Friction Coefficient Resistance Research Articles

Corrosion and Wear Resistance of Electroplating Trivalent Chromium-Carbon Coating

A decorative and high hardness chromium-carbon coating, electrodeposited with a trivalent chromium sulfate electrolyte, could improve the environment pollutions and toxicity of hexavalent chromium system. The trivalent chromium-carbon coatings can be deposited onto substrates directly without any buffer layer. The lifetime of various mechanical parts can be improved due to their high hardness and excellent corrosion resistance. The effect of different concentration of main salt on the composition, hardness, corrosion resistance, coefficient of friction and wear resistance of the coatings were investigated. The SEM observation of surface morphology showed that the appropriate concentration of main salt can diminish the defects caused by internal stress under excessive content, As increasing the concentration of main salt from 0.05M to 0.2M, the Icorr of the coatings would be raised from 1.04×10-6 A/cm2 to 1.26×10-5 A/cm2. XRD results showed that the structure of the coatings prepared by at 0.1 M main salt with a heat treatment at 400 °C for 1 h had Cr7C3 and Cr23C6 phases appeared as well as the hardness of that enhanced up to 1350 Hv than 880 Hv of the as-deposited coatings. Wear test results showed that the coatings prepared by at 0.1 M main salt via a heat treatment of 400 °C had the better wear resistance.

Sliding tribocorrosion behavior of bulk metallic glass against bearing steel in 3.5% NaCl solution

Using a pin-on-disk tribometer with a three electrode system, a BMG–steel tribo-pair composed by Zr-based bulk metallic glass (BMG) Zr55Cu30Ni5Al10 and AISI 52100 steel were studied to reveal the sliding tribocorrosion behavior of BMG against bearing steel in 3.5% NaCl solution. With the increase of applied load or sliding velocity, the wear rate of BMG was increased and the BMG surface gradually crystallized. Furthermore, crystallization leads to better wear resistance and lower coefficient of friction (COF), but worse corrosion resistance. Compared with AISI 304 stainless steel (SS), BMG not only has better tribocorrosion resistance in NaCl solution but also is beneficial to reduce the wear of bearing steel disk in the tribo-pair.

Flow and convective heat transfer characteristics of Fe2O3–water nanofluids inside copper tubes

Fe2O3–water nanofluids were prepared at mass fractions of 0.1%, 0.2%, 0.3%, and 0.4% using Fe2O3 nanoparticles with an average size of 50nm. Dispersants such as sodium dodecyl benzene sulfonate (SDBS), gum acacia, and cetyl trimethyl ammonium chloride (1361bromide) were added at various proportions to improve the stability of the nanofluids. This study analyzed the flow and convective heat transfer characteristics of the Fe2O3–water nanofluids inside inner-grooved copper and smooth copper tubes, and results indicated that the dispersants enhanced the stability of the nanofluids significantly. In particular, SDBS was the most effective among them. The frictional resistance coefficient was greater in the inner-grooved copper tube than in the copper tube under laminar flow conditions and given a constant Reynolds number. This coefficient decreased in both tubes when both the mass fraction of Fe2O3 and the Reynolds number increased. The increase in the mass fraction of Fe2O3 also enhanced the convective heat transfer performance levels of the nanofluids.

Study on Optimized Hull form of Basic Ships Using Optimization Algorithm

In order to achieve minimum resistance for a ship hull, we used an optimization algorithm and computational fluid dynamics to develop a hull-form design. An ITTC 1957 modelship correlation line formula was used to estimate the frictional resistance coefficient, and the wave-making resistance coefficient was evaluated by the Rankine source panel method with nonlinear free-surface boundary conditions. The geometry of the hull surface was represented and modified by a B-spline surface-modeling technique during the optimization process. Wigley and series 60 (C_B=0.60) hulls were selected to obtain an optimized hull that produces minimum resistance. Experimental tests were carried out for the modified series 60 (C_B=0.60) hull.

