Surface Friction Coefficient Research Articles

Research on the Relationship between Bionic Surface Friction Coefficient and Interface Medium

The convex structure on tree frogs foot pats provide huge adsorption force, we can extract this facture of tree frogs foot pats, and apply on the surface of belt conveyor drum encapsulation in order to increase friction between drum and conveyor belt. But the environment underground is complex. There is always has coal particle and water on the frictional contact surface. The friction performance test was done by MMW-1A universal friction and wear tester in order to verify the friction coefficient of bionic surface under different conditions. At last, we figure out that water or coal particle has little influence on bionic friction surface, but has huge influence on common surface.

Development of a Tactile Sensor to Measure Tire Friction Coefficients in Arbitrary Directions

In order to develop intelligent tires that measures road surface friction coefficients, the present study proposes a simple tactile sensor that measures threedimensional loads. The sensor is composed of a cantilever called a whisker that is fixed to a base. The base is an elastic plate that has three strain gauges attached to its surface equiangularly around the fixed point of the whisker. The whisker is covered in cylindrical rubber, and the bottom surface is used as a contact. When the sensor touches a surface with the contact and traces it, vertical and horizontal loads are applied to the contact, compressing and bending the whisker so that the base is deformed elastically. Strains induced on the base by this deformation are measured by strain gauges. The study proposes a method obtaining values of vertical load, horizontal load and its direction from measured strains. Accordingly, the proposed sensor measures threedimensional load and obtains the contact surface friction coefficient. In the study, we fabricate a tactile sensor prototype and show its feasibility.

Development and Validation of Analytical Model for Stiffness Analysis of Curvic Coupling in Tightening

Curvic couplings are extensively used in aerospace machinery, such as helicopters, aeroengines, or other aircraft. In this paper, the behavior of bolted joints with curvic couplings is investigated to determine a method to describe the relationship between the stiffness parameters and the geometry of the parts of curvic coupling and external loads. The validity of the method is proven through experiments and finite-element simulation. Additionally, the study investigates the effects of the curvic height, curvic width, curvic thickness, pressure angle of curvic surface, and friction coefficient of curvic surfaces on the stiffness of disc parts. The analytical results show that the compression stiffness of both the curvic and ring parts of the disc has a relationship with the curvic rotation. Although the curvic compression stiffness tends to be constant in the bolt-tightening process for different curvic geometrical dimensions, the compression stiffness of the other disc parts has obvious differences owing to the various curvic geometrical parameters. By choosing appropriate pressure angles of the curvic surface or number, the stiffness of the curvic coupling can be kept stable in the bolt tightening course. The stiffness parameters of curvic couplings can be determined by the analytical model, regardless of how the geometry of the parts of curvic couplings or the external loads are changed.

The Sensitive Parameter Study of Axial Flow Compressor Fouling

Fouling is an important performance degradation factor of axial flow compressor. Proper fouling sensitive parameter is crucial to more effectively monitor the fouling severity. Currently fouling level and cleaning necessity are judged by the decrease degree of thermodynamic performance parameter from macro point. But simulation research of NASA rotor 37 finds that tip clearance increase also causes the decrease of thermodynamic parameters such as pressure ratio, mass flow, efficiency and output power, so these parameters can’t distinguish fouling and other failure modes. Contaminated particles within air deposited on the blade surface to cause the change of blade shape and surface roughness. But from the definition of roughness, fouling and erosion can’t be distinguished by surface roughness. Finally, blade profile parameters are chosen as sensitive parameter of fouling. At the same time, with the rapid development of measure technology, profile parameter can be measured by combination of laser triangulation method and CMM (coordinate measuring machine). Based on reverse engineering, measure point clouds are reconstructed into three dimensional solid model of fouled compressor. Quantitative research shows that fouling cause increase of total temperature, total pressure and surface friction coefficient, simultaneously effective flow area is decreased, thus thermodynamic performance is degraded.

