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An analytical EHL model suitable for highly loaded point contacts operating in mixed and boundary regimes of lubrication is presented. The results are compared and validated with the experimental measurements of friction coefficient from an MTM tribometer. Measurements are carried out upon a PAO40 oil at medium to high temperatures. In general, a good agreement in trend and magnitude over a wide range of operating conditions is observed. Both the experimental findings and the model predictions show an inverse relationship between friction and contact load in mixed and boundary regimes of lubrication, an effect not hitherto reported in literature. [ABSTRACT FROM AUTHOR]

Climbing animals such as geckos and arthropods developed astonishing adhesive mechanisms which are fundamental for their survival and represent valuable models for biomimetic purposes. A firm adhesion to the host surface, in order to successfully lay eggs is necessary for the reproduction of most parasitoid insects. In the present study, we performed a comparative investigation on the attachment ability of four parasitoid species (the egg parasitoid Anastatus bifasciatus (Eupelmidae), the aphid parasitoid Aphidius ervi (Braconidae), the fly pupal ectoparasitoid Muscidifurax raptorellus (Pteromalidae) and the pupal parasitoid of Drosophila Trichopria drosophilae (Diapriidae)) with hosts characterized by a surface having different wettability properties. The friction force measurements were performed on smooth artificial (glass) surfaces showing different contact angles of water. We found that attachment systems of parasitoid insects are tuned to match the wettability of the host surface. Sexual dimorphism in the attachment ability of some tested species has been also observed. The obtained results are probably related to different microstructure and chemical composition of the host surfaces and to different chemical composition of the parasitoid adhesive fluid. The data here presented can be interpreted as an adaptation, especially in the female, to the physicochemical properties of the host surface and contribute to shed light on the coevolutionary processes of parasitoid insects and their hosts. [Display omitted] • The attachment ability of four parasitoid species is comparatively investigated. • Parasitoid hosts surfaces have different wettability properties. • Friction force is measured on glass surfaces with different water contact angle. • Attachment systems of parasitoids are tuned to match host surface wettability. • Females reveal adaptation to the physicochemical properties of the host surface. [ABSTRACT FROM AUTHOR]

This work investigates the mechanisms for friction reduction in textured journal bearings. The measured friction of laser-etched connecting-rod big-end shells was compared with a non-textured reference under engine-like conditions. Experiments covered several working conditions, and the friction and lubricant film temperatures were measured for three texture configurations. The origin of the verified friction reduction was explored using a numerical model that simulates the hydrodynamic lubrication and global thermal effects. The simulation results accurately matched the friction measurements, revealing that the microscopic mechanisms of reduction in lubricant shear stress and effective viscosity due to texture-induced cavitation act simultaneously to reduce the friction coefficient for the textured shells. The findings have practical applications for the optimal design of textured hydrodynamic bearings. • Friction in textured journal bearings was experimental and numerically investigated. • A journal bearing model with thermal effects was validated using experimental data. • Textures reduced the lubricant shear stress and viscosity and lowered friction. • The shear area reduction mechanism for textured hydrodynamic bearings was confirmed. [ABSTRACT FROM AUTHOR]

Copyright of Wool Textile Journal is the property of National Wool Textile Science & Technology Information Center and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study aims to minimize the friction forces in order to obtain the best feel and minimum effort in the command and control cable part of the shift systems. For this purpose, lubricant, amount of lubricant and application method were investigated. Theoretical and experimental approaches are discussed by examining the studies on this subject. In the presented study, friction measurements were taken in the laboratory environment by applying different amounts of lubrication on the wire exposed to friction, and the amount of lubrication required for minimum effort was determined experimentally. It was observed that the friction force was decreased about 60% with oil running compared to dry running. Studies show that friction forces increase in excessive lubrication as well as in cases where there is no lubrication and little lubrication. The optimum amount of oil was obtained to be 0.1 g. It has developed guidelines for determining the friction factor for those who design shift cable and control cable used in different areas. [ABSTRACT FROM AUTHOR]

This paper presents a general method to extract a surface pressure field from a skin friction field in complex flows as an inverse problem, focusing on its application to global luminescent oil-film (GLOF) skin friction measurements. The main technical aspects of this method are described, including the basic equation relating surface pressure to skin friction, variational method, numerical algorithm, and approximate method with the constant boundary enstrophy flux (BEF). The proposed method is evaluated through simulations in the Falkner–Skan flow and the flow over a 70°-delta wing to investigate the effects of the Lagrange multiplier, downsampling rate, noise level, and the value of a constant source term in the approximate method. Further, the approximate method is applied to the skin friction fields obtained by GLOF measurements in the flow over a 65°-delta wing and the square junction flow to obtain the normalized surface pressure fields. The proposed method provides a useful tool to obtain the high-resolution fields of both surface pressure and skin friction by GLOF measurements in complex flows (particularly at low speeds). The normalized surface pressure field extracted from the skin friction field in the square junction flow, where skin friction lines are superposed. [ABSTRACT FROM AUTHOR]

Slip‐preventing materials are often used as tertiary packaging to improve cargo securement and simplify truck loading. There are many national and international standards on their safe usage based on the extra friction they can provide. However, it is challenging to quantify the coefficient of friction (CoF) of slip‐preventing materials. This paper presents CoFs of three slip‐preventing materials and one baseline condition measured on different surfaces and contact pressures. These measurements show interesting phenomena that affect the result variability. For instance, 60% of the pairs of surfaces tested were affected by the contact pressure. Hence, the load of the freight seems to affect performance of the slip‐preventing materials. This interaction happened in different ways such as changes in the friction mode (constant slip and stick slip at difference frequencies and magnitudes). The typical CoF values available in standards as well as standardized measurement methods do not consider very well these effects nor how to deal with high variability of CoF measurements. This can lead to either over or under CoF estimations. To overcome these limitations, this paper presents a statistical method to quantify slip‐preventing material CoFs based on variability and confidence intervals of the measurements. [ABSTRACT FROM AUTHOR]

