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Industrial development has led to an increase in demand for friction materials, resulting in increasingly prominent environmental issues throughout their entire life cycle, and developing green and eco‐friendly brake friction materials has become a focus in the braking field. This paper explores the mechanical and tribological properties of fly ash (industrial waste) and sisal fiber (natural fiber) as eco‐friendly components to enhance brake friction materials. Four samples containing different ratios of fly ash and sisal fiber were prepared and tested with a variable‐speed friction testing machine. The results show that the eco‐friendly alternative combination can effectively improve the friction coefficient, and reduce friction fluctuations and thermal degradation, but the wear rate will also increase accordingly. In addition, the worn morphology reveals the formation of the contact platform and wear mechanism. A hybrid integration of analytic hierarchy process (AHP) and multi‐objective optimization by ratio analysis (MOORA) was used to weigh various evaluation indicators objectively and rank the samples. The sample with 8% fly ash and 6% sisal fiber exhibited the best comprehensive tribological performance. Highlights: Development of eco‐friendly brake friction composites with natural and waste additives.Investigation of the effect of the natural wastes' ratio on prepared composites' physical, mechanical, and tribological properties.Evaluation of brake friction composites with AHP‐MOORA.Sample S6F8 exhibits the best comprehensive tribological performance. [ABSTRACT FROM AUTHOR]

Copper‐based metal–organic frameworks is anticipated to find applications in the field of friction materials owing to its plentiful surface‐active groups and distinctive framework structure. In this study, copper‐based metal–organic frameworks was synthesized through ultrasound‐assisted method and incorporated alone into carbon fiber reinforced epoxy composites or together with SiO2 nanoparticles towards the goal of improving the composites' friction and wear properties. It is revealed that copper‐based metal–organic frameworks alone cannot improve the friction and wear of carbon fiber reinforced epoxy composites simultaneously. The combination of copper‐based metal–organic frameworks and SiO2 nanoparticles was more effective in enhancing both the mechanical and tribological properties of studied composites. The composite material exhibits a friction coefficient of 0.104 under the specified test conditions of 10 MPa and 3.75 m/s. Additionally, the specific wear rate is impressively low, measuring only 5.64 × 10−7 mm3 N/m. Through morphological and chemical analysis on the worn surfaces and transfer films, the functioning mechanism of copper‐based metal–organic frameworks in modifying the mechanical and tribological properties was discussed. It was discovered that a tribological synergy exists between short carbon fibers, copper‐based metal–organic frameworks, and SiO2 fillers, leading to a shift in the wear mechanism of the composite materials from abrasive wear to adhesive wear. Concurrently, a shear‐prone transfer film forms on the surface of the counter steel surfaces. Findings of the present study pave a new route of designing high performance epoxy based tribo‐composites by using metal–organic frameworks. Highlights: Cu‐BDC nanosheets were synthesized using ultrasound‐assisted techniques and incorporated as tribological fillers in EP composites.The combined use of Cu‐BDC, SiO2, and SCF fillers synergistically enhances the mechanical and tribological properties of EP composites.The composite material exhibits a friction coefficient of 0.104 under the specified test conditions of 10 MPa and 3.75 m/s, the specific wear rate is impressively low, measuring only 5.64 × 10−7 mm3N/m.During the sliding friction process of the composite materials, Cu‐BDC and SiO2 play a crucial role in reducing SCF pull‐out wear through their anchoring effect.The dynamic coordination bond structure of Cu‐BDC contributes to the formation of uniform and continuous transfer films on counter metal surfaces. [ABSTRACT FROM AUTHOR]

This paper studies the influence of different factors, such as polymer and fiber type and aging, on the internal friction and fractional parameter, which are determined for rubber concrete and fiber-reinforced rubber concrete by means of the Resonant Frequency and Damping Analyzer (RFDA Basic) implementing the Impulse Excitation Technique (IET). Both materials contained low molecular weight cis-polybutadiene rubber SKDN-N as the main binder. Another type of binding material has been used for further investigation of internal friction phenomena in polymer concrete. Namely, low molecular weight polybutadiene rubber (BR) of mixed microstructure was utilized to produce the samples for the experimental program. Two different types of fiber are used: metal and polymer fiber. It has been found that the addition of steel fiber reduces internal friction in the material, whereas propylene fiber acts as additional damping material and increases internal friction. BR-based concrete and fiber-reinforced concrete show rather high values of internal friction, i.e. behave more viscoelastically. BR-based concrete performs higher values of the fractional parameter, and, therefore, more obvious viscoelastic properties. Introduction of steel fiber in the mixture reduces the fractional parameter, since it plays the role of additional bonds in the material structure. However, addition of propylene fiber increases fractional parameter in both, SKDN-N and BR-based concretes. It can be explained by additional damping effect of the polymer fiber. The obtained results are compared with those for the reference specimens made of ordinary Portland cement concrete, and a certain influence of the selected parameters on the internal friction of the considered materials are established. [ABSTRACT FROM AUTHOR]

Current standardized in vitro bending experiments for orthodontic archwires cannot capture friction conditions and load sequencing during multi-bracket treatment. This means that clinically relevant forces exerted by superelastic wires cannot be predicted. To address these limitations, this study explored a novel test protocol that estimates clinical load range. The correction of a labially displaced maxillary incisor was simulated using an in vitro model with three lingual brackets. Deflection force levels derived from four different protocols were designed to explore the impact of friction and wire load history. These force levels were compared in nickel-titanium (NiTi) archwires with three commonly used diameters. The unloading path varied between protocols, with single or multiple sequences and different load orders and initial conditions. Deflection forces from the new protocol, employing multiple continuous load/unload cycles (CC incr), consistently exceeded those from the conventional protocol using a single continuous unloading path (CU decr). Mean differences in plateau force ranged from 0.54 N (Ø 0.014" wire) to 1.19 N (Ø 0.016" wire). The CC inr protocol also provided average force range estimates of 0.47 N (Ø 0.012" wire), 0.89 N (Ø 0.014" wire), and 1.15 N (Ø 0.016" wire). Clinical orientation towards CU decr carries a high risk of excessive therapeutic forces because clinical loading situations caused by friction and load history are underestimated. Physiological tooth mobility using NiTi wires contributes decisively to the therapeutic load situation. Therefore, only short unloading sequences starting from the maximum deflection in the load history, as in CC incr , are clinically meaningful. • Friction and load history affect deflection forces of orthodontic NiTi wires. • Conventional in vitro 3-bracket bending tests underestimate clinical force levels. • Physiological tooth movement must be considered to derive clinically relevant loads. • Reactive forces from wire deflection may vary because of physiological conditions. • Sequential short unloading sequences allow characterization of clinical load range. [ABSTRACT FROM AUTHOR]

This study seeks to identify the most suitable pavement texture resolution for accurately representing friction properties, employing the Dynamic Friction Model (DFM). Friction and texture measurements were conducted on various pavement surfaces at resolutions ranging from 10 μm to 5000 μm. Results indicate that the optimal resolution for accurate representation is unexpectedly found to be 500 μm, aligning with the Microtexture/Macrotexture limit. This contradicts current trends emphasizing higher resolutions for pavement surface representation. The article provides a foundational exploration, prompting discussions and further investigations into determining the ideal resolution for characterizing pavement surfaces in the context of friction properties. [ABSTRACT FROM AUTHOR]

