Increase In Friction Coefficient Research Articles

Study of Wear Resistance of a Radial Bearing Covered by a Polymer Coating with an Axial Groove on a Nonstandard Base Surface

This paper is devoted to study of increasing the wear resistance of a radial plain bearing. The operation of a bearing is considered in the hydrodynamic mode by means of application of an antifriction polymer composite coating with an axial groove and the micropolar properties on a nonstandard bearing surface adapted to the friction conditions of a bearing bush. The effect of pressure and temperature in the turbulent friction mode on the rheological properties of the lubricant is taken into account. Based on the equation for the micropolar fluid flow in a “thin layer” as well as on the dependence of the micropolar lubricant on the pressure and temperature and on the continuity equation, a self-similar solution has been found taking into account the axial groove on the surface of a bearing bush and without taking into account the axial groove. As a result, the velocity and pressure fields in the axial groove and on the surface of a polymer antifriction composite coating have been determined as has the load capacity and friction force, which make it possible to increase the load capacity, reduce the friction coefficient (increase wear resistance), and also increase the duration of the hydrodynamic mode. The results of numerical analysis of theoretical models and experimental evaluation of the suggested design are presented to verify and confirm the efficiency of the models obtained.

Research on tribological behaviour and interfacial characteristic of Polyimide-MoS2 composite under cryogenic-vacuum environment

Tribological behaviour of Polyimide (PI)-MoS2 composite, pure PI, sputtering MoS2 film is investigated under RT-vacuum and cryogenic-vacuum through in-situ methods, i.e., X-ray photoelectron spectrum (XPS), X-Ray Diffraction (XRD), residual gas analyzer (RGA). Cryogenic causes an increase of friction coefficient (friction coefficient) of PI-MoS2 and pure PI, while it is inverse for sputtering MoS2 film. The friction interface is influenced by enriched water under cryogenic, and the possible mechanism is intermolecular hydrogen bonds caused by water restrict the formation of high oriented shear layer. Due to MoS2 film is not as sensitive as PI to moisture, oxidation at friction interface is relaxed because of cryogenic, which leads to a better friction behavior. Cryogenic causes compressive stress at the interface between PI matrix and MoS2 particles, which results in high friction coefficient due to the difficulty in release of the latter and breakage in some regions in where PI covers MoS2. Local cryogenic environment complicates the investigation in which the only purpose is to study the effect of cryogenic-vacuum on tribological properties of some lubricants.

Analytical model and rotational performances of dovetail mortise-tenon connection at the column head of traditional wooden frame

This paper presents an analytical model of dovetail mortise-tenon (DMT) connection at the column head of traditional wooden frame. Firstly, the characteristic of geometric deformations at the tenon is revealed based the geometric model when the tenon rotates clockwise and anticlockwise, and the analytical expressions for these deformations are given. Then, the extension deformations are obtained based the numerical model, these extension deformations at the surface of the mortises are fitted by the two-dimensional functions in two rotational directions. Finally, the analytical model of DMT connection is derived based the stress distribution at the tenon when it rotates in two directions, and the proposed model agrees well with the corresponding numerical model. Moreover, the effect of parameters including geometric dimensions and frictional coefficient on the rotational performance of DMT connection is studied based two models. The results showed that the difference of the two models is magnified as the friction coefficient increases, the resisting moment of the DMT connection is proportional to the cube of height of tenon and the length of tenon. More refined extension deformation analysis of mortise is needed for general expression of the DMT connection, since the extended deformation of the mortise varies as the inclination angle of the side surface of tenon changes.

Tribological properties of graphene/β-Si3N4 whisker reinforced Si3N4 ceramic composites

