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The safe and efficient torque transmission of wet disk clutch systems requires high coefficients of friction. To achieve good controllability and high comfort, a positive slope of the coefficient of friction over sliding velocity is ensured by a reasonable formulation of the lubricant and choice of the friction pairing. This results in low transmittable torque at low sliding velocities. Thus, the occurrence of unwanted micro-slip in dynamic operation modes must be considered for the design of safety-relevant clutch systems. This work presents a methodology for the holistic measurement of the friction behavior of wet disk clutches. It is suitable for numerous applications and supports a sound understanding of frictional properties in the range of sliding velocities occurring in brake shifts through forced slip operation down to static torque transmission. The experimental determination of the holistic friction behavior is crucial for developing optimized design guidelines for modern clutch systems. [ABSTRACT FROM AUTHOR]

Straightforward design and long-term functionality for tribological considerations has prompted an extensive substitution of polymers for metals across various applications, from industrial machinery to medical devices. Lubrication of and by polymer gels/coatings, essential for ensuring the cost-effective operation and reliability of applications, has gained strong momentum by benefiting from the structural characteristics of natural lubrication systems (such as articular cartilage). The optimal synthetic strategy for lubricating polymer gels/coatings would be a holistic approach, wherein the lubrication mechanism in relation to the structural properties offers a pathway to design tailor-made materials. This review considers recent synthesis strategies for creating lubricating polymer gels/coatings from the molecular level (including polymer brushes, loops, microgels, and hydrogels), and assessing their frictional properties, as well as considering the underlying mechanism of their lubrication. [ABSTRACT FROM AUTHOR]

This article presents the results of a study of oil lip seals with a modified outer lip layer texture. In the first step, the interaction of flat rubber samples with different surface layer textures with the steel surface was recognised. Measurements of the friction coefficient of flat samples with different surface layer textures were carried out. The next step was an experimental study of rotating shaft lip seals in standard and prototype versions. The contact width of the sealing lip before and after durability tests was examined, and the clamping force of the lip on the shaft before and after durability tests was measured. The final step was to create a FEM model of the interaction of the sealing ring lip with the shaft to determine the lip seal pressure and width. These calculations, in cooperation with the previously determined friction coefficient and porosity of the lip seal, allowed the calculation of the friction torque. The solution proposed in this article was intended to be simple and viable for industrial applications. Satisfactory results were achieved with prototype rings in terms of reduced resistance to movement, tightness, and durability. [ABSTRACT FROM AUTHOR]

The complex dynamics of tribofilm formation on boundary-lubricated steel surfaces were investigated in real time by combining in situ measurements of the temporal variation of the coefficient of friction and contact voltage. Sliding experiments were performed with various blends consisting of base oil, zinc dialkyl dithiophosphate (ZDDP) additive, and two different dispersants at an elevated oil temperature for a wide range of normal load and fixed sliding speed. The evolution of the transient and steady-state coefficient of friction, contact voltage, and critical sliding distance (time) for stable tribofilm formation were used to evaluate the tribological performance of the tribofilms. The blend composition affected the load dependence of the critical sliding distance for stable tribofilm formation. Tribofilm friction was influenced by competing effects between the additive and the dispersants. Among various formulations examined, the tribofilm with the best friction characteristics was found to be the blend consisting of base oil, a small amount of ZDDP, and a bis-succinimide dispersant treated with ethylene carbonate. The results of this study demonstrate the effectiveness of the present experimental approach to track the formation and removal of protective tribofilms under boundary lubrication conditions in real time. [ABSTRACT FROM AUTHOR]

Slip and fall accidents are the leading cause of injuries for all ages, and for fatal injuries in adults over 65 years. Various factors, such as floor surface conditions and contaminants, shoe tread patterns, and gait behavior, affect the slip risk. Moreover, the friction between the shoe outsoles and the floor continuously changes as their surfaces undergo normal wear over time. However, continuous assessment of slip resistance is very challenging with conventional measurement techniques. This study addresses this challenge by introducing a novel approach that combines sensor fusion technology and machine learning techniques to create intelligent insoles designed for fall risk prediction. In addition, a state-of-the-art slip simulator, capable of mimicking the foot's motion during a slip, was developed and utilized for the assessment of slipperiness between various shoes and floor surfaces. Data acquisition involved the collection of pressure data and three-axial accelerations using instrumented shoe insoles, complemented by friction coefficient measurements via the slip simulator. The collected dataset includes four types of shoes, three floor surfaces, and four surface conditions, including dry, wet, soapy, and oily. After preprocessing of the collected dataset, the simulator was used to train five different machine learning algorithms for slip risk classification. The trained algorithms provided promising results for slip risk prediction for different conditions, offering the potential to be employed in real-time slip risk prediction and safety enhancement. [ABSTRACT FROM AUTHOR]