Brake friction material reinforced with coconut fiber and dypsis lutescens fiber was designed and prepared in this study. Specimens incorporating 0–8 wt.% of coconut fibers or dypsis lutescens fibers were fabricated. The effect of the content of these reinforcing fibers on the overall properties of brake friction materials was systematically investigated. The results indicate that the inclusion of reinforcing fibers in the formulation of brake friction materials can improve the physical properties and friction and wear properties of brake friction materials. The specimen incorporating 6 wt.% plant fiber obtained the optimal comprehensive performance with excellent fade resistance and recovery properties, and better wear resistance. In order to further investigate their performance, nine hybrid fiber brake friction materials were designed using the golden section method and orthogonal test method. The study indicated that the F-6 hybrid fiber-reinforced brake friction materials have better physical properties, thermal degradation resistance, recovery properties, and abrasion resistance than the single-fiber-reinforced brake friction materials. This study provides new concepts for the preparation of fiber-reinforced brake friction materials as well as formulation optimization. [ABSTRACT FROM AUTHOR]

Cardiovascular diseases, which cause ≈10 million deaths annually, underscored the importance of effective blood pressure (BP) monitoring. Traditional devices, however, faced limitations that hindered the adoption of continuous monitoring technologies. Flexible triboelectric nanogenerator (TENG) sensors, known for their rapid response, high sensitivity, and cost‐effectiveness, presented a promising alternative. Enhancing their ability to capture weak biological signals can be achieved by optimizing the material's friction coefficient and expanding the effective contact area. In this work, a flexible microcolumn‐based TENG sensor with high sensitivity is developed by fabricating microcolumns of carbon nanotube/polydimethylsiloxane (CNT/PDMS) composites on porous polyethylene terephthalate (PET) membranes using template etching and integrating these with fluorinated ethylene propylene (FEP) film. With the enhancement of microcolumn structure, the sensor possessed high sensitivity and good response, enabling it to effectively and accurately detect subtle physiological changes such as radial pulses and fingertip pulsations, with pulse wave signals highly consistent with the interbeat intervals of electrocardiograms. Leveraging these capabilities, a non‐invasive dynamic BP monitoring system capable of continuous beat‐to‐beat BP monitoring is developed. This advancement enables easier and more effective health monitoring, empowering individuals to better manage their health and improve personalized medical care. [ABSTRACT FROM AUTHOR]

In this paper, a combination of theoretical modeling, finite element simulation, and experimental methods is employed to investigate the forming mechanism and evolutionary pattern of the stagnant region during mechanical scratching with a diamond wedge tool. The study is structured as follows: Firstly, a theoretical calculation model for the geometric parameters of the stagnant region on the formed groove surface is established based on the contact friction partition mechanism and slip-line field theory. The model indicates that the geometric parameters lB-sg, lV-sg, and ∆lsg of the stagnant region are determined by the length of the stagnant region lp-sg in the plastic flow plane and the transformation parameters. Secondly, the formation process of the stagnant region in mechanical scratching is investigated using an orthogonal cutting simulation model with a negative rake angle tool. The results reveal that the stagnant region is a plastic deformation region formed due to the geometrical characteristics of the negative front surface of the scratching tool and its excessive extrusion, which leads to the formation of adhesive friction within the material. Thirdly, the characteristics of the stagnant region are determined through scratching experiments. Compared to the material in the plastic flow region, the material within the stagnant region exhibits finer and denser microstructures, reduced surface hardening peaks and hardened layer depths, and significantly improved surface roughness. Finally, the evolutionary pattern of the stagnant region under the influence of scratching processing parameters is examined based on the theoretical calculation model of the geometric parameters and the scratching experiment. The findings indicate that as the wedge angle of the scratching tool decreases, the relief angle increases, the absolute value of the rotation angle around the Y-axis decreases, the scratching speed decreases, and the material's plastic adherence improves, the PI/k value decreases, the lp-sg value increases, and consequently, the geometric parameters lB-sg, lV-sg, and ∆lsg of the stagnant region on the formed groove surface also increase. The deviation analysis of the geometric parameters of the stagnant region reveals a consistent trend between the theoretical and experimental values of lV-sg and ∆lsg, with maximum deviations of 15 μm and 4.13%, respectively. This study provides theoretical and experimental evidence for the establishment of the theoretical model of the stagnant region in mechanical scratching, the analysis of its forming mechanism, and the control of the stagnant region geometric parameters on the formed groove surface. [ABSTRACT FROM AUTHOR]

The braking system of a motor vehicle is a multi‐material system, subjected to various aggressive conditions. Corrosion of the brake disc during stationary periods can determine the onset of a high adhesion force (stiction) capable of compromising the reliability of the braking system during vehicle motion. The purpose of this work is to study the effect of the introduction of Cu and Zn in the friction material composition. This effect was investigated through electrochemical measurements (electrochemical impedance spectroscopy, potentiodynamic polarization, and stiction tests), conducted using an electrochemical cell simulating the parking brake, complemented by the examination of the brake disc and pad surfaces and water absorption tests. The results suggest that porous components, like vermiculite, in the composite friction material led to high contact force. Moreover, 10 wt% of Cu in the friction material does not significantly affect its stiction behavior in our testing configuration. In contrast, 10 wt% Zn in the friction material significantly reduces the stiction propensity by acting with a complex synergistic mechanism combining physical and chemical shielding effects. [ABSTRACT FROM AUTHOR]

We performed a gas nitriding and quenching process (GNQP) on Ti–18 mass% Nb alloy to obtain a high damping capacity and wear resistance. GNQP was performed at temperatures of 1023, 1123, and 1223 K. The outermost surface of the GNQP specimen obtained at 1023 K mainly comprised TiO2, whereas that at 1223 K mainly comprised TiN. The surface and interior of the specimens exhibited higher hardness at 1223 K than that at 1023 K. Compared to the specimen obtained by solution–quenching (AQ), the unit volume of the α" martensite phase at a depth of 320 μm of the GNQP specimen obtained at 1023 K was similar, and that at 1223 K was higher. Such a difference can be related to the difference in the core hardness of the specimens. The wear amounts of all GNQP specimens were lower than those of the AQ specimen. The coefficient of friction of the GNQP specimen obtained at 1023 K was lower than that obtained at 1223 K. The surface constituent phase and surface roughness exhibited a strong influence on the wear at a load of 500 g. Meanwhile, the nitride layer and damping capacity were considered to be related to the wear at a load of 3000 g. [ABSTRACT FROM AUTHOR]

Laser‐induced graphene (LIG) technology has provided a new manufacturing strategy for the rapid and scalable assembling of triboelectric nanogenerators (TENG). However, current LIG‐based TENG commonly rely on polymer films, e.g., polyimide (PI) as both friction material and carbon precursor of electrodes, which limit the structural diversity and performance escalation due to its incapability of folding and creasing. Using specialized PI paper composed of randomly distributed PI fibers to substantially enhance its foldability, this work creates a new type of TENG, which are structurally foldable and stackable, and performance tailorable. First, by systematically investigating the laser power‐regulated performance of single‐unit TENG, the open‐circuit voltage can be effectively improved. By further exploiting the folding process, multiple TENG units can be assembled together to form multi‐layered structures to continuously expand the open‐circuit voltage from 5.3 to 34.4 V cm−2, as the increase of friction units from 1 to 16. Last, by fully utilizing the unique structure and performance, representative energy‐harvesting and smart‐sensing applications are demonstrated, including a smart shoe to recognize running motions and power LEDs, a smart leaf to power a thermometer by wind, a matrix sensor to recognize writing trajectories, as well as a smart glove to recognize different objects. [ABSTRACT FROM AUTHOR]

