Maximum Friction Coefficient Research Articles

Fabrication of Silica Nanoparticle Monolayer Arrays Using an Anodic Aluminum Oxide Template.

Non-close-packed (NCP) silica nanoparticle monolayer arrays (SNMA) on ordered porous anodic aluminum oxide (AAO) templates were fabricated for the first time by a novel two-step spin-coating technique. The obtained NCP-SNMA-AAO was composed of silica nanoparticles (average primary particle size of 440 nm) and well-organized nanopores on the AAO substrates. NCP-SNMA-AAO with a supporting ratio of 87% silica nanoparticles showed a hydrophilic surface (water contact angle of 51.0°), while the original AAO substrate shows a hydrophobic surface (water contact angle of 107.9°). The maximum coefficient of static friction was decreased by 29% (0.327 → 0.233). The coefficient of dynamic friction was also decreased by 20% (0.281 → 0.226). We found that controlling the silica supporting ratio using the two-step spin-coating technique is an effective approach for surface modification of an AAO substrate.

Effect of Fiber Type, Water Content, and Velocity on Wetness Perception by the Volar Forearm Test: Stimulus Intensity Test.

To investigate the effect of heat, moisture transfer, and mechanical tactile properties of fabrics on skin wetness perception when fabrics were in dynamic contact with skin at three velocities, nine knitted fabrics varying in fiber composition, thickness, and surface texture were evaluated by 20 participants using a wetness rating scale. The objective physical properties of the fabrics, namely, heat and moisture transfer and surface texture, and human physiological responses, namely, skin cooling rate and myoelectric signals, under various conditions were measured, and their correlations with the subjective wetness perception were studied. While the results indicated a significant influence of fabric type, water content, and velocity on skin wetness perception, no significant relation between electromyography and wetness perception was found. Fabrics with faster water spreading speeds and lower absorption rates were perceived as less wet, and the maximum transient thermal flow and skin cooling rate had a significant positive correlation with wetness perception. Furthermore, subjective wetness perception was predicted by the physical parameters of the fabric, that is, maximum transient thermal flow, water content, and friction coefficient, with an acceptable goodness of fit ( R2 = 0.82, p < .001).

Effect of WC addition on microstructure and tribological properties of bimodal aluminum composite coatings fabricated by laser surface alloying

Successful deposition of aluminum composite coatings has been achieved by scanning the laser beam over the 304 stainless steel substrate using a mixed powder of AlSiTiNi and WC. The effects of different WC contents on the microstructure and properties of the bimodal composite coatings were investigated. The friction and wear behaviors of the laser-deposited composite coatings were evaluated using a pin-on-disc testing machine by sliding against tungsten carbide balls at room temperature with a load of 100 N, linear sliding speed of 0.031 m/s, sliding radius of 3 mm and a total sliding distance of 56.5 m. Prior to the wear test, the surface of the coating was ground and polished. For the coating with 20% WC content (wt.%), it possesses high microhardness and wear resistance as well as low coefficient of friction owing to its bimodal microstructure. The coatings are mainly composed of equiaxed crystal in the fully melted region and net structure in the partially melted region, while the partially melted particles are embedded in the fully melted region. In addition, the partially melted region is expanded to further enhance the properties of the coatings with the addition of WC. The phases of FeAl, FeNi, Al5Cr and WC are found in the coatings. The microhardness of the coating with 20% WC is 4.4 times that of the substrate. With the increase of WC content, the maximum coefficient of friction of the coatings is increased. The coating with 20% WC possesses the lowest wear rate, which mainly involves abrasive wear when sliding against the tungsten carbide ceramic counterpart.

Mathematical modelling of an experimental‐analytical method for friction coefficient determination in deep drawing

AbstractThe main aim of this paper is to determine the friction coefficient μ and maximum drawing force in deep drawing process of aluminum alloy EN AW 1050 utilizing strip drawing method. Influence and interaction between lubrication condition, blank holder force and strip surface roughness on maximum drawing force and friction coefficient are investigated. Response surface methodology and D‐Optimal design are utilized in order to create an experimental plan. According to the design, 23 strip drawings experiments are performed and statistical analysis was done. The regression and variance analysis results with 18 significant mathematical models which are derived in order to describe influence of mentioned parameters on friction coefficient and maximum drawing force. Results are discussed according to previous research. Finally, the optimization of processing parameters is performed aiming for lower friction coefficient and maximal drawing force.

