Sliding Velocity Conditions Research Articles

Friction Coefficient of Single-Crystal Aluminum Oxide under Low Sliding Velocity Conditions with Metal and Polymer Materials

Friction Coefficient of Single-Crystal Aluminum Oxide under Low Sliding Velocity Conditions with Metal and Polymer Materials

High Friction of Paper Wipers in Partially Wet Conditions: Effect of Three-dimensional Nonuniform Wetting

In wet paper wiper, three-dimensional nonuniform wetting may occur and affect frictional behavior. This study aims to clarify the frictional behavior of wet paper wiper in order to develop guidelines for controlling the frictional behavior of similar products such as clothing and sponges. Friction tests were conducted between a paper wiper and a flat glass while varying the water content of the paper wiper. The friction coefficient reached a maximum at a certain water content depending on the normal load and sliding velocity conditions. This high-friction effect may be attributed to meniscus formation at the contact interface and inside the paper wiper specimen, because the negative pressure due to the meniscus can promote the expansion of the real contact area.

Коэффициент трения при низких скоростях скольжения монокристаллического оксида алюминия в паре с металлическими и полимерными материалами

Коэффициент трения при низких скоростях скольжения монокристаллического оксида алюминия в паре с металлическими и полимерными материалами

Friction-induced ignition study of HTPB propellant based on a coupled chemo-mechano-thermodynamic model under ultrahigh acceleration overload conditions

A method is proposed to assess the friction-induced thermal safety of free-cast solid rocket motors subjected to ultrahigh acceleration overload conditions. By measuring the ignition possibility of propellant specimens during the extrusion friction process and determining the reaction kinetics and constitutive parameters, a coupling model considering the thermal, mechanical and chemical effects is proposed. The kinetic parameters of the thermal decomposition reaction and the parameters of the constitutive model are then calibrated accordingly by compression tests covering a large range of strain rates and differential scanning calorimetry (DSC) tests. Experiments on friction ignition are then conducted to validate the developed model at different extrusion pressures and sliding velocity conditions. The results show that the model developed in this work can accurately predict the ignition possibility and temperature distribution of the propellant. Based on this model, dynamic process simulations of a solid rocket motor subjected to an ultrahigh overload of 10000g were performed. Friction primarily occurs at the bottom and side surfaces of the propellant grain, and ignition is more likely to occur at the outer apex of the bottom surface. The temperature rise in the early stages of overload is primarily driven by the frictional conversion of the bottom surface.

MoVN-Cu Coatings for In Situ Tribocatalytic Formation of Carbon-Rich Tribofilms in Low-Viscosity Fuels

Inhibiting the tribological failure of mechanical assemblies which rely on fuels for lubrication is an obstacle to maintaining the lifetime of these systems with low-viscosity and low-lubricity fuels. In the present study, a MoVN-Cu nanocomposite coating was tribologically evaluated for durability in high- and low-viscosity fuels as a function of temperature, load, and sliding velocity conditions. The results indicate that the MoVN-Cu coating is effective in decreasing wear and friction relative to an uncoated steel surface. Raman spectroscopy, transmission electron microscopy, and electron-dispersive spectroscopy analysis of the MoVN-Cu worn surfaces confirmed the presence of an amorphous carbon-rich tribofilm which provides easy shearing and low friction during sliding. Further, the characterization of the formed tribofilm revealed the presence of nanoscale copper clusters overlapping with the carbon peak intensities supporting the tribocatalytic origin of the surface protection. The tribological assessment of the MoVN-Cu coating reveals that the coefficient of friction decreased with increasing material wear and initial contact pressure. These findings suggest that MoVN-Cu is a promising protective coating for fuel-lubricated assemblies due to its adaptive ability to replenish lubricious tribofilms from hydrocarbon environments.

Thermal analysis and tribo‐performance evaluation of multilayered graphene and graphite based fly ash filled banana fiber reinforced brake friction composites

AbstractThis study compared thermal and tribological properties of multilayered graphene‐based flyash filled and banana fiber reinforced brake friction composites with graphite‐based specimens. Two series of brake friction composites by varying the content of graphene/graphite (1, 2, and 3 wt%) were manufactured and tribo‐evaluated using a pin‐on‐disc type tribo‐tester. Tribological properties of the brake friction composites were studied at varying test conditions of normal load (50 and 150 N) and sliding velocity (3.3 and 9.9 m/s). Compared to graphene, the thermal stability remains higher for graphite lubricated composites and decreases with increased graphite/graphene loading. The developed graphite/graphene brake friction composites resulted in a reduction in friction coefficient with increasing sliding velocity and normal loads. The graphene‐filled composite exhibited higher friction performance with enhanced wear resistance at lower sliding velocity than graphite‐based composites. The friction performance of graphite‐filled composites and the graphene‐filled composite's wear resistance remains highest at higher sliding velocity conditions. Moreover, it is observed that the wear rate of graphene lubricated composites remains 21%–35% lowers than the graphite‐filled composite. Finally, the worn composite surfaces were analyzed using a scanning electron microscopy to study the possible wear mechanisms and to understand the nature of the formed contact patches/plateaus remain vital for deciding the tribological behavior of the composites.