The application of polymer composites is one of the most effective methods for preventing lubrication failure in deep‐sea engineering. In this study, fluorinated graphite (FGr) microsheets were incorporated into polytetrafluoroethylene (PTFE) microparticle‐filled poly(butylene terephthalate) (PBT) composites. The tribological performance in the simulated deep‐sea environment at elevated seawater pressure equivalent to 3000 m ocean depth was investigated. The results showed that FGr enhances the flexural and compressive strengths, thermal stability, and seawater resistance of the PTFE/PBT composite. The wear rate was decreased to 96% at the critical FGr content of 4% by improving the transfer onto the metallic counterfaces, preventing direct contact and shear between friction couples. Moreover, the seawater pressure impedes composite transfer, leading to a 29% increase in the wear rate. [ABSTRACT FROM AUTHOR]

Hydrogels with excellent hydrophilicity, high water content, outstanding biocompatibility, and lubrication properties are among the promising articular cartilage replacement materials. Despite extensive research focus on lubrication of hydrogels, realization of bioinspired materials with high load‐bearing, low‐friction, extraordinary lubrication, and anti‐wear properties is challenging. Herein, robust lubrication can be realized by structuring vertical and horizontal dual gradient surfaces, with structural design in vertical direction gradually transitioning from an anisotropic tubular to a compact body to provide load‐bearing, and a surface rigid porous polymer skeleton and a filled loose lubricating polymer structural design to provide lubrication in horizontal direction. What is more, gradient transition region in vertical direction greatly weakens gradient layer interface stress to increase load‐bearing, and gradient surface in horizontal direction is constructed by interconnected surface rigid polymer skeleton containing "pockets" that house highly hydrated and mechanically fragile soft lubrication polymer to prevent removal of lubrications under high load and wear. The designed hydrogel has an extremely low coefficient of friction (COF) with hard steel (COF ≈0.0036, 50 N, 35,000 cycles) and achieves a balance between lubrication and load bearing. The work opens up an avenue for rational design of high load‐bearing and ultralow friction soft material surfaces. [ABSTRACT FROM AUTHOR]

Material extrusion additive manufacturing provides an effective solution for fabrication of highly customized polyether ether ketone (PEEK) composite parts with any complex shape. Nevertheless, compared with conventional methods, the mechanical strength of 3D printed carbon fiber reinforced PEEK (CF/PEEK) composites is unsatisfactory due to the weak interface bonding strength and high voids content induced by the temperature difference. To overcome this challenge, a temperature‐control 3D printer was used to investigate the effects of ambient temperature and annealing temperature on the microstructure, crystallization behavior and mechanical properties of 3D printed parts. Moreover, the tribological properties of parts printed at different ambient temperature were also studied under various contact pressure. Experimental results showed that the ambient temperature and annealing treatment directly affected the interfacial bonding (fiber/matrix, filament/filament, layer/layer), crystallinity of printed samples, thus affecting their mechanical and tribological properties. The CF/PEEK parts printed at high ambient temperature of 200°C exhibited outstanding mechanical and tribological properties. This study has positive significance for promoting the application of 3D printed PEEK composites in the field of structural load‐bearing and friction materials. Highlights: Structure–property relationships for 3D printed CF/PEEK composites.The ambient temperature strongly affects the thermal and microstructural propertiesInteraction between crystallization and molecular interface diffusion.Interfacial bonding and crystallinity determine the mechanical properties.Tribological properties are highly dependent on applied pressures. [ABSTRACT FROM AUTHOR]

Rock avalanches typically entail the flow-like motion of angular rock blocks and fragments of diverse size. Numerical simulations are instrumental in understanding their dynamic process, supporting hazard and risk assessments. Simplified failure criteria, such as the Mohr-Coulomb or Drucker-Prager, are commonly adopted in landslide models relying on the material point method (MPM). However, these criteria cannot capture the transitions between solid-like, liquid-like, and gas-like behaviors exhibited by granular materials. Here, we relied on the moving least-squares MPM, which offers high computing efficiency and stability, and adopted a nonlocal μ(I) rheology model implemented by Haeri and Skonieczny (Comput Methods Appl Mech Eng, 2022). This approach can account for the rate-dependent, pressure-dependent, and size-dependent characteristics of friction in granular materials. By simulating a small-scale flume experiment as well as a large-scale event (the Nayong rock avalanche in Guizhou, China), we verified that the nonlocal μ(I) rheology model can capture the motion and deposition processes in rock avalanches effectively. This feature can be advantageous in physically based hazard assessments of such events. [ABSTRACT FROM AUTHOR]

The standard rate‐and‐state friction (RSF) has extensively captured frictional behaviors, but it fails to explain the velocity dependence of frictional stability transition and widespread slow‐slip events (SSEs) in experiments and nature adequately. An alternative microphysical Chen‐Niemeijer‐Spiers (CNS) model can well describe the velocity dependence of frictional behaviors of granular gouges. Using the original CNS model, standard RSF parameters can be quantified microphysically. However, some micro‐parameters are not easy to estimate quantitatively, making it difficult to extrapolate to natural and experimental conditions. Here, we simplify the microphysically‐derived RSF parameters including direct effect a, evolution effect b, and critical slip distance Dc, as well as equivalent values (aeq, beq, and Deq). The simplified friction parameters directly illustrate their velocity dependence, namely the essentially constant a, aeq, and Dc, negatively velocity‐dependent b and beq, as well as varying Deq for different laws. They are roughly consistent with experimental results in various fault gouges. A modified CNS model is further derived from the original CNS model, establishing a direct link between the standard RSF and CNS models. The modified CNS model exhibits virtually identical frictional behaviors to the original CNS, but differs from the standard RSF at large velocity perturbations. Moreover, the linearized stability analysis indicates that the critical stiffness for the modified CNS model is velocity‐dependent. Compared with the standard RSF, the modified CNS model not only explains the velocity dependence of frictional stability transition, but also exhibits a more gradual transition for SSEs with a broader range of stiffness ratios. Plain Language Summary: Geological observations have illustrated a growing body of slow fault slip events that radiate little or no seismic energy, but the underlying mechanisms are not fully understood. This study examines two widely‐used friction models, namely, an empirical friction model and a microphysically‐based model. Both of them have been employed to capture experimental and natural observations, but the microphysical model shows significant velocity dependence of friction and is able to interpret friction parameters of the empirical friction model microphysically. We further examine the microphysically‐derived friction parameters, omit some micro‐parameters that contribute negligibly, directly describe their velocity dependence, and derive a simple friction model. The modified friction model is roughly consistent with the microphysically‐based model. More importantly, the modified model can not only describe the velocity dependence of frictional stability transition, but also explain the widespread slow fault slip events in experiments and nature. Key Points: Microphysically‐derived rate‐and‐state friction parameters are simplifiedA modified Chen, Niemeijer, and Spiers (CNS) model is derived from the original microphysical modelThe modified CNS model captures a more gradual transition for slow‐slip events [ABSTRACT FROM AUTHOR]