Experimental investigation of the effect of bow profiles on resistance of an underwater vehicle in free surface motion

In this paper, towing tank experiments are conducted to study the behavior of flow on a model of the underwater vehicle with various shapes of bows, i.e. tango and standard bows in free surface motion tests. The total resistances for different Froude numbers are considered experimentally. The towing tank is equipped with a trolley that can operate in through 0.05–6 m/s speed with ±0.02 m/s accuracy. Furthermore, the study is done on hydrodynamic coefficients i.e. total, residual and friction resistance coefficients, and the results are compared. Finally, the study on flow of wave fields around bows is done and wave filed around two bows are compared. The Froude number interval is between 0.099 and 0.349. Blockage fraction for the model is fixed to 0.005 3. The results showed that the residual resistance of the standard bow in 0.19 to 0.3 Froude number is more than the tango bow in surface motion which causes more total resistance for the submarine. Finally, details of wave generated by the bow are depicted and the effects of flow pattern on resistance drag are discussed.

Dry sliding wear behavior of extruded Mg-Sn-Yb alloy

The dry sliding wear behavior of extruded Mg-9Sn and Mg-9Sn-3Yb alloys through pin-on-disc configuration was investigated at room temperature. Coefficient of friction, wear rate and wear resistance of extruded Mg-9Sn and Mg-9Sn-3Yb alloys were measured within a load range of 20–240 N and 20–380 N at a sliding velocity of 0.785 m/s, respectively. The wear tracks, worn surface and wear edge were observed using a scanning electron microscope and an energy dispersive X-ray spectrometer. The results indicated that wear rate, coefficient of friction and wear resistance changed with increasing applied load due to different wear mechanisms. Six wear mechanisms, namely adhesion, abrasion, oxidation, delamination, thermal softening and melting, were observed for both extruded alloys. The extruded Mg-9Sn-3Yb alloy exhibited good wear resistance compared with extruded Mg-9Sn alloy, which was mainly attributed to a large number of volume fraction of Mg2Sn particles, the formation of thermal stable Mg2(Sn,Yb) particles and good elevated temperature mechanical properties.

Tribological Behavior of Ferrous-Based APS Coatings Under Dry Sliding Conditions

The use of Al-alloys for engine blocks production, instead of e.g., gray cast iron, results with weight savings and lower fuel consumption and therefore, reduces pollution. Possible solution for overcoming poor tribological properties of Al-alloys is the application of thermal spray coatings. In this paper, the tribological properties of two ferrous-based coatings were analyzed and compared with gray cast iron as a standard material for engine blocks. The process used for coating deposition on an Al-Si alloy substrate was atmospheric plasma spraying. In order to investigate the tribological behavior of these coatings under dominant adhesive and abrasive wear regime, two tests were applied with different test equipments and conditions. Both tribological tests showed that, for the investigated conditions, both coatings had improved wear resistance and lower coefficient of friction compared with gray cast iron.

Numerical investigation on two-dimensional boundary layer flow with transition

As a basic problem in many engineering applications, transition from laminar to turbulence still remains a difficult problem in computational fluid dynamics (CFD). A numerical study of one transitional flow in two-dimensional is conducted by Reynolds averaged numerical simulation (RANS) in this paper. Turbulence model plays a significant role in the complex flows’ simulation, and four advanced turbulence models are evaluated. Numerical solution of frictional resistance coefficient is compared with the measured one in the transitional zone, which indicates that Wilcox (2006) k-ω model with correction is the best candidate. Comparisons of numerical and analytical solutions for dimensionless velocity show that averaged streamwise dimensionless velocity profiles correct the shape rapidly in transitional region. Furthermore, turbulence quantities such as turbulence kinetic energy, eddy viscosity, and Reynolds stress are also studied, which are helpful to learn the transition’s behavior.

Dispersion fraction enhances cellular growth of carbon nanotube and aluminum oxide reinforced ultrahigh molecular weight polyethylene biocomposites.