Structural Design and Friction Performance Test of a New Conical Groove Friction Disks in Wet Clutch

Wet clutch transmits its power by the friction torque between friction and separate disks. Conical groove friction disk is a new attempt in Wet clutch. Its configurations allow significant enhancement of torque delivery performances, compared with the traditional plane friction disk. In order to study the frictional performances of the conical groove friction configuration, the friction coefficient calculation model of conical groove friction disk was established, and experimental investigation was used to measure the friction coefficient under sliding velocity conditions. The influence of configuration parameters: cone heights and angles on friction coefficients were evaluated in a typical variable speed test. The results indicated that configuration parameters can affect friction performance in a constant speed period. The equivalent radius can directly describe the friction region of a conical groove friction disk. The constant speed test can be a useful method.

Tribology Characterization of Plasma Sprayed Zirconia-Alumina and Fused Zirconia-Alumina Composite Coated Al-Si Alloy at Different Sliding Velocity and Load Conditions

Tribology Characterization of Plasma Sprayed Zirconia-Alumina and Fused Zirconia-Alumina Composite Coated Al-Si Alloy at Different Sliding Velocity and Load Conditions

Wear and friction properties of AA 7075-T6 with × wt% of WC surface composite fabricated by FSP technique

The surface composites were prepared with Aluminium Alloy (AA) 7075-T6 by incorporating 0, 3, 6 and 9 wt% of tungsten carbide (WC) nano particles of 20 nm via Friction Stir Processing (FSP) technique under most noteworthy fixed parametric condition. The main impartial of proposed exertion is to enhance the surface composites behavior towards by attaining better resistant to wear and friction. Also, there was a drastic improvement in composites surface than base material and also higher weight percentage addition samples due to resistance occurred by plastic deformation while indenting. The main aim of this research is to perform wear and friction test by using dry sliding tribometer under room temperature environment by varying load and sliding velocity condition for composite surface stir zone with applied load of 10, 20, 30 and 40 N. The sliding velocities for the test being 1, 3 and 5 m/s respectively for which the responses like wear rate, co-efficient of friction was recorded. Increase in load and sliding velocity increases the wear rate and co-efficient of friction linearly in all the composite surface stir zone samples. Lower wear rate and co-efficient of friction was observed for 9 wt% WC nano particles reinforced stir zone samples. The presence of hard WC nano particles further reduced the grain size in the matrix stir zone which resisted the plastic flow of debris. The FSP-ed surface composites were recommended for replacing sliding components in automobiles, aerospace and marine applications.

Frictional behaviour of a greased contact under low sliding velocity condition

In greased contacts, the complex rheology of a grease, depending on thickener, base oil and additives, becomes a key point for understanding and controlling the evolution of friction coefficient at extremely low sliding velocities. Such velocity range (from 0 to few mm/s) is of main relevance for several issues, such as unstable friction-induced vibrations, which can occur as well in the case of lubricated interfaces.In this paper, a greased contact at low sliding velocities is then reproduced and analysed on a dedicated tribometer, under well controlled boundary conditions. Static and dynamic friction coefficients, as function of velocity, are obtained, considering either dry and lubricated contact, with both the grease and its base oil. The effect of DLC surface coating is analysed too. The contributions of the lubricant components on the frictional and dynamic response have been then discussed, showing a non-trivial trend of friction, with respect to speed, within the investigated velocity range.

An Experimental–Theoretical Methodology to Develop Scuffing Limits for Relatively Smooth High-Speed Contacts

In this study, a rough surface thermal elastohydrodynamic lubrication (TEHL) model tailored for the simulation of high-speed and high-temperature contacts of relatively smooth surfaces is introduced. The model uses a modified Carreau-Yasuda constitutive function to capture the non-Newtonian effects and a limiting shear formulation to consider any lubricant–solid slippage. It is employed to simulate a family of traction tests from Handschuh et al. for validation. According to the methodology of Handschuh et al., a set of two-disc scuffing experiments was performed with chemically polished surfaces under various rolling and sliding velocity conditions. Several load stages of these scuffing tests were simulated using the TEHL model with the measured surface roughness and bulk temperature as inputs. The predictions indicate that a scuffing limit based solely on the maximum surface or lubricant temperature does not exist for the contacts considered; however, a scuffing boundary based on both fluid temperature and contact pressure is evident.

