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Purpose: The purpose of this paper is to investigate the effect of mullite on the mechanical properties and friction of carbon fiber (CF)-reinforced friction material. Design/methodology/approach: CF-reinforced friction materials with varying content of mullite were fabricated by hot press molding, and then the tribological properties were tested on the MRH-3-type tribometer under ambient conditions with the ring-on-block configuration. Findings: The experimental results indicated that the addition of mullite increased the density and compressive strength of friction material. However, the flexural strength of friction material decreased by 16% with the addition of 15 Wt.% mullite. The friction coefficient was proportional to the mullite content. Friction material with 12.5 Wt.% mullite showed the highest friction stability under different loads, whereas friction material with 10 Wt.% mullite exhibited the highest friction stability under different sliding speeds. Originality/value: By boosting the resistance to deformation under load and increasing the specific heat capacity, mullite contributed significantly to the friction stability of the friction material. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to prepare an oil-impregnated porous polytetrafluoroethylene (PTFE) composite with advanced tribological properties using citric acid as a novel pore-forming agent. Design/methodology/approach: Citric acid (CA) was used to form pores in PTFE, and then oil-impregnated PTFE composites were prepared. The pore-forming efficiency of CA was evaluated. The possible mechanism of lubrication was proposed according to the tribological properties. Findings: The results show CA is an efficient pore-forming agent and completely removed, and the porosity of the PTFE increases with the increase of the CA content. The oil-impregnated porous PTFE exhibits an excellent tribological performance, an increased wear resistance of 77.29% was realized in comparison with neat PTFE. Originality/value: This study enhances understanding of the lubrication mechanism of oil-impregnated porous polymers and guides for their tribological applications. [ABSTRACT FROM AUTHOR]

Triboelectric nanogenerators (TENGs), as novel electronic devices for converting mechanical energy into electrical energy, are better suited as signal-testing sensors or as components within larger wearable Internet of Things (IoT) or Artificial Intelligence (AI) systems, where they handle small-device power supply and signal acquisition. Consequently, TENGs hold promising applications in self-powered sensor technology. As global energy supplies become increasingly tight, research into self-powered sensors has become critical. This study presents a self-powered sport sensor system utilizing a triboelectric nanogenerator (TENG), which incorporates a thermoplastic polyurethane (TPU) film doped with graphene and polytetrafluoroethylene (PTFE) as friction materials. The graphene-doped TPU nanocomposite film-based TENG (GT-TENG) demonstrates excellent working durability. Furthermore, the GT-TENG not only consistently powers an LED but also supplies energy to a sports timer and an electronic watch. It serves additionally as a self-powered sensor for monitoring human movement. The design of this self-powered motion sensor system effectively harnesses human kinetic energy, integrating it seamlessly with sport sensing capabilities. [ABSTRACT FROM AUTHOR]

This article presents a contact 3D thermomechanical finite element model of a railway vehicle disk brake. The distinctive feature of the model is the interdependence of the sliding velocity, coefficient of friction, temperature, contact pressure, and friction material wear, derived from a unified system of equations of heat dynamics of friction and wear. Another important aspect is high geometrical compatibility of the model with physical object. The radial location of the rotation point of the brake pad holder, axis of the mounting plate, and middle of the lining agree with the guidelines of UIC 541-3. All these features allow for a detail study of wear distribution and its further optimization. Based on the recorded experimental data, an analytical form of the coefficient of friction dependent on the sliding velocity and temperature was created. The single braking simulation from initial velocity of 140 km h − 1 to a stop, took into account friction material wear based on the generalized Archard's law. The analysis of the results is focused on wear, temperature, contact pressure components of the stress tensor, velocity, and coefficient of friction. The highest average temperature of the six thermocouples was equal to 130.7 °C, while the corresponding calculated value was 128.4 °C. [ABSTRACT FROM AUTHOR]