When welding ultra-fine-grained metals using conventional methods, the microstructure in the joint area is degraded (mainly due to recrystallization) in the heat-affected zone and a significant deterioration of mechanical properties, including joint strength. The aim of the research presented in this article was to identify the possibility of obtaining joints with strength close to initial material using friction welding of metal materials with ultra-fine grain. For this purpose, UFG (ultra-fine-grained) material was produced from technically pure M1Ez4 copper using a hybrid SPD (severe plastic deformation) process. The welding process was carried out on a machine with a prototype design that allows minimizing the welding time, while generating high force. The process parameters used on the prototype machine resulted in an increase in the hardness of the material by 4% in the joint area. The strength of the joint compared to the base material decreased slightly by 2%. The tests carried out proved that, using appropriate process parameters, it is possible to obtain a UFG metal joint without a decrease in its mechanical strength. [ABSTRACT FROM AUTHOR]

This paper introduces the design of an articulated wheeled robot with four links and three joints that can travel in pipes with inner diameters of 4 in with a traction force of 300 N or more. Although many in-pipe inspection robots have been reported, no examples can yet travel long distances, including many curved sections. This paper presents roller material with the best friction property and durability for in-pipe robots to possess high traction capability. Lifting payload and long distance in-pipe travel tests were also conducted for the robot with the selected elastic materials. The results demonstrate that a 16 kg weight was successfully lifted, and the robot can travel a total length of 23 m, including 19 horizontal and vertical bent sections. [ABSTRACT FROM AUTHOR]

Current-carrying friction materials with excellent electrical conductivity and anti-wear ability are in constant demand in both academia and industry. In this work, the sliver-titanium nitride (Ag–TiN) composite ceramic coating was fabricated by an arc ion plating method. The microstructure, chemical composition, crystal structure, mechanical properties and current-carrying tribological behaviors of the Ag–TiN composite coating were systematically studied and the worn surfaces were also thoroughly investigated to analyze the possible tribological mechanisms in detail. The results showed that the Ag–TiN composite ceramic coating achieved uniformly distributed co-deposition of Ag and TiN compositions and exhibited excellent mechanical properties and electrical conductivity. The current-carrying tribological tests also revealed that the Ag–TiN composite coating exhibited exceptional friction reducing, anti-wear and conductive properties during the friction process. The analysis of the worn surface showed that the excellent current-carrying tribological behaviors of the Ag–TiN composite ceramic coating were related to the excellent electrical conductivity, the appropriate mechanical properties and the tribo-layer film formed on the worn surface. [ABSTRACT FROM AUTHOR]

Nitrile butadiene rubber (NBR) and its various composite materials are widely employed as friction materials in mechanical equipment. The use of carbon nanotube (CNT) reinforcement in NBR for improved friction and wear characteristics has become a major research focus. However, the mechanisms underlying the improvement in the friction and wear characteristics of NBR with different CNT contents remain insufficiently elucidated. Therefore, we conducted a combined analysis of NBR reinforced with varying CNT contents through molecular dynamics (MD) simulations and ring–block friction experiments. The aim is to analyze the extent to which CNTs enhance the water-lubricated friction and dry wear properties of NBR and explore the improvement mechanisms through molecular chain characteristics. The results of this study demonstrate that as the mass fraction of CNTs (0%, 1.25%, 2.5%, 5%) increases, the water-lubricated friction coefficient of NBR continuously decreases. Under water-lubricated conditions, CNTs improve the water storage capacity of the NBR surface and enhance lubrication efficiency. In the dry wear state, CNTs help reduce scratch depth and dry wear volume. [ABSTRACT FROM AUTHOR]

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Strain localization frequently occurs in cohesive materials with friction (e.g., composites, soils, rocks) and is widely recognized as a fundamental cause of progressive structural failure.Nonetheless, achieving high-fidelity simulation for this issue, particularly concerning strong discontinuities and tension-compression-shear behaviors within localized zones, remains significantly constrained. In response, this study introduces an integrated algorithmwithin the finite element framework, merging a coupled cohesive zonemodel (CZM) with the nonlinear augmented finite elementmethod (N-AFEM). The coupledCZMcomprehensively describes tension-compression and compressionshear failure behaviors in cohesive, frictional materials, while the N-AFEM allows nonlinear coupled intraelement discontinuities without necessitating extra nodes or nodal DoFs. Following CZM validation using existing experimental data, this integrated algorithm was utilized to analyze soil slope failure mechanisms involving a specific tensile strength and to assess the impact of mechanical parameters (e.g., tensile strength, weighting factor, modulus) in soils. [ABSTRACT FROM AUTHOR]

Purpose. Justification of the criterion for automatic optimization of the ore grinding process in self-grinding drum mills by compiling and researching mathematical models of material movement inside the drum of a rotating mill. Methodology. Methods of mathematical modeling of the internal mechanics of drum mills in combination with experimental studies of the spectral density of the variable component of the active power consumed by the drive motor of the mills are used. Findings. As a result of the simulation, it was established that the loose material placed on the inner surface of the rotating drum undergoes periodic oscillations under certain conditions. The parameters of these oscillations depend on the radius of the drum, the amount of material and the coefficient of friction. It is theoretically justified that in the case of load fluctuations, the work of friction forces and, therefore, the process of material destruction intensifies. The theoretically obtained conclusions are confirmed by the results of experimental studies of the active power signal spectrum of the drive motor of the mills in the characteristic low-frequency range. It is found that the most intense fluctuations occur at a certain degree of filling of the drum of the mill in the working range of fillings and their intensity correlates with the productivity of the mill according to the newly created finished class. Originality. The mechanism of occurrence of fluctuations in the ore load of drum mills is revealed and the connection of this phenomenon with indicators of the technological efficiency of the grinding process is substantiated. Practical value. It is advisable to use the intensity of fluctuations of the ore load as a criterion for automatic control of mill loading, since this parameter characterizes the technological efficiency of the mill and can be measured quickly. Using the intensity of ore loading fluctuations as a control criterion allows implementing a search system for extreme control of mill loading. [ABSTRACT FROM AUTHOR]

Polyoxymethylene (POM) which shows good mechanical properties has a wide range of application in engineering. In this work, the nanoscale simulation method of molecular dynamics (MD) is used to make a more systematic simulation and calculation of the model of the resin material POM. With the application of software, the influence of friction depth, temperature, and sliding velocity on the frictional properties of POM was studied. The main conclusions are as follows: (1) In the range of 300 K–400 K, the temperature has little influence on the friction coefficient, but the fluctuation of friction force becomes larger as the temperature becomes larger. (2) When the friction depth increases, the plowing phenomenon and the accumulation of debris become more obvious and plastic deformation of POM increases. (3) When the friction velocity is changed, it is found that there is not much correlation between friction force and friction velocity, but as the friction velocity decrease, the friction force also decrease to a smaller extent. (4) The friction force will experience a growth period, and its value gradually stabilizes with some fluctuations, which are mainly caused by the atomic thermal motion, the effect of abrasive chip accumulation, and the release of stress energy caused by deformation. [ABSTRACT FROM AUTHOR]