Friction characteristics between two nanostripe surfaces

Abstract In order to elucidate the friction characteristics of different types of periodic surface patterns, friction tests were performed on nanostripe surfaces fabricated on cylindrical surfaces with a curvature radius of 150 mm at sliding speeds of 0.7 μm/s–0.7 mm/s. On the nanostripe surfaces, microgrooves were arrayed at a pitch of 6 μm, while nanogrooves were formed on the ridges between neighboring microgrooves at a pitch of approximately 500 nm. The friction coefficient was the lowest at 0.06 when a nanostripe surface was rubbed against a smooth silicon surface at a speed of 0.7 μm/s and the sliding direction was parallel to the grooves. For combinations consisting of two nanostripe surfaces, the maximum friction coefficient was measured for the configuration wherein the grooves of the nanostripes on the two surfaces were perpendicular to the sliding direction, and for the configuration wherein the grooves of the nanostripes on the two surfaces were orthogonal to each other. In the case of the former configuration, the sticking force generated by the slopes of the microgrooves had a determining effect on the measured friction force.

Velocity measurement-based friction estimation for railway vehicles running on adhesion limit: swarm intelligence-based multiple models approach

Model-based condition monitoring is an increasingly important area for rail transportation. The key elements of such condition monitoring methodologies are low-cost vehicle sensors and intelligent algorithms. In this study, a swarm intelligence-based multiple models approach is proposed to detect different friction conditions by using velocity measurements of a railway vehicle. In this case of application, estimated parameter is the maximum friction coefficient. Additionally, proposed methodology is tested experimentally by using the measurements taken from a tram wheel test stand. Multiple mathematical models of the test stand are created with different maximum friction coefficients, whereas all initial conditions and other system parameters are same for each model. Therefore, comparison of the output of each model with measurements is considered to interpret the parameter value of the model, which best represents the system, is selected as parameter estimate. Unlike the traditional multiple models approach, a swarm intelligence-based evolution of the models is proposed. Experiments carried out on the test stand reveal that the proposed methodology is promising to be used as an on-board friction condition monitoring tool for railway vehicles with traction. Furthermore, it can be considered to detect weather conditions since friction conditions change due to the weather events such as rain, ice, snowfall, condensation of water droplets, and leaves on the line and it can be used as an auxiliary system for intelligent traction and high adhesion control systems.

Research on the real-time identification approach of longitudinal road slope and maximum road friction coefficient

Real-time knowledge of maximum road friction coefficient and road slope is crucial for active vehicle control systems. Most recent researches mainly assume that the road slope is constant and the influence on the identification of the maximum road friction coefficient is not considered. In this paper, the IMM Kalman filter method for the identification of road longitudinal slope is developed. Considering the axle load transfer caused by the road slope, the current road type is recognised by comparing the samples of the estimated instantaneous road friction coefficient with each standard road, then the maximum road friction coefficient can be easily determined by an online lookup table. Finally, experimental tests on the braking system hardware-in-the-loop test rig driven by the driving simulator are conducted. The results demonstrate that the identification approach can identify the current road slope and maximum road friction coefficient with good adaptability to various vehicle conditions.

Adaptive Collision Avoidance Using Road Friction Information

Technical development with the goal of achieving zero accidents and zero fatalities is ongoing. The autonomous emergency braking systems that debuted in the late 2000s have proven their value regarding improved safety. However, the technology still presents many challenges because it is not easy to ensure that the system will operate as intended in any environment and at any time. Any system that is unaware of its environment is prone to be excessively conservative, which could adversely affect the efficacy of said system. Situation awareness is a key to resolving this problem. The present study suggests the use of warning braking to gain an awareness of the level of road friction, which is one of the major uncertainties faced on the road. During warning braking, the tire-road maximum friction coefficient is estimated in real time, and a threat assessment is performed adaptively based on the friction information. Because warning braking is momentary and applied with limited dynamics due to issues related to human factors, this study discusses the major considerations and requirements for the key parameters related to warning braking. The performance of the suggested adaptive collision avoidance scheme is verified by means of simulation and experiments.