Concrete pavements comprise a considerable portion of pavements that are currently in use. This paper presents the results from a laboratory investigation on the effect of temperature and surface texture on the skid resistance of concrete pavements. Briquettes representative of concrete pavements were created and textured in the laboratory. Readings of skid resistance on laboratory specimens were obtained using a portable British pendulum tester. Water and liquid hand soaps were used as lubricants in an attempt to separate the adhesion and hysteresis components of friction. In order to simulate the wear and ageing of concrete pavements, several cycles of polishing were applied to the briquettes. Tests were conducted at five different temperatures. The results showed that there is a correlation between the magnitude of friction components and temperature. A normalisation procedure for friction measurements based on temperature was developed, which can be used to normalise measurements to a standard temperature of 293·15 K. [ABSTRACT FROM AUTHOR]

Mechanical testers have commonly been used to measure the frictional properties of socks. However, the friction values may be susceptible to the level of stretchiness of tested fabrics or human variability. Thus, the aim of this study was to propose a novel method that enables friction measurement of socks in a sock-wearing condition with less human variability effects. Five socks with different frictional properties were chosen. Three experimental ramp tests were performed with an artificial structure shaped like the foot-ankle complex (last) and a ramp tester to quantify the static coefficient of friction (COF) at the foot against sock, at the sock against an insole, and the foot wearing socks against the insole, respectively. The angle where the last slipped while the ramp surface was gradually inclined was used to compute the static COF values for each sock. The reliability was 0.99, and COF values ranged from 0.271 to 0.861 at the foot-sock interface, 0.342 to 0.639 at the sock-insole interface, and 0.310 to 0.614 in the third test. Socks with different frictional properties were successfully distinguished each other. Thus, the suggested protocol could be a reliable option for measuring the static COF values in the tension similar with it found in a sock-waring condition with reduced effects of human variability. [ABSTRACT FROM AUTHOR]

• Measuring terrain surface roughness. • Static tyre characterisation tests on different surfaces. • Tyre characteristics for different tread wear conditions. • Static tyre vs. rolling tyre testing. Tyre characterisation is not a trivial or inexpensive exercise thus it is important to obtain representative measurements during tyre characterisation tests. Different test methods exist and vary from laboratory tests to outdoor tests on different surfaces. Each of the test surfaces have different surface roughness and will result in different tyre characteristics. This study compares friction coefficient measurements on dry non-deformable surfaces for laboratory test surfaces and outdoor test tracks on the same agricultural tyre with large lugs at two inflation pressures and three tread wear conditions. The influence of surface roughness on friction coefficient is investigated. The macrotexture and microtexture of multiple surfaces are measured and compared. The importance of measuring the microtexture of the outdoor test surface is noted. Static/Non-rolling tyre tests in a laboratory are compared to Static/Non-rolling tyre tests as well as Dynamic/Rolling tyres tests at an outdoor test facility. Excellent correlation is found between the Static vs. Dynamic and laboratory vs. outdoor tests results when the laboratory tests are conducted on a surface representing the outdoor surface. [ABSTRACT FROM AUTHOR]

In this work, an Al coating prepared using the arc spray process was carried out with a corrosion–wear analysis by a block-on-ring system. The interaction of corrosion and wear of coatings in seawater was also investigated. The effect of different corrosion potentials on the corrosion and wear of the coating was discussed, and the structure and corrosion products of the coating were observed by SEM. The results of dynamic potential polarization curves and friction coefficient measurements were used to clarify the corrosion and wear behavior of aluminum coatings in seawater. After quantitative analysis of a corrosion and wear test, it was found that with the increase in polarization potential, the total weight loss of corrosion and wear (Wtotal) of the aluminum coating increased significantly. This means that the corrosion–wear interaction accounts for most of the weight loss of the coating. [ABSTRACT FROM AUTHOR]

This study examines surface roughness measurements via piezo acoustic disks and appropriate signal processing. Surface roughness is one characteristic of surface texture that can have various irregularities inherent to manufacturing methods. The surface roughness parameters and corresponding surface profiles are acquired by a stylus profilometer. Simultaneously, elastic waves propagated along metal surfaces caused by the friction of a diamond tip are obtained in the form of raw sound via piezo acoustic disks. Frequency spectrum analysis showed apparent correlations between the traditionally obtained measurement parameters and the piezo acoustic measurement data. Thus, it is concluded that acoustic friction measurement shows promising results as a novel measurement method for the surface roughness states of certain materials. [ABSTRACT FROM AUTHOR]

Triboscopy focuses on the analysis of the temporal evolution of a tribological system, combining local and time-resolved information, most commonly the evolution of friction. In this work, this technique is applied on measurements, which were carried out with a custom-built ultra-high vacuum tribometer in ball-on-disc configuration. Based on these experiments, an extended classification to distinguish different triboscopic features is suggested, depending on the persistence in both track position and time: Uniform, Global, Local, and Sporadic. Further, a filter technique for quantifying triboscopic data regarding this classification is introduced. The new and improved triboscopic techniques are applied to various dry friction measurements of hydrogen-free carbon coatings under varying humidity and pressure. The resulting specific triboscopic features are correlated to wear phenomena, such as counter body coating abrasion, inhomogeneities in the wear track, non-uniform track wear, stick-slip and debris in the contact area, demonstrating the increased analysis and monitoring capabilities when compared to conventional friction curves and wear track images. [ABSTRACT FROM AUTHOR]

[Display omitted] Popular deep eutectic solvents (DESs) typically lack amphiphilic molecules and ions and therefore do not have the useful self-assembled nanostructures prevalent in many ionic liquids. We hypothesise that nanostructure in DESs can be induced via an amphiphilic hydrogen bond donor (HBD), and that nanostructure becomes better defined with HBD chain length. The structure of DESs formed from choline chloride mixed with either butyric acid (ChCl/BuOOH) or hexanoic acid (ChCl/HeOOH) in a 1:4 M ratio were studied using atomic force microscopy (AFM) imaging, force curves, and friction measurements combined with bulk rheology. DESs formed with both the C 4 and C 6 acids are nanostructured. As the length of the acid group is increased from C 4 to C 6 , AFM images reveal the nanostructure becomes larger and better defined due to the longer acid chain, and AFM force curves show the interfacial nanostructure extends further from the surface. Self-assembled nanostructure in these systems is a consequence of choline cations, chloride anions, and acid alcohol groups clustering together due to electrostatic attractions and hydrogen bonding to form polar domains. Acid alkyl chains are solvophobically excluded from the polar domains and aggregate into apolar domains. [ABSTRACT FROM AUTHOR]

