-precision simulation and prediction of their dynamic behaviors be more difficult; on the other hand, their subsequent wearing necessarily leads to some certain fluctuation of structure clearance parameters, which acts as one primary factor for vibration of the mechanical system. A dynamic model was established to the device for opening the deepwater robot cabin door with joint clearance by utilizing the finite element method and analysis was carried out to its vibration characteristics in this study. Moreover, its response model was carried out by utilizing the DOE method and then the robust optimization design was performed to sizes of the joint clearance and the friction coefficient change range so that the optimization design results may be regarded as reference data for selecting bearings and controlling manufacturing process parameters for the opening mechanism. Several optimization objectives such as x/y/z accelerations for various measuring points and dynamic reaction forces of mounting brackets, and a few constraints including manufacturing process were taken into account in the optimization models, which were solved by utilizing the multi-objective genetic algorithm (NSGA-II). The vibration characteristics of the optimized opening mechanism are superior to those of the original design. In addition, the numerical forecast results are in good agreement with the test results of the prototype.

Experimental dynamic response of spherical friction-based isolation devices

ABSTRACTThis article presents a summary of the experimental dynamic response of curved surface sliders as resulting from more than 1000 dynamic tests on about 60 different types of devices performed at the laboratory of the EUCENTRE foundation. Two different kinds of low-friction sliding materials have been employed in the devices, derived from polyamide (PA), or polyethylene (PE) materials.The rate of change of the dynamic friction coefficient as a function of sliding velocity and contact pressure is assessed and the transition phase between dynamic and static friction, with the consequent possible evidence of static/stick-slip phenomena, has been carefully considered.

궤도상 국부적인 위치에서의 차륜레일 마찰계수 변화가 차량 주행안전성에 미치는 영향 해석

궤도상 국부적인 위치에서의 차륜레일 마찰계수 변화가 차량 주행안전성에 미치는 영향 해석

Changes in frictional coefficient with increased tendon surface tear—An experimental animal model

AimSurface tribological properties of a tendon in terms of coefficient of friction and lubrication mechanism are expected to change with the progression of surface tears which can affect the optimal function of the tendon. This study investigated whether coefficient of friction proportionally increases with the progression of a surface tear in a bovine tendon model. MethodsThe study was performed using a pin-on-glass tribometer and bovine tendon samples (n=16) divided into 4 groups. One group of tendons had no surface tears and thus served as a control, whilst the other 3 groups comprised tendons with increasing severity of artificially-induced surface tears. The coefficient of friction and the lubrication mechanism of the four groups of samples were investigated, calculated and compared. ResultsStatistical analysis showed significant change in coefficient of friction between the control group and the group with minimal tear (p<0.05) while no difference noted between the groups of moderate to severe tear suggesting that the coefficient of friction increases initially with appearance of surface tears, though further progression to a significant tear do not cause a further increase in the frictional coefficient. There was no change in the lubrication mechanism between the groups. ConclusionThis finding appears to contradict the speculation that the frictional coefficient continues to increase with an increase in surface tear severity. The finding has not been reported before and requires validation in future with testing in human tissue.

THE ANALYSIS OF THE INFLUENCE OF GAMMA IRRIADIATED POLYSULFONES ON THE STATIC FRICTION COEFFICIENT

The paper presents the results of studies on the effects of gamma irradiation on the static friction coefficient of thermoplastic polymer – polysulfone. These polar polymers belong to the group of amorphous thermoplastics and are widely used for various applications, e.g., automotive and electronic industries (dielectrics in capacitors), waste water recovery, medical uses (hemodialysis membranes), requiring autoclave, and steam sterilization. Polysufones are known for their toughness and stability at high temperatures. The aim of this study is to analysed changes in the static coefficient of friction in association with a contact pressure (in the range 0.2 – 0.8 MPa) depending on the ionizing radiation dose of PSU (in the range 50-150 kGy). Additionally, microhardness, and wear intensity were measured, because tribological properties of polymers as well as mechanical properties that influence their durability and applications. The studies confirmed that the static coefficient of friction increases with an increase in contact pressure (in the test range). The research has shown that mechanical (microhardness) and tribological (static coefficient of friction and tribological wear) improve as the radiation dose of irradiated material increase. Moreover, the tribological wear increases with increasing the sliding velocity. This gamma irradiated polymer is characterized by higher microhardness, a static coefficient of friction, and a higher wear rate compared to PSU in the initial state, because of changes in structure. It requires further research.