Preparation and tribological properties of a microemulsion for magnesium alloy warm rolling

PurposeThe purpose of this paper is to synthesize a microemulsion and investigate its tribological properties as lubricant. Magnesium alloy warm rolling experiments were conducted. Surface morphology was observed and wear form was summarized. The composition of surface residues was analyzed, which sheds light on the lubrication mechanism of microemulsion.Design/methodology/approachA microemulsion was prepared with a proper amount of oil, surfactant, cosurfactant, water and other additives for magnesium alloy strip warm rolling. Tribological properties, such as maximum non-seizure load (PB), friction coefficient (μ) and wear scar diameter (D) of the microemulsion were measured and compared with those of emulsion and rolling oil on an MR-10A four-ball tribotester. The extreme pressure anti-wear coefficients (O) were calculated and compared. Warm rolling experiments were carried out on a Ф 170/400 × 300 mm four-high rolling mill at 240°C to compare the finish rolling thickness and surface quality of rolled AZ31B magnesium alloy strip under four lubrication states, namely, no lubrication, rolling oil, microemulsion and emulsion. The surface morphology after warm rolling was observed with confocal laser scanning microscope and scanning electron microscope, respectively. The composition of surface residues was analyzed with energy dispersive spectrometry and X-Ray photoelectron spectroscopy.FindingsSurface morphology indicated that pitting wear, adhesive wear and ploughing wear were three main forms of wear in magnesium alloy warm rolling. Microemulsion had excellent lubrication properties with less residual oil remaining. Two types of adsorption layers formed on magnesium alloy strip surface were responsible for lubrication properties. MgSO4 and magnesium stearate in the reaction layer played a key role in anti-wear and friction-reduction in warm rolling.Originality/valueThe study is original and gives valuable information on lubrication mechanism of microemulsion in warm rolling of magnesium alloy strips.

Experiment research on friction coefficient between a steel plate and rail in transient sliding thermal contact through a pendulum

Abstract The main goal of this article is to study the friction coefficient of wheel/rail transient sliding thermal contact through a pendulum. A new method is firstly established to analyze the friction coefficient. The formula for calculating the friction coefficient is not dependent on material and thermal parameters of wheel/rail. The experiment measures the sliding contact time and friction coefficient at different wheel temperature. The results show that the sliding contact time is very short and the average sliding contact time is 8 ms. The friction coefficient slowly ascends before 500 °C and then gradually decreases from 500 °C to 1000 °C. From 1000 °C to 1200 °C, the friction coefficient quickly descends. The maximum friction coefficient is 0.388. With the increase of wheel temperature, the number of small pits gradually decreases, and the scratching on the wheel surface becomes more obvious.

An Optimal Wet Friction Plate Inspired by Biological Surface Patterns

It is found that many biological organisms exhibit superior adhesion characteristics in wet environments. It has been observed that the foot pads of tree frogs and katydids are consist of a number of closely arranged polygons, most of them are hexagonal. In this paper, the common structure of two kinds of biological foot pad was extracted to model the bionic surface structure of friction plates. The friction plate prototypes were also prepared. Through the multivariate orthogonal regression design, the optimum parameter combination of the friction performances of the prototypes of the bionic plates has been obtained. The hexagonal circumcircle size is 10 mm, the groove width is 1 mm, and the hexagonal diagonal angle is 90°. Then the maximum static friction coefficient, dynamic friction coefficient and wear amount of the optimal friction plate were tested and compared with the control group friction plates. The comparative analysis of the experiment findings demonstrated that the bionic structure with hexagonal ring grooves can significantly improve the friction performance of the friction plates.

A simple experiment to measure the maximum coefficient of static friction with a smartphone

The aim of this study is to measure the maximum coefficient of static friction with a smartphone. To reach this aim a very simple experiment with few materials was designed. Different from conventional experiments, the smartphone was used like an angle meter to determine the slope angle. The experiment in this study can be more practical than the conventional ones. It also requires easily accessible materials. We think that teachers and students should carry out this experiment as a group or demonstration activity in their classrooms.

On the Temperature Effect on the Parameters of the Specific Friction Force of Metals

Temperature relationships of the maximum coefficient of static friction, maximum specific static friction force, and its parameters τ0 and β at the ball-plane contact are experimentally investigated. A ball indenter with a radius of 0.5 mm made of ZlM80 alloy contacted a flat gold sample (99.99%). The range of contact loads was 0.5–4 mN, and the temperature range was 24–160°C. The experiments have shown that the coefficient of friction, specific friction force, and parameter β increase with increasing temperature, while parameter τ0 decreases.