Exploring ceramic-based self-lubricating materials with low coefficient of friction (COF) has become one of the hot directions to advance the service performance and life of high-end equipment. In this work, the tribological properties of multilayer graphene (MLG)/β-Si3N4 whisker (β-Si3N4w)/Si3N4 ceramics were investigated. The effects of load and linear speed on the dry sliding COF were discussed. The friction-reducing and self-lubricating mechanisms of MLG and β-Si3N4w were deeply analyzed according to the wear morphology and mechanical properties of Si3N4-based ceramics. The friction frequency was proposed to analyze the wear mechanism. Results indicated that MLG and β-Si3N4w led to a breakthrough reduction in COF. At the load of 5–20 N, the COF reached an ultra-low level of 0.04–0.07, which was a further 89.86% lower than the reported studies. The comprehensive enhancement of mechanical properties and the existence of MLG lubricating film were the mainly responsible for the ultra-low COF. The COF of MLG/β-Si3N4w/Si3N4 ceramics raised to 0.24–0.31 at 50–200 mm/s, but it was still 33.88–47.64% lower than that of graphene/Si3N4 ceramics. The increase in COF was attributed to the high wear induced by the raised friction frequency. The furrow wear and adhesive wear were the main wear forms of MLG/β-Si3N4w/Si3N4 ceramics.

Rheology of gyrotactic microorganisms in Jeffrey fluid flow: A stability analysis

Non-Newtonian fluids display fascinating and versatile flow behavior, enabling applications in fields where precise control and manipulation of viscosity are required. This paper presents the rheology of Homann stagnation point flow for a Jeffrey fluid containing gyrotactic microorganisms over a biaxially stretching surface. The system of equations is solved numerically using appropriate similarity transformations and conditions. The boundary conditions are set to maintain a fixed physical environment, and the far field values are defined accordingly. The dual solutions are found and expressed in terms of relevant quantities, and their behavior is analyzed using graphical representations via bvp5c. Stability analysis is conducted as well. The model is extended to study the behavior of Jeffrey nanofluids under the influence of various physical phenomena such as thermophoresis, Brownian motion, Ohmic heating, heat source/sink, radiation, and chemical reaction. The model presented in this paper can help researchers predict and optimize the behavior of such systems for a range of industrial and biomedical applications. It is observed that when the smallest eigenvalue is positive, the disturbance initially decreases, and the flow is stable, otherwise unstable. The stretching/shrinking parameters affect the flow field and boundary layer characteristics, leading to changes in the skin friction forces and an increase in the skin friction coefficient. Moreover, the Peclet number augmented the concentration of microorganisms due to gyrotactic bioconvection for first and second solutions, whereas bioconvective Lewis number shows an opposite trend. The comparison of the present results, as a simplified case, with existing literature demonstrates good agreement.

Theoretical analysis, finite element modeling and experimental investigation of the impact of friction between tube and bending die on the formability of the tube during the free-bending process

In the free-bending process, the tube undergoes bending and deformation due to the action of a guide mechanism and bending die. The plastic deformation zone of the bent tube is less constrained by the die, and the quality of the formed tube is significantly affected by the friction between the tube and the die. To assess the impact of friction between tube and die on the formability of the bent tube, the theoretical modeling that considers the friction coefficient is conducted. Afterward, the free-bending experiments and finite element simulations are performed using Cr12MoV and ceramic bushing. The theoretical and experimental results are compared with those obtained from finite element simulation under different friction conditions to confirm the validity of finite element simulation. The influence of friction on the arc radius, wall thickness variation, and cross-section deformation of the curved tube is explored and discussed. With the increase of friction coefficient, the arc radius decreases gradually, the wall thickness thickens more obviously, and the cross-sectional distortion becomes more serious. Furthermore, the effect of different bushing materials on the surface quality of aluminum alloy and stainless-steel bent tubes is experimentally investigated. Those findings expand our understanding of the influence of tube-die friction on deformation behavior and it is necessary to first determine the friction condition during the actual free-bending forming process.

Study of Wear Resistance of a Radial Bearing Covered by a Polymer Coating with an Axial Groove on a Nonstandard Base Surface

This paper is devoted to study of increasing the wear resistance of a radial plain bearing. The operation of a bearing is considered in the hydrodynamic mode by means of application of an antifriction polymer composite coating with an axial groove and the micropolar properties on a nonstandard bearing surface adapted to the friction conditions of a bearing bush. The effect of pressure and temperature in the turbulent friction mode on the rheological properties of the lubricant is taken into account. Based on the equation for the micropolar fluid flow in a “thin layer” as well as on the dependence of the micropolar lubricant on the pressure and temperature and on the continuity equation, a self-similar solution has been found taking into account the axial groove on the surface of a bearing bush and without taking into account the axial groove. As a result, the velocity and pressure fields in the axial groove and on the surface of a polymer antifriction composite coating have been determined as has the load capacity and friction force, which make it possible to increase the load capacity, reduce the friction coefficient (increase wear resistance), and also increase the duration of the hydrodynamic mode. The results of numerical analysis of theoretical models and experimental evaluation of the suggested design are presented to verify and confirm the efficiency of the models obtained.