Accurate tyre models are important to ensure valid and reliable simulation of vehicle behaviour. To this purpose, the Magic Formula (MF) became the de facto standard for vehicle dynamics simulations, despite requiring many empirically derived coefficients. This paper shows how the accuracy of a simple physical-based brush-type tyre model can be enhanced to simulate tyre behaviour that closely matches MF results. To do so, the real, highly complex rubber friction characteristics are incorporated into the brush model. The friction characteristics were obtained from friction measurements with a tread rubber block. The developed model is validated against experimental tyre data obtained on a flat-track test rig and the corresponding MF model. Results show that the inclusion of friction characteristics allow accurate simulation of longitudinal and lateral slip conditions over a wide range of normal loads with the simple brush model. At extreme loading scenarios, the simulation accuracy deteriorates because of the significant influence of highly nonlinear deformation behaviour of the tyre that is not accounted for in the brush model formulation. [ABSTRACT FROM AUTHOR]

Objective: Drawing parallels from rheotribology can be used to develop a robust instrumental protocol for non‐subjective characterization, product development and design of topical dosage forms with desired sensory attributes. However, instrumental characterization of cosmetic products can be influenced by the measurement protocol, thixotropy, flow anomalies like shear banding or wall slip and nature of the film formed on the skin surface. In this study, we evaluated the influence of above parameters on the instrumental sensory evaluation of 12 topical formulations of different galenic forms. Methods: Oscillatory strain sweep measurements (SAOS and LAOS) were performed to investigate the influence of frequency and wall slip on the material parameters. The textural attributes at different consumer touchpoints were evaluated by accounting time‐dependent simulation of viscoelastic flow. Further, the influence of film thickness and sample drying on the tactile properties of the topical formulations were studied on a non‐biological skin model using a sliding probe tribometer. Results: The study shows that the flow properties of the semi‐solid formulations depend on the timescale of the problem. A few formulations exhibited wall slip to varying degrees in the linear viscoelastic regime where the behaviour was found not to be characteristic of a particular topical dosage form. The material functions obtained from the Lissajous plots suggest that the non‐linear flow behaviour of different galenic forms is least influenced by the boundary conditions imposed by the measurement geometry. The results were statistically analysed using principal component analysis where the attributes used for discriminating skin creams during pick up and rub out are found to be closely associated with non‐linear rheology. The friction coefficient exhibited speed dependence where it formed different parametric group with rheological data depending on the lubrication regime. Conclusion: The study highlights that correlations are possible amongst rheological, tribological and instrumental textural analysis data, which can act an impetus for the development of models to predict attributes that drive perception at different consumer touchpoints. However, the choice of instrumental settings, anomalies associated with rheological measurements and friction dependence on a number of parameters can influence the model prediction. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to investigate the microstructural anisotropy of Ti-6Al-4V samples fabricated by selective laser melting. Design/methodology/approach: Specimens are fabricated through a Renishaw AM400 selective laser melting machine. Three microstructures (as-built, 850°C annealed and 1,050°C annealed) and two building orientations, parallel (PA) and perpendicular (PE) to the building platform, are considered. Starting from in-depth microscopic observations and comprehensive electron backscattered diffraction imaging, the study addresses non-conventional techniques such as internal friction and electrical resistivity measurements to assess the anisotropy of the fabricated parts. Findings: Microscope observations highlight a fine texture with columnar grains parallel to the building direction in the as-built and 850°C annealed samples. Besides, coarse grains characterized the 1,050°C annealed specimens. Internal friction measurements pointed out the presence of internal stress while storage modulus analyses appear sensitive to texture. Electrical resistivity is resulted to be dependent on grain orientation. Originality/value: The work uses some novel characterization techniques to study the anisotropy and internal stresses of Ti-6Al-4V samples processed by selective laser melting. Mechanical spectroscopy results suitable in this kind of study, as it mimics the operating conditions of the material. [ABSTRACT FROM AUTHOR]

Pavement texture is an important characteristic affecting user safety and satisfaction. Despite the large number of studies on pavement texture, there is still a need to further explore the models relating texture to tyre-pavement interaction. In this study, 29 cores were extracted from 15 different pavement surfaces and tested in the laboratory by Ohio department of transportation. The data set includes high density texture scans, modified mean texture depth (MMTD) values estimated using a modified sand patch test, and friction measurements acquired using dry and wet British pendulum (BP) testes. The texture scans were characterised using the mean profile depth (MPD) and wavelets energy. The correlation between MPD values and the coefficients of friction (COF) estimated using BP tests were not as strong as the correlation between the wavelet energies and the wet and dry COFs. Statistically significant models were derived using the wavelet energies to predict the MMTD (R2 = 0.94) as well as the dry and wet COF (R2Dry = 0.49/R2Wet = 0.60). The principle component analysis was used to decorrelate the wavelet energies and overcome the multicollinearity, while the least absolute shrinkage and selection operator was used to reduce the number of variables in the model. [ABSTRACT FROM AUTHOR]

This study aimed to test the friction coefficient of cryogenic bearing lubrication materials. A ball-on-disc type friction tester was developed in our lab using air bearings that could simulate the movement of cryogenic bearings under sliding-rolling contact. The tester is equipped with a temperature-controlled chamber to provide a minimum −175 °C low-temperature environment. Using air bearings is an important technique to reduce the base friction of the tester measurement system and ensure the accuracy of the friction coefficient measurement. The friction coefficients of the Ag coating and the PTFE coating were measured at different sliding-rolling velocities on this tester, and the results showed that the friction coefficient curves agreed well with the Gupta sliding model. The developed tester will provide important data for the dynamic analysis and life evaluation of the cryogenic bearings. [ABSTRACT FROM AUTHOR]

To study the friction of cell monolayers avoiding damage due to stress concentration, cells can be cultured on fibrin gels, which have a structure and viscoelasticity similar to that of the extracellular matrix. In the present research, we studied different gel compositions and surface coatings in order to identify the best conditions to measure friction in vitro. We examined the adhesion and growth behavior of mesothelial cell line MET-5A on fibrin gels with different fibrinogen concentrations (15, 20, and 25 mg/mL) and with different adhesion coatings (5 μg/mL fibronectin, 10 μg/mL fibronectin, or 10 μg/mL fibronectin + 10 μg/mL collagen). We also investigated whether different substrates influenced the coefficient of friction and the ability of cells to stick to the gel during sliding. Finally, we studied the degradation rates of gels with and without cells. All substrates tested provided a suitable environment for the adherence and proliferation of mesothelial cells, and friction measurements did not cause significant cell damage or detachment. However, in gels with a lower fibrinogen concentration, cell viability was higher and cell detachment after friction measurement was lower. Fibrinolysis was negligible in all the substrates tested. [ABSTRACT FROM AUTHOR]

