Increase In Friction Coefficient Research Articles

Numeric simulation of steel twin disc system under rolling-sliding contact

Various mechanical parts come into high-load rolling and sliding contact at the contact surface. Even with technological advancements, mechanical failures still occur. Rolling-sliding mechanical contact issues are the primary cause of over 90 % of surface and subsurface metallic failures and they are only becoming worse. Using discretised continuum 2D finite element methods (FEM), this research investigates the parametric contact effect of a steel twin disc system subjected to rolling-sliding contact at varied surface friction and comprehensive load condition. The equivalent von Mises stress distribution, contact pressure distribution and shift position of maximum subsurface stress on the contour region are all influenced by changes in compressive load and coefficient of friction, according to a numerical surface-to-surface contact simulation performed with Abaqus at mean Hertzian pressure. The maximal equivalent stress, for a given load, reaches a peak in the subsurface and moves farther away from the surface when the coefficient of friction decreases and comes close to the contact surface when the coefficient of friction increases. Consistency is shown by the analytical and numerical results.

Влияние гидрофобных частиц пыли на параметры ветровых волн в зоне генерации

The paper investigates the effect of a film of natural dust deposited from the air on the generation of gravitational-capillary wind waves with a length of 𝜆<0.06 m. It is shown that with an increase in the deposition time of hydrophobic dust particles on the water surface, the contact wetting angle between the water surface and the hydrophobic particle increases, which indicates an increase in the surface tension coefficient. At the same time, the time of convergence of hydrophobic particles increases. It was found that with increasing film concentration for a given wind speed, the length of the wind wave in the generation zone decreases, and the steepness increases, which is associated with an increase in roughness and coefficient of friction at the interface. Nonlinear plane waves with a steepness of 0.13 <ak<0.25 arise in the generation zone. A method for calculating the phase velocity of such waves has been obtained and verified. The critical value of the wind speed at which the generation of wind waves begins decreases with an increase in the concentration of the dust film, and the values lie in the range 2.3 < Umin < 3 m/s.

Exploring dual solutions and thermal conductivity in hybrid nanofluids: a comparative study of Xue and Hamilton-Crosser models.

Hybrid nanofluids show great potential for heat transport applications such as solar thermal systems, car cooling systems, heat sinks, and thermal energy storage. They possess better thermal stability and properties compared to standard nanofluids. In this study, a base fluid, methanol, is injected into an electrically conducting heat-generating/absorbing disk of permeable boundary, and dual solutions are obtained. Two alternative models, Xue and Hamilton-Crosser are considered, and their thermal conductivities are contrasted. Furthermore, thermal radiation and ohmic heating are also considered, and convective boundary conditions are utilized to simulate overall heat gains or losses resulting from conduction, forced or natural convection between nearby objects of nearly constant temperature. Using a similarity transform, the governing equations are obtained and numerically solved via bvp4c, a finite difference method. It is observed that the presence of a magnetic field and the shrinking of the disk elevate the energy transport rate and wall stress. Additionally, the skin friction coefficient and thermal distribution rate increase with wall transmission constraint while fluid flow and energy transport diminish. Furthermore, particle clustering and nano-layer creation suggest that the Hamilton-Crosser model exhibits better thermal conductivity than the Xue model.

Numerical simulation of forced convection of ferro-nanofluid in a U-shaped tube subjected to a magnetic field

In this paper, the forced convection of forced convection of ferro-nanofluid in a U-shaped tubed subjected to a magnetic field is investigated. Modeling is performed in three sizes of the bending radius. The Reynolds number and Hartmann number ranges are 600 ≤ Re ≤ 1200 and 2 ≤ Ha ≤ 12, respectively. The ferro-nanofluid is composed of water-based Fe3O4 particles that vary in volume fraction from 0.01 to 0.03. The simulation is carried out under a 3-D model, incompressible, laminar and steady-state by using the finite volume method. The results show that at a constant bending radius, as the Hartmann number increases, the current density increases. In addition, in all cases, as the Hartmann number increases, the coefficient of friction increases, and the presence of a magnetic field reduces the velocity of the fluid flow. Also, the maximum and minimum friction coefficients are related to the minimum Reynolds number and the maximum Reynolds number, respectively. The results also show that the effect of flow velocity on the heat transfer rate is much more significant than the intensity of the magnetic field and increasing the bending radius of the tube leads to a further reduction of fluid energy and the fluid receives less heat flux from the wall.