Seizure is a severe accident that can abruptly stop or even damage running equipment. Improving the anti-seizure properties of friction pair materials is also crucial as lubricating and wear resistance. While the tribological performances of molybdenum disilicide (MoSi2) and ferrophosphorus (FemPn) particle-doped copper-tin-bismuth (Cu-Sn-Bi) composites have been investigated in previous studies, the specific effects of MoSi2 and FemPn particles on the anti-seizure property of Cu-Sn-Bi materials remain unclear. This study explores the seizure resistance of Cu-Sn-Bi composites containing MoSi2 and/or FemPn under conformal and nonconformal contact conditions. The materials were prepared using powder sintering technology, and the metallographic structures of four types of self-lubricating copper composites were observed. Seizure resistance under starved lubrication conditions was investigated, and the worn surfaces under different contact types were discussed and analyzed. The results indicate that the addition of MoSi2 and/or FemPn particles effectively refines the grain size, and these particles exhibit different distribution trends after powder sintering. The MoSi2 and FemPn particles improved the maximum seizure load of copper-based composite samples by 66.67% and 84.62%, respectively. The seizure forms under different contact types were also discussed. [ABSTRACT FROM AUTHOR]

Ultra-low friction is crucial for the anti-friction, anti-wear, and long-life operation of nanodevices. However, very few two-dimensional materials can achieve ultra-low friction, and they have some limitations in their applications. Therefore, exploring novel materials with ultra-low friction properties is greatly significant. The emergence of ternary two-dimensional materials has opened new opportunities for nanoscale ultra-low friction. This study introduced nickel phosphorous trisulfide (NiPS3, referred to as NPS), a novel two-dimensional ternary material capable of achieving ultralow friction in a vacuum, into the large nanotribology family. Large-size and high-quality NPS crystals with up to 14 mm × 6 mm × 0.3 mm dimensions were grown using the chemical vapor transport method. The NPS nanosheets were obtained using mechanical exfoliation. The dependence of the NPS nanotribology on layer, velocity, and angle was systematically investigated using lateral force microscopy. Interestingly, the coefficient of friction (COF) of NPS with multilayers was decreased to about 0.0045 under 0.005 Pa vacuum condition (with load up to 767.8 nN), achieving the ultra-low friction state. The analysis of the frictional dissipation energy and adhesive forces showed that NPS with multilayers had minimum frictional dissipation energy and adhesive forces since the interlayer interactions were weak and the meniscus force was excluded under vacuum conditions. This study on the nanoscale friction of a ternary two-dimensional material lays a foundation for exploring the nanoscale friction and friction origin of other two-dimensional materials in the future. [ABSTRACT FROM AUTHOR]

Polyimide (PI) has good mechanical properties and thermal stability, while high coefficient (COF) and wear rate limit its wide application. In order to endow PI with better friction and wear resistance, Mo2Ti2C3 MXene was used as solid lubricant to prepare Mo2Ti2C3/PI nanocomposites with different content of Mo2Ti2C3. The effect of the amount of Mo2Ti2C3 on the tribological behavior of PI was explored and the tribological mechanism was also analyzed Tribological tests showed that at 1.2 wt% of Mo2Ti2C3 addition, the composite material demonstrated superior friction and wear resistance, exhibiting a 19.9% decrease in the COF and a 79.7% decrease in the wear rate compared to single PI due to the good self‐lubricating properties of Mo2Ti2C3 MXene. Moreover, Mo2Ti2C3 can also effectively assist PI to form sleek transfer films without interruption or gaps on the steel balls, resulting in a reduced friction COF and wear rate of the material. This work demonstrates that Mo2Ti2C3 MXene is an aussichtsreich additive for polymers to improve the tribological properties and broadens the applications of Mo2Ti2C3/PI composites in friction material area. Highlights: Mo2Ti2C3 significantly improves the tribological performance of polyimide.The thermal properties of Mo2Ti2C3/polyimide are enhanced by the introduction of Mo2Ti2C3.The minimum coefficient of Mo2Ti2C3/PI composites was only 0.246 at the 1.2 wt% content of Mo2Ti2C3.The wear rate of Mo2Ti2C3/PI composites was decreased by 79.7% at the 1.2 wt% addition of Mo2Ti2C3.Mo2Ti2C3 promotes the establishment of tribo‐film to protect the Mo2Ti2C3/PI composites from friction. [ABSTRACT FROM AUTHOR]

Aiming to solve the problem of thermal decay of resin-based friction materials at high temperatures, rare-earth-lanthanum-oxide-/cerium-oxide-reinforced resin-based friction plates were prepared using a hot-pressing molding process. The effect of lanthanum/cerium oxide with different contents on the mechanical and tribological properties of the resin-based friction of materials was studied, and its mechanism was explored. The result shows that lanthanum/cerium oxide improves the mechanical and tribological properties of materials so that the coefficient of friction of the specimen is more stable on adding lanthanum/cerium oxide at 5% and 1%. Lanthanum/cerium oxide improves antidegradation properties of resin-based material and reduces the high-temperature wear rate by enhancing the interfacial effect so that the wear form of the specimen changes from predominantly adhesive wear to predominantly abrasive wear. [ABSTRACT FROM AUTHOR]

Braking systems are extremely important in any vehicle. They convert the kinetic energy of motion into thermal energy that is dissipated into the atmosphere. Different vehicle groups have different nominal and maximum speeds and masses, so the amount of thermal energy that needs to be absorbed by the friction pads and then dissipated can vary significantly. Conventional friction materials are composite materials capable of withstanding high temperatures (in the order of 500–600 °C) and high mechanical loads resulting from braking intensity and vehicle weight. In small vehicles traveling at low speeds, where both the amount of thermal energy and its density are limited, the use of slightly weaker friction materials with better ecological properties can be considered. This work proposes a prototype composite friction material using flax fibers as reinforcement instead of the commonly used aramid. A number of samples were prepared and subjected to laboratory tests. The samples were prepared using components of plant origin, specifically flax fibers. This component acted as reinforcement in the composite friction material, replacing aramid commonly used for this purpose. The main tribological characteristics were determined, such as the values of the coefficients of friction and the coefficients of abrasive wear rate. For this purpose, an authorial method using ball-cratering contact was used. The results were analyzed using statistical methods. It was found that the composite material using flax fibers does not differ significantly in its tribological properties from conventional solutions; so, it can be assumed that it can be used in the vehicle's braking system. [ABSTRACT FROM AUTHOR]

The ball-on-disk friction and wear tests were conducted using the materials of carbon/silicon carbide (C/SiC) carbon-ceramic composite disk and SiC ball at air atmosphere with different temperatures, including room temperature, 400 °C, and 700 °C. Then, the coefficients and wear rates were obtained, and changes in microstructure and chemical element composition were examined before and after the wear tests. On this basis, the mechanisms of wear and weight loss at different temperatures were analyzed. The results indicated the tribological properties of the composite can be significantly affected by high-temperature oxidation reactions. The frictional coefficients under high temperature conditions of 400 °C and 700 °C are significantly larger than those at room temperature. However, due to the smooth oxidation product of the SiC matrix at temperatures exceeding 700 °C in worn area, the frictional coefficient at 700 °C is slightly smaller than 400 °C. The weight loss of C/SiC composite after high temperature wear test is attributed to the combined effects of oxidation and abrasion. Due to different material consumption mechanisms, although the C/SiC composite can obtain higher frictional coefficient under high temperature condition, the overall consumption of the composite at high temperature is larger than that at room temperature. [ABSTRACT FROM AUTHOR]

