Friction Force Changes Research Articles

Research on the Friction Force Characteristics for the Double O-ring Seal of the Cylinder under the Small Displacement Condition

In order to obtain a high-precision pneumatic control system, it is necessary to study the friction force of the cylinder. However, few have considered the cylinder's frictional characteristics at small-displacements. This study investigated the influence of different conditions on the cylinder friction characteristics during the process from static to small-displacement of pneumatic double O-ring seal. A set of experimental apparatuses controlled by an electric actuator perform a seal ring small-displacement friction test to achieve the goals. The working principle of sealing rings in different deformation stages is expounded. According to experiments, the sealing ring's friction force in small-displacement movement can be separated into tilt, elastic deformation, pre-sliding, and sliding friction stages. Furthermore, the clearance characteristics between the sealing ring and the piston groove are verified, which decreases with the sealing ring thickness. Finally, the friction displacement characteristics of sealing rings under different pressures and materials during the elastic deformation stage were verified. It can be concluded that when the displacement is between 0.05-0.25mm, the friction of the sealing ring is almost linear with the displacement; when the displacement reaches 0.25mm, with the increase of the displacement, the friction force changes in a similar parabola manner. This study provides a detailed analysis of the friction characteristics of the seal in different stages of small displacement, which plays an important reference role in overcoming cylinder friction and promotes the development of pneumatic systems in the field of accurate position and speed control.

Effect of Ellipsoidal Particle Shape on Tribological Properties of Lubricants Containing Nanoparticles

Adding nanoparticles can significantly improve the tribological properties of lubricants. However, there is a lack of understanding regarding the influence of nanoparticle shape on lubrication performance. In this work, the influence of diamond nanoparticles (DNPs) on the tribological properties of lubricants is investigated through friction experiments. Additionally, the friction characteristics of lubricants regarding ellipsoidal particle shape are investigated using molecular dynamics (MD) simulations. The results show that DNPs can drastically lower the lubricant's friction coefficient μ from 0.21 to 0.117. The shearing process reveals that as the aspect ratio (α) of the nanoparticles approaches 1.0, the friction performance improves, and wear on the wall diminishes. At the same time, the shape of the nanoparticles tends to be spherical. When 0.85 ≤ α ≤ 1.0, rolling is ellipsoidal particles' main form of motion, and the friction force changes according to a periodic sinusoidal law. In the range of 0.80 ≤ α < 0.85, ellipsoidal particles primarily exhibit sliding as the dominant movement mode. As α decreases within this range, the friction force progressively increases. The friction coefficient μ calculated through MD simulation is 0.128, which is consistent with the experimental data.

Phonon energy dissipation in friction between black phosphorus layers.

Herein, we employ molecular dynamics simulations to decode the friction properties and phonon energy dissipation between black phosphorus layers. The observations reveal the influence of three factors, temperature, velocity, and normal load, on the friction force of monolayer/bilayer black phosphorus. Specifically, friction is negatively correlated with layer thickness and temperature, and positively correlated with velocity and normal load. The change in friction force is further explained in terms of frictional energy dissipation, and supplemented by the height of potential barriers as well as the number of excited phonons. From the phonon spectrum analysis, the phonon number at the contact interface is found to be higher than that at the non-contact interface. This is due to the larger distance of the contact interface atoms deviate from their equilibrium positions, resulting in higher total energy generated by more intense oscillations, and therefore contributes greater to friction.