Structure and properties of diamond-like carbon thin films synthesized by biased target ion beam deposition

Biased target ion beam deposition (BTIBD) was firstly used to synthesize hydrogen free diamond-like carbon (DLC) thin films. The structure and properties of the synthesized films were characterized by atomic force microscopy (AFM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), nanoindentation, and ball-on-disk testing. The effect of target bias voltage, ranging from −200 to −1000V, on the structure and properties of the films was investigated. The results show that the sp3 bonding content increases from 20% to 60%, the root-mean squared (RMS) roughness decreases from 0.2nm to 0.05nm, the coefficient of friction (COF) decreases from 0.3 to 0.06, the hardness increases from 4.5GPa to 15GPa, and the Young's modulus increases from 65GPa to 170GPa with increasing the absolute value of target bias voltage from 200V to 800V. However, when the target bias voltage further increased to −1000V, the sp3 bonding content decreases to 44%, RMS roughness increases to 0.09nm, COF raises to 0.11, hardness decreases to 12.9GPa and Young's modulus is lowered to 150GPa. It has been found that the higher the fraction of sp3 bonds, the lower the surface roughness and friction coefficient, and the higher the hardness and Young's modulus.

Annealing temperature effect on the mechanical and tribological properties of molybdenum nitride thin films

Mo thin films with 100-nm thickness were deposited on silicon substrates using DC magnetron sputtering method. Mo thin films were subsequently annealed at different temperatures (400°C to 900°C) with flow of nitrogen. The crystallographic structure of the samples was obtained using X-ray diffraction method. Atomic force microscopy and scanning electron microscopy were used for surface morphology investigation. Nano-indentation and scratch tests were performed to obtain the surface hardness and friction coefficient of the samples, respectively. Results show that the γ-Μο2Ν(111) phase of molybdenum nitride with face-centered cubic structure and higher hardness, elastic modulus, and lower coefficient of friction and scratch volume is formed when the sample is annealed at 650°C, while the Mo2N phase with tetragonal structure and lower hardness, elastic modulus, and higher scratch volume and friction coefficient is formed at higher temperatures of 775°C and 900°C. It is found that increasing the annealing temperature causes an increase of the grain size and film surface roughness. From the mechanical results, it may be deduced that 650°C is a critical temperature for variation of mechanical and tribological properties.

Effect of different nitriding processes on the friction coefficient of 304 austenitic and 420 martensitic stainless steels

PurposeThe purpose of this paper is to present the results of a study on friction characteristics of plasma, salt‐bath and gas nitrided layers produced in AISI 304 type austenitic and AISI 420 type martensitic stainless steels.Design/methodology/approachPlasma nitriding processes were carried out with DC‐pulsed plasma in 80% N2+20% H2 atmosphere at 450°C and 520°C for 8 h at a pressure of 2 mbar. Salt‐bath nitriding was performed in a cyanide‐cyanate salt‐bath at 570°C for 1.5 h. Gas nitriding was also conducted in NH3 and CO2 atmosphere at 570°C for 13 h. Characterization of all nitrided samples has been carried out by means of microstructure, microhardness, surface roughness measurement and friction coefficient. The morphologies of the worn surfaces of the nitrided samples were also observed using a scanning electron microscope. Friction characteristics of the nitrided samples have been investigated using a ball‐on‐disc friction and wear tester with a WC‐Co ball as the counterface under dry sliding conditions.FindingsThe plasma nitrided and salt‐bath nitrided layers on the 420 steel surfaces were much thicker than on the 304 steel surfaces. However, there was no obvious and homogeneous nitrided layer on the gas nitrided samples' surface. The plasma and salt‐bath nitriding techniques significantly increased the surface hardness of the 304 and 420 samples. The highest surface hardness of the 304 nitrided samples was obtained by the plasma nitrided technique at 520°C. On the other hand, the highest surface hardness of the 420 nitrided layers was observed in the 450°C plasma nitrided layer. Experimental friction test results showed that the salt‐bath and 450°C plasma nitrided layers were more effective in reducing the friction coefficient of the 304 and 420 stainless steels, respectively.Originality/valueThe relatively poor hardness and hence wear resistance of austenitic and martensitic stainless steels needs to be improved. Friction characteristic is a key property of performance for various applications of austenitic and martensitic stainless steels. This work has reported a comparison of friction characteristics of austenitic 304 and martensitic 420 stainless steels, modified using plasma, salt‐bath and gas nitriding processes. The paper is of significances for improving friction characteristics, indirectly wear performances, of austenitic and martensitic stainless steels.

