Measurement Of Friction Coefficient Research Articles

Low Friction at the Nanoscale of Hydrogenated Fullerene-Like Carbon Films

Friction force microscopy experiments at the nanometer scale are applied to study low friction of hydrogenated fullerene-like carbon films. The measured friction coefficients indicate that lower hydrogen concentration during preparation is beneficial to enter the low friction regime, especially in combination with only methane as precursor. Furthermore, two regions are found with distinct friction coefficients and surface roughnesses related to different surface structures. One is rich in amorphous carbon and the other is rich in fullerene-like carbon, dispersed on the same surface. Transmission electron microscopy and Raman spectroscopy images verify this observation of the two separated structures, especially with the extracted fullerene-like structures in the wear debris from macro friction experiments. It is speculated that hydrogen may tend to impair the growth of fullerene-like carbon and is therefore detrimental for lubricity.

Friction induced heating properties of the polyamide/steel type contacts

The endurance and the life time of the mechanical transmissions are highly influenced by the functioning conditions and, not at least, by the materials that they are manufactured from. The increase of the endurance and functioning life time, corroborated with a friendly impact with the environment, is one of the main aims of the worldwide research areas of today. According to this, the development of new materials characterised by low costs and high endurance represents one of the solutions obtained by the specific scientific research. The paper investigates the friction induced heating properties of the polyamide/steel type contacts by considering dry friction conditions. It is studied the contact between a steel made pin and a PA46 and PTFE added PA46 polyamide made disk, under different testing conditions, depending on the rotational speed of the disk and the normal force, at the environmental temperature. The tests are achieved on a tribometer equipped with a pin-on-disc module and, as output, the friction coefficient is measured. Due to the friction is developed a heating of the local contact area. The heat is calculated according to the measured friction coefficient, the normal load and the relative sliding velocity. Finally there are given conclusions regarding the friction induced heating properties of the tested materials.

Friction and wear in railway ballast stone interfaces

Particle friction in railway ballast influences strongly the behaviour of ballasted tracks. New challenges posed on railway infrastructure increase the requirement for simulations, which need the friction coefficient as an input parameter. Measured friction coefficients of ballast stone contacts were found only in two studies, both under constant loads. In this work, two types of ballast were investigated in cyclic friction tests with incremental increase of the applied load after several cycles. Before each load increase, 3D-scans of some ballast stones allowed to calculate the contact area. Estimating the stress in the contact, the stress-dependency of the friction coefficient and wear were investigated. These experimental observations are discussed regarding their impact for friction modelling in the simulation of railway ballast.

Evaluation of kinetic friction coefficients between single carbon fibers

A device for assessing the kinetic friction between carbon fibers (CFs) was developed. It enabled precise load measurement, in the order of a few mN, upon detection of the extraction movement of a single CF from a CF bundle. The coefficients of friction were evaluated by considering the packing states of the CF bundle. It was found that the packing states strongly affected the kinetic friction coefficient and were largely changed due to compression stress. Stable measurement of the kinetic friction coefficient was achieved when the volume fraction of the CF bundle was within 0.4.–0.5, with a measured kinetic friction coefficient of 0.13 ± 0.1.

Determination of material and interaction properties of maize and wheat kernels for DEM simulation

The discrete element method (DEM) has become popular for modelling the behaviour of grain kernels during agricultural production, processing, and transportation. DEM simulations provide both qualitative and quantitative information on particle flow, which helps improve the understanding, design, and optimisation of grain handling equipment. The accuracy of the DEM models is greatly affected by the model input parameter values, such as the grain kernel material and interaction properties. However, precisely and properly quantifying these properties remains a challenging task due to the irregular shapes of kernels and the heterogeneity of these biological materials. In this study, the DEM simulation material and interaction properties of maize and wheat kernels were determined with a combination of direct measurements and calibration tests and validated against bulk material tests. The characterisation tests include X-ray micro-CT scanning for acquiring kernel size and shape information, the use of a reciprocating pin tribometer for coefficients of friction, and an inclined surface drop test for calibrating the coefficients of restitution. The measured model parameter values were used in DEM simulations of two common bulk material tests: the poured bulk density test and an angle of repose test. The percentage error of the bulk density test was 4.0% for maize and 8.4% for wheat, and the error in the angle of repose test was 0.4% for maize and 1.3% for wheat. DEM simulations of bulk density and angle of repose tests using the parameters measured with the characterisation tests are able to accurately predict the experimental measurements. • Material and interaction properties of maize and wheat were determined. • Glued-sphere particles were generated based on 3D scanned models. • A calibration test was developed to determine the coefficient of restitution. • Tribometer test provided measurements of the grain kernel friction coefficients. • Image analysis was used to quantitatively compare angles of repose.