This review reports on the influencing parameters on the joining parts quality of tools and techniques applied for conducting process analysis and optimizing the friction stir welding process (FSW). The important FSW parameters affecting the joint quality are the rotational speed, tilt angle, traverse speed, axial force, and tool profile geometry. Data were collected corresponding to different processing materials and their process outcomes were analyzed using different experimental techniques. The optimization techniques were analyzed, highlighting their potential advantages and limitations. Process measurement techniques enable feedback collection during the process using sensors (force, torque, power, and temperature data) integrated with FSW machines. The use of signal processing coupled with artificial intelligence and machine learning algorithms produced better weld quality was discussed. [ABSTRACT FROM AUTHOR]

Efforts to enhance quality control (QC) practices in chip seal construction have predominantly relied on single surface friction metrics such as mean profile depth (MPD) or friction number. These metrics assess chip seal quality by targeting issues such as aggregate loss or excessive bleeding, which may yield low friction numbers or texture depths. However, aggregate loss, particularly due to snowplow operations, does not always result in slippery conditions and may lead to uneven surfaces. The correlation between higher MPD or friction number and superior chip seal quality is not straightforward. This research introduces an innovative machine learning-based approach to enhance chip seal QC. Using a hybrid DBSCAN-Isolation Forest model, anomaly detection was conducted on a dataset comprising 183,794 20 m MPD measurements from actual chip seal projects across six districts in Indiana. This resulted in typical 20 m segment MPD ranges of [0.9 mm, 1.9 mm], [0.6 mm, 2.1 mm], [0.3 mm, 1.3 mm], [1.0 mm, 1.7 mm], [0.6 mm, 1.9 mm], and [1.0 mm, 2.3 mm] for the respective six districts in Indiana. A two-step QC procedure tailored for chip seal evaluation was proposed. The first step calculated outlier percentages across 1-mile segments, with an established limit of 25% outlier segments per wheel track. The second step assessed unqualified rates across projects, setting a threshold of 50% for unqualified 1-mile wheel track segments. Through validation analysis of four chip seal projects, both field inspection and friction measurements closely aligned with the proposed methodology's results. The methodology presented establishes a foundational QC standard for chip seal projects, enhancing both acceptance efficiency and safety by using a quantitative method and minimizing the extended presence of practitioners on roadways. [ABSTRACT FROM AUTHOR]

Although rotary shaft seals have been used successfully in many industrial applications for decades, their tribological behavior is still not completely understood. In-depth knowledge of the structural mechanics is essential for the design and optimization of such sealing systems. High complexity results from the multiscale interactions in the tribological system rotary shaft seal. Large macroscopic deformations occur due to the hyperelastic material behavior of elastomers coupled with microscopic tangential distortions of the sealing edge surface in the contact area. This paper includes both numerical and experimental studies on the tribological behavior of rotary shaft seals. A multiscale finite element model provides the simulation of the macroscopic deformations and the microscopic displacements. A test rig equipped with a hollow glass shaft enables in situ visual contact analyses, qualitative determinations of pressure distributions and quantitative measurements of elastomer surface distortions. The optical phenomenon of frustrated total internal reflection enables qualitative evaluations of the pressure distribution. Particle image velocimetry (PIV) is employed to quantify the tangential distortions. The test rig enables the measurement of the friction torque with the same configuration. The results of the numerical and experimental investigations for the radial load, friction torque and tangential distortions are compared and discussed. This serves to validate the simulation methods and the correlation of the measured parameters. This finally results in a solid and validated basis for further tribological investigations of rotary shaft seals. [ABSTRACT FROM AUTHOR]