Continuous friction measurement equipment (CFME) has been demonstrated as an appropriate method to acquire friction around the critical slip ratio for the Pavement Friction Management (PFM) programme. Through a comprehensive field data collection on testing sites with different preventive maintenance (PM) treatments, this study assessed the influences of various characteristics on the CFME measurements. Field friction data were collected by a Grip Tester, one type of CFME, and the corresponding texture profiles were acquired by a high speed texture profiler. For each testing site, friction data was measured under nine operational conditions with three water film depths and three testing speeds. An adaptive signal processing technique, Hilbert-Huang Transformation (HHT), was applied to extract amplitude and instantaneous frequency of profiles as the texture parameters. Subsequently, the HHT texture parameters, along with pavement conditions and testing operational characteristics, were deployed as the influencing factors for the development of statistical friction model. The results reveal that the CFME measurements are most sensitive to the change of water film depth and pavement surface texture properties. This study is anticipated to gain a better understanding of the characteristics of CFME measurements and implement CMFE to support PFM programme effectively. [ABSTRACT FROM AUTHOR]

Continuous polishing is the first choice for machining optical elements with a large aperture. The lubrication in the continuous polishing is an important factor affecting the surface quality of the optical elements. In this study, the lubrication system between the optic element and polishing lap was analyzed firstly and then was verified by the measurement experiment of the friction coefficient. In addition, the numerical simulation model of the mixture lubrication was established. The polishing pressure distribution and material removal distribution can be obtained by the model. The influences of the rotating speed, optical element load, and surface roughness of the polishing lap on polishing pressure were also analyzed. Finally, the influence rules of the lubrication on the surface shape of optical elements were revealed by the polishing experiments. [ABSTRACT FROM AUTHOR]

It is extremely difficult, if not impossible, for existing force balances to capture very small skin-friction drag (SFD) in a perturbed turbulent boundary layer (TBL), which is characterized by the unpredictable, nonuniform distribution of static surface pressure. A novel force balance is proposed, which combines the level principle, as deployed in Cheng et al.'s (2020, "A High-Resolution Floating-Element Force Balance for Friction Drag Measurement," Meas. Sci. Technol., 32, p. 035301) force balance, with a single-degree-of-freedom air bearing mechanism. This mechanism acts to eliminate disturbances, such as nonuniform static pressure on the wall associated with high Reynolds number TBL or a TBL under control. As a result, the developed balance may be used to accurately measure SFD in the order of 10-3 N in a TBL with or without control. This balance has been successfully applied to measure the drag reduction (DR) of a TBL manipulated using one array of streamwise microjets, at friction Reynolds number Reτ = 3340 ~?5480. [ABSTRACT FROM AUTHOR]

Health monitoring of robot manipulators is crucial for their long-term reliable operation. Since the feedback data provided by the controller of robot manipulators are most often from the actuator's side, health monitoring of rotate-vector (RV) reducers housed on the output of actuators is challenging. To avoid the increased cost and complexity of adding sensors to robot manipulators, this paper investigates the long-term health monitoring of RV reducers, using only feedback data from the controller. A generic model for RV reducers is first developed to characterize their nonlinear behaviours and performance degradation. The model is then extended to robot manipulators to analyse their dynamic response under the time-varying excitation generated by healthy and faulty RV reducers. Next, a new motor-torque-based residual together with an adaptive threshold is proposed for the health monitoring of RV reducers, taking payload, measurement noise and friction disturbance into account. The proposed threshold depends only on the variance of measurement noise, and is therefore easy to implement in practice. Extensive simulations and experiments are conducted on two robot manipulators to validate the proposed model, residual and threshold. The results show that the proposed model is able to account for the effects of faults and nonlinear behaviours of RV reducers on the motor performance. The proposed residual with an adaptive threshold is sensitive to faults in RV reducers and robust to friction disturbance and time-varying payload, and it outperforms conventional momentum-based residuals. • RV reducers generic model with nonlinear behaviour & performance degradation • Manipulator dynamics including excitations caused by normal & faulty RV reducers • Torque-based residual w. adaptive threshold for RV reducers health monitoring [ABSTRACT FROM AUTHOR]

• An automated system is developed for ultrasonic fatigue and internal friction testing. • Fatigue damage can be effective monitored using system damping. • Internal frictions of damaged copper specimens are over 3 times of fresh specimens. • Yield stresses of damaged specimens are obviously lower than the fresh specimens. • A practical damage variable based on internal friction is proposed. Fatigue damage in metals and alloys would reduce their strength and should be identified as early as possible. However, fatigue damage is usually difficult to detect even using advanced nondestructive testing method. Here we developed an automated damping monitoring system for ultrasonic fatigue testing based on a quantitative electromechanical impedance method. During fatigue testing, the damping and resonance frequency of the Piezo actuator/horn/specimen system is measured regularly using an impedance analyzer. When the system damping suddenly increases, it implies that fatigue damage may be generated in the specimen. Separate impedance measurements on the copper specimen in a vacuum chamber show that the internal frictions of damaged specimens are much larger than the fresh specimens. Subsequent X-Ray micro-CT scanning shows that microcracks up to 0.8 mm in length were generated in those fatigued specimens with increased internal frictions. Further tensile testing shows that compared to the fresh specimen, specimens with fatigue damage exhibits reduced tensile strength and elongation at break. Furthermore, the larger the internal friction, the smaller the remaining yield strength and a nearly linear relationship between them holds. Finally, a damage variable D Q is defined based on internal friction which can act as a measure of fatigue damage in metals. [ABSTRACT FROM AUTHOR]