Ultrahigh molecular weight polyethylene (UHMWPE) is widely used as bone-replacement material for articulating surfaces due to its excellent wear resistance and low coefficient of friction. But, the wear debris, generated during abrasion between mating surfaces, leads to aseptic loosening of implants. Thus, various reinforcing agents are generally utilized, which may alter the surface and biological properties of UHMWPE. In the current work, the cellular response of compression molded UHMWPE upon reinforcement of bioactive multiwalled carbon nanotubes (MWCNTs) and bioinert aluminum oxide (Al2O3) is investigated. The phase retention and stability were observed using X-ray diffraction, Raman spectroscopy and Fourier transform infrared (FTIR) spectroscopy. The reinforcement of MWCNTs and Al2O3 has shown to alter the wettability (from contact angle of ~88°±2° to ~118°±4°) and surface energy (from ~23.20 to ~17.75 mN/m) of composites with respect to UHMWPE, without eliciting any adverse effect on cytocompatibility for the L929 mouse fibroblast cell line. Interestingly, the cellular growth of the L929 mouse fibroblast cell line is observed to be dominated by the dispersion fraction of surface free energy (SFE). After 48 h of incubation period, a decrease in metabolic activity of MWCNT-Al2O3 reinforced composites is attributed to apatite formation that reduces the dispersion fraction of surface energy. The mineralized apatite during incubation was confirmed and quantified by energy dispersive spectroscopy and X-ray diffraction respectively. Thus, the dispersion fraction of surface free energy can be engineered to play an important role in achieving enhanced metabolic activity of the MWCNT-Al2O3 reinforced UHMWPE biopolymer composites.

The thermal non-equilibrium porous media modelling for CFD study of woven wire matrix of a Stirling regenerator

Different numerical methods can be applied to the analysis of the flow through the Stirling engine regenerator. One growing approach is to model the regenerator as porous medium to simulate and design the full Stirling engine in three-dimensional (3-D) manner. In general, the friction resistance coefficients and heat transfer coefficient are experimentally obtained to describe the flow and thermal non-equilibrium through a porous medium. A finite volume method (FVM) based non-thermal equilibrium porous media modelling approach characterizing the fluid flow and heat transfer in a representative small detailed flow domain of the woven wire matrix is proposed here to obtain the porous media coefficients without further requirement of experimental studies. The results are considered to be equivalent to those obtained from the detailed woven wire matrix for the pressure drop and heat transfer. Once the equivalence between the models is verified, this approach is extended to model oscillating regeneration cycles through a full size regenerator porous media for two different woven wire matrix configurations of stacked and wound types. The results suggest that the numerical modelling approach proposed here can be applied with confidence to model the regenerator as a porous media in the multi-dimensional (multi-D) simulations of Stirling engines.

Numerical Investigation of Flow in an Asymmetric Plane Diffuser Using a Multi-Scale Turbulence Model

The flow in an asymmetric plane diffuser was simulated using both the multiscale turbulence model based on the variable interval time average method and the standardk-εmodel based on the Reynolds average method. The numerical method used in this simulation is an unstructured staggered mesh scheme. The capability of the multi-scale model to simulate flow in an asymmetric plane diffuser has been validated. Pressure coefficient, frictional resistance coefficient and mean velocity profiles downstream are in agreement with experiments. Moreover, the results predicted by the multi-scale model are better than that predicted by the standardk-εmodel. The computational results show that the multiscale turbulence model can successfully simulate this type of separated flow.

Numerical Investigation on Resistance Reducing Effect by Mass Injection through Porous Wall

A numerical study of flow in two-dimensional turbulent boundary layer flow with mass injection through a porous wall is conducted by Reynolds averaged numerical simulation (RANS) in this paper. Numerical results with available experimental data show that Wilcox (2006) k-w turbulence model can give good prediction in this complex flow. The comparison between mass injection and no mass injection for the local frictional resistance coefficient are performed. Numerical investigation indicates that mass injection may reduce the resistance significantly, which is confirmed by comparison of velocity profiles qualitatively.