Modeling lateral vibration of bottom hole assembly using Cosserat theory and laboratory experiment verification

Lateral vibrations are a complex form of vibrations that may occur while drilling. The understanding of their motion has been relatively comprehensive; however, further studies on their internal mechanisms are required. Existing dynamics models of the drill string are difficult to apply owing to the large number of assumptions and simplifications. The curved elastic rod described by the Cosserat theory can be used as an ideal model to study the motion and mechanical characteristics of drill string because of its large deformation and extreme slenderness. On the basis of existing research, this study proposes a comprehensive drill string dynamics model based on the Cosserat theory. The model is applied to study the lateral vibrations of a bottom hole assembly (BHA), considering factors such as the mass eccentricity, material viscosity, and weight-on-bit (WOB). The established model and experimental device were used to conduct simulations of specific schemes and examine the lateral vibrations of the BHA under the influence of the deviation angle, rotational speed, WOB, and friction coefficient. The accuracy of the established model and its generality were verified by comparing the data from theoretical calculations and experimental simulations. The results demonstrate that the lateral vibrations of the BHA in a nonvertical well indicate the reciprocating oscillation located at the lower right side of the wellbore. The amplitude of the lateral vibration can be increased by reducing the deviation angle or increasing the rotational speed and the friction coefficient. In a vertical well, the BHA exhibits forward whirl, irregular motion, and backward whirl as the rotational speed and friction coefficient increase. Increasing the WOB has insignificant effect on the lateral vibrations of the BHA at the maximum WOB value achieved by the experimental device. However, further increasing the WOB in the theoretical calculation could cause the buckling and backward whirl of the BHA in a vertical well.

Impact of temperature and reaction time on the conversion of polystyrene waste to pyrolytic oil and its diesel engine performance, emission, and lubricity characteristics

The focus of this research is to see how temperature and reaction time affect the yield and quality of liquid oil obtained by pyrolysis. In a small batch pyrolysis reactor, polystyrene waste was employed as a feedstock. This study also studied the performance and emission characteristics of liquid oil produced at optimal condition (PS100), and its tribological characteristics in diesel engine. The ideal temperature and reaction time were discovered to be 400 °C and 30 min, where the liquid oil yield was 92.94% by mass. PS100 had similar properties to commercial diesel. PS100 comprises 34.6% aromatics, 25.2% alkanes, and 4.3% alkenes. PS100 delivered superior performance than B10 diesel. The brake thermal efficiency, brake power, and brake torque were up by 15.5, 5.6, and 2.38%, respectively, while the brake-specific fuel consumption was down by 8.00%. PS100 emitted 97.06 and 17.3% more hydrocarbon and carbon dioxide than B10, respectively. Its poor exhaust gas emissions have proven a key stumbling block in its application in diesel engine. PS100 demonstrated 27.6% increase in coefficient of friction and 29.8% increase in lubricant contamination as compared to B10. Despite its low lubricity and emissions, PS100 has a lot of potential as a diesel engine alternative fuel.

Atomic-scale analysis of mechanical and wear characteristics of AlCoCrFeNi high entropy alloy coating on Ni substrate

High entropy alloys (HEAs) are potential materials for coating due to their high hardness and wear resistance. This study builds molecular dynamics models to explore the mechanical characteristic and wear behavior of AlCoCrFeNi HEA coating on Ni substrate during scratching. The scratching force and friction coefficient of HEA coating on Ni are larger than the pure Ni due to the HEA coating with high strength and good adhesion. The Ni substrate protection mechanism exhibits deformation absorbed by the HEA coating, so the shear strain of HEA coating is more severe than the pure Ni. The Ni substrate is protected by HEA coating, which causes less wear, as shown by the higher wear atom number of pure Ni than the HEA coating on Ni. More resistance to tool motion as increased scratching depth results in an increased friction coefficient, while the friction coefficient decreases with increasing scratching speed due to the influence of thermal softening and strain rate hardening. The accumulation of scratched atoms and energy due to insufficient relaxation time around the tool leads to considerable deformation and temperature increase. The HEA coating reduces the wear of Ni substrate when the scratching depth is smaller than the HEA coating thickness.

Uncovering the roles of laser action modes in surface mechanical properties of 2024 aluminum alloy

The surface state/performance after laser action is as essential as the interplay mechanism between laser and material. Through the designed experiments, the effect of distinct laser action modes on the evolution mechanism of aluminum alloy surface's microstructure and mechanical property was discussed. Under laser-induced thermal effect, the procedure of “vaporization - plasma plume - recoil effect - solidification” occurred. The grains grew longitudinally with an average size of 13.49 μm, which is smaller than that of substrate. Under the thermal oxidation, new oxides were formed. However, laser-induced force effect did not purpose a change in the composition. Importantly, force effect refined the grains to an average grain size as low as 6.21 μm. Notably, an anomaly was discovered. The thermal effect produced stress concentration that increases the residual stress by 64.7%, which caused the hardness to rebound. Additionally, surface composition and microstructure evolution led to the first decrease and then increase of friction coefficient. Due to grain refinement and residual stress induced by force effect, the hardness improved continuously and the friction coefficient decreased continuously. Understanding the influence mechanism of laser action modes on surface structure/property can furnish theoretical guidance for development of laser processing technology in the industrial field.