Friction on snow surface, especially in relation to winter sports, is difficult to measure directly because of its complexity and variability. In this work, a wearable snow friction measurement device for cross-country skiing was designed and constructed to calculate the friction force and monitor movement signals through the logical placement of three-component sensors and connection parts on skis. Both theoretical simulation and experiments have been conducted, which proved that the deformation of cross-country skis outputs few abnormal force signals during applying large load. Through the static validation in the laboratory, the output accuracy and stability of the device were confirmed. To verify the availability of the device, measurements on a skiing treadmill were conducted, and the results showed that the device can work well and distinguish the different friction behaviors of various waxes. More important, through the ski field test, the device was able to monitor the technical actions and evaluate the frictional coefficient of different ski waxes on snow surface comprehensively, which provides a scientific reference for athletes and coaches in routine training. [ABSTRACT FROM AUTHOR]

Geophysical flows, characterized by diverse particle-size mixtures, pose challenges for hazard risk assessment due to their anomalous fluidity and rheological behavior. This study investigates the rheological behavior of dry granular mixture flow in a flume setup using particle image velocimetry and triaxial force measurement. Key findings include a power-law relationship between the inertia value and the internal friction coefficient, affirming the applicability of the monodisperse friction model in mixed particle-size scenarios. A strong positive correlation is identified between the effective basal friction coefficient and internal friction coefficient, suggesting an influence of internal frictional properties on basal friction for granular flows on a flat surface. Additionally, positive correlations are observed between normalized stress fluctuation and both internal friction coefficient and inertia number, linking basal stress fluctuations to variations in internal frictional characteristics. These insights enhance our understanding of granular material dynamics, holding potential implications for geological disaster risk assessment. [Display omitted] • Experimental verification the μ (I) rheological law of dry granular mixtures. • The relationship between the effective basal friction coefficient and internal friction coefficient is analyzed. • The internal friction between particles is emphasized as a controlling factor for basal stress fluctuation. [ABSTRACT FROM AUTHOR]

High static friction between functional surfaces poses a serious challenge for industrial valves, particularly for those used in the advanced ultra-supercritical power generation industry that requires raising the steam temperature to 760 °C. In this context, we established the static friction measurement methodology by evaluating the effects of temperature, loading time, and number of static cycles on the evolution of the static coefficient of friction up to 800 °C. This methodology was applied on a nickel-based solid lubricant coating that appears an attractive candidate to withstand very harsh environments. The tribological behavior is explained in terms of a competition of three mechanisms governing the static friction processes: micro-welding or sintering of asperities, creep of asperities, and formation of lubricious oxides. • Establishment of the static friction measurement methodology to simulate valve applications. • First time to systematically report the evolution of static COF with number of static test cycles, time and temperature. • Three main mechanisms governing the static friction processes. [ABSTRACT FROM AUTHOR]

Ungrooved stone mastic asphalt (SMA) provides an alternate to grooved dense graded asphalt (DGA) as a runway surface. To be verified as suitable in this application, SMA must provide similar or better asphalt surface performance, compared to DGA, and must achieve regulated aircraft skid resistance requirements. A pilot runway resurfacing project provided the basis for this laboratory and field comparison of ungrooved SMA to grooved DGA as a runway surface. Laboratory performance testing demonstrated adequate and comparable deformation, fatigue and moisture resistance of SMA, while the quality assurance records indicated acceptable asphalt production. The construction records indicated that SMA had a lower air void content in the compacted layer, which can only provide a more durable surface. Most importantly, the aircraft skid resistance of SMA exceeded that of grooved DGA, based on surface macro-texture and wet friction measurements. It was concluded that SMA performed equal to or better than DGA, particularly with regard to surface texture and wet friction and it is recommended that airports consider ungrooved SMA as a runway surface in the future. The demonstration project should also be monitored in the future, to verify the long-term performance of SMA, compared to the DGA. [ABSTRACT FROM AUTHOR]

The aim of the work was to identify the physical parameters relevant to different perceptual attributes by comparing a range of commercial skin creams with various compositions. We investigated the possibility of predicting sensory properties using rheological and tribological methods. Rheological evaluations of the skin creams were carried out using continuous shear, creep, creep recovery, rheodestruction and recovery measurements, oscillatory strain sweep measurements [small amplitude oscillatory shear (SAOS) and large amplitude oscillatory shear (LAOS)], and frequency sweep measurements. Friction measurements were performed on the nonbiological skin model to investigate how surface properties are influenced by the application of different topical formulations. Furthermore, the formulations were characterized by a broad range of instrumental texture measurements. In vivo sensory analysis based on the spectrum descriptive analysis method was performed to discriminate the skin creams during pickup, rub out, and after feel. Using principal component analysis meaningful correlation relating rheotribological properties and sensory attributes during the entire process of product application was carried out. Rheological parameters deduced from the nonlinear regime were found to be important parameters affecting the frictional response of skin creams. In addition, friction data were correlated with slipperiness and stickiness—subjective attributes used for the sensory evaluation of after feel. Furthermore, a number of key textural parameters and sensorial data showed good correlation with results obtained from linear and nonlinear rheological measurement, indicating rheological analysis can be sufficiently used as a precise and valid tool for sensorial mapping of topical formulations. Our study further suggests that objective evaluation based on the flow curve, oscillatory strain sweep (SAOS and LAOS), and friction measurements can be used for sensorial screening of large number of prototype formulations, which otherwise may be time consuming and costly using a sensory panel. [ABSTRACT FROM AUTHOR]

Copyright of China Mechanical Engineering is the property of Editorial Board of China Mechanical Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Featured Application: The magic formula (MF) is used to estimate the road friction characteristics. This study deals with the possibility of construction of a database on the braking friction coefficient for actual roads from the viewpoint of traffic safety, especially for automated driving, such as level 4 or higher. At these levels of automated driving, the controller needs to control the vehicle. However, the road surface condition, especially the road friction coefficient on wet roads and snowy or icy roads, changes greatly, and in some cases, changes by almost one order. Therefore, it is necessary for the controller to constantly collect environment information, such as the road friction coefficients, and prepare for emergencies, such as obstacle avoidance. However, at present, the measurement of the road friction coefficients is not systemically performed, and a method for accurately measuring has not been established. In order to improve this situation, this study examines a method for continuous measurement of the road friction characteristics, such as the μ-s characteristics. It is shown that the μ-s characteristics are continuously measured using the MF generally used in tire engineering, and the friction characteristics identified from the results are sufficiently satisfactory. [ABSTRACT FROM AUTHOR]