Test Modes for Establishing the Tribological Profile under Slip-Rolling

The complex nature of slip-rolling contacts in many applications such as gear tooth flanks, rolling bearings, and heavy machinery often makes determining the friction and wear properties, as well as the fatigue resistance, of tribosystems difficult. The establishment of the tribological profile of a tribocouple under high Hertzian contact pressure and under slip-rolling will allow for the measurement and comparison of friction and wear coefficients as well as slip-rolling resistance by continuously monitoring the wear rate, coefficient of friction, temperature, oil film thickness, and/or electrical contact resistance using high-resolution signal analysis (HRA). A twin disc system can provide insight into the adhesive behavior of material and lubricant products such as alternative base oils and additives, ceramics, alloys, and thin film coatings. The strength and endurance of these products are often characterized through fatigue and resistance tests, which apply high Hertzian contact pressures to the rolling contact until seizure or failure is obtained. The further observation of the formation of tribofilms on the surface of contact yields information about the reactivity and thermochemical properties of additives. This review aims to illustrate how the implementation of different screening methodologies can be used as a meaningful tool for assessing the aforementioned tribological profile properties for the development of slip-rolling tribosystems.

Experimental simulation on the high-temperature friction property of slag in slab continuous casting mold

The lubricating property of mold slag is significant to determine the surface quality of strands. To investigate the friction property of mold slag in the mold, the friction coefficient of the crystalline slag and glassy slag at high temperatures was measured through using a friction and wear testing machine. An edible oil was selected to simulate the lubrication behavior of liquid slag. The results show that during raising temperature from 25°C, the friction coefficient of slag will increase due to the surface softening. The surface sintering will obviously reduce the friction coefficient of crystalline slag at around 800°C. The friction coefficient of glassy slag is smaller than that of crystalline slag. The equivalent friction coefficient of liquid slag is below 0.2. The measured friction coefficient can be applied in mathematical models of friction.

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.

Coefficient of Friction Measurements on Transfemoral Amputees

Friction at the residual-limb socket interface affects amputees' comfort since it has a direct impact on the pain and functionality of the prosthesis. In this research, the coefficient of friction was measured at the volar forearm and three regions of the transfemoral residual limb (i.e., pressure tolerant, pressure sensitive, and scar region). The socket internal texture was replicated on a probe made of polypropylene to resemble the interface conditions. Besides the anatomical location, the presence and absence of sweat at the interface were evaluated. The statistical analysis included an ANOVA for two-factor experiment with repeated measures on one factor (sweat), where only sweat was found to be statistically significant (p − value = 0.001). Furthermore, regression analysis for the presence and absence of sweat condition was developed since its presence seems to homogenize the interaction conditions by surpassing the effect of other factors on skin friction. The presence of stick-slip phenomenon at the interface, the skin deformation during measurements, and the use of a portable tribometer led to the large variability in results, with larger variability in the presence of sweat. Hence, the relationship between the sweat layer thickness and the coefficient of friction should be explored.

An experimental approach to study thermal and tribology behavior of LPG refrigerant and MO lubricant appended with ZnO nanoparticles in domestic refrigeration cycle

The present article experimentally examines the application of ZnO nanoparticles in refrigeration cycle. Nanoparticles overcome the energy consumption issue by improving the compressor lubrication characteristics. In this study, the ZnO nanolubricant is proposed as a promising lubricant to improve the lubrication characteristics of domestic refrigerator compressors. Effect on compressor suction-discharge characteristics as well as energy consumption of refrigeration cycle has been observed using ZnO nanoparticles with pure refrigerant (Liquid Petroleum Gas). The physics involved behind the communication of nanoparticles with base refrigerant has been more clarified by performing tribological tests (i.e., measurement of viscosity and friction coefficient) of compressor lubricant for dissimilar fractions of nanoparticles. Thermal conductivity test on lubricant with distinct fractions of nanoparticles has also been conducted. The results showed that ZnO nanoparticles additive in mineral oil increases the viscosity which leads to a significant reduction in friction coefficient inside the compressor piston cylinder assembly which leads to a significant improvement in compressor energy consumption. The friction coefficient of nanolubricant with fraction of 0.7 g/L are about 11.1–25% lower than that of base lubricant. The compressor energy consumption was saved about 0.44–10% for employing ZnO nanolubricant with a mass fraction about 0.1 g/L to 0.7 g/L. Thermal conductivity was significantly enhanced (about 41%) using ZnO nanoparticles in mineral oil. The results of the present study assure better, effective and suitable performance of LPG as alternative refrigerant in refrigeration cycles.