Simulation study and performance analysis of free piston linear generator (FPLG) used for ORC system

Due to advantage of low friction loss, simple structure and good sealing, free piston linear generator (FPLG) presents great application potential in ORC system. In this study, the FPLG simulation model was built using GT Suite and MATLAB/Simulink, and the model accuracy was verified through comparison with experimental data and error analysis. The influence of FPLG operation parameters, model parameters and full consideration of friction and EV characteristics on FPLG performance were studied. All the relative errors are within 10%, namely, the FPLG model has high reliability. Each indicator varies significantly with intake pressure, but relatively weakly with intake temperature. There is an optimal external load for maximum power output, and an optimal pipeline diameter for maximum velocity and average power output. As friction coefficient increases, both velocity and power output increase first and then decrease. When friction coefficient is 1200 N-s/m, average power output and velocity reach the maximum value of 102 W and 0.83 m/s, respectively. The velocity gradually decreases with the increasing flux linkage, while electromagnetic force and power output show a increasing trend. The research results can provide reference significance for optimization of FPLG and provide guidance for the application in ORC system.

Tribological and thermomechanical evaluation of polypropylene nanocomposites containing different dimensional structures of carbon and ceramic nanoparticles

ABSTRACT This study describes the development of PP nanocomposites using hydrothermally assembled carbon nanotubes (CNTs)/barium titanium (BT) (denoted as BTC) and graphene nanosheets (GNs)/boron nitride (BN) (denoted as BNG) nanoparticles. The PP nanocomposites were fabricated via the development of a masterbatch using polypropylene maleic anhydride (PPMA), followed by diluting with pure PP via melt compounding. The wear resistance and thermomechanical properties of the nanocomposites exhibited a substantial improvement, where about 96.8% increase in wear resistance and low coefficient of friction were recorded. While about 230% increase in glass transition temperature was measured with the nanocomposites relative to the pure PP. The developed nanocomposites have potential applications in automobile and other machine components where high wear resistance and thermal-mechanical properties are required.

Immature bovine cartilage wear is due to fatigue failure from repetitive compressive forces and not reciprocating frictional forces

Wear of articular cartilage is not well understood. We hypothesize that cartilage wears due to fatigue failure in repetitive compression instead of reciprocating friction. This study compares reciprocating sliding of immature bovine articular cartilage against glass in two testing configurations: (1) a stationary contact area configuration (SCA), which results in static compression, interstitial fluid depressurization, and increasing friction coefficient during reciprocating sliding, and (2) a migrating contact area configuration (MCA), which maintains pressurization and low friction while producing repetitive compressive loading in addition to reciprocating sliding. Contact pressure, sliding duration, and sliding distance were controlled to be similar between test groups. SCA tests exhibited an average friction coefficient of μ=0.084±0.032, while MCA tests exhibited a lower average friction coefficient of μ=0.020±0.008 (p<10-4). Despite the lower friction, MCA cartilage samples exhibited clear surface damage with a significantly greater average surface deviation from a fitted plane after wear testing (Rq=0.125±0.095 mm) than cartilage samples slid in a SCA configuration (Rq=0.044±0.017 mm, p=0.002), which showed minimal signs of wear. Polarized light microscopy confirmed that delamination damage occurred between the superficial and middle zones of the articular cartilage in MCA samples. The greatest wear was observed in the group with lowest friction coefficient, subjected to cyclical instead of static compression, implying that friction is not the primary driver of cartilage wear. Delamination between superficial and middle zones implies the main mode of wear is fatigue failure under cyclical compression, not fatigue or abrasion due to reciprocating frictional sliding.

