Friction Coefficient Test Research Articles

Performance evaluation of asphalt pavement groove-filled with polyurethane-rubber particle elastomer

Considering the influence of road icing on traffic safety in winter, a pavement surface treatment technology with groove-filled polyurethane rubber particle elastomer (PRPE) was proposed. The optimum ratio of PRPE was determined by testing the mechanical properties, bonding properties and construction properties. Then the bonding durability, ice-breaking performance and skid resistance of PRPE were tested. The results showed that 40 mesh rubber particles, 60% polyurethane binder content, 3‰ catalyst and 5% diluent were selected as the optimal ratio of PRPE. Three test environments (Freeze-thaw, High temperature and immersion, High temperature and immersed in saltwater) have no obvious influence on the interface bonding performance of PRPE, only a slight reduction. The ice-breaking effects of the four pavement types are in order the PRPE and groove level > the PRPE lower than groove > the PRPE higher than groove > the grooved pavement (unfilled). Finally, through BPN and friction coefficient test, the skid resistance performance of the three pavement types under dry, wet and icing conditions is verified. Compared with the AC-13 asphalt mixture, the skid resistance of groove-filled pavement is improved by 4.5%, 10.8% and 24.6% under dry, wet and icing conditions respectively.

Characteristics of wood powder, coconut fiber and green mussel shell composite for motorcycle centrifugal clutch pads

This research is motivated by the need for environmentally friendly motorcycle centrifugal clutch pads. Utilization composites of wood powder, coconut fiber, and green mussel shells for centrifugal clutch pads have not been much discussed in the research. Centrifugal clutch functions to transmit power from the engine to the drive train with a centrifugal force mechanism. This study aims to determine the characteristics of the hardness, wear, coefficient of friction, and microstructure of the composite. Composite material was made with three variations, namely specimen 1 consisting of 20% wood powder, 20% coconut fiber, 60% resin, and 0% shells. Specimen 2 made of 20% wood powder, 20% coconut fiber, 50% resin, and 10% shells. Specimen 3 is made from 20% wood powder, 20% coconut fiber, 40% resin, and 20% shells. All specimens were characterized by hardness testing according to ASTM E92 by the Vickers FV-300e. Each specimen was tested three times and the average data was taken. Wear resistance testing according to ASTM G99 by OGOSHI machine. Friction coefficient testing is based on the principle of friction in the inclined plane. While microstructure testing uses SEM by JEOL JSM-6510LA. The results shows that the composition of wood powder, coconut fiber, and shell influenced the test results. Specimen 3 shows the highest value of hardness, wear and coefficient of friction compared to others so that it can be used for the centrifugal clutch.

Minimum clearance technology to improve performance of twin-screw refrigeration compressors by spraying coating on rotors

During the operating of twin-screw refrigeration compressors, the leakage has a significant influence on the performance of compressors. In this paper, a novel minimum clearance technology that applies the abradable coating to the rotor surface is proposed to lessen the leakage. In order to adapt to the application of the abradable coating, the deformation of rotors during operation is analyzed and a suitable clearance is designed based on the fluid-solid coupling analysis. Then, a suitable coating pre-treated by sandblasting is obtained according to the results of friction coefficient and abradability test. Finally, a prototype is tested and the total efficiency, volumetric efficiency, refrigerating capacity, and COP of the prototype are compared before and after spraying the coating. Test results show that the volumetric efficiency and refrigerating capacity increase significantly after spraying the abradable coating, and the input power decreases slightly. As a result, the COP increases by 6.71% and 7.89% at two nominal operating conditions.

Comparison of friction coefficient and surface roughness on stainless steel nickel titanium, and nickel-titanium copper wires to standard edgewise brackets: An experimental in vitro study

Aim: The aim of this study was to investigate the friction and the difference in the roughness of the wire on the standard edgewise bracket. Materials and Methods: This was an experimental laboratory study with a posttest only control group design. The number of samples in this research was 21. The samples were divided into three groups (n = 7) consisting of 0.016′′ x 0.022′′ stainless steel archwire (SS group), 0.016′′ x 0.022′′ nickel-titanium archwire (NiTi group), and 0.016′′ x 0.022′′ nickel-titanium copper archwire (NiTiCu group). The bracket used in each group is standard edgewise slot 0.018. Friction coefficient test was conducted by creating an examination tool from acrylic to fixate the bracket with a size of 2cm x 5cm. The bracket was then attached using glue (polyvinyl acetate) and the archwire was fixated to the bracket using power O. After the friction test, three samples were taken from each group to be tested morphology and topography of each type using scanning electron microscope (SEM). Statistical analysis used in this research is using one-way analysis of variance (ANOVA) to find out the comparison of variables and Tukey’s honest significant difference (HSD) to find out the comparison between three groups (P < 0.05). Results: The lowest friction coefficient was found in SS archwire, which consecutively followed by NiTiCu and NiTi. The smoothest archwire surface observed by SEM was SS, followed by NiTiCu and NiTi. Conclusion: SS wire has the smoothest archwire surface and the lowest frictional force, so it is well used for the teeth movement in space closing on edgewise bracket.