The tribological performance of C/C–SiC paired semi-metallic brake pads suitable for automobiles was investigated in this study. Factors on tribological properties of semi-metallic brake pads such as the contents of phenolic resin, copper fibers, steel fibers and MoS 2 were tested by the orthogonal experimental. According to the SAE-J2522 test procedure, an optimized compositional formulation was derived based on the brake test results combined with fuzzy comprehensive evaluation. The wear mechanism of brake pairs was discussed, and the compositional formulation of the brake pad was further optimized after the analysis of the friction surface morphology before and after braking. The results showed that copper fibers had the greatest effect on the friction performance of brake pads. Copper fibers contributed to stabilization of the coefficient of friction (COF) and effectively improved the wear resistance. However, at higher braking speeds (≥120 km/h), the copper fibers were converted from fibrous to flaky and softened, acting as a solid lubricant on the friction surface, resulting in a low COF of brake pads. The tribological performance of brake pads could be improved by reducing the content of copper fiber and increasing the content of hard particles. [ABSTRACT FROM AUTHOR]

Triboelectric nanogenerators (TENGs) have emerged as viable micro power sources for an array of applications. Since their inception in 2012, TENGs have been the subject of significant advancements in terms of structural design and the development of friction materials. Despite these advancements, the complexity of their structural designs and the use of costly friction materials hinder their practical application. This study introduces a simplified TENG model utilizing an economical composite film of fullerene carbon soot (FS)-doped polydimethylsiloxane (PDMS) (FS-TENG). It confirms the FS-TENG's ability to convert mechanical energy into electrical energy, as demonstrated through experimental validation. The generated electricity by the FS-TENG can power devices such as light-emitting diodes (LEDs), digital watches, kitchen timers, and sports stopwatches, highlighting its efficiency. This research enhances the development of TENGs featuring low-cost, streamlined structures for sustainable and autonomous energy sensing applications. [ABSTRACT FROM AUTHOR]

To address the problem of tribological failure in an aircraft piston pump valve plate pair, the friction and wear properties of the valve plate pair materials (W9Mo3Cr4V-HAl61-4-3-1) of an axial piston pump at a certain speed and load were studied using a disc-ring tester under lubrication with No. 15 aviation hydraulic oil. The results show that the friction coefficient (COF) fluctuated in the range of 0.019~0.120 when the load (L) increased from 30 N to 120 N, and the speed increased from 100 r/min to 500 r/min. With the increase in the rotational speed, the COF of the valve plate pair decreased first and then increased. When the rotation speed (V) was 300 r/min, the relative COF was the smallest. Under L lower than 60 N, abrasive wear was the main wear mechanism. Under L higher than 90 N, the main wear mechanism was adhesive wear but mild oxidation wear also occurred. In addition, based on the V, L, radius (R), and test duration (T), which affected COF, the random forest regression (RFR) algorithm, the bagging regression (BR) algorithm, and the extra trees regression (ETR) algorithm were used as machine learning methods to predict the COF of the valve plate pair. Mean absolute error (MAE), root mean square error (RMSE), and coefficient of determination (R2) were used to evaluate its performance, with the results showing that the ETR prediction model was the best method for predicting COF. The results of the machine learning also showed that the contributions of V, L, R, and T were 43.56%, 36.76%, 13.13%, and 6.55%, respectively, indicating that V had the greatest influence on the COF of the W9Mo3Cr4V/HAl61-4-3-1 friction pair. This study is expected to provide support for the rapid development of new valve plate pair materials. [ABSTRACT FROM AUTHOR]

Brake wear particles, as the major component of non-exhaust particulate matter, are known to have different emissions, depending on the type of brake assembly and the specifications of the vehicle. In this study, brake wear and wear particle mass emissions were measured under realistic vehicle driving and full friction braking conditions using current commercial genuine brake assemblies. Although there were no significant differences in either PM10 or PM2.5 emissions between the different cooling air flow rates, brake wear decreased and ultrafine particle (PM0.12) emissions increased with the increase in the cooling air flow rate. Particle mass measurements were collected on filter media, allowing chemical composition analysis to identify the source of brake wear particle mass emissions. The iron concentration in the brake wear particles indicated that the main contribution was derived from disc wear. Using a systematic approach that measured brake wear and wear particle emissions, this study was able to characterize correlations with elemental compositions in brake friction materials, adding to our understanding of the mechanical phenomena of brake wear and wear particle emissions. [ABSTRACT FROM AUTHOR]

Water-lubricated material is the fundamental ingredient of a water-lubricated bearing (WLB), of which the friction and wear properties directly affect the working performance and service life of a WLB. We designed a micron-scale stripe texture and fabricated a negative microtexture mold by femtosecond laser etching. The microtextures were fabricated onto the surface of Thordon and polyurethane water-lubricated materials by a precision thermoforming machine. Tribological tests showed that the microstripe texture on water-lubricated materials had lower friction and wear properties than that on pristine surface materials. The results demonstrated that the presence of the microstripe texture effectively improved the friction and anti-wear properties of the water-lubricated materials. This study provides a new idea for the design and preparation of water-lubricated materials with good water-lubricating and anti-wear properties. [ABSTRACT FROM AUTHOR]

Skin contact with cold objects can induce the perception of wetness, known as the wetness illusion, even in the absence of actual moisture. However, the differences between wetness perceived from moisture and cooled-dry soft materials and how the material parameters affect the wetness illusion from cooled-dry soft materials remain unclear. This study recruited 12 women and 12 men to touch paired moisture and dry fabrics to compare the prescription and intensity of wetness, suggesting that the wetness illusion focused more on roughness and stickiness while the wetness of moisture fabrics sensed more on coldness. Another 12 women touched cooled-dry materials with different temperatures (10°C and 15°C), thicknesses (0.75/0.73 and 1.99/1.96 mm), and dynamic friction coefficients (mean coefficient of friction) (0.17 and 1.88), rating on wetness dissimilarity and intensity of wetness, coldness, softness, and roughness. Data were illustrated in a two-dimensional space by multidimensional scaling, in which dimension 1 represented the haptic perception in wetness, most related to the mean coefficient of friction, and dimension 2 represented the coldness perception in wetness, most related to temperature. Overall, the mean coefficient of friction and the temperature of the material had a strong influence on the wetness illusion, while the thickness had less impact. This study improves the understanding of wetness illusion and sheds light on the reproduction of wetness perception in multisensory augmented virtual reality, such as immersive gaming and virtual dress fitting. [ABSTRACT FROM AUTHOR]