Aiming at the problem of mechanical seal failure due to serious wear and tear in operation, the numerical model of the thermal–solid coupling wear of the seal ring is established by taking the friction sub-material as the research object, and the hardness, wear coefficient, and friction coefficient of different soft-ring materials are obtained by a test to verify the accuracy of the numerical model of wear. Additionally, the temperature field and deformation field of the seal ring of different materials are calculated, and the effects of the material parameters, such as elasticity modulus and thermal conductivity, on the temperature, relative deformation, and axial deformation trend are reported. The wear relation of the mechanical seal was optimized, and the correction coefficients of several materials were calculated. The results show the following: the main wear of the seal ring is due to adhesive wear leading to particle shedding and extrusion, adhesive wear causes material transfer, which alters the composition of the worn surface.in turn leading to cratering, which also causes the wear of the seal ring; the friction performance is better when the soft-ring material is graphite (C); the temperature, as well as the deformation, is smaller when the soft-ring material is silicon carbide (SIC); the correction coefficients for the life of SIC are calculated to be 0.23, for C, to be 0.14, and for stainless steel (Ss), to be 0.31, and the corrected equations can more accurately predict the corresponding material. The corrected equation can more accurately predict the service life of the corresponding material. [ABSTRACT FROM AUTHOR]

In this work, the frictional traction forces developing in the annular space between two concentric vertical cylinders consisting of the outer surface of a cylindrical rod and the inner sidewall of a wider circular cylinder will be analyzed. The experiments carried out for this study allowed us to measure the traction on the rod for several filling heights, H. For the rod, it is possible to find a linear relation between the theoretically computed traction T r o d and the traction measured experimentally, T r o d M . Based on these results, it is possible to understand the fascinating phenomenon of the lifting, by the rod, of the weights of the mass of grains and of the outer cylinder. Finally, a physical analogy between this problem and the upward movement of trees in tornadoes can be identified. [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]

The forecasted global population growth is poised to create a greater exigency for livestock-derived food production, leading to a significant waste generation from the industrial-scale livestock operations, which necessitates to develop sustainable waste management solutions. The heightened demand for livestock and dairy products has driven a surge in cow waste (CW) production. While CW is typically used as organic fertilizer or solid fuel, improper disposal poses potential environmental hazards. Anaerobic digestion and composting transform CW into valuable products, such as biofuels and organic fertilizers, with the potential for electricity and heat generation, biochar production, and advanced friction materials. The CW contains essential inorganic and organic compounds vital for plant functions, including lignin, cellulose, hemicellulose, nitrogen, and minerals such as potassium, sulfur, iron, magnesium, copper, cobalt, and manganese. Additionally, the rich microbial diversity in cow dung drives the production of bioenergy carriers like biomethane and biohydrogen, promoting cost-effective energy generation and environmental sustainability. This review employs bibliometric analysis to explore the latest trends in CW applications, with a particular focus on innovative applications such as cellulose extraction, biochar production, microbial fuel cells, and nanoparticle synthesis. It further evaluates the environmental impacts of these technologies and assesses their potential to advance sustainable and cleaner frontiers in the valorization of CW. [ABSTRACT FROM AUTHOR]

Copyright of Metal Working (1674-165X) is the property of Metal Working Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]

Highlights There has been growing interest in using sustainable and eco‐friendly products to produce engineering materials. For this purpose, composite material applications obtained from agricultural wastes are gaining popularity. This study examines the synergistic effect of rice husk and rice stalk wastes on the fade and recovery performance of brake friction composites. Brake friction materials were developed using rice husk and rice stalk separately and in two different weight percentages as a 5–10 ratio in the formulation. For comparison purposes, a reference brake pad using copper as a substitute and a commercially available brake pad were used. Various physical, mechanical and thermal properties were analyzed. The tribological behavior of friction composites was evaluated on the Krauss test device in line with the ECE R90 procedure. The worn surface properties were analyzed using scanning electron microscopy. Tribo test results of friction composites were taken as criteria for performance optimization. While the importance weight of the criteria was determined by AHP, the VIKOR method was used in the sorting of alternatives. The experimental results have revealed that rice husk‐added friction composites had a good coefficient of friction value with better fade and recovery performance compared to rice stalk‐added ones. Increasing the amount of rice husk and rice stalk in the formulation tended to decrease the fade performance; however, it has increased the wear rate and recovery properties. Optimization results have shown that the brake friction composite containing 5 wt % rice husk ranks first in meeting the desired tribological criteria. Cu‐free rice husk and rice stalk‐added friction composites were developed. Fibrous structure in the matrix developed the contact plateaus. Rice husk‐based tribo‐layer protected the composite from further wear damage. The addition of agro‐waste to friction composites exhibited good potential. [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]

