Decrease Of Friction Force Research Articles

Effect of temperature on the friction behavior and mechanism of DLC film in CO2 foam fracturing environment

Diamond-like carbon (DLC) film is considered to be an attractive candidate material for reducing friction and wear in oil and gas equipment due to its low friction and high wear resistance. This study investigated the evolution of friction interfaces and tribochemical reaction at three different temperatures through reactive molecular dynamics simulations. The results reveal that the synergistic effect of atomic transfer layer and chemical passivation of DLC film leads to the decrease of friction force with increasing ambient temperature. The cumulative atomic transfer layer with increasing ambient temperature also contributes to the increase of wear amount, while the atomic lattice transition dominates friction temperatures. More importantly, the phenomenon of increased sp3 carbon atoms in DLC film is also temperature dependent.

Molecular dynamics study on nanoscale scratch characteristics of FeNiCrCoAl high-entropy alloy

The preparation process of FeNiCrCoAl high-entropy alloy at the atomic scale was simulated using molecular dynamics, and its microstructure was analyzed to study its micro-mechanical properties during nanoscale scratching. The simulation results showed that FeNiCrCoAl primarily experienced main frictional forces from the [010] direction and radial frictional forces from the [001] direction during the nanoscale scratching process. All three frictional forces exhibited certain fluctuations, which were partly attributed to the formation of face-centered cubic and hexagonal close-packed atomic structures during frictional wear. In addition, plastic flow was observed continuously within the high-entropy alloy matrix. Furthermore, the effects of temperature and Fe atomic content on the nanoscale scratch characteristics of FeNiCrCoAl high-entropy alloy were investigated. The results indicated that an increase in temperature resulted in a nonlinear decrease in frictional forces and a reduction in the quantity of the two types of phase-transition atomic structures formed. Increasing the Fe atomic content induced lattice distortion effects in the high-entropy alloy, leading to an increase in the potential energy of the matrix and the formation of more phase-transition atomic structures, thus hindering the frictional wear process of FeNiCrCoAl high-entropy alloy.

A Tribo‐Dynamic Model of a Helical Gear Pair Based on the Finite Line Contact Theory

In this article, a finite line contact tribo‐dynamics model of helical gears is established by coupling the tooth surface friction, friction moment, and vibration velocity. To obtain convergent results, a cycle iteration strategy is adopted to solve the two submodels, the dynamic model and the thermal elastohydrodynamic lubrication model. The parameters obtained from the dynamic model such as the dynamic load, dynamic transmission error, and instantaneous speed of the teeth surfaces are used as the boundary conditions for solving the lubrication model. Meanwhile, the friction force and friction moment obtained by the lubrication model are used as parametric excitations of the dynamic model. Based on the proposed model, the influence of dynamic effect, thermal effect, rotational speed, and tooth surface roughness on the tribological and dynamic properties of helical gears are discussed. The results show that the tribological and dynamic parameters deviate significantly from the quasistatic values, especially at the characteristic speed. The vibration along the off‐line‐of‐action direction is obviously affected by the friction excitation. As the rotational speed increases, the friction coefficient and friction force decrease as well as the vibration of the gear pair along the off‐line‐of‐action direction weakens. In addition, the surface roughness has the greatest influence on the vibration of the off‐line‐of‐action direction in all directions of gear vibrations.

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.

Structural and chemical changes in He+ bombarded polymers and related performance properties

The paper presents the effect of He+ ion irradiation of selected polymeric materials: poly(tetrafloroethylene), poly(vinyl chloride), ethylene-propylene-diene monomer rubber, nitrile-butadiene rubber, styrene-butadiene rubber, and natural rubber, on their chemical composition, physical structure, and surface topography. The modification was studied by scanning electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, and differential scanning calorimetry. Irradiation with a high-energy ion beam leads to the release of significant amounts of hydrogen from the surface layer, resulting in an increase in cross-linking that manifests itself by shrinkage of the surface layer, which in turn causes significant stresses leading to the formation of a crack pattern on the polymer surface. The development of microroughness is combined with oxidation. Shallow range of the ions makes the modified layer “anchored” in the substrate via bulk macromolecules, assuring its good durability and adhesion to elasto-plastic substrates. Changes in the surface layer were manifested by the modification of functional properties of the polymers. The hardness of the layer subjected to the ion irradiation process increases even up to 10 times. After modification with the ion beam, a significant decrease in frictional forces was also observed, even up to 5–6 times. The microscopic analysis of wear traces confirmed that the wear resistance also significantly increased. However, ion bombardment of polymeric materials caused a reduction in their mechanical strength (despite the range limited to the surface layer of the order of micrometers) and electrical resistance, which has a negative impact on the possibility of using the materials in some applications.