Tribological Behavior of a Self-Lubricant Surface Film of H<sub>3</sub>BO<sub>3 </sub>Formed on a Borided Biomedical Steel by a Post-Treatment

This paper evaluates the tribological behavior of borided AISI 316L steel after being exposed to a secondary process to form a thin film of a solid lubricant. The process known as Short Annealing Process (SAP), allows creating a thin film of boric acid (H3BO3) on the surface of metallic materials previously exposed to boriding. The H3BO3 film acts like solid lubricant due to its lamellar crystalline structure. First samples of AISI 316L were exposed to boriding to temperatures of 875, 925 and 975 °C during 2, 4 and 6 h each temperature. Then, samples were heated to 750 °C during 5 min and cooled to room temperature at 60 % of Relative Humidity. The tribological behavior of the treated samples was evaluated by pin-on-disk test equipped with friction coefficient measurement system. Samples were characterized by Scanning Electron Microscopy, X-Ray Diffraction and Vickers microhardness test. The results showed an evident influence of the experimental parameters on the thickness of the boride layers and their mechanical properties. The layer ́s thickness was ranged from 10.51±0.71 to 51.57±5.12 μm. The hardness of the coatings was increased from 264 to 1685 HV. Finally, the Coefficient of Friction was diminished from values of 0.7 for the as-received material to 0.29 for the borided samples and to 0.06 for those after SAP, which indicates that the post-treatment SAP enhances the tribological properties of the biomedical steel.

Measurement of Kinetic Friction Coefficient through Magnetic Induction Using Audacity Application in Physics Learning

This study is designed to produce an experimental device for the measurement of the kinetic friction coefficient of material through magnetic induction using Audacity application. The objects of material the kinetic friction coefficient of which is going to be measured is rough acrylic with rough acrylic and wood with rough acrylic. The experimental setup was performed on the motion system of the mass of objects m1 and m2 that were connected through a pulley on a table and three solenoids are put under a table as the Electromagnetic Field (EMF) sensor. Analysis of the calculation of kinetic friction coefficient used two concepts, i.e. the kinematics concept to identify the load acceleration and the concept of the dynamic to find the kinetic friction coefficient. The results of the measurement of kinetic friction coefficient in this study have a match with the results obtained in the other studies. Hence, the tools and experimental approaches generated in this study are excellent for use in the learning activities so that teachers can teach physics applicatively.

Structural and mechanical properties of tantalum thin films ected by nitrogen ion implantation

Tantalum bulk were implanted with nitrogen ions at different dose of [Formula: see text] ions/cm2 to [Formula: see text] ions/cm2 and at a energy 30 keV. The implanted samples were characterized using X-ray diffraction (XRD), atomic force microscopy (AFM), microhardness testing, friction coefficient measurements and wear mechanism study. Scanning electron microscopy (SEM) images were used to analyze the friction of samples. The XRD results confirmed that the increasing dose affects the formation of the TaN phase. Based on AFM images, the morphology and surface roughness change proportionally to grain size after implantation. It was found that hardness increases as energy increases. From the friction coefficient measurement, this coefficient decreases as energy increases. For the un-implanted sample, the wear mechanism has abrasion, and with increasing the energy, it shifts to being flake and sticky.

Effect of Sample Tilt on Measurement of Friction Coefficient by Constant-Load Scratch Testing of Copper with a Spherical Indenter

Abstract A copper microscratch test was carried out with a spherical indenter under constant normal load of 150 mN. The effect of sample tilt on the measurement of friction coefficient was investigated by rotating the sample with surface inclination between successive tests so that the indenter could experience different surface height slopes. It was found that the experimentally measured friction coefficients linearly depended on surface height slope (or surface tilt angle) under small angle tilt and became larger when the indenter climbed over the sample surface, which was explained by a geometrical intersection model. Accurate determination of the friction coefficient requires either two scratch tests with reversed sliding directions or 180° rotation of the sample with the average value being used as the coefficient of friction under nontilting condition. The true friction angle for the condition without surface inclination can be obtained by summing the experimentally measured friction angle and surface tilt angle.

Experimental test of a frictional contact model for shear thickening in concentrated colloidal suspensions

Rheological experiments on model and industrial colloidal dispersions that exhibit reversible shear thickening are compared to a recent model that correlates simulation results for the shear rheology of bidisperse suspensions of particles with varying levels of contact friction. Comparisons are presented with rheological results for a variety of colloidal dispersions varying from model systems to industrially relevant, commercial dispersions where both shear and first normal stress differences are available. Particle-scale measurements of particle friction coefficients are provided through a survey of the literature. The comparisons show under which conditions the model can quantitatively describe the measured rheology and how the model can be used to correlate data for systems with more complex interactions when allowances are made for effective volume fractions and adjustments in friction coefficients. Discrepancies evident in comparisons for the first normal stress differences highlight the importance of enhanced hydrodynamic friction in many systems, especially for continuous shear thickening, in qualitative agreement with recent simulations that incorporate enhanced lubrication hydrodynamics due to elastohydrodynamics or particle roughness. Finally, a literature survey of measurements of jamming volume fractions and particle friction coefficients indicates that the model overestimates the experimentally observed jamming volume fraction. The comparisons presented in this work provide quantitative information valuable for those modeling suspension processing as well as suggestions for further model improvement.