An engineering approach to dry friction behaviour of numerous engineering plastics with respect to the mechanical properties

Twenty-one different commercial-grade engineering polymers, including virgin and composite types, were selected for testing, based on mechanical engineering practices. Three groups were formed according to typical applica- tions: 1) Sliding machine element materials; 2) Mechanically load-carrying machine element materials that are often sub- jected to friction and wear effects; and 3) Additional two amorphous materials used as chemically resistant materials that have rare sliding load properties. The friction running-in state was tested using a dynamic pin-on-plate test rig. During steady-state friction tests, two pv regimes (0.8 and 2 MPams -1 ) were analysed by a pin-on-disc test system. Based on the measured forces on ground structural steel, surface friction coefficients were calculated and analysed with respect to the mechanical effects of friction. The friction results were evaluated by the measured mechanical properties: yield stress, Shore D hardness, Young's modulus and elongation at the break. The three material groups exhibited different trends in friction with respect to changing mechanical properties. Linear (with varying positive and negative slopes), logarithmic and exponential relationships were observed, and occasionally there were no effects observed. At steady-state friction, the elongation at the break had less effect on the friction coefficients. The dynamic sliding model, which correlates better to real machine element applications, showed that increasing hardness and yield stress decreases friction. During steady-state friction, an increase in pv regime often changed the sign of the linear relationship between the material property and the friction, which agrees with the frictional theory of polymer/steel sliding pairs.

Investigates of Fabric Coating Approaches: Process and Observation

In this work, polyurethane coating on the fabrics is studied in the Basecoater 200. The structure and morphology of coated fabrics were investigated using SEM and soaking test in the cured coated samples. Coating thicknesses, surface friction coefficient and surface roughness variation of the samples were measured using the surface tester of the KESF. Results showed that uniform and cross linking degree of the surface layer of coated samples have close relevant with coat processing. The performance quality of end products can be achieved by optimization of process variables, including coating speed, coating solution, and cure temperature and fabric matrixes during fabric coating processing.

Evaluation of Surface Characteristics of Fabrics Using Tactile Sensor

Weave, yarn density, yarn count, fiber material and so on of woven fabrics greatly affect their surface characteristics. Surface characteristics of a fabric are important factor for consumers and textile producers in order to evaluate its fabric hand. However, there is no simple system to easily measure its surface characteristics. This study uses a simple tactile sensor that can measure the friction coefficients of fabric surfaces and tries to evaluate their surface characteristics from obtained values. We traced surfaces of plural fabrics that differ in yarn, weave and yarn density with the tactile sensor, and measured variation of the friction coefficients with respect to the trace distance. This study introduces some evaluation values from the measured variation of the friction coefficients and compares them with results by KES, which is the ordinary system to evaluate surface characteristics of a fabric. As a result, the study confirmed that proposed method easily evaluates the geometrical and frictional properties of woven fabrics as their fabric hand, and also can estimate the yarn density of woven fabric by analyzing the oscillation period of variation of friction coefficient.

Tribological Properties of Ultrasonic Vibration Assisted Milling Aluminium Alloy Surfaces

Kinematics analysis of tool-tip in milling process with ultrasonic vibration in feed direction was conducted. Ultrasonic vibration assisted milling (UVAM) aluminium alloy experiments were designed to investigate the morphologies of machined surfaces. Research results showed that some regular scaly textures distributed evenly on the UVAM surfaces, which are consistent with the theoretical analysis results of tool-tip trajectory. The tribological properties of machined surfaces were tested by using UMT-2 friction and wear testing machine. Test results showed that scaly textures enhanced the adsorption capacities of UVAM surfaces to oil film; as well, it played an important role for oil storage and trapping wear particles, resulting in better friction stabilities. Compared to traditional milling surfaces, the friction coefficients of UVAM surfaces decreased about 20%, and their bearing capacity of oil films increased about 140%.