Tribological performance of SiC coating for carbon/carbon composites at elevated temperatures

SiC coating was deposited on carbon/carbon (C/C) composites by chemical vapor deposition (CVD). The effects of elevated temperatures on tribological performance of SiC coating were investigated. The related microstructure and wear mechanism were analyzed. The results show that the as-deposited SiC coating consists of uniformity of β-SiC phase. The mild abrasive and slight adhesive wear were the main wear mechanisms at room temperature, and the SiC coating presented the maximum friction coefficient and the minimum wear rate. Slight oxidation of debris was occurred when the temperature rose to 300 °C. As the temperature was above 600 °C, dense oxide film formed on the worn surface. The silica tribo-film replaced the mechanical fracture and dominated the frication process. However, the aggravation of oxidation at elevated temperatures was responsible for the decrease of friction coefficient and the deterioration of wear rate. The SiC coating presented the minimum friction coefficient and the maximum wear rate when the temperature was 800 °C.

The effect of temperature and time on microstructure and friction performance of RE-borosulphurizing composite coatings

In this study, 45 carbon steel was RE(rare earth)-borosulphurized at 850 °C, 900 °C, and 950 °C for four different periods of time: 3, 5, 7 and 9 h. The microstructure examination and thickness measure of the diffusion layers were carried out by metallographic microscope and Scanning Electron Microscope (SEM). X-ray diffraction (XRD) was used to characterize the phase composition of the coatings. A ring-on-block wear tester was employed to measure the coatings friction coefficients. The results revealed a saw-tooth shaped and compact morphology of the RE-borosulphurizing layers (RBSL). The coatings thickness was found to increase with the increase of temperature and time. The maximum and the minimum values of the coating thickness were determined to be 98 μm and 32 μm, respectively. The minimum value of the FeB phase thickness was about 7.23 μm. The lowest friction coefficient value was 0.212 which occurred at 850 °C with a 10 N applied load and the maximum friction coefficient value was 0.571 which occurred at 850 °C with a 100 N applied load. The activation energy of RBSL was determined to be 138.6 kJ mol−1 using Arrhenius approach, which is lower than those of other boronizing processes.

The friction and wear properties of steel wire rope sliding against itself under impact load

Friction and impact between steel wire rope always exist in multi-layer winding hoist during the winding-in process, in particular for an ultra-deep coal mine. To understand the friction and wear mechanisms of wire rope among the layers in the winding hoist, a series of sliding friction experiments were carried out using a self-made friction test rig. The results show that the coefficient of friction (COF) of the wire rope changes little with increasing load and stabilizes at approximately 0.73, but decreases with the sliding velocity under dry-friction condition. However, under lubrication condition, there is almost no effect of the contact load and sliding velocity on the COF, which stabilizes at approximately 0.35. Additionally, the temperature rise is concentrated at the contact area, and it increases with the load and the sliding velocity. The maximum temperature rise with the lubrication is much lower, approximately 10 °C, than that under the condition of dry-friction, which is approximately 103 °C. Furthermore, the maximum of the COF under the impact load is significantly lower than that for the stable contact friction. With the impact and sliding velocities increase, the maximum COF under the impact load experiences a slight increase and reaches a maximum value of approximately 0.36. As the impact load increases, the COF changes little, but the impact process occurs more than once.

Controllable wear behaviors of silicon nitride sliding against sintered polycrystalline diamond via altering humidity

AbstractThe tribological behaviors of silicon nitride (Si3N4) sliding against sintered polycrystalline diamond (PCD) were investigated by varying the relative humidity (RH) in the testing atmosphere. The results indicated that higher RH corresponds to higher wear loss of Si3N4 and the wear loss of PCD almost fell close to zero. Especially in the case of 85% RH, both a maximum wear loss of Si3N4 and a maximum friction coefficient were achieved. In addition, this study revealed insights into the interface chemistry effects on the wear behavior of Si3N4 under humidity. When water molecules were introduced into the testing atmosphere, the hydrolysis reaction occurred on the Si3N4 surface with the formation of the Si‐O‐Si bond across the sliding interface. And then, the hydration reaction dominated the process, during which Si‐OH was formed through the bond fracture of the Si‐O‐Si. The X‐ray photoelectron spectroscopy results showed that the ratios of Si‐OH/Si‐O and Si‐N/Si‐OH+Si‐O bonds increased as the relative RH levels increased. As a consequence, the wear loss of Si3N4 significantly increased. Thus, due to the hydrolysis and hydration reactions, the tribological behaviors of Si3N4 against sintered polycrystalline diamond can be essentially controlled via varying RH levels.