Aiming at the lack of accurate and reliable discrete element simulation parameters for the design of buckwheat metering devices and seeders based on the discrete element simulation method, an accurate buckwheat seed model was obtained by calibrating the discrete element simulation parameters. In this study, buckwheat seed particle models were established based on the manual and automatic filling methods. In order to improve the accuracy of the models, discrete element simulation parameters were calibrated, and the static cylinder-lifting test and dynamic seed-metering test were used to verify the simulation results. A 3D model of buckwheat seed was obtained using the CT scanning method, and a manual filling 7-sphere particle model and an automatic filling multi-sphere particle model were established. The physical parameters and contact parameters were measured using the uniaxial compression test, the drop test, and the friction coefficient measurement test. The Plackett–Burman test and steepest ascent path were used to obtain the optimal parameter combination based on the static cylinder-lifting test. We conducted dynamic seed-metering tests using the two particle models under the optimal parameter combination. The results show that, compared with the measured values of stacking angle, the relative errors of the simulation values of the manual filling 7-sphere and automatic filling 36-sphere particle models are 1.04% and 0.50%, respectively. When the rotation speed range of the seeding wheel is 20~60 r/min, the average relative errors between the simulated value and the measured value are 15.85% and 4.69%, respectively. When the effective working length range of the seeding wheel is 20~40 mm, the average relative errors between the simulated value and the measured value are 22.18% and 9.07%, respectively. Regardless of whether the manual filling 7-sphere or the automatic filling 36-sphere particle model of buckwheat seed was used for static motion parameter simulation or dynamic motion simulation, the automatic filling 36-sphere particle model has a higher accuracy. The buckwheat seed particle model established in this study will provide support for the design of buckwheat special seed-metering devices and improve the quality of buckwheat mechanized sowing operation. [ABSTRACT FROM AUTHOR]

In this paper, the influence of a nominal bearing clearance on the lift-off behaviour and the load-carrying capacity of gas polymer bearings (GPBs) is investigated. For this purpose, an experimental study with five different bearing gap configurations and a range of static loads is carried out. Furthermore, the test rig for the clearance and friction torque measurements is illustrated and discussed from a practical point of view. The experimental gap measurement results of all the bearing configurations and the method used are explained and discussed. Finally, the friction torque during the lift-off and run-up phases is measured for a range of static loads. A method that uses the time derivative of the measured friction torque during the run-up tests as a criterion for the lift-off detection is explained and applied to the measured data. The results of this study indicate that there are large differences between the most studied bump-type and gas polymer bearings in terms of the dependence of the load-carrying capacity on the bearing gap. Furthermore, the recorded effects are described, and possible explanations are given. Finally, the differences in characteristics from those of bump-type bearings are described and their importance for the design process of rotors supported in GPBs is explained. [ABSTRACT FROM AUTHOR]

The mechanical behaviour of materials can be described by a phenomenological relationship that binds strain to stress, by the complex modulus function: M (ω) , which represents the frequency response of the medium in which a transverse mechanical wave is propagated. From the experimental measurements of the internal friction obtained when varying the frequency of a transverse mechanical wave, the parameters that characterize the complex module are determined. The internal friction or loss tangent is bound to the dissipation of the specific mechanical energy. The non-equilibrium thermodynamics theory leads to a general description of irreversible phenomena such as relaxation and viscosity that can coexist in a material. Through the state variables introduced by Ciancio and Kluitenberg, and applying the fractional calculation due to a particular memory mechanism, a model of a viscoanelastic medium is obtained in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

The article deals with the replacement of hard chrome plating by applying the duplex system plasma nitriding + CrN coating (hereinafter referred to as PN + CrN). The goal of the research was to find a suitable alternative for steel surface treatment that would replace hard chrome plating and ensure similar mechanical and tribological properties. An exposed part of a small-bore weapon was selected for evaluation, namely the gas piston of the 42CrMo4 steel breech mechanism drive. The PN + CrN duplex system was compared with a hard chrome coating as well as a self-deposited CrN coating. The mentioned surface treatments were evaluated in terms of metallography, mechanical and tribological properties and surface texture. From the mechanical properties, the hardness of the surface was analyzed, an indentation test was performed (Mercedes test) and adhesive-cohesive behavior was evaluated (Scratch test). Furthermore, an instrumented penetration test was performed (an evaluation of plastic and elastic deformation work and indentation hardness). As part of the assessment of tribological properties, the Ball-on-Flat test, the measurement of the coefficient of friction and the measurement of traces of wear were performed. The surface texture was evaluated in terms of morphology and surface roughness measurement by selected 2D and 3D parameters. The PN + CrN duplex system showed higher hardness than hard chrome, better tribological properties (lower friction coefficient), but worse surface texture. The PN + CrN duplex system has proven to be a suitable alternative to the hard chrome coating for exposed parts of small-caliber weapons, which can be applied in arms production. [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]