The Effect of Clamping Force and Friction Coefficient on The Clamping Clamp

In order to study the influence of clamping force and friction coefficient on the stress distribution of drill pipe joint during the buckling process, the nonlinear contact problem and elastoplastic mechanical properties of Φ139.7mm × 9.17mm drill pipe were simulated by finite element analysis method in this paper, and the stress distribution and size of drill pipe joint during the buckling process were obtained. And the effect of clamping force and friction coefficient on the joint of drill pipe. It is found that the stress of drill pipe joint is mainly concentrated in the contact position of drill pipe and the stress value of drill pipe joint shows a trend of increasing. When the friction coefficient is 0.15 and the clamping force is 600KN, although there is stress concentration in the contact position between the clamp teeth and the drill pipe joint, it does not exceed the yield limit of the drill pipe joint, and no plastic deformation occurs. Through the simulation calculation, it is found that the maximum clamping force and the maximum torque are 1200KN and 81.9KN.m respectively. When the torque is fixed, the change of friction coefficient has a great influence on the maximum clamping force of drill pipe joint. With the increase of friction coefficient, the maximum clamping force of drill pipe joint decreases continuously, and the friction coefficient is inversely proportional to the maximum clamping force. The research in this paper enriches the understanding of the buckling process of punching pliers and provides a reference for the rational buckling of pipe string.

Atomic simulation for the effect of nano-cutting parameters on the 3D surface morphology of polycrystalline γ-TiAl alloy

γ-TiAl alloy is one of the most potentially lightweight and high-temperature structural materials, and its machined surface quality has a significant effect on member service performance. Despite the extensive research on plastic removal and defect evolution under different cutting parameters, the forming mechanism of surface topography is not perfect under different cutting parameters. It is necessary to study the variation law of surface topography under the influence of different cutting parameters from the atomic scale. To this end, the influence of cutting depths and cutting speeds on the machined surface topography is investigated during nano-cutting of polycrystalline γ-TiAl alloys based on molecular dynamics simulation methods, and the effect of defective grain boundaries on cutting force fluctuations is analyzed. The results show that the effect of grain boundary on material deformation and dislocation obstruction is the main reason for the peak cutting force; with the increase of cutting depth, the average cutting force and friction coefficient increase, and both Sa and Sq show an increasing trend, which is the result of the joint action of plowing effect and grain boundary distribution; Sa and Sq show a decreasing and then increasing trend with the increase of cutting speed, and the critical cutting speed is 200 m s−1. This indicates that a smaller cutting depth and an appropriately higher cutting speed can effectively improve the surface quality of the polycrystalline γ-TiAl alloy, and optimize its nano-cutting process.

Using the improved inner slider to enhance overturning resistance of DFPB-isolated structure subjected to poundings

The overturning resistance of structures isolated by double friction pendulum bearing (DFPB) would be significantly reduced due to the presence of pounding. To this end, an improved inner slider (IIS) is introduced to enhance the overturning resistance of the DFPB-isolated structure when it is subjected to poundings. Numerical simulations were conducted to investigate the performance of IIS in reducing the potential overturning risk of isolated structure as well as the seismic responses. Influences of displacement ratio, friction coefficient ratio and radius ratio on coefficient of overturning resistance of the structures isolated by DFPB with IIS were also evaluated though parametric studies. The pounding force and its transmission to the superstructure can be significantly mitigated by IIS, and the overturning resistance performance of structures isolated by DFPB with IIS is superior to those isolated by DFPB with traditional inner slider. The threat of overturning for isolated structures is generally greater with lower displacement ratios. Structures equipped with IIS in DFPB experience a decrease in their coefficient of overturning resistance as the friction coefficient increases, and the coefficient of overturning resistance first increases and then decreases with the increase in radius ratio.

Entropy generation due to nanofluid flow in porous media over radiative permeable exponentially surface with nanoparticle aggregation effect

