Friction Coefficient Resistance Research Articles

Numerical simulation of turbulent boundary layers of surfaces covered with foul release and antifouling coatings

In order to compare the frictional resistance of three kinds of ship’s hull coatings (Foul Release, SPC copper, SPC TBT) in the unfouled conditions, the numerical studies have been made. Simulations have been carried out for different Reynolds numbers in the range of 2.85 × – 5.5 × based on the plate length and flow velocity. Antifouling coatings have a larger mean roughness than Foul Release. The results have indicated that frictional resistance coefficient of Foul Release test plate is lower than SPC copper and SPC TBT test plates. The total resistance obtained by computational fluid dynamics has been compared with the experimental data and good agreement in results has been found which those have shown the ability of CFD modeling in calculating of fluid flow resistance by considering the coating characteristics.

On the mechanism of formation of wear-resistant coatings on the friction surfaces of technical products in the presence of these drugs Tribo

Extending the service life of technical devices by exposing the surface of the friction tribo different drugs is an established fact. There are various hypotheses to explain the mechanism of formation of coatings with high wear resistance and low coefficient of friction on the mating surfaces of friction units of machines and mechanisms during their operation with the presence of drugs Tribo. All these conflicting hypotheses. The proposed technology without the wear operation of equipment using Tribo drugs differ in content and methodology of processing machinery. In this paper, an analysis of existing hypotheses formation mechanism of these coatings. The authors have their own experience in the development and application of technologies without the wear operation of equipment using Tribo drugs. This allows them to develop their own hypothesis of the mechanism of formation of coatings with high wear resistance and low coefficient of friction on the mating surfaces of friction units of machines and mechanisms during their operation with the presence of drugs Tribo.

A new methodological approach for shoe sole design and validation

Shoe soles are extremely complex to design and manufacture due to their organically shaped but technically precise nature and their manufacturing constraints. Consequently, there is a need for the increased design process flexibility offered by the use of specific CAD methodologies and techniques, to facilitate the work of expert designers and permit effective construction of the three-dimensional elements comprising the complete structure. Recent advances in additive manufacturing systems have extended the possibilities of shoe sole design. These systems can be used to create the final mould and to incorporate dynamic elements that are of particular value in sports footwear. In this article, we present a new methodology for the design and validation of shoe soles. The methodology assists designers in the design concept process and in transfer of the design to manufacturing. The model incorporates both a structural and a functional approach. To this end, a set of specific tools have been developed that can be used to quantify design quality. For example, the model calculates the coefficient of friction or slip resistance, necessary to comply with international standards concerning safety footwear.

Tribological and Frictional Characteristics of Alsi7mg-Wc-Graphite Hybrid Composites

Al based metal matrix composites offer higher specific strength, light weight along with enhanced wear resistance and lower coefficient of friction. In the present investigation, aluminium alloy hybrid composites containing 3 weight % graphite(size less than one micron) and 3%, 6% and 9 wt % tungsten carbide powder(size less than one micron) were produced by stir casting. Addition of tungsten carbide (WC) increases strength and wear resistance of composites, while graphite (Gr) reduces the coefficient of friction, thus improving the overall tribological characteristics. Composite specimens were tested at loads of 10N, 15N and 20N with the sliding speeds of 1m/s, 1.5m/s and 2m/s to evaluate their wear behaviour. Co efficient of friction was also analysed. As the applied load increased, the coefficient of friction and wear rate of the composite increased. Coefficient of friction showed a decrease with increasing sliding speed and reinforcement content. Hardness of the composite increased with an increase in WC content.

Tribological Characterization of TiN Coatings Prepared by Sputtering

The aim of this paper is to study tribological properties of titanium nitride (TiN) coating deposited on various substrates by DC magnetron sputtering technique. The DC power of metallic titanium target was varied from 200 to 350W at an increment of 50W. The effect of power variation on structure and surface morphology was characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). The tribological properties of coating were investigated using pin on disk apparatus. TiN coating exhibited a higher wear resistance and low coefficient of friction compared to uncoated substrates of mild steel, aluminum and brass.