Influence of Adsorption Characteristics of Surfactants Sodium Dodecyl Sulfate and Aerosol–OT on Dynamic Process of Water-Based Lubrication

Surfactant solutions are widely used in industry, and their steady-state lubrication properties have been comprehensively explored, while the “dynamic process” between steady states attracts much less attention. In this study, the lubrication behaviors of sodium dodecyl sulfate (SDS) and sodium bis (2–ethylhexyl) sulfosuccinate (Aerosol–OT, AOT) solutions were comparatively and extensively discussed. Experimental results showed that the duration of the dynamic process of AOT solution lubrication was significantly shorter than that of SDS. The essence of the dynamic process was revealed from the aspects of the running-in of solid surfaces and the adsorption process of surfactant molecules. Unlike the general recognition that the friction force evolution mainly corresponds to the running-in of surfaces, this study indicated that the dynamic adsorption behavior of surfactant molecules mainly contributes to this process. Various experiments and analyses showed that the smaller steric hindrance and lower orientation speed of SDS molecules led to longer diffusion into the confined contact zone and a longer duration of friction force decrease. This work enhances our understanding of the dynamic friction process in water-based lubrication, which could also have important implications for oil-based lubrication and its industrial applications.

Tribological study on the surface modification of metal-on-polymer bioimplants

The tribological performance of artificial joints is regarded as the main factor of the lifespan of implanted prostheses. The relationship between surface roughness and coefficient of friction (COF) under dry and lubricated conditions is studied. Results show that under dry test, friction coefficient is not reduced all the time with a decrease in surface roughness. On the contrary, a threshold of roughness value is observed, and frictional force increases again below this value. This critical value lies between 40 and 100 nm in Sa (roughness). This phenomenon is due to the transfer of friction mechanisms from abrasion to adhesion. Under wet test, COF always decreases with reduction in surface roughness. This result is mainly attributed to the existence of a thin layer of lubricant film that prevents the intimate contact of two articulating surfaces, thus greatly alleviating adhesion friction. Furthermore, surface texturing technology is successful in improving the corresponding tribological performance by decreasing friction force and mitigating surface deterioration. The even-distribution mode of texturing patterns is most suitable for artificial joints. By obtaining the optimal surface roughness and applying texturing technology, the tribological performance of polymer-based bioimplants can be greatly enhanced.

Effect of Temperature on Fe–Polytetrafluoroethylene Friction Coefficient Using Molecular Dynamics Simulation

We established a coarse-grained molecular dynamics (MD) model of polytetrafluoroethylene (PTFE) at elevated temperatures. The nonbonding and bonding interaction parameters among PTFE beads were estimated. Then a friction model for simulating the Fe-PTFE friction process was developed on the basis of the estimated interaction parameters. The influence of elevated temperature on friction coefficient of Fe-PTFE was investigated. We found that the friction coefficient of Fe-PTFE decreases with an increase in temperature of 300–500 K. This is in a good agreement with experiments. Moreover, we comprehensively analyzed the variations in energies; that is, the bond energy, bond angle energy, and deformations of PTFE molecules. The elevated temperature reduces the interaction forces among PTFE beads, thereby leading to a decrease in friction force. Although the elevated temperature can enhance the bond energy, bond angle energy, and kinetic energy of PTFE molecules, the increase in kinetic energy has an unremarkable influence on the interaction forces between Fe and PTFE layers compared with the effect of the bond energy and bond angle energy on the interaction forces.

CFD Analysis of the Effect of Dimples and Cylinder Liner Honing Groove on the Tribological Characteristics of a Low Displacement Engine

The contact between the piston rings and the cylinder liner is an interface with a strong influence on the tribological behavior and, therefore, directly affects the useful life of the engine components and fuel consumption. Due to this importance, the present investigation carried out an analysis of the effects of dimples and the honing groove in the cylinder liner on the tribological characteristics. A tribological model was developed to study the friction forces, minimum film thickness, and friction coefficient for the present investigation. Similarly, a computational fluid dynamics model was built to determine the dynamic movement of the piston. The validation of the numerical model showed a close similarity with the real behavior of the engine, obtaining an average relative error of 14%. The analysis of the results showed that a 3% increase in dimples’ density leads to a 3.79% increase in the minimum lubricant film and a 2.76% decrease in friction force. Additionally, it was shown that doubling the radius and depth of the dimple produces an increase of 3.86% and 1.91% in the thickness of the lubrication film. The most suitable distribution of the dimples on the surface of the cylinder liner corresponds to a square array. In general, the application of dimples and honing grooves in the cylinder liner are promising alternatives to reduce energy losses and minimize wear of engine components.