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

Wear caused by friction is one of the main causes of most mechanical component failures. The application of powders as anti-wear lubricating materials has achieved great advances, which are of great significance in reducing friction and wear. This review focuses on the applications of phyllosilicates mineral powders as anti-wear lubricating materials in lubricating oil. The tribological behaviors of phyllosilicates mineral powders and the combination of phyllosilicates mineral powders with other materials as lubricant additives are provided. Moreover, the fundamental mechanism are systematically reviewed and concluded based on tribology data and surface, and interface analysis. Finally, current unsolved issues and suggestions for future research on phyllosilicates mineral powders as lubricant additives are proposed. [ABSTRACT FROM AUTHOR]

Hot stamping is a forming process widely used in the manufacturing of structural components in automobiles. It is a versatile process that enables the fabrication of complex-shaped components with high strength. It also facilitates the manufacturing of components that incorporate high-strength sections and high-ductility sections, by controlling the cooling rate. The process is versatile in terms of the microstructures and mechanical properties that can be obtained. This versatility, however, puts high demands on the materials pertaining their stability, wear resistance, costs, etc. This study has focused on understanding the effect of temperature on the tribological response of different tool materials when these are exposed to high temperatures. The results show that friction significantly stabilises with increased temperature for most tool steels. One tool steel behaves more unstably at high temperature, and this is attributed to the presence of Cr7C3, MoO3, and VO and severe wear on the workpiece material. The most severe wear on the workpiece is caused by a partially melted interdiffusion layer, which facilitates the detachment of the Al-Si coating and subsequent transfer onto the tool; this effect is maximised at the highest temperatures of the workpiece. An important finding is that friction and material transfer severity decrease as the workpiece temperature decreases, and friction is stabilised as tool temperature increases without minimising wear or the average friction coefficient. [ABSTRACT FROM AUTHOR]

This work studied the proximate property and thermal stability of chemically activated carbon developed from agrowaste materials for organic friction linings. The proximate property, degradation steps, optimum degradation temperature (ODT) and oxidative stability (oxidation onset temperature (OOT) and oxidation temperature (OT)) characterizations were performed on two processed samples. Coconut shell activated carbon (CSAC) and palm kernel shell activated carbon (PKSAC) were used to prepared three compositions (%vol.) and particle sizes (µm); 0% CSAC : 100% PKSAC, 50% CSAC : 50% PKSAC, and 100% CSAC : 0% PKSAC and 60, 105 and 150 µm. Thermogravimetric analysis (TGA) and modulated differential scanning calorimetry (MDSC) methods were used to perform the characterizations and results compared with two commercial brakepads (CB1 and CB2) as controls. The proximate analysis showed that 60µm of 0% CSAC : 100% PKSAC had the best results with 6.04% moisture, 3.99% volatile matter, 84.8% fixed carbon and 4.79% ash and compared well with the commercial friction lining materials (CB1: 2.27% moisture, 2.18% volatile matter, 45.47% fixed carbon, 48.86% ash; CB2: 1.92% moisture, 1.49% volatile matter, 37.21% fixed carbon, 58.07% ash). The thermal stability of 0% CSAC : 100% PKSAC, 50% CSAC : 50% PKSAC and 100% CSAC : 0% PKSAC samples with 150µm particle size showed percentage ODT increase of 18.3% and 15.8%; 37.1% and 34.2%; 17.8% and 15.3% when compared with CB1 and CB2 respectively. For all developed activated carbon compositions and particle sizes, the oxidation onset temperature (OOT) compared well with CB2 while oxidation temperature (OT) compared well with CB1. Overall, the developed activated carbon compositions showed suitability for organic friction lining applications. [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]

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

Shear spinning is a bulk forming technique used to produce hollow, rotationally symmetric parts. Although the shear spinning process has been used for the last six decades in numerous industries, in the literature, the understanding of the mechanics of the process is limited. This study provides insight into process mechanics using physical trials and numerical models. Modelling the process is challenging because of the incremental nature of the process; existing numerical models in the literature suffer from lengthy computational times and simplifications. In this study, two numerical models with different approaches to the kinematics of the spinning process are modelled with input from tests to determine friction coefficient and material properties. Then they are validated against physical trials by comparing both part geometry and strain distribution. Validated numerical models are then employed to investigate the fundamental aspects of shear spinning mechanics; evolution of strains, roller forces and part geometry in a broad range of process conditions. [ABSTRACT FROM AUTHOR]