Titanium Compound Erosion-Resistant Nano-Coatings

The main objective of this paper is to offer ion-plasma technology for production of Ti (titanium) and titanium nitride (TiN) erosion-resistant nanocoatings for the machine building products, which ensures the coatings with optimum and stable properties. As a result of experiments and processing experimental data the optimum composition of ion-plasma titanium and titanium nitride nanocoatings was obtained and offered.The approbation of the developed technology on the existing machine building products (compressor blade of the helicopter gas turbine; base material: Incoloy 800) was carried out. The comparative study on the influence of the coating on the surface quality, coefficient of friction, adhesion strength and erosion resistance was done. For evaluation of the obtained nanocoating surface’s quality 2D and 3D surface description approaches were applied. Achieved results prove the effectiveness of offered ion-plasma technology for production of titanium and titanium nitride erosion-resistant nanocoatings with appropriate and stable properties.

Experimental Determination of Added Hydrodynamic Resistance Caused by Marine Biofouling on Ships

An extensive series of towing tests using flat plates covered with artificial barnacles were carried out at the Kelvin Hydrodynamics Laboratory (KHL) at the University of Strathclyde. The tests were designed to examine the effect of the coverage percentage of barnacles on the resistance and effective power of ships, over a range of Reynolds numbers.This paper presents the added resistances due to calcareous fouling in terms of the added frictional resistance coefficient for a surface coverage of fouling of up to 20%, over different speeds (Reynolds numbers). The drag coefficients and roughness function values of each surface were evaluated. Roughness effects of the given fouling conditions on the frictional resistances of an LNG tanker were then predicted for different ship speeds using an in-house code which was developed based on the similarity law analysis of Granville (1958). Added resistance diagrams were then plotted using these predictions. Finally, powering penalties of the LNG tanker were predicted using the generated diagrams.

Studies on the surface modification of TiN coatings using MEVVA ion implantation with selected metallic species

Improvement in the performance of TiN coatings can be achieved using surface modification techniques such as ion implantation. In the present study, physical vapor deposited (PVD) TiN coatings were implanted with Cr, Zr, Nb, Mo and W using the metal evaporation vacuum arc (MEVVA) technique at a constant nominal dose of 4×1016ionscm−2 for all species. The samples were characterized before and after implantation, using Rutherford backscattering (RBS), glancing incident angle X-ray diffraction (GIXRD), atomic force microscopy (AFM) and optical microscopy. Friction and wear studies were performed under dry sliding conditions using a pin-on-disc CSEM Tribometer at 1N load and 450m sliding distance.A reduction in the grain size and surface roughness was observed after implantation with all five species. Little variation was observed in the residual stress values for all implanted TiN coatings, except for W implanted TiN which showed a pronounced increase in compressive residual stress. Mo-implanted samples showed a lower coefficient of friction and higher resistance to breakdown during the initial stages of testing than as-received samples. Significant reduction in wear rate was observed after implanting with Zr and Mo ions compared with unimplanted TiN. The presence of the Ti2N phase was observed with Cr implantation.

Effect of Heat Treatment on the Microstructure and Properties of HVOF-Sprayed Co-Cr-W Coating

Co-Cr-W HVOF-sprayed protective coatings are used for their high oxidation and wear resistance. Apart from the oxidation resistance, the stability of their mechanical properties in relation to thermal loading is crucial with respect to the most common high-temperature application areas. This work is focused mainly on evaluation of the heat-induced changes in the phase composition and related mechanical properties. It was shown that the original powder, composed fully from face-centered cubic Co-based alloy, partly changes its phase composition during spraying to a hexagonal close-packed (hcp) structure. The annealing further increases the ratio of the hcp phase in the structure. The heat-induced phase changes are accompanied by an increase in the coatings’ hardness and cohesion strength. The abrasive and adhesive wear behavior was evaluated. While the coatings’ heat treatment had a positive effect on the coefficient of friction, the abrasive and adhesive wear resistance of annealed coating was lower compared to as-sprayed coating.

Study of Froude and Hughes methods by numerical towing tank

The resistance of a cargo ship is calculated by numerical towing tank. RANSE multi-phase parallel solver with K-w SST turbulent model and VOF formulation is applied. Computational results from double model (without free surface) are used to obtain 1+k in Hughes’ method and those with free surface are analyzed by both Froude and Hughes’ approaches to investigate model and full scale correlation. ITTC recommended uncertainty study is carried out to evaluate numerical error due to grid density. The computed wave elevation, wake distribution and resistance components by fine, medium and coarse meshes are cross-compared and validated against experiment data where applicable. It is found that grid resolution has most effect on wave pattern. The predicted friction and viscous-pressure resistance coefficients are relatively grid independent from present numerical simulation

The potential of hBN nanoparticles as friction modifier and antiwear additive in engine oil