This study investigated the effect on piston assembly friction after treating piston surfaces with a fine particle bombarding process, using a friction measurement apparatus with a floating cylinder liner, similar to an eco-mileage vehicle engine. Friction was measured in four conditions: (1) no treatment (standard piston in a commercially-available engine), (2) micro dimple treatment (45 µm ceramic particles were air-blasted onto the piston surface), (3) molybdenum disulfide (MoS2) shot treatment (1 µm MoS2 particles were air-blasted onto the piston surface), and (4) combination of the previous two micro dimple and MoS2 shot treatments (first 45 µm ceramic particles and then 1 µm MoS2 were air-blasted onto the piston surface). Results indicated that friction decreased in the following order: no treatment > micro dimple treatment > MoS2 shot treatment > combination of micro dimple and MoS2 shot treatments. [ABSTRACT FROM AUTHOR]

Maintaining desired pavement friction is an effective way to reduce the crash rate. Pavement texture plays an important role in tire-pavement friction performance. However, the contribution of texture at different depths or wavelengths to friction measurement has not been fully understood. This study conducts a multiresolution analysis using three-dimensional (3D) asphalt pavement texture data to correlate pavement texture to friction measurements. Between 2014 and 2018, multiple rounds of pavement texture and friction data were acquired on two field sites. The top-surface topography of 3D texture data is sliced with eight depths to explore the critical contact depth between pavement texture and tire rubber for friction testing. At each depth, 3D texture data is decomposed into sub-images via discrete wavelet transform to extract texture features at 11 wavelengths ranging from 0.1 mm to 102.4 mm. Subsequently, the wavelet energy of each wavelength is calculated as the texture indicator. Finally, the texture energy matrix at different wavelengths and depths along with the ambient temperature during friction testing are correlated with the measured friction data using cross-validation and step-wise multivariate linear regression. The pavement texture of wavelengths up to 3.2 mm at the top 2.5 mm of top-surface topography is identified as the critical contact zone for pavement-tire interaction. [ABSTRACT FROM AUTHOR]

Petrus van Musschenbroek was a famous scientist and inventor, natural philosopher, experimental physicist, engineer, instrument builder, experimenter, in the continental Newtonian tradition of Boerhaave and 's Gravesande. And: a tribologist. He is one who deserves more fame than he has received so far, and which is well documented in this publication. Van Musschenbroek coined the name tribometer for his device to measure friction in a journal bearing, and some authors rightly refer to this. However, what seems to have remained unnoticed until now is that he also published quantitative results of his friction measurements and tried to arrive at general laws of friction based on them. He reported in detail on friction experiments on sliding, dry as well as lubricated, sliders and journal bearings, a novum in his time, as early as in 1734. When the data from Van Musschenbroek's tables are mapped into graphs, a method which was not in use at that time, two Stribeck curves for journal bearings emerge. Van Musschenbroek's work deserves much more acclaim in the tribology community than it has now. [ABSTRACT FROM AUTHOR]

During the autoclave manufacturing of sandwich components, several defects may arise. A typical defect in the use of honeycombs is core crush. The occurrence of this defect depends, among other things, on the angle of the honeycomb chamfer. To design this angle, the friction between honeycomb and prepreg must be known. Due to the low rigidity of Nomex® honeycomb in lateral direction, the determination of the frictional behavior between face sheets and honeycomb is a particular challenge. This paper shows the development of a test device for measuring the friction between honeycomb with film adhesive and carbon/epoxy prepreg for different temperatures and compressions corresponding to realistic manufacturing conditions. The device is also suitable for the evaluation of interlaminar friction between prepreg plies and tool-part-interaction. The requirements for the device are shown in detail. Advantages and disadvantages of various concepts for the individual modules are discussed in order to select the most promising design. As proof of concept, friction measurements between honeycomb and prepreg as well as prepreg to prepreg measurements are carried out. In the case of interlaminar measurements, the friction coefficient determined at 1 mm deformation deviates by 5.3% from already published values obtained with another device and is within the stated scatter range. The measurement results for honeycomb against prepreg are in direct correlation with manufacturing trials performed. Using the lowest coefficient of friction established, a critical angle of the honeycomb chamfer was determined. Subsequently, component samples were manufactured with an inclination angle of 7.5° above and 7.5° below the critical angle. The specimens with larger angle showed a strong core crush, whereas those with smaller angle exhibited no core crush. This demonstrates that with this device the honeycomb chamfer of sandwich components can be dimensioned based on the lowest friction coefficient determined between honeycomb and prepreg. [ABSTRACT FROM AUTHOR]

In this paper the characteristics of a Europium-based temperature-sensitive paint (TSP) in polyurethane (PUR) clear coat submerged in water are investigated. It is shown that the temperature sensitivity is not affected by water. However, the optical transmission of the PUR is reduced, which reduces the measurable emission of the TSP. Furthermore, a TSP measurement in the laminar water channel at the Institute of Aerodynamics and Gas Dynamics, University of Stuttgart, was set up. In this experiment the skin friction field for two types of roughness elements, i.e. a truncated cylinder and an array of cuboids, in a Blasius-like boundary layer is investigated. Additionally, the temperature field was recorded with sub-millimeter resolution while an artificial heat flux was applied. A modification of the Colburn analogy is used to derive the skin friction from the temperature measurement. Skin friction results derived from velocity measurements are in good agreement with the TSP results. The experimental setup provides a resolution of the temperature and skin friction measurement of K and N m−2 (skin friction of the undisturbed flow), respectively. Additionally the uncertainty of the temperature and skin friction measurement is analyzed. [ABSTRACT FROM AUTHOR]

• Variations in the relative surface roughnesses can be neglected when ε/D < 0.0025. • The average accuracy of the model was practically unaffected by this. • At ε/D < 0.0025, metastability can have a much larger impact than these variations. • The developed correlation determined 84% to 95% of mass flow rates within ±10%. • It was validated with independent measurements for R600a, R134a, R290, and R410A. Capillary tube models frequently rely on friction factor correlations, which are functions of the Reynolds number, and the tube's relative surface roughness. However, this study shows that explicitly correlating the friction factor with the relative surface roughness is unnecessary, at least when the latter is lower than 0.0025. To test this a correlation was fitted directly onto friction factor measurements obtained in an adiabatic flow of R600a, through nine capillary tubes from three manufacturers. The friction factor was correlated exclusively as a function of the Reynolds number, meaning that the impacts of the relative surface roughnesses on the friction factor were averaged, and included only implicitly. This correlation, and an existing correlation, which allows the specification of the relative surface roughness, were then implemented in a capillary tube model. The accuracy of the capillary tube model, using either the developed or existing correlation was then evaluated by comparing the results to experimental data. No significant decrease in the accuracy of the model was observed when the relative surface roughnesses, ranging from 0.0012 to 0.0025, were not individually specified for each capillary tube. To further verify this, the procedure was repeated on a larger database of friction factor and mass flow rate measurements, which also consisted of data from independent studies. Similar conclusions were drawn, as the average accuracy of the model differed only by 1 to 3% among different studies, and not always in favor of the correlation where the relative surface roughnesses could be specified. [ABSTRACT FROM AUTHOR]