A novel self-powered triboelectric sensor for early waring of lubrication failure

In tribology, maintaining good lubrication of friction pairs is an important technical means to reduce wear and failure, which is very important but difficult to monitor the lubrication state of friction pairs. In this paper, when measuring the thickness and shape of the lubricating oil film by the ball-disk elastohydrodynamic oil film measuring instrument, a current amplifier is integrated to measure the electrical signal generated during the friction process. By monitoring the change of lubricating oil film, the change of ball-disk friction force, and the change of triboelectric signal during the friction process in real time, the relationship between the tribological behavior and the triboelectric behavior of the friction pair is explored. The experimental results show that under the conditions of limited oil supply, different rotational speeds and different lubricating oil viscosities, the time of the discharge phenomenon of the steel ball corresponds one-to-one with the time when the friction pair starts to wear under oil-scarce lubrication. The discharge occurs due to the electric charge breaking through the air in the micro-gap of the wear scar. The results demonstrate that the formation of the oil-depleted state has an important influence on the triboelectric process. Based on the relationship between the two, the state of the lubricating oil can be reflected in real time by using the triboelectric signal, which provides a reliable method for the real-time monitoring of the lubrication state.

Experimental study on the feasibility of alternative materials for tilting pad thrust bearings operating in transition to mixed friction

In hydrodynamic bearings traditional bearing alloys: Babbitts and bronzes are most frequently utilized. Polymer sliding layers are sometimes applied as a valuable alternative. Hard diamond-like carbon (DLC) coatings, which are also considered for certain applications may show some advantages, as well. Although material selection is of secondary importance in a full film lubrication regime it becomes important in mixed friction conditions, which is crucial for bearings with frequent starts and stops. Experimental research aimed at studying the performance of fluid film bearings in the specific operating regime, including the transition to mixed friction, is described in the paper. The tests were carried out on four tilting pad bearings of different material compositions: Steel/bronze, DLC/steel, steel/polyether ether ketone (PEEK), and steel/Babbitt. The tests comprised stopping under load and reproduction of the Stribeck curve by decreasing rotational speed to very low values, and observing the changes of friction force during the transition to mixed friction regime. Analysis of the transition conditions and other results showed clear differences between the tested bearings, illustrating the feasibility of less popular material compositions for bearings operating in specific conditions. More specifically, the DLC/steel bearing was demonstrating superior performance, i.e. lower friction, transition to mixed friction occurring at higher load, and more stable performance at start-stop regime over the other tested bearings.

Performance Analysis of Thermal and Surface Roughness Effect of Slider Bearings with Unsteady Fluid Film Lubricant Using Finite Element Method

The streamline upwind Petrov‐Galerkin (SUPG) finite element method was used in this study to investigate the thermal and surface roughness effects on an inclined slider bearing with an unsteady fluid film. One‐dimensional transverse and longitudinal surface roughness models were considered with the supposition that roughness is stochastic and has a Gaussian random distribution. For simplicity of numerical computation, the irregularity caused by the texture of the surface is transformed into a regular domain. The bearing performance of the combined effect is lower than the thermal and surface roughness effects of the one‐dimensional longitudinal surface roughness for all modified Reynolds numbers of nonparallel slider bearings; this means that for nonparallel (w = 0.4) between the surface roughness effect and the combined effect condition, there is a decrease of 13% in load‐carrying capacity performance and a minimal change in friction force, respectively. However, in the case of nonparallel one‐dimensional transverse type slider bearings, the bearing performance of the thermal effect is lower than the combined and surface roughness effects for all modified Reynolds numbers, where between the combined effect and the thermal effect condition, there is a reduction of 19% in load‐carrying capacity performance and 2% in friction force practically for all changed Reynolds values, respectively. Furthermore, the combined effects at various temperatures have been investigated. As a result, in both longitudinal and transverse models, in the case of the pad temperature being lower than the slider, the load‐carrying capacity performance is higher than in other cases for nonparallel slider bearings, whereas when the slider temperature is lower than the pad temperature, the drag frictional force is the leading one in both models. In general, considering surface texture and inertial effects will increase the performance of a slider. The results obtained are displayed using figures and tables.