Investigation of Usage of Milled Pine Cone in Brake Pads

Automotive brake pads are polymer composites containing polymer matrix and various fibers and obtained by mixing and pressing different powder materials. Each material added to the content has one or more tasks. Therefore, the properties and quantities of the materials added to the content are very important in terms of braking performance. In this study, the use of milled pinus brutia cone and pinus nigra cone from the pine cone family in the automotive brake pad was investigated experi-mentally. First of all, cones are ground and powdered. The milled 10% pinus brutia cone and 10% pinus nigra cone were added to the pad com-ponent. The performance tests of the pads were carried out on pin on disk type test device. Friction coefficient, wear, density and hardness tests of the pads were done. The test results have been shown to affect the brak-ing performance of milled pine cone.

Comparisons Between Braking Experiments and Longitudinal Train Dynamics Using Friction Coefficient and Braking Pressure Modeling in a Freight Train

Background: This paper describes the predictions and validation of the pneumatic emergency braking performance of a freight train consisting of a locomotive and 20 wagons, generally operated in Korea. It suggests the possibility of replacing the expensive and time-consuming train running tests with longitudinal train dynamic simulations. Methods: The simulation of longitudinal train dynamics of a freight train uses the time integration method of EN 14531. For reasonable simulation results, the characteristics of the train and brake equipment must be considered. For the train characteristics, specifications provided by the vehicle manufacturer are used. The braking characteristics are analyzed by friction coefficient tests and a braking pressure model. The friction coefficients of a locomotive and wagons are tested with a dynamo test bench and statistically expanded to account for variability. Freight trains should take into account the braking delay time. To reflect this in the simulation, the brake cylinder pressure pattern model uses pressures and exponential empirical equations measured at selective positions in a train of 50 vehicles. The simulation results are validated in comparison with those of the braking tests of a freight train consisting of 1 locomotive and 20 wagons. Results: The results of the longitudinal dynamics simulation show very similar results to the running test results based on the speed profile and braking distance. Conclusion: In particular, the statistical expansion method of the friction coefficient enables robust prediction of the distribution of the braking distance. The simulation can reduce or make up for costly and time-consuming repeated braking tests and reduce the risks that may arise during testing.

Increasing inter-yarn friction to ultra-high molecular weight polyethylene yarns for ballistic application by sol-gel treatment

Ultra-high molecular weight polyethylene fibre is popularly used in military for ballistic protection owing to its low density but high modulus and high tenacity. However, the inter-yarn friction in the corresponding ballistic fabric is too low and thus the yarns in the fabric are easily pulled out, in which lowers down the ballistic performance. This paper aims to improve the inter-yarn friction in the fabric by sol-gel method using TiO2/ZnO hydro-sols and investigate the ballistic performance of fabric treated. The results from the coefficient of friction test have showed that the inter-yarn friction treated with TiO2/ZnO hydro-sol can be increased 40%. Moreover, tensile test indicates that the tenacities of yarns after different treatments are increased whereas the strains and moduli of the yarns almost kept unaffected. Through ballistic performance test, the treated fabric displays higher ballistic energy absorption compared with the original one, indicating that higher inter-yarn friction is beneficial to fabric against ballistic impact.