The effect of space irradiation on the lubricating performance of perfluoropolyether greases in simulated space environment

AbstractIn this paper, 2 kinds of commercial perfluoropolyether (PFPE) greases were coated on the polyimide (PI) blocks, which were placed within simulated space environment including atomic oxygen (AO), proton (Pr), ultraviolet (UV), and electron (El) irradiations, and then the tribological performance has been investigated with a ball‐on‐disc tribometer. Results indicated that the MoS2‐grease showed better lubrication performance than the PTFE‐grease. The changes in infrared spectroscopy induced by Pr and El irradiations were more obvious than that by AO and UV irradiations. Results of energy dispersive X‐ray spectroscopy indicated that Pr and El irradiations caused carbonation of greases, and AO and UV irradiations induced oxidation of greases. Referred to the tribological properties of PI coated with PFPE oil, PI coated with PFPE greases showed minor changes in friction coefficient and wear rate, and the MoS2 additives could significantly improve the lubrication properties of PFPE greases in simulated space environment.

The Application of Vibration Accelerations in the Assessment of Average Friction Coefficient of a Railway Brake Disc

Abstract Due to their wide range of friction characteristics resulting from the application of different friction materials and good heat dissipation conditions, railway disc brakes have long replaced block brakes in many rail vehicles. A block brake still remains in use, however, in low speed cargo trains. The paper presents the assessment of the braking process through the analysis of vibrations generated by the components of the brake system during braking. It presents a possibility of a wider application of vibroacoustic diagnostics (VA), which aside from the assessment of technical conditions (wear of brake pads) also enables the determination of the changes of the average friction coefficient as a function of the braking onset speed. Vibration signals of XYZ were measured and analyzed. The analysis of the results has shown that there is a relation between the values of the point measures and the wear of the brake pads.

Application Study of Magnetorheological Elastomer to Rolling Friction Control

Magnetorheological elastomers (MREs) are smart materials that have been studied widely for their material properties. The elasticity modulus or hardness of an MRE can be changed when an external magnetic field is applied. In this study, a study of MREs applied to rolling friction control under various external magnetic strengths is conducted. To accomplish this, the rolling friction property of an elastomer on a rigid plate is analyzed. Then, MREs are prepared, and a rolling friction tester is designed to evaluate the changes in the rolling friction coefficient. The results show that the rolling friction coefficient can be changed with different magnetic field strengths. The rolling friction coefficient of the MRE can be controlled by the applied magnetic field, which can be applied to control the slip rate and be adapted to achieve the optimal friction effect in the future.

Turbulence structures in high-speed air flow along a thin cylinder

ABSTRACTTurbulent flow in the axial direction along a cylinder representing a monofilament yarn was reproduced for a relatively wide range of radius Reynolds numbers using direct numerical simulations. In the simulation of the thinnest cylinder, the friction coefficient agreed with a previously published formula. A pair of high- and low-speed streaks was detected around even the thinnest cylinder, whereby it was confirmed that turbulence was sustained according to the analysed turbulence statistics. Even when only a single pair of streaks around the cylinder was detected, the characteristics of the turbulence structures, such as the mean streak spacing based on the viscous length scale, were the same as those in flows over a flat plate. It was found that the friction coefficient changes in a way that maintains the structural characteristics of the flow, consistent with the view that universal characteristics of turbulence structures exist.