Optimization of wear and friction characteristics of Phyllanthus Emblica seed oil based lubricant using response surface methodology

The escalating prices, rapid diminution of fossil fuels, tenacious regulations of the authorities, etc. enforced towards the alternate biogenic fuel for lubrication. The present study assessed the lubricity characteristics of Phyllanthus Emblica seed oil based lubricants by using a pin on disc (POD) tester. The design of experimentations has been carried out using response surface methodology (RSM). The value of parameters such as blend ratio, load and sliding speed ranges from 0 to 20%, 50 to 100 N and 1.3 to 3.8 m/s, respectively, are used to assess the value of specific wear rate (SWR) and coefficient of friction (COF). Test results illustrate that the adhesive wear occurred during the experiments. It has been observed that AB10 shows the probable results in terms of wear and friction characteristics as compared to other lubricant variants at low load and high sliding velocity conditions and perform as an excellent lubricant additive. This contributes towards the replacement of petroleum based lubricants. Analytical ferrography and total acid number (TAN) analysis of the used oil was also done to study the wear debris in the oil.

Synthesis and characterisation of hot extruded aluminium-based MMC developed by powder metallurgy route

BackgroundImprovement of the mechanical and tribological properties due to extrusion can be attributed to the improved density and excellent bond strength due to high compressive stress.MethodsTo avoid the product defects mathematically contoured cosine profiled die was used for the thermomechanical treatment. Improvement of mechanical characterization like density, hardness, compression test and three-point-bend test was inquired. Two body dry sliding wear behaviour of the prepared AMCs before and after extrusion were investigated by using a pin-on-disc wear testing method by varying the variable parameters like load (N), track diameter (mm) and RPM of the counter disc.ResultsThe effect of hot extrusion on mechanical and tribological characteristics of aluminium matrix composites (AMCs) developed by powder metallurgy route followed by double axial cold compaction and controlled atmospheric sintering was studied.ConclusionShearing of the fine distributed graphite particles at the tribosurface acts as a solid lubricant and decreases wear rate. At higher loading and sliding velocity condition a mixed type of wear mechanism was observed.

Dry wear behavior of rheo-casting Al–16Si–4Cu–0.5Mg alloy

Dry wear behavior of the rheo-casting Al–16Si–4Cu–0.5Mg alloy was investigated by micro-scratch and dry sliding wear tests. Analyses of the microstructure, scratch grooves, wear tracks, worn surfaces and wear debris of the alloy were carried out by optical microscope and scanning electron microscope. The microstructural analysis showed that via rheo-processing, the primary Si was refined and rounded, eutectics dispersed more homogenously, and even the skeleton AlFeMnSi phase was fragmented into facet shape. Micro-scratch test showed that the microstructural refinement resulted in better wear resistance. Dry sliding wear test revealed that the rheo-processed sample exhibit obviously superior wear resistance because of the microstructure improvement. The dominant mechanism in mild wear condition is abrasion, but it turned to adhesion and oxidation in high applied load and fast sliding velocity conditions.

Fabrication of Thermally Stable Polysulfone Microcapsules Containing [EMIm][NTf2] Ionic Liquid for Enhancement of In Situ Self‐Lubrication Effect of Epoxy

Microcapsules containing an ionic liquid (IL) are potential candidate materials for preparing in situ self‐lubricating composites with excellent tribological properties. 1‐ethyl‐3‐methylimidazolium bis[(trifluoromethyl) sulfonyl]imide ([EMIm]NTf2) IL encapsulated polysulphone microcapsules are synthesized. The mean diameter and wall thickness are about 128 μm and 10 μm, respectively. Microcapsules have excellent thermal stability, with a thermal degradation onset temperature of 440 °C compared to traditional lubricants‐loaded microcapsules. In situ self‐lubricating composites are prepared by incorporating the IL‐encapsulated microcapsules into epoxy matrix. When the concentration of the IL microcapsules is 20 wt%, the frictional coefficient and specific wear rate of composites are reduced by 66.7% and 64.9% under low sliding velocity and middling applied load conditions, respectively, as compared to the neat epoxy. The tribological behavior of the self‐lubricating composites is further assessed in different applied load and sliding velocity conditions. The in situ self‐lubricating mechanism of composites is proposed.image

Wear mapping and transitions in wheel and rail materials under different contact pressure and sliding velocity conditions

The objective of this study is to construct wear mapping and transitions of wheel/rail materials under different contact pressure and sliding velocity conditions by means of comprehensive consideration of both wear rates and surface damage morphology of wheel/rail rollers. The results indicate that, both the wear rates of wheel rollers and the wear rates of rail rollers increase with contact pressure increasing. With sliding velocity increasing, the wheel wear rates show an increase trend and the rail wear rates decrease. Wear regime maps of wheel/rail materials are divided into two regions: mild wear regime and severe wear regime, and both the wear rates of wheel roller and the wear rates of rail roller are about 2.0×10−6g/m on the transition boundaries. The wear mechanisms of the wheel and rail materials are significantly different and transform in different wear regimes. Based on the damage characteristics in different wear regimes, the wear mechanism maps of wheel and rail materials are constructed. Fatigue cracks of wheel material develop along with soft ferrite lines in the plastic deformation area. Furthermore, cracks on the rail rollers develop into the material a depth, then become parallel with the surface and turn towards it.