The effect of hard segment content of polyurethane on the performances of polyurethane porous mixture

To study the effects of the hard segment content of Polyurethane (PU) on the performances of polyurethane porous mixture (PPM), three PUs with different hard segment contents are selected in this paper. Firstly, the properties including hardness, elongation, e-modulus of PU were tested. Secondly, the cantabro test was used for analyzing the effect of hard segment content on the cantabro losses of the open-graded friction course 16 (OGFC16), OGFC13 and OGFC10 at the different immersed times and temperatures. Thirdly, the freeze–thaw splitting test, rutting test, friction coefficient test and three-point bending test were used for studying the road performances of OGFC13. The results of tests show that the elongation decreases with the increasing of hard segment content. The water and temperature have significant effects on the cantabro losses of PPM. The cantabro loss of PPM increases with the increasing of the immersed time and temperature. And the cantabro losses of PPM are higher than that of asphalt mixture (AM) overall. In terms of the road performance, the hard segment content of PU has a significant effect on the cantabro losses of PPM, has no effect on the tensile strength ratio (TSR). Therefore, the hard segment content of PU has a significant effect on the water stability of PPM in some cases. Besides, the hard segment content has a significant effect the dynamic stability, flexural strength and flexural tensile strain of PPM, has an effect on anti-skid ability in some cases. In the whole, the PU with smaller hard segment content is beneficial to has better road performances. Finally, the PU with the hard segment content from 41% to 51% is recommended.

Effects of Soil Conditioning on Characteristics of a Clay-Sand-Gravel Mixed Soil Based on Laboratory Test

Soil conditioning is of great significance for tunneling in soft ground with earth pressure balance shield (EPBS) machines, which leads to safe, highly efficient, and high-quality tunneling. To study the effects of soil conditioning on properties of a clay-sand-gravel mixed soil encountered in an EPBS tunneling project in Beijing, a series of geotechnical test methods was carried out based on laboratory test in this paper. The decay behaviors of foam particles generated by the Waring-Blender method were studied first using the image particle analysis system, and then the feasibility of soil conditioning on the mixed soil was qualitatively and quantitatively assessed through the mixing test, slump test, and friction coefficient test. The preliminary test results indicate that drainage of water in liquid film plays an important role in the decay of foam microstructure. The viscosity and flowability of the conditioned soil were modified dramatically by using various amount of water and foam, and a suitable state meeting the requirement of EPBS machines was obtained. The net power and mixing time, which reflects the interaction between the blending rods and tested soils, as well as the slump value, providing the overall indication for liquidity of the conditioned soils, and friction coefficient, reflecting the friction between steel and tested soils, were used to provide insight into the variation in viscosity and flowability of the tested soils.

Experimental tests of static friction coefficient for selected material combinations of expanded graphite - steel used in sealing nodes

The paper presents the results of static friction coefficient tests of selected material sets used in sealing nodes. Four graphite materials were tested - pure expanded graphite, expanded graphite with the addition of PTFE plastic of different densities (1.4 and 1.8 [g/cm3]) and expanded graphite laminated with austenitic steel foil - matching the steel surface. The combinations operated in a reciprocal movement. The measurements were made at different unit pressures (0.5, 2 and 5 MPa) and for different work cycles (0, 500, 1500 and 3000). On the basis of the results obtained, it was found that both the load and the number of work cycles have a significant influence on the value of the static friction coefficient of the tested materials. Not without significance is also the density of selected graphite materials. It was found that expanded graphite with PTFE and density of 1.8 g/cm3 was characterized by the lowest static friction coefficient in comparison with other materials. It is also worth noting the fact of a layer on the steel surface of combination which promotes the formation of stick-slip phenomenon.

A biomimetic urethral model to evaluate urinary catheter lubricity and epithelial micro-trauma

The standard method of evaluating the lubricity of intermittent urinary catheters with coefficient of friction (CoF) testing is not physiologically relevant, while there is also a dearth of published research on catheter-associated urethral micro-trauma. We developed a novel human urethral epithelial cell-seeded model of the urethra to replace the rubber counter-surface used in standard CoF testing. This cell-seeded model, in conjunction with a novel testing device, allows an investigation of catheter-associated epithelial micro-trauma in vitro for the first time. The CoF of four brands of commercially-available hydrophilic-coated intermittent catheters was measured using both the rubber and urethral model counter-surfaces. Post-catheterisation of the urethral model, the damage to the epithelial layer was analysed using standard cell imaging. The rubber counter-surface was shown to over-estimate the CoF of gel-coated catheters compared to our urethral model due to stick-slip behaviour caused by polymer-on-polymer interaction of the catheter base material on the rubber counter-surface. We identified no deleterious effect due to the presence or design of catheter eyelets to either the CoF measurements or the degree of epithelium damage in our model. Furthermore, the epithelial damage did not correlate with the measured CoF of the low friction catheters, suggesting a more nuanced pathogenesis of urethral irritation and casting doubt on the translatability of a solely mechanical assessment of lubricity of urinary catheters to a clinical effect.