An experimental investigation was conducted to investigate the potential of hexagonal boron nitride (hBN) nanoparticles as friction modifier and antiwear additive in engine oil. In this study, an optimal composition (0.5 vol.%) of 70 nm hBN nanoparticles was dispersed in SAE 15W-40 diesel engine oil by sonication technique. Sample was stabilized using 0.3 vol.% oleic acid as a surfactant. The tribological test was performed using a four-ball tribometer. Surface morphology and its chemical composition were carried out using a profilometer, Scanning Electron Microscopy (SEM) and Energy-dispersive X-ray Spectroscopy (EDX). It was found that the optimized nano-oil could reduce the coefficient of friction and increase wear resistance, as compared with conventional diesel engine oil. Some adhesive and abrasive wear types were identified as predominant wear mechanisms.

Numerical Calculation of the Tee Local Resistance Coefficient

The local head loss of tee could be calculated with the determination of local resistance coefficient by CFD simulation and test. Based on the mesh-independent feature identified, the flow field inner tee was numerically simulated by the standard k - ε turbulent model and SIMPLEC algorithms, which has revealed the mainstream was obliged to turn to the opposite side of tee junction, and a rise in pressure drop between upstream and downstream was caused as a result. Furthermore, the frictional resistance coefficient was calculated for eliminating the frictional head loss of model, which decreased from 0.0207 to 0.0133 when the inlet velocity increased from 1 m/s to 12 m/s. Additionally, the local resistance coefficients of tee at flow conditions were attained, and the quadratic polynomial between the local resistance coefficient and flux ratio was presented due to the influence of branch on mainstream. Through the test, the simulation result has been compared and the effectiveness of simulation has been verified.

Comparative modeling of hull form resistance for three ocean going vessels using methodical series

This paper presents a comparative estimation of the hull form resistance for Cargo ship, Ocean-going Tug and Container ship. The research study evaluates the influences of various ship hull parameters in relations to the vessel speeds and level of turbulence (Reynolds number). The modeling was done using MATLAB software and the model test technique based on the ITTC, ATTC, Granville and Hughes friction line application. The result shows that the hull form resistances follow the same trend in the ITTC, ATTC and Granville models, while the Hughes model gave a different trend with other techniques. It further revealed that as the speed increases by 10knots, the frictional resistance coefficients decrease by 11.86% for the ITTC & Granville models, and 12.03% for the Hughes model. For Ocean-going Tug and Container Ship, the frictional resistance coefficient decrease by 12.31% for the ITTC & Granville models, and 12.14% for the Hughes model. The Reynolds number increase by 62.52% for every 10knots increase in the speed of the Cargo ship and 62.23% for every 10knots increase in the speed of the Ocean going tug and Containership. At various experimental speeds, the results showed that for every 1 knots increase in the speed of the Containership, the effective power developed increases by 9.45%. This provides a technical and analytical guide on hull form resistance trend for engineers and ship operators.

Study of Microstructure and Wear Behavior of T6 Heat Treated as Cast Al-25Mg<sub>2</sub>Si-2Cu Alloy

In the present investigation, microstructural characteristics and dry sliding wear behaviour of T6 heat treated conventionally cast Al-25Mg2Si-2Cu alloy have been discussed. The as cast alloy was subjected to solutionizing at 500°C for 5h and isothermal aging treatment at 190°C for different aging times. The micro structural characterization was studied using Scanning Electron Microscope with EDS analysis. The microstructure of as cast alloy consists of intermetallics of coarse block like sharp edged β-(Mg2Si), θ-(Al2Cu) and Q-(Al-Mg-Cu-Si) in the form of Chinese scripts and needles distributed randomly in the Al-matrix. The microstructure of heat treated alloy shows spheroidization of β phase and fine precipitation of θ-(Al2Cu) and Q phases. The dry sliding wear test was carried out using pin-on-disc machine. Age hardened alloy exhibits high wear resistance and minimum coefficient of friction over the entire range of applied loads and sliding velocities. Furthermore, high wear resistance was observed in the under aged condition compared to over ageing conditions.