Calculation and influence analysis of tooth surface friction coefficient of planetary gear system in mixed lubrication condition

Based on the gearing theory, the calculation formulas of comprehensive curvature radius, relative sliding speed and tooth surface contact stress of internal and external meshing gear pair of the planetary gear system are deduced in this paper. Combined with load sharing theory and thermal elastohydrodynamic lubrication analysis method, the oil film thickness, film bearing ratio and friction coefficient are solved and the effects of roughness and input power on the friction coefficient are studied. The results show that with the increase of tooth surface roughness, the film bearing ratio decreases and friction coefficient increases; As the input power increases, the film temperature increases, the oil viscosity and film thickness decreases, which causes the tooth surface friction coefficient increases.

The effect of the coefficient of friction between the roller and the powder on the rolling process

The friction coefficient between the roller and the powder is one of the important factors affecting the rolling process. Since the friction coefficient is difficult to measure during rolling, it is usually regarded as a constant value in previous studies. However, the friction coefficient changes with the changes in process parameters such as the gap size and the rolling speed. In order to study the effect of the friction coefficient between the roller and the powder on powder rolling, the Drucker Prager Cap model for nickel powder rolling was established by ABAQUS. Firstly, the changes of contact stress (CPRESS) between the roller and the powder, the width (PE33), and relative density (SDV1) of the strip during rolling were analyzed. Then, the effect of the friction coefficient between the roller and the powder on the contact stress, the width, and the relative density of the strip was studied especially. The results show that during the rolling process, the contact stress remains basically unchanged. However, a large transverse deformation occurs on both sides of the strip, and the deformation in the middle is basically small. The relative density is greatest at the smallest seam between the rollers, and it decreases slightly after moving away from the roller, and then it remains stable. The coefficient of friction between the roller and the powder has an impact on the rolling result, in which the contact stress between the roller and the powder, the width, and the relative density of the strip will increase as the friction coefficient increases.

Thermo-fluidic characteristics of ice slurry flows in U-bend pipes for cold thermal energy storage

Thermal energy storage plays an important role in improving the efficiency of refrigeration systems. Ice slurries have a high potential for thermal energy storage due to their high latent energy storage properties and almost uniform temperature field. Ice slurry flows in heat exchangers can assist in peak load conditions of refrigeration systems. In the present study, the thermo-hydraulic behavior of ice slurry in U-Bend pipes as a component of heat exchangers was investigated. Numerical simulations were perforfemd using multiphase two-fluid model. Kinetic theory of granular flows were used for modeling the viscosity of ice particles. The effect of geometry of U-Bend pipes on heat transfer rate, pressure drop and ice slurry phase change were investigated. Numerical results were in good agreement with the experimental data. The results showed that heat transfer coefficient and pressure drop increase with Reynolds number, ice volume fraction and ice particle diameter. Tripling the particle diameter leads to the Nusselt number increase by 76 %. It was also found that by reducing the radius ratio, the heat transfer coefficient and the average skin friction coefficient increase, but overally it improves the performance. With a 100 % increase in Reynolds number, the average Nusselt number increases by 80 %, and by decreasing the radius ratio to 50 %, the Nusselt number increases by <1 %.

Investigation of whipping effect on high energy pipe based on fluid-structure interaction method

A fluid-structure interaction numerical model has been established to investigate the whipping effect on high energy pipe in this study. The validation test has been performed by the comparison with the experimental results and it is found that the fluid-structure interaction model can well predict the displacement and the maximum restraint force of the piping system. Then, the dimensionless displacement of the cantilever pipe and U-bolt restraints, the maximum restraint force and the maximum strain energy are used to evaluate the effect of flow rate, pulsation frequency, overhang length, initial clearance and friction coefficient on the whipping effect. The results illustrate that the dimensionless root-mean-square displacement of the cantilever pipe and U-bolt restraints increase to 5.31 times and 9.41 times, respectively as the flow rate increases. The mode transition phenomenon occurs as the flow rate increases to over 180 kg/s and 284 kg/s, respectively. When the pulsation frequencies are close to the first natural frequency of the cantilever pipe, the resonance effect can enhance the whipping effect and enlarge the displacement of U-bolt restraints. The increase of overhang length, initial clearance and friction coefficient can also intensify the whipping effect.