Behavior of the submicrocrystalline Y–TZP–Al2O3 composite in dry friction with steel

The paper discusses the wear resistance, friction coefficient, and structure of friction surfaces of submicron crystalline Y–TZP–Al2O3 composite rubbed against a steel disk counterface at a pressure of 5 MPa in a range of sliding speeds from 1 to 20 m/sec. It is shown that, starting at 2 m/sec, the friction surface is subdivided by a crack network into separate regions within which local spalling occurs at the maximum wear rate and a sliding speed of 5 m/sec. X-ray diffraction reveals inversion (with respect to the initial state) of the peak intensities of the tetragonal phase with random crystalline grain orientation. The degree of this inversion increases with sliding speed. These results are discussed in terms of the effects exerted by the reorientation of martensite-free deformation twins in the tetragonal phase and the formation of a quasi-liquid film on the wear resistance of Y–TZP–Al2O3.

Integration of UTIS and WIS information for Determining Speed Limits of Variable Speed Limit System

There has been a strong demand for providing diverse services to drivers utilizing existing ITS infrastructure. To this end, this study is aiming at improving the accuracy of a variable speed limit system by determining recommended speeds for the system utilizing the information from Urban Traffic Information System(UTIS) and Weather Information System(WIS). In order to determine appropriate speed limits under inclement weather conditions for the variable speed limit system, this study examined three methods: i) the method utilizing the information from WIS, ii) the method utilizing the information from UTIS, and iii) the method which combines the information from WIS and UTIS using different weights for diverse weather conditions. Finally, this study selected the third method which determines an appropriate speed limit using the relationship between the vehicle operating speed and the minimum stopping distance which is estimated using the existing speed limit, surface coefficient of friction and superelevation.

Effect of substrate bias on microstructure and tribological performance of GLC films using hybrid HIPIMS technique

The Cr-doped hydrogen-GLC films were prepared by a hybrid magnetron sputtering system composed of a direct current magnetron sputtering (DC-MS) source of carbon and a high power impulse magnetron sputtering (HIPIMS) source of Cr with reactive gas of C2H2. The hydrogen-free GLC and Cr-doped GLC films were also prepared for comparison. The influence of substrate bias on the Cr-doped hydrogen-GLC films was investigated. With the increase of substrate bias from −100 V to −250 V, the re-sputtering of weak bonding sp2 firstly occurred and induced an increased sp3 bonding. However, the following sp3 to sp2 transformation resulted in a decreased sp3 bonding. The change trends of surface roughness and friction coefficient with the increased bias voltages were the same as those of sp3 bond. The lowest surface roughness and lowest friction coefficient corresponded to the highest sp3 with the Cr-GLC-H films at the bias voltage of −100 V.

Minimization of surface friction effect on scratch‐induced deformation in polymers

AbstractSurface friction plays an important role in influencing the stress field development during scratch process, thus, scratch‐induced deformation mechanisms. In this study, three‐dimensional finite element method (FEM) parametric study was performed along with experimental validation to investigate the effect of surface friction on scratch‐induced deformation and its correlation with the constitutive behavior of polymers. As scratch depth and shoulder height are the key parameters for causing scratch visibility, the focus is to investigate the effect of surface friction on these two scratch‐induced deformation features and how the surface friction effect can be altered by varying the constitutive parameters. The FEM findings and experimental observations indicate that onset of groove formation during the scratch process is strongly influenced by yield stress and coefficient of surface friction. Also, the relative frictional effect on scratch‐induced deformation becomes minimal if the post‐yielding strain hardening slope of the polymer is high. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers

Changes in the surface roughness and friction coefficient of orthodontic bracket slots before and after treatment

In this study, we tested the surface roughness of bracket slots and the friction coefficient between the bracket and the stainless steel archwire before and after orthodontic treatment. There were four experimental groups: groups 1 and 2 were 3M new and retrieved brackets, respectively, and groups 3 and 4 were BioQuick new and retrieved brackets, respectively. All retrieved brackets were taken from patients with the first premolar extraction and using sliding mechanics to close the extraction space. The surface roughness of specimens was evaluated using an optical interferometry profilometer, which is faster and nondestructive compared with a stylus profilometer, and provided a larger field, needing no sample preparation, compared with atomic force microscopy. Orthodontic treatment resulted in significant increases in surface roughness and coefficient of friction for both brands of brackets. However, there was no significant difference by brand for new or retrieved brackets. These retrieval analysis results highlight the necessity of reevaluating the properties and clinical behavior of brackets during treatment to make appropriate treatment decisions.