In recent years, energy scarcity has emerged as a serious problem for manufacturing since most of the power produced is lost as heat during transportation. Due to the irreversible nature of heat transfer processes, it is crucial to minimize the development of entropy during nanofluid flow and heat transmission. Therefore, the purpose of this study is to inquire entropy generation on viscous TiO2−C2H6O2 nanofluid through a permeable exponentially surface with porous media and effect that nanoparticle aggregation with thermal radiation, mixed convective stagnation point flow. The controlling partial differential equations were simplified by using an appropriate similarity transformation, resulting in a set of ordinary differential equations. After that, we used Mathematica's shooting technique and fourth order Runge-Kutta integration to get a numerical answer to these equations. The current study showed that increasing the volume percentage of nanoparticles, the porosity of the nanofluid, the mass suction, and the mixed convection parameters all led to an increase in the skin friction coefficient. The heat transfer rates increased by 6.7021% points when the suction settings were set to values between 2.0 and 2.5 and the nanoparticle volume fraction was set to 1%. The average reduction in heat transfer efficiency for the aggregation model was around 4.249% for the range of 0–1% nanoparticle volume fraction. Since aggregation models may provide more accurate velocity and skin friction profiles, they are often preferred over homogeneous models. The growing use of aggregation models may largely be attributed to their improved profile prediction accuracy. Improving Ω's values is known to lessen the onset of entropy. An increase in Ec is shown to be beneficial to the entropy inception field. Increasing the Brinkman number accelerates the entropy production rate.

Research on the longitudinal movement and influence of restraint parameters of the long-span suspension bridge’s main girder

The long-span suspension bridge has suffered from multiple failures of restraints such as supports, dampers, and expansion joints due to excessive accumulated displacement at the girder end. To investigate the main girders’ characteristics in the longitudinal motion of these bridges and the influence of the restraint device on the longitudinal displacement, the motion characteristics were first analyzed based on the measured displacement data of a certain bridge’s main girder; a dynamic finite element model of the bridge’s random traffic flow was then established based on the measured WIM data; combined with the girder end displacement monitoring data, the Euclidean distance was used to verify the correctness and rationality of the proposed model; finally, the model is used to discuss the influence of restraint devices (i.e., viscous dampers and supports) on the main girder in the longitudinal direction. The results show that dynamic loads (such as vehicles and wind) are the principal reasons for huge accumulated travel at the girder end; The viscous damper can effectively control the longitudinal movement; in a certain range, the larger the damping index, the better the control effect of the damper; meanwhile, the friction coefficient of the support also affects the longitudinal motion, but the effect is limited. When the friction coefficient is ≤ 0.03, the girder end’s cumulative displacement gradually decreases with the increasing friction coefficient, and compared to the damping index, the friction coefficient plays a major controlling role in the girder end displacement; when the friction coefficient is &amp;gt;0.03, the damping index plays a major controlling role in the girder end displacement.

Impacts of thermal radiation with nanoparticle aggregation and variable viscosity on unsteady bidirectional rotating stagnation point flow of nanofluid

Interest in nanofluids with nanoparticle-induced aggregation effects like solar-powered energy and crossflow heat transfer is growing in the modern industrial sector. The main goal of this research is to find out how nonlinear radiation, changes in viscosity, and aggregation affect the flow of ethylene glycol-based nanofluids in three dimensions. It is concerned with stagnation point flows that are not axisymmetric and that take place on stretching sheets. In accordance with the imposed hypotheses, the governing equations will be modelled. With the help of a similarity transformation, a complicated set of nonlinear partial differential equations can be turned into a simpler set of ordinary differential equations. This simplification facilitates the process of solving the equations. The algorithm will then be used to perform a numerical solution of the simplified set of equations. Runge-Kutta (RK-IV) and the shooting method are used to derive the numerical results. Different parameters and their effects are graphically displayed. As the concentration of nanoparticles in the skin increases, it appears that both the rate of heat transmission and the coefficient of friction increase. The heat transfer rate and the skin coefficient of friction inclination both increase as the instability parameter is increased. To the contrary, it was found that delaying boundary layer's separation by increasing stress rate of surrounding fluid was effective. Tables also compare the nanoparticles aggregation effects with and without radiation and show the variation in Nusselt numbers. High levels of agreement were found between the findings of the current study and those of a previous publication for the same instance, lending further support to the findings.