Research of influencing factors on tripping speed of double plungers turbine overspeed protector

The over-speed protection mechanism is very important for the safe operation of the steam turbine, but in actual production, the tripping speed often fluctuates and deviates from the set value, resulting in a decrease in the reliability of the unit operation. In this paper, the factors that affect the tripping speed of double plungers turbine overspeed protection mechanism are analysed, the mechanism of mechanical vibration and friction that cause the tripping speed to fluctuate is explored through theoretical calculation and simulation analysis, and the change of spring dynamic stiffness by using the dynamic stiffness matrix method and finite element simulation is analysed. The change of friction force under different contact modes is calculated by using the L-N contact force model and the modified Coulomb friction model, and the change of tripping speed under non-ideal friction conditions is explored through dynamic simulation.

Intelligent Detection of Robotic Arm Roller Wear Based on Combined DWAE and GRUNN Models

Abstract Long time and high intensity work makes the wear of the roller of the robotic arm increase gradually, which will affect the performance and service life if not regularly overhauled. In this paper, the sensor is used to obtain roller data from the mechanical arm, and the roller wear characteristics are extracted by combining them with the LSTM model. Based on the autoencoder, the wavelet function is introduced to establish a deep wavelet autoencoder, and the DWAE-GRUNN model is established by combining the gated recurrent unit neural network, which is used for the intelligent detection of the wear of the roller of the robotic arm. The model’s classification performance can be improved by using the CTC loss function, and the parameters can be optimized using the sparrow search algorithm. For the application of the DWAE-GRUNN model in the intelligent detection of roller wear of mechanical arms, this paper validates the model based on the aspects of performance, coefficient selection, and detection results. It is found that the average correct detection rate of the model in this paper is 95.97%, and the optimal accuracy is obtained when the weight attenuation coefficient of the DWAE structure is 0.005. The friction force changes inversely with the degree of smoothness after 3.1h of the detection time of the robotic arm roller, and the stiffness, cumulative large abrasive grains, and cumulative small abrasive grains also show significant changes. Using the DWAE-GRUNN model, changes in the wear of the robotic arm roller can be obtained, providing data support for timely maintenance.

Molecular dynamics study on friction of high-entropy alloy FeNiCrCoCu

High-entropy alloy (HEA) is composed of five or more metal elements. It has excellent mechanical properties, tribological properties, corrosion resistance, high temperature resistance and other properties. The friction behavior of FeNiCrCoCu High-entropy alloy was studied using molecular dynamics (MD) simulation method at the nanometer level. The influence of friction depth, temperature, sliding speed and cobalt content on the frictional properties of FeNiCrCoCu High-entropy alloy was studied with the help of LAMMPS and OVITO software. The main research results are as follows: (1) The change in friction force will first go through a growth period, and then gradually stabilize. The fluctuation of its value is due to the release of stress energy caused by dislocations and the accumulation of wear debris. (2) As the friction depth increases, the plowing phenomenon and the accumulation of debris become more obvious and plastic deformation increases. (3) Temperature has no significant effect on the magnitude of friction force and the morphology of the alloy substrate surface. (4) There is an insignificant positive correlation between sliding speed and friction force and sliding speed does not have a significant impact on the amount of debris. (5) With the increase of the content of cobalt, the hardness and friction force of FeNiCrCoCu High-entropy alloy increase significantly at 600 K while the amount of wear debris decreases.

Friction Properties of Crystalline Cellulose Sliding on Chromium under Water Lubrication Based on Molecular Dynamics Simulations.

This work studies the friction and wear behaviors of chromium (hard material) and crystalline cellulose (soft material) under water lubrication considering the loading and sliding velocity on friction force, temperature of contact interfaces, and worn atoms from the atomic view. The change of friction force with sliding velocity is greater than that with loading, and it is easier to obtain a stable friction at high velocity. The average friction force in the stabilization gradually increases with loading and velocity, and the growth rate decreases with loading, while it increases with velocity. The temperature of contact interfaces at the beginning of sliding changes rapidly and gradually becomes stable. The temperature at the stabilization increases distinctly with velocity, while it does not change much with loading. Both the loading and sliding velocity have an important influence on the wear of soft material; it is noticed that the amount of worn atoms increases close to exponentially with velocity and linearly with loading. However, the wear of hard material changes less with increasing loading and sliding velocity.