Experimental investigation on rheological properties and friction performance of thickened CO2 fracturing fluid

Abstract For the purpose of guiding the field treatment of CO2 stimulation, the experimental investigation on rheological properties and friction performance of thickened CO2 fracturing fluid system is performed in the pressure range of 10–30 MPa and the temperature range of 0–100 °C by using high-parameter fracturing fluid test system. The correlations for thickened CO2 fracturing fluid rheological parameters have been obtained. The results present that the effective viscosity decreases with increasing shear rate and the change below 500 s−1 is more sharp. The effective viscosity decreases from 20 mPa s to 8.2 mPa s with increasing temperature at 20 MPa, 3.0 wt% and 393 s−1, and shows a small increase with increasing thickener concentration. Temperature and shear rate influences on the rheological properties are larger in various influencing factors. The frictional resistance coefficient of the thickened CO2 fracturing fluid decreases from 0.69 to 0.12 with increasing flow velocity at 20 MPa, 15 °C and 3.0 wt%, and levels off as the flow velocity reaches 0.4 m/s. The friction resistance coefficient presents a decrease trend with increasing temperature, and increases with increasing pressure or thickener concentration at the constant temperature, however, the change range is smaller.

Plasma modified Polytetrafluoroethylene (PTFE) lubrication of α-olefin-copolymer impact-modified Polyamide 66

Tribological and mechanical properties of α-olefin-copolymer, impact-modified Polyamide 66, containing pristine and plasma treated Polytetrafluoroethylene (PTFE) micro-powders as solid-lubricants have been investigated. The PTFE powders were subjected to low pressure 2.45GHz microwave plasma treatment with H2 and NH3 as the process gases to aid their dispersion in PA66. Formation of polar surface groups in conjunction with significant defluorination was observed for both H2 (F/C atomic ratio 1.30) and NH3 (F/C atomic ratio 1.13) plasma treated powders. The H2 PTFE-impact modified PA66 composites exhibited a 25% increase in their impact energy absorption capabilities (25.0J) than their pristine counterparts (20.0J), along with a significant reduction of the specific wear rate at higher pv-values. At the pv-value of 6MPam/s, the specific wear rates for composites containing hydrogen plasma treated PTFE and nitrogen plasma treated PTFE were reduced by 33% (0.7×10−6mm3/Nm) and 50% (0.6×10−6mm3/Nm), respectively, as compared to pristine PTFE–α-olefin PA66 composites (1.1×10−6mm3/Nm); while showing similar coefficient of friction values. The use of plasma functionalized PTFE powders thus provides a facile route for the production of impact modified PA66 compounds with significantly lower coefficient of friction and higher wear resistance for applications like bearings and sliding elements where impact strength as well as good tribological properties are required.

Turbulence model investigations on the boundary layer flow with adverse pressure gradients

In this paper, a numerical study of flow in the turbulence boundary layer with adverse and pressure gradients (APGs) is conducted by using Reynolds-averaged Navier-Stokes (RANS) equations. This research chooses six typical turbulence models, which are critical to the computing precision, and to evaluating the issue of APGs. Local frictional resistance coefficient is compared between numerical and experimental results. The same comparisons of dimensionless averaged velocity profiles are also performed. It is found that results generated by Wilcox (2006) k-w are most close to the experimental data. Meanwhile, turbulent quantities such as turbulent kinetic energy and Reynolds-stress are also studied.

Formation of Friction Layers in Graphene-Reinforced TiAl Matrix Self-Lubricating Composites

The friction layer structure has been proved to be formed during severe plastic deformation and markedly improves the tribological properties of material. The dry friction and wear performance of graphene-reinforced TiAl matrix self-lubricating composites (GTMSC) at different sliding velocities are systematically researched. GTMSC show the best tribological properties and special friction layer structure containing a wear-induced layer and a grain refinement layer with a nanocrystalline (NC) structure under surface after sliding at a sliding speed of 1.1 m/s. Nanoindentation results show that the grain refinement layer has a higher hardness and elastic modulus than the wear-induced layer. This special microstructure of friction layers beneath the surface after sliding leads to a low coefficient of friction and high wear resistance of GTMSC. Moreover, it is deduced that the appearance of an NC structure results in hardening of the material. The formation mechanisms of friction layers are researched in detail. It can be concluded that the formation of a wear-induced layer results from frictional heat and fracture of the counterpart. The formation of a grain refinement layer is due to severe plastic deformation and dynamic recrystallization. Severe plastic deformation results in the formation of an NC structure and dynamic recrystallization leads to grain refinement.