Analysis of anchor force for pipeline walking induced by SCR tension

The deep-sea pipeline exposed on the seabed is prone to pipeline walking under the influence of thermal loading cycles. Anchors are commonly used to prevent the pipeline walking from causing the end connection of the pipeline system to break. The development of a simple and practical method for calculating anchor force is essential for the preliminary design of the project. In this paper, a finite element model for calculating anchor force is established, and the factors affecting the accumulated length of effective axial force are analyzed. A strain diagram method is proposed for calculating the anchor force under partial accumulated length, and an analytical solution for the rigid anchor force is derived based on the strain diagram method. To address the problem of large anchor force at the end anchor, a flexible anchor is proposed to reduce the anchor force, and a formula for predicting the flexible anchor force is fitted. The study shows that the accumulated length proportion of anchor force increases with the increase of loading temperature and SCR tension, and decreases with the increase of pipeline length and friction coefficient. Flexible anchors can significantly reduce the anchor force. The proposed analytical solution for anchor force can comprehensively consider the influence of factors such as pipeline length, SCR tension, loading temperature, and friction coefficient, and has certain advantages over traditional analytical solutions.

The Synergistic Lubrication Effects of h-BN and g-C3N4 Nanoparticles as Oil-Based Additives for Steel/Steel Contact.

The synergistic effect of different types of solid particles in liquid lubricants is of great interest. In this work, g-C3N4 nanosheets were initially prepared using a calcination method and then as-prepared, and h-BN were used as lubricating additives to the white oil. A comparison between the mixed additives and the single g-C3N4 or h-BN additives revealed that the base oil with the addition of g-C3N4 and h-BN showed the best lubricating properties. The results show a 12.3% reduction in friction coefficient, resulting in a 68.6% reduction in wear rate compared to the white oil when filled with 0.5 wt% g-C3N4 and h-BN (1:1 by weight). Moreover, the addition of g-C3N4 and h-BN improves the high-temperature lubrication properties of the white oil. However, the friction coefficient and wear rate increase with increasing oil temperature. The large contact area between g-C3N4 and its sliding counterpart and the strong adhesive force between h-BN and its sliding counterpart improve the film formation efficiency, leading to enhanced tribological properties under oil lubrication conditions.

High-temperature wear and oxidation behavior of (CrNbTaMoVW)N high entropy films deposited by reactive magnetron sputtering

Rapid advancements in industrial technology necessitate mechanical parts capable of operating at high temperatures. High entropy alloy films have emerged as promising material for high-temperature resistant coatings, providing improved friction control and wear reduction. In this study, (CrNbTaMoVW)N high-entropy films were fabricated on YG6 cemented carbide substrates using reactive DC magnetron sputtering. The oxidation and tribological performance of the films were investigated across a temperature range from room temperature to 800 °C. Oxidation results revealed that (CrNbTaMoVW)N film maintained its simple Face-Centered Cubic (FCC) structure up to 600 °C for 3 h in the presence of air. At 800 °C, complete oxidation occurred, resulting in the formation of complex metal oxides and metal oxynitrides, and a structural transformation from FCC to these compounds. Following oxidation at 600 °C for 3 h, High-Entropy Alloy (HEA) film exhibited the maximum values of hardness (30.6 GPa) and modulus (301.7 GPa). Tribological results demonstrated an increase in both friction coefficient and wear rate with rising test temperature. However, (CrNbTaMoVW)N film showed a relatively low wear rate ranging from room temperature to 600 °C, approximately 10−15 m3/N•m, thus indicating excellent high-temperature tribological properties. Notably, the wear resistance of (CrNbTaMoVW)N film was significantly compromised at 800 °C due to the formation of loosely bonded metal oxides with reduced hardness, in contrast to the test temperature of 600 °C.

Heat transfer analysis of turbulent forced-convection flow in a wavy absorber tube containing a molten salt-based hybrid nanofluid filled with a porous material

The thermal performance of turbulent forced-convection flow was investigated in a wavy absorber tube containing a hybrid nanofluid consisting of salt molten filled with a porous material. The nanoparticles dispersed in the working molten salts are Al2O3 and graphene, which have a spherical shape and a diameter of less than 100 nm. The assessments were performed under turbulent forced convection flow conditions using k--ε model with enhanced wall treatment. The effects of porous media features, nanoparticle concentrations, and molten salt type on flow, thermal exchange, drop pressure, pumping power, skin friction factor, and efficiency are discussed. Outcomes indicated that boosting the values of increases friction coefficient, drop pressure, pumping power, and and system efficiency. Molten Hitec salt has a lower friction coefficient and pressure loss than Hitec XL and solar salt. The use of solar salt improved the heat transfer rate by and compared to Hitec and Hitec XL, respectively.