TiC bonded diamond composites were prepared from a mixture of Ti, graphite, and diamond powders as raw materials, with Si as sintering additives, through high-temperature and high-pressure (HTHP) technology. The reaction between Ti and graphite under 4.5–5 GPa pressure and 1.7–2.3 kW output power can produce TiC as the main phase. The diamond particles are surrounded by TiC, and the interface is firmly bonded. The coefficient of friction (COF) of TiC–diamond composites with POM and PP balls decreases with increasing load for a specific friction velocity. However, the COF of TiC–diamond composites with agate, Cu and Al balls increases with the rising load because of the enhanced adhesive wear effect. The COF of PP, Cu and Al balls slightly increases with the increase in friction velocity at a certain load. SEM results show that the surface of agate balls has rough, pear-shaped grooves and shallow scratches. The scratches on the surface of POM balls are wrinkled. The PP balls have pear-shaped groove scratches on their wear surfaces. The wear mechanism of TiC–diamond composites with Cu ball pairs is primarily adhesive wear. The abrasion of TiC–diamond composites with Cu ball pairs remains almost unchanged as the load increases. However, the depth and width of the pear-shaped grooves on the wear surface of TiC–diamond composites are significantly increased. This phenomenon may be attributed to the high rotational speed, which helps to remove the residual abrasive debris from the friction grooves. As a result, there is a decrease in both the depth and width of the pear-shaped grooves, leading to a smoother overall surface. The wear mechanism of TiC–diamond composites with Al ball pairs is abrasive wear, which increases with an increasing load. When the load is constant, as the speed increases, the wear morphology of TiC–diamond composites with Al ball pairs transitions from rough to smooth and then back to rough again. This phenomenon may be attributed to the wear mechanism at low speeds being groove wear and adhesive wear. As the speed increases, the wear particles are more easily removed from the wear track, leading to a reduction in abrasiveness. As the speed increases, the wear surface becomes roughened by a combination of grooves and dispersed wear debris. This can be attributed to the increased dynamic interaction between surfaces caused by higher speed, resulting in a combination of abrasive and adhesive wear. In addition, Cu and Al ball wear debris appeared as irregular particles that permeated and adhered to the surface of the TiC phase among the diamond particles. The results suggest that TiC–diamond composites are a very promising friction material. [ABSTRACT FROM AUTHOR]

Dry storage canisters of used nuclear fuels are fabricated using SUS 304L stainless steel. Chloride-induced stress corrosion cracking (CISCC) is one of the major failure modes of dry storage canisters. The cracked canisters can be repaired by friction stir welding (FSW), a low-heat input 'solid-phase' welding process. It is important to evaluate the ClSCC resistance of the friction stir welded material. Stress corrosion cracking (SCC) studies were carried out on mill-annealed base materials and friction stir welded 304L stainless U-bend specimens in 3.5% NaCl + 5 N H2SO4 solution at room temperature and boiling MgCl2 solution at 155 °C. The engineering stress on the outer fiber of the FSW U-bend specimen was ~60% higher than that of the base metal (BM). In spite of the higher stress level of the FSW, both materials (FSW and BM) showed almost similar SCC failure times in the two different test solutions. The SCC occurred in the thermo-mechanically affected zone (TMAZ) of the FSW specimens in the 3.5% NaCl + 5 N H2SO4 solution at room temperature, while the stirred zone (SZ) was relatively crack-free. The failure occurred at the stirred zone when tested in the boiling MgCl2 solution. Hydrogen reduction was the cathodic reaction in the boiling MgCl2 solution, which promoted hydrogen-assisted cracking of the heavily deformed stirred zone. The emergence of the slip step followed by passive film rupture and dissolution of the slip step could be the SCC events in the 3.5% NaCl + 5 N H2SO4 solution at room temperature. However, the slip step height was not sufficient to cause passivity breakdown in the fine-grained SZ. Therefore, the SCC occurred in the partially recrystallized softer TMAZ. Overall, the friction-stirred 304L showed higher tolerance to ClSCC than the 304L base metal. [ABSTRACT FROM AUTHOR]

To address the problem of frequent battery replacement for wearable sensors applied to fall detection among the elderly, a portable and low-cost triboelectric nanogenerator (TENG)-based self-powered sensor for human gait monitoring is proposed. The main fabrication materials of the TENG are polytetrafluoroethylene (PTFE) film, aluminum (Al) foil, and polyimide (PI) film, where PTFE and Al are the friction layer materials and the PI film is used to improve the output performance. Exploiting the ability of TENGs to monitor changes in environmental conditions, a self-powered sensor based on the TENG is placed in an insole to collect gait information. Since a TENG does not require a power source to convert physical and mechanical signals into electrical signals, the electrical signals can be used as sensing signals to be analyzed by a computer to recognize daily human activities and fall status. Experimental results show that the accuracy of the TENG-based sensor for recognizing human gait is 97.2%, demonstrating superior sensing performance and providing valuable insights for future monitoring of fall events in the elderly population. ARTICLE HIGHLIGHTS: HIGHLIGHTS • A triboelectric nanogenerator (TENG) does not require a power source to convert physical signals into electrical signals. • TENG-based sensors can monitor human gait to identify daily activities and falls. • This work represents an important development of nanotechnology for wearable flexible sensors. [ABSTRACT FROM AUTHOR]

Particulate matter (PM) still poses a significant threat leading to air pollution which is responsible for continued damage to human health and the environment. Particulate matter resulting from non-exhaust emissions are considered as viable a source comes mostly from brake pad wear concept. The scientific challenge of this work is to stimulate a new generation of green friction materials to reduce particle emissions having low-environmental impact. The specificity of braking materials, their effects on the environment and human health are studied. To minimize the levels of air pollution, the use of green friction composites collected from natural elements reducing human diseases is discussed. For this purpose, the novel and high-performance friction composite materials synthesized from vegetable and animal waste used as a raw material are reported. The natural powder and fiber treatments, the optimum formulation and the binder materials related to the green friction composites are reviewed. An overview of environmentally ecofriendly green friction materials embedded by reinforcing phases of natural elements exhibiting excellent mechanical and tribological properties are mentioned. Therefore, scientific and industrial efforts should concentrate on the development of green friction materials to minimize the effect of transport related air pollution. [ABSTRACT FROM AUTHOR]

The filling efficiency during the hot embossing process at micro scale is essential for micro-component replication. The presence of the unfilled area is often due to the inadequate behavior law applied to the embossed materials. This research consists of the identification of viscoplastic law (two-layer viscoplastic model) of polymers and the optimization of processing parameters. Mechanical tests have been performed for two polymers at 20 °C and 30 °C above their glass transition temperature. The viscoplastic parameters are characterized based on stress–strain curves from the compression tests. The influences of imposed displacement, temperature, and friction on mold filling are investigated. The processing parameters are optimized to achieving the complete filling of micro cavities. The replication of a micro-structured cavity has been effectuated using this process and the experimental observations validate the results in the simulation, which confirms the efficiency of the proposed numerical approach. [ABSTRACT FROM AUTHOR]