Mechanical response of ZrxCu100-x layer on Cu(001) substrate using molecular dynamics

The molecular dynamics simulations method is applied to survey the deposition and annealing processes of ZrxCu100-x film on a Cu(001) surface. The influences of ZrxCu100-x compositions and depths on the force, deformation behavior, pile-up, and hardness are investigated using nano scratching and nanoindentation processes. We find out that the structure of ZrxCu100-x alloy has stability increases when decreasing the Zr content. The surface roughness of Zr-Cu film increases when improving the Zr content. After annealing, the morphology surface of the Zr-Cu amorphous alloy becomes smoother. The scratching forces and average friction coefficient of the Zr20Cu80 film surge as the scratching depth rises. While the pile-up height, normal force, and friction force decrease as increasing the Zr ratio. Under the plastic and elastic deformations, shear transformation zones are formed in the Zr-Cu amorphous film. While in the nanoindentation process, the hardness of ZrxCu100-x film amorphous film tends to decrease when increasing the Zr content.

Effect of layer thickness and raster angle on the tribological behavior of 3D printed materials

Additive manufacturing (AM) is a manufacturing process which add material into a solid 3-dimensional product. Fused Deposition Modelling (FDM) or Fused filament Fabrication (FFF) is one of the most common additive manufacturing methods. Parts processed by FDM are usually serve as prototypes of concept design and unable to use a functioning part due to their mechanical and tribological properties. Material wear has been a huge problem for machines as it is the main contributor to machine failures. Tribological behavior of AM part are required to be enhanced if AM parts are purposed to be functioning parts. Due to the nature of manufacturing technique, the tribological properties are affected by the FDM printing parameters. In current work, tribological properties of 3D printed pins, printed at different raster angle and layer thickness were investigated. FDM printed Acrylonitrile Butadiene Styrene (ABS) and Polylactic Acid (PLA) samples were printed at three raster angle 0°, 45° and 90° and three layer thickness of 0.127 mm, 0.254 mm and 0.33 mm. Experiments were conducted on a pin-on-disk tribometer apparatus under dry sliding condition and fixed load of 10 N and 300 rpm. Results has shown that an increase of layer thickness promotes a decrease in friction force while an angle of 45° displays the best wear resistance. ABS is proofed to have better wear resistance than PLA.

Evaporation and drying characteristics of the sessile ferrofluid droplet under a horizontal magnetic field

In this study, the evaporation characteristics and drying patterns of various sessile ferrofluid droplets on certain substrate under horizontal magnetic fields of controlled intensities are reported. The effects of droplet concentration and magnetic field intensity on the duration of each evaporation stage and drying patterns of droplets have been systematically investigated. It turned out that a plateau appears at the initial stage of evaporation in the absence of magnetic field and it was found that the plateau value is positively correlated with the concentration of ferrofluid droplets. Under the external magnetic field, the evaporation time of droplets decreases, the stage of contact line retreat extends, the stage of late pinning mode shortens, and the deposition area of ferrofluid droplet decreases compared to that of without magnetics field. The deposition area increases gradually and becomes more uniform with the increase of magnetic field. The decrease of friction force which is due to the decrease of the number of nanoparticles at the contact line under external magnetic field is the main reason for the observed phenomena. We found that the coffee ring and the uniform deposition inside the droplet will be destroyed when the magnetic field intensity is higher than a critical value. Our work has a significant reference value for the evaporation of sessile magnetic fluid droplets under the applied magnetic field, especially when the drying pattern needs to be precisely controlled, such as in spray or biomedicine.