Analysis of Skid Resistance and Noise Characteristics for Varieties of Concrete Pavement

To establish evaluation criteria for the pavement skid resistance and noise level in tunnels pavements, the zoning and control standards for skid resistance and concrete pavement noise were examined. Transverse friction coefficient (TFC) test equipment and the on‐board sound intensity (OBSI) method were used to evaluate the antisliding characteristics and noise levels of several tunnel pavements. The results indicated poor antisliding characteristics and noise levels in ordinary grooved cement concrete pavement, whereas new types of cement concrete pavements, such as exposed concrete pavements and polymer‐modified cement concrete pavements, had good antisliding characteristics and achieved low noise levels. Combined with the cluster analysis method, a zoning method for the antisliding and noise level in concrete pavement is proposed. The antisliding characteristics and noise levels of the pavement are divided into three zones. To ensure safety and comfort during driving, the antisliding value (SFC) of the tunnel pavement should be more than 50, and the noise level should not exceed 105 dB. Finally, the correlation between the antisliding and noise levels for pavement was analyzed. The results indicated that the antiskiding value of pavement has a strong correlation to the noise level.

Study on ameliorating friction noise of ABS materials by lubrication

In this study, the stick-slip mechanism of ABS resin friction noise and the effect of different lubricants on the friction noise were investigated by means of friction coefficient test instrument and self-designed noise test method. It was found that different types of lubricants have different effects on ameliorating the noise and stick-slip phenomena of ABS material. As the content of lubricant increased, the friction noise and stick-slip phenomenon of ABS were reduced. According to the study, reducing the dynamic and static friction △F was the key factor to reduce the stick-slip phenomenon and reduce the friction noise.

Effect of friction coefficient on the mixed lubrication model of rotary lip seals

This study is devoted to the effect of different coefficients on the calculation results of the rotary lip seal mixed lubrication model. It was proved by experiments that the dry friction coefficient used in the previous models was quite different from the boundary lubrication friction coefficient, which was theoretically more accurate. The pumping rate, friction torque, pressure distribution, and oil film thickness were calculated using both the dry friction coefficient and the boundary lubrication coefficient and the results were quite different. A friction coefficient test method under boundary lubrication condition for numerical simulation of rotary lip seals and an improved method for numerical calculation using the boundary lubrication coefficient instead of the dry friction coefficient were proposed. It was verified that the accuracy of numerical calculation can be improved, and the calculation result was closer to the actual working state.

Crystal structure and tribological properties of molybdenum disulfide films prepared by magnetron sputtering technology

Molybdenum disulfide (MoS2) is widely used in practice due to its excellent lubricating properties. However, research on the tribological properties of magnetron sputtering for depositing MoS2 films remains limited. Herein, the tribological properties of MoS2 films were investigated in detail through a series of characterization and friction coefficient tests. MoS2 films were deposited onto silicon substrates by magnetron sputtering under different radio-frequency powers (Prf). With increased Prf, the crystallinity of the films gradually increases, whereas the friction coefficient initially decreases and then increases. Prf also affects the chemical composition, surface morphology, and grain size of MoS2 films. At Prf = 300 W, the film surface is dense and smooth, the grain distribution is uniform. Moreover, the films have superior tribological properties and low friction coefficient, which can be attributed to the weak van der Waals force among MoS2 layers and the microscopic morphology of the films. All these results indicate that by reasonably controlling the preparation parameters, MoS2 films with excellent tribological properties can be prepared by magnetron sputtering.

Mechanism Analysis and Experimental Study of Emulsified Wax Curing Agent as an Isolation Layer for Concrete Pavement

Abstract The functional mechanism of emulsified wax curing agent (EWCA) as an isolation layer of cement concrete pavement (CCP) was analyzed. Reducing the friction between layers and improving the hydrophobic function of concrete surface can weaken the combination of surface course and base course, as well as the formation of weak transition layer, which is generated during the construction of concrete undersurface course. After the cement concrete surface was sprayed with EWCA, its contact range was measured to be 97.3°∼101.1° in the contact angle test. With the nuclear magnetic resonance equipment, the study on the microstructure of the pavement slab of EWCA’s isolation layer was carried out. The isolation layer of EWCA can reduce the porosity of transition layer and enhance its compatibility. The effect of EWCA on the interlayer performance of concrete pavement was explored by the interlayer bonding and friction coefficient tests with different amounts of EWCA and different texture depths of base course. The Coulomb model of interlayer bonding and frictional resistance was established, which preliminarily indicated the functional mechanism of CCP’s emulsified isolation layer.