Experimental investigation on the efficiency of flat-plate solar collectors with nanofluids

In this study, Cu–H2O nanofluids with different mass fraction and size were prepared through two-step method. Its thermal conductivities and the effect of Cu–H2O nanofluids on the efficiency of a flat-plate solar collector was investigated experimentally. Meanwhile, the water temperature, heat gain of the flat-plate solar water heater and the frictional resistance coefficient of working fluid were also investigated. The mass flow rate of medium was 140 L/h. The experimental results show that the thermal conductivities can be enhanced observably. The efficiency of solar collector was enhanced by 23.83% with using Cu–H2O nanofluids (25 nm, 0.1 wt%) as the absorbing medium. The efficiency of Cu–H2O nanofluids (25 nm, 0.2 wt%) is lower than that of Cu–H2O nanofluids (25 nm, 0.1 wt%). With the nanoparticle size increasing, the efficiency of solar collector decreased. The highest temperature and highest heat gain of water in the nanofluid (25 nm, 0.1 wt%) tank can be increased up to 12.24% and 24.52% compared with water tank, respectively. The increment rate of the frictional resistance coefficient is less than 1% in the whole working temperature area. From the results, it can be indicated that the Cu–H2O nanofluids is suitable for enhancing the efficiency of flat-plate solar collector.

Analysis of flow and heat transfer in a new lattice

The turbulent flow and heat transfer in a new lattice with non-uniform wall thickness are simulated and discussed by Unsteady Reynolds-Averaged Navier–Stokes (URANS) method with the Reynolds Stress Model (RSM). The simulation results agree well with the experimental data. It is shown that this new lattice with plum blossoms shape is propitious to the reasonable distributions of velocity and temperature as compared with the lattice with uniform wall thickness within a certain spanwise angle (θ). The amplitude of transverse oscillation velocity monotonically increases with the increase of thickening height (e/D), and the frequency first increases and then decreases. The frictional resistance coefficient and Nusselt number will reach their peak values when e/D=0.03. The lattice with plum blossoms shape and non-uniform wall thickness is superior to the traditional lattice when 0<e/D⩽0.06 and inferior to the traditional lattice when 0.06<e/D<0.12.

Coefficient of friction and wear resistance of zirconia–MWCNTs composites

Composites of 3mol% yttria-doped tetragonal zirconia (3Y-TZP) reinforced with multiwalled carbon nanotubes (MWCNT) up to 2wt% content have been produced using spark plasma sintering (SPS). The theoretical densities of the studied composites were found to be between 99.4% and 97.4%. The addition of MWCNT content resulted in reduction of 3Y-TZP grain size from 174 to 148nm. The effect of MWCNT on the friction coefficient (COF) was studied by performing nano- and macro-scratches using diamond Berkovich and Rockwell indenters, respectively. Moreover, the COF and the wear rate were also investigated in reciprocating sliding against a zirconia ball under a load of 5N. The results showed that the COF decreased upon the increase in MWCNT content. However, in macro-scratch testing, there was a critical load over which brittle fracture sets in and its value decreases as the MWCNT content increases. The wear resistance was found to be decreasing very slightly for less than 1wt% MWCNT, while it increases strongly for the addition of 2wt% MWCNT under the conditions studied. The results were discussed in terms of material properties, scanning electron microscopy observations of the wear track and nanoindentation tests.

Tribocorrosion Behavior of [Ticn/Tinbcn]n Coating on Austenitic Steels Substrate in Hanks' Balanced Salt Solution

Multilayer coatings [ TiCN / TiNbCN ] n were fabricated with periods of bilayers 1, 50 and 200 deposited on substrates of austenitic steels type fermanal, using R.F. reactive magnetron sputtering with a radio frequency source (13.56 MHz) and two TiC and Nb targets. The multilayers were characterized using X-ray diffraction and scanning electron microscopy. The tribo – electrochemical behavior simulating hostile body environment was evaluated by testing tribocorrosion ( combination of wear and corrosion in aqueous environment ) which were carried out with a Gamry PCI 4 equipment to which adapted a pin on disk tribometer, the tests were made immersed in Hanks solution (Hanks balanced salt solution). A cell comprising a platinum counter-electrode, an Ag/AgCl reference electrode and the and a working electrode ( austenitic steels) at a temperature of 37 ± 0.2 ° C. the evaluation tests were performed using electrochemical techniques of Tafel polarization curves. Regarding the results, the hard coating [ TiCN / TiNbCN ] n improved polarization resistance and lower coefficient of friction than that reported for the substrate is provided , which indicates a good resistance to corrosion and wear.