This article presents a novel experimental test rig for the investigation of friction between a ball and cage of a deep groove ball bearing (DGBB). The experimental apparatus was designed and developed to replicate the orientation and dynamics of a full bearing in steady-state operation while collecting measurements of cage friction. A six-axis load cell was used to record force and torque values generated due to a rotating ball inside of a rigidly fastened cage segment. The test rig can be set up in two different configurations to collect cage friction measurements: (a) A position control configuration where measurements of friction torque on the ball are collected for specific positions of the ball and the cage and (b) a load control configuration where a constant force is applied between the ball and the cage and a friction coefficient is calculated from the results. The test rig was used to investigate four different DGBB cage varieties: (a) a snap-on polymeric cage, (b) a low-profile polymeric cage, (c) a stamped steel cage, and (d) a machined brass cage. The friction performance of each cage type is shown to be related to the shape of the lubricating film between the ball and the cage wall. In addition, measurements of friction torque at specific positions provide insight into the mixture of oil and air inside the cage pockets. Friction coefficients from experiments in the load control configuration are shown to increase with speed and reduce with applied load for all four cage varieties. [ABSTRACT FROM AUTHOR]

Six-axis force/torque sensors are increasingly needed in mechanical engineering. Here, we introduce a flexure-based design for such sensors, which solves some of the drawbacks of the existing designs. In particular, it is backlash-free, it can be wirelessly monitored, it exactly enforces 90° angles between axes, and it enables visual inspection of the monitored system, thanks to its hollow structure. We first describe the generic design, implementation, and calibration procedure. We then demonstrate its capabilities through three illustration examples relevant to the field of tribology: low friction measurements under ultra-high vacuum, multi-directional friction measurements of elastomer contacts, and force/torque-based contact position monitoring. [ABSTRACT FROM AUTHOR]

In absence of any direct measurement method of rolling friction for particles that deviate from perfectly spherical shape, most DEM simulation studies use bulk calibration approach to estimate an acceptable value of this parameter. A novel method based on image analysis of static grains is proposed to calculate the rolling friction coefficient of particles that deviate slightly from the spherical shape. To compare these values obtained from image analysis, direct measurement of the rolling friction coefficient of industrial pellet particles of slightly non-spherical shape is done using two different methods. The first method involves video analysis to track the position of particles rolling over an inclined plane. The second method proposes modifications to the ASTM standard method of rolling friction measurement of spherical particles to enable measurements for slightly non-spherical particles. Results obtained from the image analysis method are found to be in very good agreement with directly measured rolling friction values. Following this approach, it is possible to measure the rolling friction coefficient of particles using image analysis in a manner similar to measuring the particle size distribution. The image analysis method can be utilised for rolling friction estimation in situations where direct measurement is not possible and has potential for wide usage in DEM simulations of the powders and bulk solids. [ABSTRACT FROM AUTHOR]

The existing investigation highlights oblique Jeffrey fluid with mixed convection on a stretched surface. Also chemical reactions with properties of homogeneity and heterogeneity are considered. The leading physical model is converted in a nonlinear system of ODE by means of proper similarity alterations. Influence of all relative physical constraints on velocity, temperature as well as on concentration are expressed geometrically. Physical magnitudes of interest like friction measurements, thermal and concentration transport rates of chemical spices at the surface are studied numerically. [ABSTRACT FROM AUTHOR]

Accidents in which aircrafts veered off the runway when landing have occurred frequently, which pose a considerable threat to people’s lives and property. Friction, produced by the contact patch between the tires and the runway, has long been known as a crucial factor for a safe landing. Therefore, accurately measuring the friction coefficient (F-Coe) is regarded as an effective means to reduce accidents, especially in extreme weather. This review article aims to summarize and analyze the state-of-the-art techniques of runway friction characteristics measurement to provide all stakeholders a broader understanding and more valuable references. First, the methods available for measuring (or estimating) the friction characteristics are reviewed, such as American Society of Testing Materials (ASTM) standard test, the caused-based method, the effect-based method, modeling method, and fusion method. Second, the pros and cons of these methods are discussed from two aspects: conventional method and the tribo-system-based method. Third, the research progress of the correlation between the F-Coe obtained by ground measurement equipment and the aircraft braking F-Coe (ABF-Coe) is summarized and discussed. Finally, the measurement policies, about runway surface friction characteristics, proposed by International Civil Aviation Organization (ICAO), Federal Aviation Administration (FAA), and European Aviation Safety Agency (EASA) in recent years are summarized and the measurement methods are proposed or improved according to these policies. For developing better and proper measurement methods of runway F-Coe (RF-Coe), the future envisaged research lines should focus on the new measurement techniques and methods under the joint action of tires, runway, contaminants, and atmospheric condition. [ABSTRACT FROM AUTHOR]

The friction coefficients of single-layer epitaxial graphene grown on the Si-terminated and C-terminated faces of Silicon Carbide (SiC) substrate were measured under ambient conditions using Friction Force Microscope (FFM). The lateral friction force measurements acquired in the applied normal force range between 4.0 and 16.0 nN showed that the friction coefficient of graphene on the C-terminated face of SiC is about two times smaller than the one grown on its Si-terminated face. The lateral friction was found to be decreased as the average of root mean square roughness increases suggesting the observed difference in the friction coefficients cannot be related to the roughness of the graphene layers. DFT calculations demonstrated that the altered periodicity of charge distribution on graphene due to the specific interactions with two distinct polar faces of SiC substrate might explain the observed difference in the friction coefficients. [Display omitted] [ABSTRACT FROM AUTHOR]