Temperature dependence of contact quality inducing suppression of stick–slip friction

Atomic-scale stick–slip friction of monolayer graphene on a copper substrate is computationally studied at a wide range of temperatures, which reveals strong temperature dependence of friction force and friction mode. The increase in temperature distorts regular stick–slip behavior and causes a nonlinear decrease of friction force, demonstrating a friction behavior transition from athermal friction to thermally activated. By analyzing atomic morphologies, the true contact area, defining the number of atoms interacting across the interface, shows a weak temperature dependence, yet the quality of interfacial contact substantially varies with temperature. Spatial distributions of atomic friction force uncover the significant effect of Moiré superlattices, that act as strong pinning sites at low temperatures, partly change to pushing due to nonconcurrent atomic jumps at high temperatures, which leads to a chaotic friction mode with reduced lateral force. Additionally, we demonstrate the role of superlattices in strengthening friction and dictating the periodic stick–slip motion of interfacial sliding.

Experimental Research on Sliding Friction of Dense Dry Particles Lubricated Between Parallel Plates

Particle flow lubrication is a promising choice for extreme working conditions. Lubricated by dense dry particles between parallel plates, clarifying the sliding friction characteristics are significant to the design and parameter selection of particle-lubricated warm forming die, which is not well studied yet through the experimental methods. A self-developed testing apparatus was used to study the sliding tribological characteristics of parallel plates under dense particle lubrication. The experimental results showed that the dry particle lubrication between parallel-plates behaves excellent lubrication characteristics on sliding friction. The average coefficient of friction between the upper palate and particles increases rapidly with the increase of pressure load while corresponding to the change of average coefficient of friction, the average friction force increases linearly with the increase of pressure load. The force chain line between the upper plate and the particle lubrication media becomes thicker with the increase of pressure load, indicating that the contact force and contact stress are increasing. The average coefficient of friction and average friction force decrease with the increase of sliding velocity. The force chain line between the upper plate and the particle lubrication media becomes thinner with the increase of the sliding velocity, indicating that the contact force and contact stress are decreasing. The greater the contact stress is, the greater the average coefficient of friction will be. This study provides a deep understanding of the sliding tribological behaviors of the warm-forming die lubricated by the particle media.

Effect of cutting parameters and high-pressure coolant on forces, surface roughness and tool life in turning AISI 1045 steel

Abstract The machining industries constantly look for novel techniques to decrease the forces generated in metal cutting, enhance the tool life and improve the surface quality. High-pressure coolant delivery is one such technique that is believed to enhance the overall machining process with its superior cooling capabilities. Hence, an investigation was made to compare the behavior of a turning tool in machining AISI 1045 steel material under conventional coolant (CC) and high-pressure coolant (HPC) conditions. The influence of applying coolant at high pressure on forces and surface finish was measured at various cutting speeds and feeds, and tool life analysis was performed at a constant cutting parameter. The study reveals that a 12–23% reduction in cutting force, a 17–27% reduction in feed force, and a 14–33% reduction in surface roughness values can be obtained when a high-pressure coolant is used. Besides, around 40% improvement in tool life was also seen. The capability of the coolant in the effective removal of heat from the tool-chip interface zone, decrease in frictional forces between the tool and work material, and superior chip breaking capabilities at high-pressure conditions are attributed to the performance improvement.

Bucket working bodies with conveyor bottom: systematics and design features

Introduction. The creation of new types of bucket working bodies of excavators through synthesizing technical solutions to improve the transporting functions of the bottom is considered. These solutions are based on reducing the resistance and energy consumption under digging-in and scooping due to the transition from sliding friction to rolling friction during the movement of the rock mass along the bottom of the bucket. Materials and Methods. Analysis of the bulk materials handling processes using existing loading appliances identified design flaws that affect the efficiency of their operation. Advanced design diagrams of loading bodies were searched on the basis of the accumulated experience and the study of the morphological features of the existing equipment. Combinatorial analysis of possible combinations of elements with their various qualitative compositions, mutual arrangement, imposed links, and synthesis of new technical solutions for loading and transportation modules are carried out. Results. The results of the morphological synthesis implementation were the systematization and development of designs of bucket working bodies with a bottom in the form of a roller surface and a closed belt, as well as with a conveyor-type drive mechanism. The application of rollers as a supporting surface of a loaded rock mass causes a decrease in friction forces and in the power capacity of the work process. In addition, rotating rollers provide uniform abrasion of the working surface, which increases significantly the time to the equipment breakdown and increases the process efficiency. Working bodies with a drive mechanism make it possible to activate the interaction of the conveyor bottom in the form of a closed belt with the rock mass and, as a result, to accelerate the process of filling the bucket container. Discussion and Conclusions. The bucket working bodies described in the paper compare favorably with existing analogues in that they provide a reduction in the time to digging-in, scooping and unloading, a decrease in specific energy consumption, an increase in bucket filling, which ultimately contributes to an increase in productivity. A slight increase in the structural complexity and cost of the working body causes additional capital costs, which are paid back within two to four months.