Friction and Wear in Nanoscratching of Single Crystals: Effect of Adhesion and Plasticity.

Friction and wear are two main tribological behaviors that are quite different for contact surfaces of distinct properties. Conventional studies generally focus on a specific material (e.g., copper or iron) such that the tribological result is not applicable to the other contact systems. In this paper, using a group of virtual materials characterized by coarse-grained potentials, we studied the effect of interfacial adhesion and material plasticity on friction and wear by scratching a rigid tip over an atomic smooth surface. Due to the combined effects of adhesion and plasticity on the nanoscratch process, the following findings are revealed: (1) For shallow contact where interfacial adhesion dominates friction, both friction coefficient and wear rate increase as the adhesion increases to a critical value. For deep contact where plasticity prevails, the variation of friction coefficient and wear rate is limited as the adhesion varies. (2) For weak and strong interfacial adhesions, the friction coefficient exhibits different dependence on the scratch depth, whereas the wear rate becomes higher as the scratch depth increases. (3) As the material hardness increases, both the friction coefficient and wear rate decrease in shallow and deep contacts.

Influence of structural parameters of unbonded flexible pipes on bending performance

Unbonded flexible pipes have complex structural forms and numerous structural parameters. There are different degrees of contact and slip between the structural layers under bending loads, which brings challenges to the structural design and bending characteristics analysis of flexible pipes. In this paper, according to the law of energy conservation and deformation geometry theory, the mechanical equilibrium equation of each layer of unbonded flexible riser under bending load is established and the contact condition between layers is introduced in the first step. According to the slip state of the spiral strip, the response of the flexible riser under bending load was divided into three stages: no slip, partial slip and complete slip. The expressions of bending moment and bending stiffness were derived. The influence of structural parameters of tensile armor layer of unbonded flexible pipes on its bending performance under bending load is studied by using MATLAB software to compile the corresponding calculation program. The results show that the increase of friction coefficient between layers of tensile armor will improve the bending resistance of flexible pipes. The increase of helix angle will reduce the bending stiffness of flexible pipes in the initial stage. The increase of the number of spiral strips will increase the bending stiffness of flexible pipes in the initial stage. In the process of structural design of flexible pipes, the influence of the above structural parameters on the bending characteristics of flexible pipes should be taken into account.

Probing the effect of the electric current on the tribological performances of the electrical contact surfaces with graphene coating

A simple and effective method is used to construct graphene coating on brass surface, and the effect of electric currents on tribological performances are studied. Results show that larger current can reduce the friction coefficient and contact resistance, moreover, larger current can suppress the generation of friction-induced vibration. Surface analysis results show the graphene coating is seriously damaged at a low current input, result in the increase of friction coefficient and generation of vibration. Numerical analysis results suggest a larger input current can help reduce the contact pressure and accordingly improve the wear. Moreover, larger current causes the graphene coating to expand, leading to a better contact with the friction pair, so the graphene can better exploit its properties.

Computational intelligence for MHD mixed convection Williamson fluid flow along a stretched surface under Dufour and Soret impacts

The importance of the Soret and Dufour influences upon this mixed convective flow of the Williamson fluid (SDE-MCFWF) along a stretched surface is investigated in this paper. The stiff highly nonlinear fluid flow system represented via partial differential equations is simplified and converted to simple fluid flow system in terms of ordinary differential equations. The resultant collection of ODEs is turned into a system of ODEs, which is then resolved using artificial neural networks back propagated using the Levenberg Marquardt technique (ANNB-LMT). To evaluate the recommended model's abilities, these obtained non-linear ODEs are solved by applying the ND-solve technique to get data sets from (ANNB-LMT). Error plots, regression tests, and the mean squared error guidance are used to further assess the correctness of the established outcomes for SDE-MCFWF. Tables and graphs demonstrate the trend of different physical factors on velocity, temperature, and concentration profiles, such as the curvature parameter, Prandtl number, magnetic field parameter, Dufour number, non-linear stretching parameter, Schmidt number, Porosity parameter, Brickman and Soret number. It shows that rise in Soret number causes the temperature to drop and the concentration profile to rise, but the Dufour number has the opposite effect. Using numerical simulations, the skin-friction coefficients, Sherwood number, and Nusselt number are studied. For rising levels of the Prandtl number and the power law stretching index, the skin friction coefficient and Nusselt number increase, whereas the Dufour number and curvature parameter drop. Higher Dufour and power law stretching index values cause the Sherwood number to increase, but lower Prandtl and curvature parameter values cause it to drop.