Three congenetic Cd-MOFs with different pores were successfully synthesized via solvent-regulated strategy, and they were used as friction materials to regulate the TENG output, which could drive electrolysis systems to promote the direct bromination of aromatic compounds in high yields with good regioselectivity. [Display omitted] Optimizing friction materials based on molecular diversity in a molecular framework system is an effective method to improve the output performance of triboelectric nanogenerators (TENGs). In this study, three cadmium(II) metal–organic frameworks (Cd-MOFs) with different cavities were synthesized solvothermally by the assembly of cadmium nitrate (Cd(NO 3) 2 ·4H 2 O), 4′,4′''-carbonylbis(([1,1′-biphenyl]-3,5-dicarboxylic acid)) (H 4 CBBD), and trans -1,2-bis(4-pyridyl)ethylene (4,4′-bpe) via a solvent-regulated strategy. The topology and porosity of Cd-MOFs could be controlled effectively by the solvent constituents and were demonstrated to be closely related to their triboelectric behaviors. Theoretical calculations and experimental characterizations revealed that the TENGs fabricated by the Cd-MOF with maximum porosity exhibited the best triboelectric performance owing to the enhanced specific surface area and surface potential. In the applications, the high-output TENGs can be successfully used as an efficient power supply for electrochemical systems, enabling the direct bromination of aromatic compounds in high yields with good regioselectivity. This study provides a simple and feasible method to optimize positive friction materials at the molecular level and develops the practical applications of TENGs in electrochemical systems. [ABSTRACT FROM AUTHOR]

Resin‐based friction materials (RFM) are widely used in vehicle brakes. However, the thermosetting resins and rigid fillers in RFM have low toughness and produce strong vibration behavior during continuous friction processes, which adversely affects the equipment. This work proposed a method for co‐blending modification of RFM with silicone rubber powders (SRP) to mitigate friction‐induced vibrations, and the mechanism of silicone rubber modification on the vibrational behavior of RFM during friction was investigated. The results demonstrate that SRP‐modified RFM exhibit excellent damping property and frictional characteristics. SRP modification improves the stability of the coefficient of friction and reduces fatigue wear. The wear rate of RFM modified with 10 wt% SRP reduced by 29% and the average amplitude of friction‐induced vibration decreased by 35.5% compared to unmodified RFM. This work provides both theoretical and practical foundations for designing and developing RFM with high damping, low wear, and low vibration characteristic. [ABSTRACT FROM AUTHOR]

Polyimide (PI) is a special engineering plastic, widely involved in mechanical components, instruments, and petrochemicals. However, single PI material is inevitably subject to wear and tear in practice, which leads to weakened material properties. In this work, Ti3C2Tx@SiO2 was prepared to enhance the wear resistance and lubrication properties of PI by intercalating SiO2 into the interlayer of Ti3C2Tx sheets. Ti3C2Tx@SiO2/PI composites were fabricated in two steps to test the tribological performances. SiO2 particles change the form of interfacial friction from sliding to rolling, thus relieving direct friction between material and steel ball. So, the composites have a minimum COF (COF = 0.33) when the content of Ti3C2Tx@SiO2 is 0.80 wt%. Moreover, the average value of wear rate was 0.24 × 10−5 mm3/(N·m) when Ti3C2Tx@SiO2 content was 1.60 wt%, which was 91.0% lower compared to the PI matrix. During the friction process, the abrasive chips of the material migrate to the surface of the steel ball to form a transfer film, which protects the material and thus reduces the wear rate. Therefore, the hybrids Ti3C2Tx@SiO2 are effective and important wear‐resistant agents and solid lubricants to improve the wear resistance and lubricity of PI or other polymer materials. Highlights: SiO2 insert Ti3C2Tx is a key factor in changing sliding friction into rolling friction, effectively reducing the COF.The average wear rate was 91.0% lower than that of the polyimide matrix when Ti3C2Tx@SiO2 content was 1.60 wt%.The minimum COF of Ti3C2Tx@SiO2/PI composites reached 0.33 when the content of Ti3C2Tx@SiO2 was 0.80 wt%.The transfer film effectively reduces further wear of the material during friction. [ABSTRACT FROM AUTHOR]

Deformable linear objects (DLOs), such as rods, cables, and ropes, play important roles in daily life. However, manipulation of DLOs is challenging as large geometrically nonlinear deformations may occur during the manipulation process. This problem is made even more difficult as the different deformation modes (e.g., stretching, bending, and twisting) may result in elastic instabilities during manipulation. In this paper, we formulate a physics-guided data-driven method to solve a challenging manipulation task—accurately deploying a DLO (an elastic rod) onto a rigid substrate along various prescribed patterns. Our framework combines machine learning, scaling analysis, and physical simulations to develop a physics-based neural controller for deployment. We explore the complex interplay between the gravitational and elastic energies of the manipulated DLO and obtain a control method for DLO deployment that is robust against friction and material properties. Out of the numerous geometrical and material properties of the rod and substrate, we show that only three non-dimensional parameters are needed to describe the deployment process with physical analysis. Therefore, the essence of the controlling law for the manipulation task can be constructed with a low-dimensional model, drastically increasing the computation speed. The effectiveness of our optimal control scheme is shown through a comprehensive robotic case study comparing against a heuristic control method for deploying rods for a wide variety of patterns. In addition to this, we also showcase the practicality of our control scheme by having a robot accomplish challenging high-level tasks such as mimicking human handwriting, cable placement, and tying knots. [ABSTRACT FROM AUTHOR]

Based on the material properties and fuzzy theory, a new design method of TiB2‐based composite ceramic tool material was proposed, and the TiB2‐based composite ceramic tool material with excellent friction and wear resistance was designed. Initially, the fuzzy evaluation method was used to establish the matrix of the friction and wear resistance of the material, and the TiB2‐based material component with excellent friction and wear resistance was determined. Ultimately, based on the principle of fuzzy cognitive map, the correlation mapping of "sintering process–microstructure–mechanical properties" was established, and the composition ratio and sintering process were optimized. The results show that the TiB2–TaC–TiC ceramic tool material had excellent friction and wear resistance. When the volume content of TaC was 8 vol.%, the volume content of TiC was 20 vol.%, the heating rate was 100°C/min, the holding time was 8 min, the sintering temperature was 1600°C, and the sintering pressure was 50 MPa, the mechanical properties were hardness 23.5 GPa, bending strength 438 MPa, and fracture toughness 10.26 MPa∙m1/2. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study is to investigate the accumulation process of transfer film formation and dissipation and its effect on friction coefficients in non asbestos organic friction materials with various lubricant FeS2 contents. Design/methodology/approach: In total, 2.5%, 5% and 10% FeS2 were added as lubricating components to the friction materials. Friction tests composed of two stages were conducted for these friction materials, and the friction surfaces of the counterpart discs were examined using scanning electron microscopy. Findings: The transfer film formation reduced the friction coefficients, and the transfer film dissipation influenced the recovery of the friction coefficients. The effect of a high content of FeS2 was to promote the transfer film formation at high temperatures and to hinder the transfer film dissipation at low temperatures, thus resulting in a decrease in the friction coefficients at high temperatures together with recovery retardation at low temperatures. Originality/value: FeS2 contributed to the transfer film formation at high temperatures in the fade test but hindered the transfer film removal in the recovery test, resulting in the retardation of friction coefficient recovery. The mechanism by which the FeS2 lubricant component affected the transfer film formation and dissipation was analyzed and attributed to the different levels of FeS2 pyrolysis at different temperature levels. [ABSTRACT FROM AUTHOR]