Estimation of Crystalline Structure and Gas Transport Properties of Crystalline Fluorinated Copolymer

PFA has a unique role in the plastics industry due to its inertness, heat resistance, and low coefficient of friction in a wide temperature range. Generally speaking, fluorinated compounds and fluoropolymers have excellent chemical resistance, and oil- and water-shedding resistance. They have been used as rubbers at high temperatures and in several lubricating fluorine manufactured products. Anyway, the crystalline polymers were used in the gas permselective, barrier and separating films. The gas transport properties are related to solubility, diffusivity and permeability in a polymer. In general, gas permeability, diffusivity, and solubility decrease with increasing crystallinity in a polymer film, because of gas molecules cannot diffuse and dissolve in the crystalline region. A few paper reported gas transport properties of PFA. In these papers discussed film thickness, pressure and grade dependence of gas permeability in PFA. However, there has been no systematic research on the relationship between gas transport properties and crystalline structure in PFA. We have investigated the relationship between amorphous structure and its gas permeability of Poly(tetrafluoroethylene-co-perfluoroethylvinylether) (PFA) films using differential scanning calorimetry (DSC), wide-angle, small-angle X-ray scattering and quasi-elastic neutron scattering measurements. We focused on the hierarchical inter-lamellar amorphous structure of various gas-permeable PLA films. For controling cooling rate from the molten state, we prepared various crystallinity sample. The crystallnity range is between 29.3% (melt quenched) and 38.3 % (cooling rate, 0.5 K/min). From wide-angle x-ray scattering measurements, the crystal lattice is independent of cooling rate, however, the lamellar crystal structure is strongly dependence on the cooling rate. The thickness of lamellar crystal and amorphous increase with decreasing cooling rate. The gas permeability coefficient was almost independent of crystallinity, that is, below crystallinity of 32 %, the gas permeability and diffusivity decreases with increasing crystallinity, while above that of 32%, it is independent of crystallinity. The order of gas permeability coefficient of all PFA films was the same as that of gas size such as the kinetic diameter: 2.89 Å (H2), 3.30 Å (CO2), 3.46 Å (O2), 3.64 Å (N2), 3.80 Å (CH4). The gas molecules might pass through the amorphous region of inter-lamellar crystals. Furthermore, we evaluated the relaxation processes of various crystallnity PFA films with quasi-elastic neutron scattering measurements. The films has two relaxation mode, 10^-12 s and 10^-13 s. The longer relaxation time component (~10^-12 s), which was assigned as "relaxation of side chain", has correlated with gas permeability.

The Electrochemical Properties of Diamond and Tetrahedral Amorphous Carbon Electrodes in Room Temperature Ionic Liquids

Room temperature ionic liquids (RTILs) are emerging as a new medium for redox reactions as these liquids possess high solubilizing power, electrical conductivity, wide breakdown voltage and low volatility. Being composed entirely of ions (no solvent) and possessing wide electrochemical windows ( ca. 5 V), it is not difficult to see why these liquids are viewed by electrochemists to be attractive electrolytes for investigation. Our group is (i) studying the wetting of these ionic fluids on different carbon electrode surfaces and how this wetting affects the capacitance-potential relationships and (ii) investigating how the carbon electrode surface chemistry and microstructure affect the heterogeneous electron-transfer rate constant of different inorganic and organic redox systems in these ionic liquids. It is well established that the in aqueous electrolyte solutions, the heterogeneous electron-transfer rate constant for certain redox-systems at ordered HOPG and more microstructurally-disordered glassy carbon is strongly affected by the electrode surface microstructure and chemistry. We seek to learn if these same trends hold in ionic liquids. In this presentation, we will compare the electrochemical behavior of boron-doped nanocrystalline diamond and nitrogen-incorporated tetrahedral amorphous carbon thin-film electrodes. Specifically, contact angle measurements of the surface wettability, measurements of the double-layer capacitance (C dl) and its variation with potential, and heterogeneous electron-transfer rate constants for redox systems in structurally distinct RTILs will be presented. These two carbon electrodes have distinct microstructures as compared to their sp2 carbon counterparts. Nitrogen-incorporated tetrahedral amorphous carbon (ta-C:N) is a composite material consisting of a mixture of sp2 and sp3-bonded carbon. Impurities can be incorporated during growth (e.g., N) further adding to their complex structure. These films typically possess 40-60% sp3-bonded carbon. It has been widely used as a protective coating due to its hardness, high wear resistance and low coefficient of friction. The growth temperature for ta-C is usually from 25 to about 100 °C. This means that non-traditional materials, such as plastics, can be used as substrates for deposition. Importantly, these carbon materials possess some electrochemical properties that are similar to those of diamond.