Dry sliding wear behavior of SiC and B4C-reinforced AA6351 metal matrix composite produced by stir casting process

In the present study, the influence of Boron Carbide (B4C) particles on the dry sliding wear behavior of aluminum matrix alloy (AA6351) – Silicon Carbide (SiC) composite – produced by the stir casting method is investigated. The wear test is carried out by pin-on-disc apparatus over an applied load range of 20–100 N and sliding velocity ranging from 1 to 5 m/s. The worn surfaces are discussed in detail with the Scanning Electron Microscopic (SEM) image. The experimental results show that the maximum wear rate of 21.91 × 10−3 mm3/m is achieved for the AA-5 wt. % SiC composite at 100 N load and 2 m/s sliding velocity. However, the inclusion of B4C particles on the composite reduced the wear rate significantly. Thus, the increased wt. % of B4C particles in the composite exhibits a good wear resistance behavior at higher load and sliding velocity conditions.

Tribological Charecterization of Carbon Epoxy Composite Materials with Particulate Silane Treated SiC Fillers

The polymeric matrix Composite Materials is widely used for automotive and aeronautical industry applications due to its superior properties. The tribological properties of the Carbon Epoxy Composites with 5% of silane treated SiC and 10% of silane treated SiC which were added separately and it has been investigated experimentally by the dry sliding wear test using the Pin-on-Disc type wear test rig. The main parameters Sliding Speed (S), Applied Load (L) and Sliding Distance (D) which were considered for the experimental investigation and evaluated the dry sliding wear characteristics of composites. Under increased levels of loads and sliding velocity conditions higher wear loss was noted. The coefficient of friction values from the result shown that the increased value with addition in load and also sliding velocity. It results was compared that the Carbon Epoxy Composites containing ST - SiC Fillers having lower Coefficient of Friction than plain Carbon Epoxy Composites. From the observations maximum wear resistance were found and discussed.

Tribological capabilities of chiral nematic liquid crystal additives in mineral motor oil

This article presents the results of experimental investigation of tribological properties of commercial mineral motor oil with chiral nematic (also known as twisted nematic or cholesteric) liquid crystal additives. Cholesteryl stearate and valerate (fatty acid cholesterol esters) liquid crystals were used as oil additives in investigation. Tribological experiments were performed using a block-on-disc-type tribo-test machine at constant experiment time and sliding velocity conditions. The load (contact pressure), concentration of liquid crystalline additive in oil and Rz roughness of steel–steel friction surfaces were taken as variable parameters. The mean coefficient of friction of steel–steel friction pair lubricated by oil with and without liquid crystal additives and near-contact temperature were taken as dependent variables. Regression equations were then derived for each lubricant and tribological efficiency of liquid crystals as oil additives was evaluated. It was established that coefficient of friction of steel–steel friction pair and near-contact temperature are reduced to about a half in the presence of liquid crystal additives. Results of tribological experiments show that tribological efficiency of liquid crystals as oil additives increases with increase in their molecular mass.

Multi-walled Carbon Nanotube-Imidazolium Tosylate Ionic Liquid Lubricant

Multi-walled carbon nanotubes (MWCNTs) were added in a 0.5 wt% proportion to 1-alkyl-3-methylimidazolium room temperature ionic liquids (IL) The new IL + MWCNTs dispersions obtained by mechanical grinding were used as lubricants of the polycarbonate (PC) disc/AISI 316L stainless steel pin contact, and their tribological performance compared with that of the corresponding IL. The highest friction reduction at 0.98 N and 0.10 m s−1, of a 54 %, was obtained when MWCNT were added to 1-ethyl-3-methylimidazolium tosylate ([EMIM]Ts). The [EMIM]Ts + MWCNT dispersion was further characterised by rheological measurements, contact angle, DSC, TGA, FTIR and Raman spectroscopies, TEM microscopy and XRD. The addition of MWCNTs increases the viscosity of the IL in a 50 % at room temperature and the wettability on the PC surface, while the IL increases the purity and alignment of the nanotubes. The variation of friction coefficient was determined under variable sliding velocity conditions. The higher friction reduction for [EMIM]Ts + MWCNT with respect to [EMIM]Ts is observed for sliding velocities higher than 0.075 m s−1. Under the experimental conditions, the surface damage on the PC and AISI 316L surfaces was negligible.