The effect of contact compliance of sliding pair on friction force reduction at longitudinal tangential vibrations

The main purpose of this work was to experimentally test the impact of modification to the tangential contact stiffness of the friction pair, caused by changing the kind of material, roughness of the contact surfaces and surface pressures, on the level of friction force reduction in the sliding motion, under the influence of high-frequency longitudinal tangential vibrations introduced into the contact area. The tests were carried out on an original test stand for three kinds of friction pair materials, such as: steel C45, cast iron GGG40 and polytetrafluoroethylene PTFE – Teflon, working in homogeneous connections: steel – steel, cast iron – cast iron and Teflon – Teflon and in mixed connections: steel – Teflon, steel – cast iron and cast iron – Teflon. For each friction pair, at defined values of normal pressures, the compliance characteristics of the contact in the tangential direction were determined. On their basis, as a function of normal pressures, values of the tangential contact stiffness coefficient were calculated. Then, also as a function of normal pressures, experimental tests were carried out on changes in the friction force in sliding motion occurring in the contact under the influence of longitudinal tangential vibrations. The tests were carried out for different speeds of the drive, with fixed vibration parameters, such as amplitude and frequency. On the basis of obtained results of the dependence of contact compliance on the kind of material of the friction pair, contact surface roughness and surface pressures, as well as on the dependence of friction force changes under the influence of tangential vibrations on the same factors, the relationship between the level of friction force reduction under the influence of these vibrations and contact compliance was examined.

Contribution of hardness and work hardening to the wear resistance of Pt-based metallic surfaces revealed by nanoscale reciprocating sliding

The contribution of hardness and work hardening to the wear resistance of Pt-based metallic surfaces under reciprocating sliding contact have been investigated by atomic force microscopy. The atomically flat surfaces of the Pt-BMG and Pt (111) enable the sliding friction to be a single-asperity contact. It was found that at low loads where the sliding contact was primarily elastic, the Pt(111) produced a larger adhesion than the Pt-BMG, which was ascribed to the larger mixing enthalpy between counterbodies. When the sliding contact entered into wear regime at high loads, the Pt-BMG that displayed a high hardness nearly-six times of Pt (111) was expected to have a higher wear resistance according to the Archard’s law, yet the Pt(111) actually performed better. We further explore that the work hardening mechanism associated with dislocated-mediated deformation contributes to the high wear resistance of Pt(111), as corroborated by a significant friction force decrease within scratched region on Pt(111) surface. However, such a hardening mechanism is not expected to operate in Pt-BMG due to the lack of mobile structural defects like dislocations, as confirmed by the little change in friction force between scratched and unscratched regions.

Barkas effect in strongly magnetized plasmas

Strongly magnetized plasmas, which are characterized by the particle gyrofrequency exceeding the plasma frequency, exhibit novel transport properties. For example, recent work showed that the friction force on a test charge moving through a strongly magnetized plasma not only consists of the typical stopping power component but also includes components perpendicular to the test charge's velocity. However, these studies only considered test charges that have the same sign as the charge of the plasma particles. Here, we extend these calculations to the case of charges with opposite signs (such as an ion interacting with strongly magnetized electrons). This is done with both a novel generalized Boltzmann kinetic theory and molecular dynamics simulations. It is found that the friction force changes dramatically depending on the sign of the interacting charges. Likewise, the stopping power component for oppositely charged particles decreases in magnitude compared with like-charged particles, and the perpendicular components increase in magnitude. Moreover, the difference between the two cases increases as the gyrofrequency becomes larger compared with the plasma frequency. The electrical resistivity is calculated from the friction force, where it is found that strong magnetization in conjunction with oppositely charged interactions significantly decreases the parallel resistivity and increases the perpendicular resistivity.