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]

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 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]

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]

To evaluate the effect of long-term in-vivo aging on orthodontic archwires, we aimed to assess the triboelectrochemical and mechanical characteristics of as-received and in-vivo aged nickel-titanium (NiTi) and stainless-steel (SS) orthodontic archwires. Four consecutive tribocorrosion cycles on six NiTi and six SS archwires, as-received and in-vivo aged, were performed on a reciprocal tribometer. Electrochemical noise and friction coefficient measurements, three-dimensional surface profiling, and hardness measurements were performed. Repassivation times of as-received archwires were longer than of the in-vivo aged; however, were shorter for NiTi. Friction coefficients were higher for NiTi than for SS archwires. Sudden major current drops concomitant with inverse potential shifts and friction coefficients' fluctuations, were seen for as-received (last cycle) and in-vivo aged (last three cycles) NiTi archwires. More pronounced tribocorrosion damage was observed on in-vivo aged NiTi than on other archwires. Hardness was generally higher inside the wear track of archwires. Long-term in-vivo exposure decreases the corrosion susceptibility of archwires, more evidently for the NiTi ones. Sudden major fluctuations in electrochemical current, potential, and friction coefficient detected for NiTi archwires, might be related to localized residual parts of the oxide layer persisting due to increased surface roughness or to phase transformations of the alloy's crystal structure. [ABSTRACT FROM AUTHOR]

Nowadays, the replacement of a hip joint is a standard surgical procedure. However, researchers have continuingly been trying to upgrade endoprostheses and make them more similar to natural joints. The use of 3D printing could be helpful in such cases, since 3D-printed elements could mimic the natural lubrication mechanism of the meniscus. In this paper, we propose a method to deposit plastics directly on titanium alloy using 3D printing (FDM). This procedure allows one to obtain endoprostheses that are more similar to natural joints, easier to manufacture and have fewer components. During the research, biocompatible polymers suitable for 3D FDM printing were used, namely polylactide (PLA) and polyamide (PA). The research included tensile and shear tests of metal–polymer bonds, friction coefficient measurements and microscopic observations. The friction coefficient measurements revealed that only PA was promising for endoprostheses (the friction coefficient for PLA was too high). The strength tests and microscopic observations showed that PLA and PA deposition by 3D FDM printing directly on Ti6Al4V titanium alloy is possible; however, the achieved bonding strength and repeatability of the process were unsatisfactory. Nevertheless, the benefits arising from application of this method mean that it is worthwhile to continue working on this issue. [ABSTRACT FROM AUTHOR]

There are many moving machine assemblies with conformal tribological contacts at very high contact pressures, e.g., sliding bearings, propeller shaft bearings and machine guideways. Furthermore, applications such as trunnion and guide vane bearing in Kaplan turbines have very low sliding speeds and oscillatory types of motion. Although there is a vast selection of tribology test rigs available, there is still a lack of test equipment to perform friction and wear tests under high contact pressure, reciprocatory sliding and large area contact. The aim of this work is thus to develop a novel reciprocating tribometer and test method that enables friction and wear tests under low-speed reciprocatory sliding with contact pressures up to 90 MPa in a flat-on-flat contact configuration. First, a thorough description of the test rig design is given. Secondly, the influence of contact pressure and stroke length on the tribological properties of a stainless steel and polymer composite material combination is studied. The significance of considering creep, friction during the stroke and contact temperature is specifically highlighted. The novel tribometer can be used to screen different bearing and shaft material combinations and to evaluate the friction and wear performance of self-lubricating bearings for the specific operating conditions found in Kaplan turbines. [ABSTRACT FROM AUTHOR]