Effects of microstructures on the sliding behavior of hot-pressed CoCrMo alloys

Cobalt–chromium–molybdenum (CoCrMo) alloys are widely applied as wear-resistant material. This article aims to illustrate the influence of phase constitution and precipitate morphology on the wear behavior of hot-pressed high carbon alloys. Wear behavior of two kinds of CoCrMo alloys, HP (hot-pressed) and HPA (hot-pressed+annealing) with various microstructure, hardness and surface topography were evaluated in detail. The ε phase dominant HP alloy with homogenous lamellar precipitates demonstrates higher hardness, consequently lower coefficient of friction and prominent wear resistance with mild sliding wear. In contrary, the γ phase dominant HPA alloy with carbide-free grains was characterized by abrasive wear of micro grooves. The matrix hardness strengthened by ε phase is more significant to affect wear behavior than precipitate hardening. Homogenous lamellar precipitates have a stand-out effect to block abrasion and accumulate tribochemical products.

Tribological properties of Hot forged Al2024-TiB2 in-situ composite

A B S T R A C T Al2024-TiB2 in-situ composite was fabricated by liquid metallurgy route using Al-Titanium and Al-Boron master alloys. The developed composites were subjected to hot forging at a temperature of 500oC using a 200T hydraulic hammer. Microstructure studies, X-ray diffraction studies(XRD), grain size analysis, microhardness and dry friction and wear tests were carried out on as cast and hot forged matrix alloy and its composites. Pin on disc type machine was employed to perform friction and wear tests over a load range of 20-100N and sliding velocities of 0.314-1.57m/s. Microstructure and XRD studies reveal presence of fine TiB2 particles in both as cast and hot forged condition. It is observed that, both as cast and hot forged composites do exhibit significant grain refinement. When compared with as cast matrix alloy and its composite, hot forged alloy and its composite exhibits higher extent of grain refinement. Both as cast and hot forged composites exhibit improved microhardness, wear resistance and lower coefficient of friction when compared with the unreinforced alloy under identical test conditions.

Flow resistance characteristics of pulsating laminar flow in rectangular channels

Experimental investigations on the resistance characteristics of pulsating laminar flow in different sizes rectangular channels are performed at ambient temperature and pressure. The influence of the pulsating period was checked for 6<T<600s; the relative amplitude of Re ranged from 0.05 to 0.92. Both the experiments and the theory show that, the ratio Cf signified the time average pulsating frictional resistance coefficient to that of steady flow equals one for the same Reynolds number in part of the laminar region which the time average Re, the pulsating frequency and the relative amplitude of Re are as small as possible. And in this laminar region, the aspect ratio of rectangular channel has no significant effect on the ratio Cf. However, as the time average Re and the relative amplitude of Re increase, the flow regime becomes no longer laminar even though the real time pulsating Re is less than the transition Reynolds number. Two reasons leading to the phenomenon: (1) the acceleration decreases the transition Re, (2) and the maximum of pulsating Re exceeds the transition Reynolds number. The results of pulsating flow experiments on four kinds of different sizes rectangular channels are consistent.

Analysis of flow frictional resistance in U-tubes under ocean conditions

The additional forces in U-tubes under ocean conditions, which include heaving and rolling as well as pitching motion, are investigated, respectively. Based on the Navier–Stokes equations of turbulent flow, the correlations of frictional resistance coefficient of single-phase flow in U-tubes under ocean conditions are derived theoretically. The effects of some important parameters on the frictional resistance coefficient are also analyzed. It is shown that the frictional resistance coefficient will fluctuate with time under ocean conditions, and the more severe the motion is, the bigger the oscillating amplitude of the frictional resistance coefficient is. Further the oscillating amplitude of the frictional resistance coefficient is related to the fluid Reynolds number, the U-tube radius and the fluid density difference between the inlet and outlet of the U-tubes.