Nonlinear characteristics of the driving model of the coaxial integrated macro–micro composite actuator

Abstract. Nonlinearity is one of the important factors affecting the positioning accuracy of the macro–micro composite actuator. To improve the positioning accuracy of the driving model of the macro–micro composite actuator, this paper combines the research phenomenon of the nonlinear characteristics of the voice coil motor to model the nonlinear factors that affect the macro-moving part of the macro–micro composite actuator. Firstly, based on analyzing its structure and working principle, the variation law of the magnetic field intensity at the working air gap of the macro-motion part is analyzed by the finite element method, and the driving force model of the macro-motion part is established. Secondly, through the magnetic field simulation analysis, there is a magnetization phenomenon in the mover part, and the static friction model is established. Then, the experimental data are acquired and processed by building the experimental test platform of the actuator, and the variation model of the electromechanical time constant with the macro-motion displacement is established. Then, combined with the Stribeck model and the static friction model, the kinetic model of the macro-motion part is established. Finally, using the least square method identify the parameter model, the results are compared with the experiment. The results show that the magnetic field distribution at the working air gap of the macro-motion part of the macro–micro composite actuator is relatively uniform, but it is related to the macro-motion displacement and the macro-motion coil current. When the macro-motion part of the macro-micro composite actuator starts, the friction model can approximately reflect the change of friction force, the kinetic model of the macro-motion part can reflect the dynamic characteristics of the macro-motion part, and the matching degree is 92.97 %. The research results lay a theoretical and technical foundation for the development of a high-speed and large-stroke positioning controller of the macro-motion micro composite actuator.

Effect of load on the stick-slip phenomenon and wear behavior of EPDM

Reciprocating friction and wear tests of the EPDM are carried out under various loads, and the composition of groups and compounds of EPDM before and after wear is revealed by FTIR and XRD. Then, the stick-slip behavior and wear resistance of EPDM under various loads are analyzed and investigated by real-time curves of the coefficient of friction, friction force, location and the change of friction force. Finally, the wear mechanism of EPDM under various loads is analyzed by the results of SEM. The results show that the stick-slip phenomenon occurs on the EPDM in different degrees under different loads. Neither the wear nor the change in load leads to the formation of new groups and compounds or the decomposition of existing groups and compounds in EPDM. The coefficient of friction does not change monotonically with increasing load, but tends to increase and then decrease. In addition, although the increase in load leads to increases in the lag time and the intensity of noise generated during the wear process, the rate of increase in the lag time and the intensity of noise slows down with increasing load. Meanwhile, with the increase in load, the number of granular debris changes, and banded debris and Schallamach waves become larger, which results in a change in the wear form between the grinding ball and EPDM.

A New Test Method to Simulate Deep Drawing Phenomena on the Lab Scale

Expedient simulations and numerical modelling of forming processes depend on a good knowledge of the friction at the tool–sheet metal contact. The absolute value of the friction force or relative changes of this force due to changing conditions are vital input for a reliable numerical model. For that reason, a good selection of a laboratory experiment that can measure the friction under forming conditions is an essential step. This work is part of a large European Union project named ASPECT, which evaluates the friction force evolution in sheet metal forming as a result of changes in contact conditions. Simplified tribological lab-scale techniques showed an temperature dependence of friction opposite to what is measured in state-of-the-art macroscopic flat strip drawing tests. To understand and overcome this contradiction, a new method was developed to integrate the deformation aspect into a friction test; this approach assures closer resemblance to the actual forming conditions. The aim is to develop a method that measures the effect of temperature and speed on the resistance to sliding and deformation, and to provide an efficient prescreening and ranking of forming oils.