Effects of process parameters during turn-milling of microstructured surfaces on the coefficient of static friction

Increasing power densities in current technical systems as well as lightweight requirements demand the transmission of higher specific forces or torques respectively. The static friction, determining the transferable torque in friction-locked connections, is affected considerably by the properties of the surfaces in contact. A predefined microstructuring of the surface by turn-milling can increase the coefficient of static friction. Specimens of the steel 42CrMo4+QT (1.7225) are machined using single-edged TiAlN-coated cemented carbide end milling cutters. Two different tool corner geometries (sharp, chamfered 0.2mm x 45°) are applied to generate protruding microstructures with different profile tip angles. For each tool type the influence of the cutting parameters cutting speed vc, feed per tooth fztan and radial feed frad on the surface structure and the coefficient of static friction is investigated by using a 2k full factorial design with centre point. For both tool types the feed per tooth fztan is the crucial parameter with a significant influence on the coefficient of static friction. The feed per tooth fztan is responsible for the generation of superimposed surface structures and affects the real contact area with the counterpart. The maximum average coefficient of static friction is μ0.1° = 0.63 for using the sharp tool corner and μ0.1° = 0.44 for using the chamfered corner. This represents approximately a tripling or rather doubling of the values that are achieved with unstructured specimens. Furthermore a good correlation between the peak material volume Vmp and the coefficient of static friction is determined.

Friction Measurements with Molten Chocolate

A novel test is reported which allows the measurement of the friction of molten chocolate in a model tongue–palate rubbing contact. Friction was measured over a rubbing period of 150 s for a range of commercial samples with different cocoa content (85–5% w/w). Most of the friction curves had a characteristic pattern: initially a rapid increase occurs as the high-viscosity chocolate melt is sheared in the contact region followed by friction drop as the film breaks down. The exceptions were the very high (85%) and very low (~ 5%) cocoa content samples which gave fairly constant friction traces over the test time. Differences were observed in the initial maximum and final friction coefficients depending on chocolate composition. Generally, the initial maximum friction increased with increasing cocoa content. At the end of the test, the rubbed films on the lower slide were examined by optical microscopy and infrared micro-reflection spectroscopy. In the rubbed track, the chocolate structure was severely degraded and predominately composed of lipid droplets, which was confirmed by the IR spectra. The new test provides a method to distinguish between the friction behaviour of different chocolate formulations in a rubbing low-pressure contact. It also allows us to identify changes in the degraded chocolate film that can be linked to the friction profile. Further development of the test method is required to improve simulation of the tongue–palate contact including the effect of saliva and this will be the next stage of the research.

Jet pulse electrodeposition and characterization of Ni–AlN nanocoatings in presence of ultrasound

In current study, Ni–AlN nanocoatings were successfully prepared by adopting the jet pulse electrodeposition (JPE) technique with ultrasound. The scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Vickers microhardness test, electrochemical workstation and friction wear tests were utilized to investigate the microstructure, mechanical properties, corrosion degree and wear resistance of the coatings. The results indicated that the Ni–AlN nanocoatings deposited by using ultrasound demonstrated the minimum and most compact surface structure compared to the other coatings. The thicknesses of Ni coating and Ni–AlN nanocoatings were approximately 56µm. The average atomic percent of Al and Ni elements in the Ni–AlN nano-coating prepared by using ultrasound, were approximately 21.4at% and 47.5at%, respectively. The maximum kinetic energy of the jet plating solution was 916m2/s2 during JPE-deposited Ni-AlN nanocoatings including ultrasound. The average micro-hardness value of the nano-coating prepared by using ultrasound equaled 767.9 HV. The Ni–AlN nanocoatings prepared using ultrasound had the minimum Ecorr and Icorr values of − 0.167V and 6.363 × 10−6mA/cm2, respectively. In this case, the demonstrated corrosion resistance was the most efficient. The Ni–AlN nanocoatings prepared using ultrasound sustained the minimum friction coefficients and the average friction coefficient was approximately 0.52. In contrast, the JPE-deposited Ni coating presented the maximum friction coefficient, while the average friction coefficient was approximately 1.43.