This study shows that the progressive adhesion of weld material to the tool in friction stir welding AA 2024-T3, up to tool saturation, brings about a decrease in power consumption until a plateau is reached. The cause of this behavior is the hindering of the stirring action of the tool due to the material accumulated on it. The built-up material changes the nature of the tool/material interaction and then the friction condition at their interface. The direct consequence is a decrease in the shearing strain and therefore in the heat generated by friction. Bits of this adhering material break off from the tool at intervals. Macro and micro detachments are identified. Micro-detachments happen continuously at small periodic intervals and produce vibrations. The amplitude of these vibrations increases in all their characteristic spectral components up to tool saturation. Macro-detachments generate oscillations in power consumption and leave galling on the weld bead. [ABSTRACT FROM AUTHOR]

Design and testing of real materials is a costly process and usually requires some specific equipment. To alleviate this task numerical methods can be leveraged. In this work we show possible modelling technique for closed-cell material structure using Weaire–Phelan unit cells. As an example existing aluminum structures were used and modelled parametrically, allowing to establish different geometrical models for different applications. Numerical simulations for compression was also done on the developed models to reveal the material response. The influence on the cell wall thickness and the friction between the material and the compression plate was investigated. It was found that the friction coefficient has no significant effect on the material response, except in the case where bonded connection was assumed. It was also demonstrated that material response and the porosity controlled by cell wall thickness have an approximately linear relationship with each other. This method proved to be a flexible and alternative solution of real laboratory tests and targeted to reduce costs of material design. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) materials are potential candidates for electronic devices due to their unique structures and exceptional physical properties, making them a focal point in nanotechnology research. Accurate assessment of the mechanical and tribological properties of 2D materials is imperative to fully exploit their potential across diverse applications. However, their nanoscale thickness and planar nature pose significant challenges in testing and characterizing their mechanical properties. Among the in situ characterization techniques, atomic force microscopy (AFM) has gained widespread applications in exploring the mechanical behaviour of nanomaterials, because of the easy measurement capability of nano force and displacement from the AFM tips. Specifically, AFM-based force spectroscopy is a common approach for studying the mechanical and tribological properties of 2D materials. This review comprehensively details the methods based on normal force spectroscopy, which are utilized to test and characterize the elastic and fracture properties, adhesion, and fatigue of 2D materials. Additionally, the methods using lateral force spectroscopy can characterize the interfacial properties of 2D materials, including surface friction of 2D materials, shear behaviour of interlayers as well as nanoflake-substrate interfaces. The influence of various factors, such as testing methods, external environments, and the properties of test samples, on the measured mechanical properties is also addressed. In the end, the current challenges and issues in AFM-based measurements of mechanical and tribological properties of 2D materials are discussed, which identifies the trend in the combination of multiple methods concerning the future development of the in situ testing techniques. [ABSTRACT FROM AUTHOR]

The friction properties and heat resistances of the iron-copper based powder metallurgy friction materials were tested by MM3000 friction and wear testing machine under 7 continuous braking conditions. The wear mechanism of the friction materials at two different rotate speeds (line speed in equivalent radius) was studied by scanning electron microscopy and energy disperse spectroscope analysis. The results show that when the line speed is 19.40 m·s−1, the dynamic friction coefficient of the friction materials decreases slightly with the increase of surface pressure, which is 0.267~0.312 at 0.44 MPa and 0.258~0.308 at 0.80 MPa. Under the continuous braking condition as the line speed of 19.40 m·s−1, the surface pressure of 0.44 MPa, and the braking energy in unit area of 268 J·cm−2, the dynamic friction coefficient fluctuates greatly, while under the other conditions, the dynamic friction coefficient fluctuates little. With the increase of braking energy, the average dynamic friction coefficient under 7 kinds of continuous braking conditions changes between 0.300~0.334, and the dynamic friction coefficient is above 0.250, without the obvious decline phenomenon, indicating that the iron-copper based powder metallurgy friction materials have the good heat resistance. Under the line speed of 19.40 m·s−1, the friction and wear mechanism of the iron-copper based friction materials is mainly abrasive wear and oxidation wear. Under the line speed of 30.00 m·s−1, the friction and wear mechanism of the iron-copper based friction materials is mainly fatigue wear and oxidation wear.