Research of Safe Speed at Snow on Freeway Based on Braking Model of Stopping Sight Distance

The brake model derivation based on the kinematics of the stopping sight distance analysis, considering the freeway visibility and road surface friction coefficient, put forward freeway safety speed calculation model in snow condition, reach maximum safe speed of snow freeway in a different visibility and road adhesion coefficient snow condition, provide a management reference for freeway snow driving safety.

Fractal Theory Applied to Evaluate the Tribological Performances of Two Greases Demonstrated in Four-Ball Tests

In the present study, two commercial greases with different rheological properties were subjected to four-ball tests to identify their performance in anti-wear and anti-scuffing. A wear test machine equipped with a data acquisition system was used to collect and analyze the experimental data of electrical contact resistance (ECR) and friction torque (Tf). Fractal theory was used to deal with the signals of the above two parameters simultaneously. The fractal dimension (Ds) and topothesy (G) of the signals were used to establish their magnitude in relation to the tribological parameters, such as worn surface roughness and friction coefficients. The variations in the fractal parameters can be used to determine the possibility of surface scuffing under the given operating conditions. The frictional energy required for surface scuffing decreases with increasing normal load. Worn surface roughness (Ra) that varies with test time depends strongly on the amount of oxide residual on the worn surface. If the oxide amount increases with time, the surface roughness decreases, which increases the fractal dimension and topothesy of ECR. For grease, the time starting the net growth of oxides is thus the governing factor for variations in worn surface roughness. The fractal dimension of friction coefficients varied in a narrow range regardless of scuffing. However, scuffing in the wear process affected the topothesy of the friction coefficient. The fractal analysis of friction coefficients is an efficient method for determining the possibility of scuffing that arises at contact surfaces during the wear testing processes.

Study on Properties and Preparation of Films by Unbalanced Magnetron Sputtering

TiAlN films were prepared by closed field Unbalanced Magnetron Sputtering ion plating. EDS, XRD and SEM were used to test the films’ chemical composition, microstructure and surface morphology. In addition, the films’ surface microhardness, bonding strength and friction coefficient were also determined. The experimental results indicate that the TiAlN films of different substrate hardness have dense film structure and the same chemical composition, the hard substrate microhardness of the film can reach 2575 HV0.025 and soft substrate can be up to 2295 HV0.025, the bonding strength of which is respectively 59N and 56N, Friction coefficient is 0.45 and 0.5.

MoSx-Ta composite coatings on steel by d.c magnetron sputtering

Sputter-deposited MoS2 films have been often used as dry lubricant in various industrial fields, such as space application and much attention has been paid to reduction of friction coefficient and improvement of mechanical properties in recent decades. One way to achieve this is to deposit a MoS2 film doped with another metal. The MoSx-metal films were found to be denser, more adhesive and more oxidation-resistant than pure MoS2. In this study, MoSx-Ta composite films were synthesized by Electron Cyclotron Resonance microwave source enhanced DC sputtering with different target powers. The effects of doping Ta on mechanical properties of MoSx-Ta films were investigated. The morphology and structure of films were investigated using a scanning electron microscope (SEM), X-ray diffraction (XRD) and atomic force microscopy (AFM). The microhardness was evaluated using microhardness test instrument, and the adhesion strengths were obtained using a scratch tester. The results showed that the S/Mo ratio was influenced by the dc sputtering target power. Typical MoS2 (100) (103) (002) orientations were present in pure MoSx films, but disappeared with the increase in doped Ta, with the S/Mo content ratios decreasing from 1.52 to 0.84, and the hardness increasing from 3.55 to 15.23 GPa. The roughness and surface topography, friction coefficient and adhesion were significantly affected by the Ta, Mo and S content. The content of doped Ta plays a dominant role on the change in the Mo/S ratio, thereby influencing the mechanical and tribological properties of the MoSx-Ta composite films.