Friction transitions and connections to third bodies for a Cd coating on steel substrate

Cd coating is used in aerospace industries from last five decades due to its sacrificial protection and lubrication properties. Although Cd coating is primarily used due to its sacrificial corrosion protection when applied on steel substrate, the added benefit of modifying the tribological behavior by acting as a lubricious layer gives it a leading-edge than other coatings. Often the measurement of friction coefficient (CoF) is reported as a value generated after full sliding cycle. This measurement of average CoF generally limits the study of local variation in CoF occurring within one sliding cycle, which can be significantly different with change in spatial position due to change in third body morphology. In this study, a linearly reciprocating sliding test is used to measure the CoF at a sampling rate of 800 Hz along the track length to generate triboscopic image with steel countersphere. The instantaneous CoF obtained with triboscopy is correlated with the wear track morphology using scanning electron microscope (SEM) and optical profilometer for variation in contact conditions. Tribological test performed in dry atmosphere shows an average CoF of 0.4 till the end of the test whereas with increase in relative humidity to 60%, the average CoF changes from 0.4 to 0.8 at the end of the test due to change in contact conditions. Soft Cd coating on low carbon steel substrate is used to study these variations in third body morphology.

Measurement of road surface friction coefficient in real-time with measuring the tire deformation

Measurement of road surface friction coefficient in real-time with measuring the tire deformation

Interplay between Microscopic and Macroscopic Properties of Charged Hydrogels

We have investigated aqueous charged poly(acrylamide-co-acrylate) gels by varying polymer concentrations at fixed concentrations of added sodium chloride salt. Using a combination of static and dynamic light scattering, rheology, and water permeation experiments, we have made independent measurements of shear modulus, friction coefficient, diffusion coefficient, and mesh size of the gel. We have also derived a generalized mean field theory for charged gels by including electrostatic interactions between polymer segments, in addition to the contributions from free energy of mixing, elasticity, and the Donnan equilibrium. The measured dependencies of modulus, friction coefficient, and gel diffusion coefficient on polymer concentration are in accordance with the predictions of the generalized mean field theory, enabling a reliable bridge between the macroscopic and microscopic properties of polyelectrolyte gels. When the contributions to free energy of the gel from fluctuations in polymer concentration and c...

Wear performance investigation of PVD coated and uncoated carbide tools during high-speed machining of TiAl6V4 aerospace alloy

Selection of hard PVD coatings for the machining of Ti6Al4V alloy should be based on the dominant tool wear mechanism and tribological phenomena occurring at the chip-tool-workpiece interface. The present work investigates the effect of AlTiN and CrN hard coatings on the wear performance of cemented carbide cutting tools during high-speed finish turning of Ti6Al4V. The wear characteristics of the tools were evaluated by SEM and 3D wear volume measurements. The in-situ tribological performance of the coatings was characterized by chip morphology analysis, in combination with coefficient of friction measurements using a high temperature/heavy load tribometer that mimics actual machining conditions. Micro-mechanical characteristics of the coatings were also studied in detail. The results obtained show that the application of a CrN coating significantly improves tool performance due to a combination of the micro-mechanical properties of the coating and the tribological characteristics of the surface engineered layer.

Design of a Tribotester Based on Non-Contact Displacement Measurements.

A tribotester with an integrated load sensor based on a strain gauge is typically used to measure the friction coefficient generated by the contact-related sliding motion of two objects. Since the friction coefficient is obtained by dividing the measured friction force by the applied normal force, the normal and friction forces must be measured for accurate analysis. In this study, a tribotester was used to measure the displacement of a cantilever tip using the fiberoptic sensor in a non-contact method. The friction coefficient measurement using the fiberoptic sensor was proven to be valid by calibrating the tip displacement due to normal/friction forces after designing a basic structural cantilever tip based on experiments and simulation analyses. The results obtained by using the fiberoptic sensor-cantilever tip-based tribotester were compared with those obtained using commercial and/or custom-built tribotesters under the same conditions. By designing various shapes of cantilever tips and using simulation analysis, the calibrations of the normal/friction forces and tip displacement could be verified and the coupling effect was evaluated. The performance and reliability of the fiberoptic sensor-cantilever tip-based tribotester, which can be used to determine the normal/friction forces by non-contact displacement measurements without a strain gauge, were verified.