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]

Timber structures are vulnerable to failure and collapse under seismic action. To improve the seismic performance of such structures, a replaceable displacement amplification rotary friction damper was proposed and designed. Six specimens were fabricated, each varying in pretension strains and employing three different composite friction materials as control parameters, followed by low cyclic loading tests. The study investigated the working mechanism, hysteresis performance, energy dissipation capacity, performance stability, and displacement amplification effect of the dampers. A finite element model was developed to analyze the hysteresis performance of the damper and evaluate the impact of various parameters on its overall effectiveness. Furthermore, a comparative analysis of the damper's hysteresis characteristics was conducted. The theoretical calculations and finite element analysis were validated using experimental results, showing a relative error within 10%. The specimens demonstrated a notable displacement amplification capability, which increased as the intermediate connector length decreased. By reducing the length by 200 mm, the maximum damping force could be amplified by 5.5 times, while the nodal rotation values increased by 3.92 times. Additionally, for every 50 με increment in pretension strain, energy consumption increases by an average of 148%, and for each unit increase in the friction coefficient, energy consumption increases by an average of 172%. [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]

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]

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]

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]

The article analyses the results of an experimental study devoted to the impact of the mutual overlap coefficient on the friction factor of the model brake lining and brake disk in a disk brake.The mass ratio of the brake lining and brake disc models is 1:200 (the brake lining mass is 8 grams and the brake disk mass is 1,600 grams). The load level has been 0.2–0.5 N. This mass ratio and load level ensure an effective heat removal from the friction zone. The brake disk model is made of 35GS steel. The brake linings are made of two friction materials, i.e. CSiC and SCh25 cast iron. The mutual overlap coefficients for the experiments have been 0.25, 0.5, 0.75, and 1.0. It has been shown that when the mutual overlap coefficient rises from 0.25 to 1.0, there is a tendency for the friction factor to increase in the ‘SCh25 cast iron – 35GS steel’ and ‘CSiC- 35GS steel’ friction units. An increase in the friction factor by approximately 10–12% is observed for the ‘SCh25 cast iron – 35GS steel’ friction pair. An increase in the friction factor is 8–10% for the ‘CSiC- 35GS steel’ friction pair.With effective heat dissipation, the increase in the coefficient of friction occurs due to the reduction in mechanical pressures in the contact area and the increase in the number of micro-irregularities involved in the friction process. [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]

Rotary friction welding is a solid-state welding process that involves the joining of two materials through friction heat generated by the rotational motion of one component against the other. The friction and forging pressures applied during the process can affect various properties of the welded joint, including the corrosion resistance of stainless steel. 18-8 austenitic stainless steel similar pipes were having been welded frictionally by four various friction-forging pressures at the same time of 10 seconds and a rotational speed of 1120 revolutions per minute. After that, the soundness and the corrosion behavior of the welded samples had been examined by visual inspection and potentiodynamic measurements after immersion in 3.5 wt. percentage NaCl as an artificial electrolyte simulates the seawater. The results showed that the higher friction-forging pressures imply better joint quality and more uniformity formed flash. The corrosion potential of the S1 sample with (3-3) friction- forging pressures is (-0.635 v) which means it has less corrosion resistance in comparison with S4 sample (-0.417 v) with (12-12) friction- forging pressures. As a conclusion to the paper, the corrosion rate of frictionally welded austenitic stainless steel similar pipes specimen's decreases with increasing friction-forging pressures due to the plastic deformation and the heat generated that contribute of refining the grains size and stronger bonds. [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]

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]

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Theoretical and experimental studies on the choice of coolants for forced cooling systems and the requirements for their designs for brake friction pairs allowed to establish the following. The choice of coolants for systems of forced cooling of friction pairs depends on their energy content and is determined by the share of heat by convective heat transfer in complex heat exchange with the environment. The heat carrier must ensure the energy load of the friction pairs at a level lower than that permissible for friction lining materials, based on their regulated wear and friction properties. The most effective are nanofluids, which are metal powders (Li, Na, Al, Cu, Zn, etc.) with a high coefficient of thermal conductivity, diluted in certain proportions with water, acetone, and other refrigerants. The research and development of the system must correspond to the modern level of braking, and the forced circulation of the nano-fluid in a different aggregate state, which increases-decreases and vice versa, convective heat transfer. [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]

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]