Study of friction force behaviour of red-mud based aluminium matrix composites under influence of various operating parameters

Fabrication of particulate composite with aluminum6061 reinforced with red-mud as reinforcement has been done by stir-casting. Uniform distribution of red-mud particles in aluminum matrix has been examined by Scanning electron microscopy. For confirmation of red-mud in the matrix, energy dispersive spectroscopy spectrum has been obtained from the surface. The results show that there has been first increase in friction force upto 12% red-mud and then decrease in friction force. Value of friction force has been found minimum at 125 µm particle size and maximum at 250 µm. Analysis reveals that friction force increases with increase in applied load and sliding distance. The effect of load and sliding speed on friction force has been reported significant by ANOVA analysis. Load has been found most effective parameter on friction force followed by sliding speed, sliding distance, particle size and aging time. Response table shows percentage reinforcement has least effect on friction force.

Pile-up and heat effect on the mechanical response of SiGe on Si(0 0 1) substrate during nanoscratching and nanoindentation using molecular dynamics

Molecular dynamics (MD) simulations are performed to study the mechanical behavior of SiGe thin film during nanoindentation and nanoscratching processes. The MD simulations of deposition and annealing process are conducted to create the Si80Ge20 thin film deposited on Si(0 0 1) substrate. MD simulations of nanoindentation and nanoscratching processes are carried out to study the influence of the temperature on deformation behaviors and mechanical properties of this material. Moreover, the influences of the scratching depth, tool velocity, and temperature on the deformation behavior during nanoscratching process are also surveyed. It is found that the elastic and plastic deformations occur and the shear transformation zones (STZs) are independently developed in the contact region. The force, hardness, and Young’s modulus of the Si80Ge20 thin film deposited on the Si substrate decrease as increasing the temperature during the indentation process. The pile-up, friction force, and normal force grow as increasing the scratching depth. As increasing the scratching speed, the pile-up increase while the normal force and the friction force reduce due to the effect of heat and strain rate are more efficient than the effect of the pile-up. As increasing the temperature, the height of pile-up increases while the normal force and the friction force decrease as a result of a higher temperature leads to softening the workpiece because the thermal expansion causes a reduction of the bonding strength of atoms.

Physical Characteristics of Friction Processes in a Columnar Approach-Separation Model with Tangential Force

Three-dimensional molecular dynamics (MD) simulation is conducted to understanding the dynamics processes of atomic-scale friction, which takes place in the columnar approach-separation model. A cylinder-cylinder sliding simulation model with tangential stress for Cu/Cu is built. Embedded atom potential (EAM) is employed for simulation. Based on the simulation result and the adhesion theory, the temperature change, friction force evolution and microstructures are systematically analyzed. The simulation results show that the temperature is related to the friction force, both increased during the transient sliding period. The friction force curve is analyzed by real contact area with tangential stress. Fluid mechanics is implanted to explain the decrease of friction force. An epitaxial bcc (body center cubic) copper layer is formed inducing adhesion during sliding. The rough peaks break causing the atoms leaving from interface.

Interfacial friction properties in diamond polishing process and its molecular dynamic analysis

The friction properties play an important role in diamond polishing, which significantly affect the interfacial contact and material removal. In this paper, the friction force and coefficient of friction (COF) during diamond polishing process were monitored under different loads and rotating speeds. The results show that the friction force and COF both increase with the load, and decrease with the rotating speed. The bearing capacity of liquid film is enhanced at large rotating speed, which leads to the decrease of friction force. According to the binomial law of friction, the increase of actual contact area caused by high load contributes to the increase of COF. Besides, it is found that the addition of H2O2 reduces the friction coefficient through surface adsorption. In order to further reveal the mechanism of friction variation at the atomic level, the friction behavior at a local area of interface between the diamond substrate and the abrasive particle in diamond polishing process was investigated by molecular dynamics (MD) method. The simulation results indicate that the interfacial bridge bonds formed between the substrate and particle under the action of load lead to the increase of friction force.