Deformation characteristics and performance evolution of superalloy capillary drawn by electrically assisted microforming

Thin-walled superalloy capillaries are considered the core components of the heat exchanger in the hypersonic vehicle. To achieve the precise and efficient fabrication of capillaries, this study proposes an electrically assisted (EA) microforming process and investigates the deformation characteristics and performance evolution of capillaries under electric current. Experimental results show the EA drawing at 600 °C enhances the grain coordinated deformation capacity and dislocation recovery, while the ultrafast complete recrystallization and gradient grain microstructure are achieved by the EA annealing above 800 °C for 15 s. The microstructural evolution improves ductility and avoids macro defects, which is related to the reduction of activation energy of dislocation and grain boundary motion under the electroplastic mechanisms. In addition, the inhibition of the electric current on the increase in wall thickness is attributed to the increase in friction coefficient and the shedding of the oxide layer, while the electric current improves surface quality by forming ultrafine grains, oxidizing peaks, and healing troughs. Compared with the conventional manufactured capillaries, the surface quality, tensile strength, and elongation of the EA manufactured capillaries with the size of φ0.9 mm × 58 μm are increased by 129.0%, 31.1%, and 9.4%, respectively. A heat exchanger module integrated by the EA manufactured capillaries can cool the 25 m/s airflow from 1000 to 672 °C within 1 ms.

Structural and mechanical characterization of as-cast CuAlBe alloy

Copper-Beryllium (Cu-Be) materials are known as non-sparking elements and are used for tools in gaseous rich atmospheres. In this article we present few preliminary results from the obtaining and analyze of a new chemical composition CuAlBe alloy. The experimental alloys were cast in a vacuum induction furnace from CuBe master alloy and high purity aluminium using a graphite crucible and a metal casting mold. The alloys obtained were analyzed by chemical composition homogenization point of view (energy dispersive spectroscopy – EDS), microstructure (optical – MO and electronic microscopy - SEM) and mechanical properties (microhardness, Young modulus and contact stiffness). The addition of beryllium present an increasing of hardness effect collaborated with an increase of friction coefficient.

Friction dependence on the textured structure of an amorphous carbon surface: A reactive molecular dynamics study

Amorphous carbon (a-C) film provides ultralow friction when combined with lubricating oil. However, it is unclear how textured surfaces affect the friction behavior of a-C at atomic scale, specifically the transformation of interfacial structure and the flow of lubricating oil, owing to the limitations of experimental characterization. Here, a-C films with different textured surfaces were fabricated, and the friction behaviors of mating a-C surfaces with textured parameters, including nanoscale depth and width, were examined by reactive molecular dynamics simulation. Results indicate that compared to that under dry condition, the introduction of a textured surface reduces the friction coefficient of a-C under oil lubrication condition. However, its efficiency highly depends on the depth and width of textured surface, exhibiting different effects on hydrodynamic lubrication. The increase in textured depth causes the friction coefficient decreased first and then increased, attributing to the lubrication from hydrodynamic to boundary state as primary mechanism. The regional aggregation of lubricant atoms with a textured width on the a-C surface occurs at the friction interface following the increased friction coefficient. These results provide insights into the underlying friction mechanism of a-C films induced by surface texturing and enable the development of highly efficient lubrication systems for applications.

Properties of compression molded ultra-high molecular weight polyethylene: effects of varying process conditions

Abstract Ultrahigh molecular weight polyethylene (UHMWPE) has been extensively used in various tribological systems because of its outstanding tribological properties and excellent overall performance. Compression molding is the main molding method for UHMWPE, and the process parameters of molding have a profound effect on its material properties. In this study, three groups of UHMWPE samples were prepared, and their physical, mechanical, and tribological properties under different molding process parameters were examined—with a particular focus on the frictional and wear behavior of the material under various heating-temperatures, pressing-temperatures and pressures—and the friction and wear mechanisms of UHMWPE were analysed. Studies have shown that the rise in heating-temperature promotes the diffusion of polymer chains, resulting in an increased friction coefficient and wear loss of UHMWPE. The main wear mechanism switches from plastic deformation to fatigue wear. With an increase in the pressuring-temperature, the friction coefficient first increases and then decreases, while the wear loss increases, and the dominant wear mechanism switches from fatigue wear and plastic flow to plastic flow. With an increase in pressure, the friction coefficient and wear loss first decrease and then increase, and the prime wear mechanism changes from plastic deformation and fatigue wear to fatigue wear.