Nanomechanical tribological characterisation of nanostructured titanium alloy surfaces using AFM: A friction vs velocity study

Medical-grade titanium alloys used for orthopaedic implants are at risk from infections and complications such as wear and tear. We have recently shown that hydrothermally etched (HTE) nanostructures (NS) formed on the Ti6AlV4 alloy surfaces impart enhanced anti-bacterial activity which results in inhibited formation of bacterial biofilm. Although these titanium alloy nanostructures may resist bacterial colonisation, their frictional properties are yet to be understood. Orthopaedic devices are encapsulated by bone and muscle tissue. Contact friction between orthopaedic implant surfaces and these host tissues may trigger inflammation, osteolysis and wear. To address these challenges, we performed simulation of the contact behaviour between a smooth control Ti6Al4V alloy and HTE surfaces against a hardwearing SiO2 sphere using Atomic Force Microscopy (AFM) in Lateral Force Microscopy mode. The friction study was evaluated in both air and liquid environments at high (5 Hz) and low (0.5 Hz) scan velocities. Lower scan velocities demonstrated opposing friction force changes between the two mediums, with friction stabilising at higher velocities. The friction measured on the NS alloy surfaces was reduced by ~20% in air and ~80% in phosphate buffered saline, in comparison to the smooth control surface, displaying a non-linear behaviour of the force applied by the AFM tip. Changes in friction values and cantilever scan velocities on different substrates are discussed with respect to the Stribeck curve. Reduced friction on nanostructured surfaces may improve wear resistance and aid osseointegration.

Investigation of frictional behavior of steel and aluminum at different temperatures

In order to evaluate the performance of the press line, it is essential to investigate the frictional behavior and properties of materials under production temperatures. In servo press line production conditions, the tooling temperature can reach 45-55 °C after around 150 stampings. In this investigation, a clamping fixture with drawbead and flat plate inserts was employed to conduct the friction tests at room temperature and an elevated temperature (54 °C). Three mild steels and two aluminum grades (5000 and 6000 series) were used in the tests. The results from drawbead tests showed that friction force on the two aluminum materials increased by 10% at 54 °C compared to that at room temperature. However, for the 3 steels the change of friction force was negligible from 22 °C to 54 °C. This implies that for exposed panel applications, the selected steel grades might have a more controlled sliding behavior potentially resulting in better control of formability than aluminum grades for the range of temperatures observed during production stamping.

Periodic self-organising frictional process of granular cereal material

The paper analyses the phenomenon of friction of granular cereal materials, at very low sliding velocities. Wheat was used as a test material. Tests were carried out for sliding velocities (0.05, 0.1, 0.2, 0.5, 1, 5, 10, 20, 50 [mm/min]) and loads (14.22, 26.00, 43.65, 65.34 [N]). At low slip velocities, a regular periodic change of the friction force (stick-slip) is observed, which disappears as the velocity increases. For each load value, velocity values were determined for which this phenomenon disappears. This confirmed the significant influence of not only velocity but also load on the nature of periodic changes the friction force. Three characteristic phases of friction force changes were identified (I) regular periodic frictional process; (II) no-regular periodic frictional process; (III) no periodic frictional process. In addition, for phase (I) the profile of periodicity was described by mean amplitude (Ap) and mean periodical distance (Pf) of friction profile. The correlation between Ap, Pf with load and velocity was confirmed.

Ortopedik Matkaplar İçin Bozucu Gözlemci Tabanlı Kemik Doku Değişim Tahmin Yaklaşımı Benzetimi

Orthopedic drills are currently used for various operations in surgical fields such as orthopedics, ear, nose, and throat surgery. The path that orthopedic drills travel through the tissue is controlled manually by surgeons, and manual control leads to the risk of damaging areas such as nerves and tissues. In our study, an innovative approach is presented against existing drill designs and breakthrough detection problems. In the proposed model, the change in the load torque and the change in friction force caused by the tissue change in the drilling path are considered as a disturbance effect, and a disturbance observer has been developed that allows these disturbances to be observed. Observation of the disturbance effects allows the perception of the hardness of tissue change during drilling since it gives the change of load torque changes and friction coefficient, which cannot be measured under normal operation. The performance of the proposed approach has been proven by simulation study.