An Experimental Study of Chilton–Colburn Analogy Between Turbulent Flow and Convective Heat Transfer of Supercritical Kerosene

In this paper, characteristics of turbulent flow and convective heat transfer of supercritical China RP-3 kerosene in a horizontal straight circular tube are studied experimentally, and the validity of Chilton–Colburn analogy is examined. Using a three-stage heating system, experiments are conducted at a fuel temperature range of 650–800 K, a pressure range of 3–4 MPa, and a Reynolds number range of 1 × 105–3.5 × 105. The Nusselt number and skin friction coefficient are calculated through control volume analysis proposed in this paper. Heat transfer enhancement and deterioration were observed in the experiments as well as the similar change of skin friction coefficient. The present results show that Chilton–Colburn analogy is also valid for turbulent flow and heat transfer of supercritical kerosene in horizontal straight circular tubes.

Axisymmetric mixed convective stagnation-point flow of a nanofluid over a vertical permeable cylinder by Tiwari-Das nanofluid model

In this article, the steady axisymmetric mixed convective stagnation-point flow of an incompressible electrically conducting nanofluid over a vertical permeable circular cylinder in the presence of transverse magnetic field is investigated. The mathematical model has been formulated based on Tiwari-Das nanofluid model. In this study, the water as the base fluid and three different types of nanoparticles; copper, aluminum oxide (alumina) and titanium dioxide (titania) are considered. Using appropriate transformations, the system of partial differential equations is transformed into an ordinary differential system of two equations, which is solved analytically by the well-known homotopy analysis method (HAM) and numerically using the fourth-order Runge–Kutta method with shooting technique. The present analytical and numerical simulations agree closely with the previous studies in the especial cases. The effects of the five key thermophysical parameters governing the flow; the nanoparticle volume fraction (ϕ), the magnetic parameter (M), the wall permeability parameter (Vw), the mixed convection parameter (λ) and the curvature parameter (γ) on dimensionless velocity and temperature distributions, skin friction coefficient and local Nusselt number are presented graphically and discussed in details. Our results demonstrate that, the enhancement of heat transfer is a function of particle concentration, small fraction of metallic particles leading to significant changes in both skin friction coefficient and local Nusselt number. The results illustrate that selecting alumina and copper as the nanoparticle leads to the minimum and maximum amounts of skin friction coefficient value, and also copper and titania nanoparticles have the largest and lowest local Nusselt number. In addition, our computation shows that the curvature parameter has a strong additive effect on the skin friction coefficient and local Nusselt number. Moreover, it is observed that the highest velocity and thermal boundary layer thickness are related to the opposing flow, while the smallest one is for assisting flow.

Effect of moving load due to irregularity in ice sheet floating on water

The present paper is concerned with the stresses produced due to a load moving on the irregular surface of an ice sheet floating on water. The irregularity of the ice medium is of parabolic type, and a rectangular irregularity has also been considered as a special case. The mathematical formulation of this physical problem gives rise to a boundary value problem with the specified boundary conditions. The perturbation method is applied to find the displacement field. Closed-form expressions of the normal and shear stresses developed in the ice medium and semi-infinite water medium due to moving load and irregularity have been derived using the boundary conditions. The variations of dimensionless normal and shear stresses with different depth below the surface are computed for a realistic numerical model and discussed. The same numerical data are used for surface plots to analyze the combined variation of non-dimensional stresses and velocity ratio against depth. From the outcome of the numerical study, the normal and shear stresses developed in both the ice and water media are found to be very sensitive to the changes in frictional coefficient, dimensionless wave number and irregularity factor present in the medium.

Implementation of Theory of Plasticity for Parametric Study on the Relation Between Thickness Change and Central Deflection and Fracture Point Location During Small Punch Test

This parametric study explored the correlation between minimum thickness (t/t0) and central deflection (δ/t0) and change in location of fracture point in small punch test specimens due to change in friction coefficient between ball and specimen. A detailed finite element studies were conducted to investigate the effect of parameters that could influence this correlation. The parameters considered in this study are material hardening, coefficient of friction, and initial thickness of the specimen. The correlation and location of fracture point were independent of a change in the material hardening parameter. Moreover, the coefficient of friction less than 0.2 simulates the location of fracture point below the hemi-spherical ball while fracture point location shifted towards periphery of the ball beyond 0.2 value. However, a change in thickness significantly affected the correlation but not fracture point location.