Friction and wear properties of base oil enhanced by different forms of reduced graphene

In this study, the tribological effects of three different forms of reduced graphene oxide (rGO)-2D nano-additives in base oil were investigated. Reduced graphene oxide nanoplatelets were manufactured using a modified Hummers’ method. However, different filtration methods were used to obtain rGO nanoplatelets at three different bulk densities. After adding nano-additives to the base oil at 0.01%w/w concentration, physical and chemical characterization tests were performed such as viscosity test, four-ball wear test, rotating pressure vessel oxidation test (RPVOT), resistivity test and friction coefficient test. The presented results show that material-1 with the lowest bulk density and less lattice defect can perform better by reducing wear of the material by 10.63% as well as the coefficient of friction (COF) by 6.3% with respect to the base oil and under test conditions. The presented results show the promising effect of rGO as nano-additives to fluid lubricants on wear preventive properties without compromising the physical and chemical characteristics of the lubricants.

Study on Road Performances of Ultra-thin Wearing Layer Small Particle Size Asphalt Mixture

In order to find out that if it is available to apply the asphalt mixture with small particle size and large porosity to the ultra-thin wearing layer, a kind of open-graded asphalt mixture whose nominal maximum aggregate size is 4.75mm and void ratio is greater than 20% is designed in this article. The rutting test, low-temperature bending test, freeze-thaw split test, pendulum friction coefficient test, manual sand patch test and permeability test are conducted to evaluate the road performance and surface behavior like high-temperature stability, low-temperature, water stability, friction and permeability. The test results shows that the asphalt mixture’s 60℃ dynamic stability is 8201 times /mm, ultimate bending strain is 2896 μe, the residual strength ratio of freeze-thaw split is 83.94%, BPN is 69, the texture depth is 0.71mm, and water permeability coefficient is 6857mL/min. It can be concluded that the asphalt mixture with small particle sized aggregate and large porosity has good road performance, whose high-temperature stability, anti-skid performance and drainage performance are excellent. Compared with road performance of OGFC-13, small particle asphalt mixture can also be used as ultra-thin wearing course.

An experimental characterization of the friction coefficient of a wind turbine gearbox lubricant

AbstractIn this study, a method to predict the contact friction coefficients at the rolling‐sliding contacts of isotropic superfinished and axially ground gear and bearing surfaces in wind turbine gearboxes is proposed. A two‐disc test rig was used to measure friction coefficient values within a slide‐to‐roll ratio range of −0.8 to 0.8, rolling velocities of 2 to 12 m/s, at oil temperatures of 50°C, 70°C, and 100°C and Hertzian contact pressures of 1.2, 1.6, and 2.0 GPa. A polyalphaolefin (PAO) International Standards Organization (ISO) viscosity grade (VG) 320 was the lubricant. Data from 90 individual friction coefficient tests were combined to develop two closed‐form friction coefficient formulae. A multivariable linear regression analysis was used to derive the regressed formulae. Using the developed regressed formulae, the predicted friction values follow the trend of measured values at all of the operating conditions. The results show that the regressed formulae are close to experimental friction coefficient values. The friction coefficient predictions confirm that the regressed formulae are capable of simulating contact friction values for the lubricated contact conditions considered.

Experimental analysis of the surface roughness in the coefficient of friction test

Mechanical wear has its origin in the friction of surfaces under contact and it is characterized for low normal forces by the mean coefficient of friction (COF) test on tribometers. The roughness of the worn surfaces is well established that is independent of the wear. Nevertheless a main hypothesis of this work is the research for evidences of the friction test variability influence on the surface roughness of worn materials in the test. The experimental setup includes the COF test ball-on-flat with steel on titanium and the surface roughness measured with an optical profilometer (confocal microscope) is analyzed. The space domain study of roughness parameters is developed on profiles (1D) and the surface (2D). The correlation study of the variability of the COF test with roughness metrics seeks the most significant roughness parameters. Its coherence and significance to respect the friction process are discussed. The similarities in the surface topography and its link with the COF signal are analyzed in the frequency domain based on power spectral analysis (PSA) from the fast Fourier transformation (FFT). Next, the whole profiles are also decomposed in frequency ranges by wavelet filtering that reveal the traces of the COF test on the surfaces and their similarities in the frequency domain.