In Sweden today, friction measurements are performed manually, often using methods generating spot‐wise measurements. Because the low numbers of measurements provided by these methods are insufficient to follow up on the friction requirements set by the Swedish Transport Administration, the Administration has initiated the Digital Winter project. In Digital Winter, floating car data (FCD) are utilised for road friction estimation. The focus in this investigation is on coverage, and on whether the FCD detects harsh weather conditions with decreasing road friction. Two different methods—one continuous and one slip‐based—are implemented in this investigation. Furthermore, different approaches on how to build the vehicle fleet to collect the FCD have been applied using different combinations of commercial and private vehicles. The results showed that both methods detect low‐friction events, and for roads with high annual average daily traffic (AADT), the data collection using slip‐based methods and larger fleets gives more data points than for smaller fleets using continuous methods, and the reverse is true for lower AADT. The results showed differences between the two fleets in terms of coverage for the weekly and daily distributions, but overall, the method of using FCD for road friction estimation seems promising for the follow‐up of winter road maintenance. [ABSTRACT FROM AUTHOR]

In geotechnical tests, a thin layer of lubricants is usually applied along interfaces between tested soils and the sidewall of a container to minimize interface friction (shear strength). The effectiveness of lubricants in reducing the interface friction has not yet been fully evaluated. In this paper, the effectiveness of several commonly used lubricants in reducing the sidewall friction is presented through backfilling and stress measurement tests performed in a lightly instrumented column. The interface friction angles are back calculated from the measured stresses, using an arching analytical solution. The results show that the most efficient among the tested lubricants is a combination of Teflon and silicone grease, which can reduce the interface friction angle to 16.8°, a value far from being qualified as negligible. For most cases, the application of lubricants has little or no effect in reducing the sidewall friction. For some cases, the application of a lubricant material can even increase the sidewall friction angle. To verify these somehow surprising results, direct shear tests were performed to obtain direct measurements of the interface friction angles between the tested sand and the tested lubricant materials. Very small normal stresses were applied and the sand was gently placed in the shear box to imitate the testing conditions of column filling tests. The good agreement between the directly measured and back-calculated interface friction angles indicates that the column tests and the back-calculated results are reliable. Further analysis reveals that the small cohesion of lubricant materials can become negligible under a high stress state. Under a low stress state, this small cohesion can be translated into high friction. It is concluded that the tested lubricants may be efficient under high stress conditions, but not efficient under low stress conditions. For the latter case, the consideration of zero sidewall friction between the tested soil and lubricated sidewall of the container can lead to inaccurate and even totally wrong results. [ABSTRACT FROM AUTHOR]

Atmospheric icing on structures and equipment represents a challenge for operation and safety. Passive ice removal by ice-phobic coatings has received much attention over the last decades. The current state-of-the-art methods for quantifying the ice-release properties of such coatings suffer from a range of drawbacks, including poor reproducibility and high complexity test setups. Here, a facile rotational tribometer approach for measuring the static friction between polymeric coatings and ice is presented. The torque necessary to initiate motion at the coating-ice interphase was used as a measure of ice release. For a polydimethylsiloxane-based coating (Sylgard 184), the effects of ice-temperature, normal force, coating thickness, and dwell time (contact time between coating and ice at rest with fully applied normal force prior to applying torque) were established along with the conditions resulting in least data variation. With these conditions, tribology-based friction measurements were carried out on two additional coatings; a two-component polyurethane, and a commercial foul release coating. The outcome of the method, i.e., grading of the coatings in terms of antiicing effect, matched those obtained with a widely used ice adhesion test method based on ice shear adhesion testing. The same trends are revealed by the two methods. However, the findings from the proposed tribology-based method result in consistently lower variation in outcomes and offer more detail on the ice adhesion and friction mechanisms. [ABSTRACT FROM AUTHOR]

Accurate friction-slip modelling is particularly important for locomotive traction and rail damage studies. This paper compares friction-slip measurement results from a hand operated (HO) tribometer and a twin disc tribomachine on AS60 rail. The results were used to calibrate traction coefficient-slip curves using the Modified Fastsim contact model. The differences between the two friction measuring instruments including scale, speed, and rail cleaning effect influenced the friction coefficient and slip value at which the friction peak occurred. The proposed equalisation technique was able to match the HO tribometer traction coefficient-slip curve with the tribomachine curve while preserving most of the Modified Fastsim contact parameters. • Friction-slip behaviour is characterised for locomotive traction and rail damage. • Friction measurements using tribomachine and hand-operated tribometer are compared. • Tribomachine and hand-operated tribometer results implemented in Modified Fastsim. [ABSTRACT FROM AUTHOR]

Real contact area is a challenging phenomenon in tribology, where despite established theoretical models, detailed experimental studies are still lacking. This work is focused on the evolution of the real contact area of multi-asperity steel contacts during sliding, by using sub-micron characterisation of entire multi-asperity contact area and simultaneous measurement of the friction force. Steel-sapphire contact was monitored by using an in-situ optical system in real time during 5 mm of unidirectional sliding in surface roughness range R a = 0.1–1.0 µm and normal loads up to the nominal contact pressure equal to steel yield strength (Y). The results showed that the initial real contact area caused by static loading increased during sliding. At low nominal contact pressure of 0.3 Y , the increase in real contact area was the largest: for R a = 0.1 µm it went from 9.5% of the nominal area under static conditions to 15.0% after sliding, a 56% relative increase, and for R a = 1.0 µm it went from 5.0% to 11.5% after sliding, a 106% increase. The increase in real contact area was smaller at higher nominal contact pressures of 0.6 Y and 1.0 Y. At 1.0 Y for R a = 0.1 µm the real contact area went from 18.0% to 21.8% after sliding and for R a = 1.0 µm it went from 9.4% to 12.9% after sliding. The coefficient of friction increased with roughness at the lowest nominal contact pressure 0.3 Y (for R a = 0.1 µm it was 0.24 and for R a = 1.0 µm it was 0.29) but became independent of roughness at higher contact pressures (on average 0.18). • In-situ measurement of real contact area evolution during 5 mm of sliding. • Whole multi-asperity steel contacts observed using optical method. • Real contact area increased due to sliding from the initial static conditions. • The largest increase from static to sliding conditions was at the lowest load. [ABSTRACT FROM AUTHOR]