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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]

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]

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]

Cu-containing silicon oxycarbide (SiOC) ceramic composites have been prepared by thermal pyrolysis of polymeric precursors and subsequent spark plasma sintering at 1600 °C. The resulting composites consist of SiO 2 , SiC, free carbon, and Cu-Si alloys. The microstructure of the composites has been identified via optical microscope and SEM. The mechanical properties, including the Vickers hardness, nano-indentation hardness, and Young's modulus, of the SiOC composites have been assessed via indentation methods. The effects of Cu content on the tribological properties of the composites have additionally been investigated under different sliding frequencies against Al 2 O 3 spheres at room temperature. It is shown that the introduction of the Cu-Si alloys is effective in reducing the friction coefficient of the material system, which decreases linearly from 0.27 of monolithic SiOC to 0.15 of SiOC with 7 wt% Cu content at 1 Hz. Raman spectroscopy has highlighted the friction-driven evolution of the free carbon phase in the SiOC ceramics. Finally, a correlation between the sliding frequency, Cu-Si content, and tribological properties of SiOC is established. [ABSTRACT FROM AUTHOR]

Ni-containing SiOC bulk ceramics have been prepared by spark plasma sintering at 1300 °C from polysiloxane at Ar atmosphere in the present work. The microstructure and properties of SiOC ceramics with different Ni content were studied. The resultant Ni-containing SiOC ceramics consists of in situ formed turbostractic layer carbon, CNTs (C nanotubes) and SiC crystals which dispersed in the SiOC matrix. With increasing content of Ni, the Ni-containing SiOC ceramics displayed less porosity. And the increasing Ni improved the mechanical, thermal and friction properties of SiOC ceramics. Ni-containing SiOC ceramics developed a carbon friction layer, which enhanced abrasion resistance to provide friction materials with stable friction coefficients and low abrasion values. A decrease in wear mass, from 2.06 to 0.18 mg was observed as the Ni content increasing from 0 to 2 wt%. The primary wear mechanisms of SiOC ceramics were recognized as abrasive wear, fatigue wear, and adhesion wear. [ABSTRACT FROM AUTHOR]

With the advantage of high temperature resistance, low expansion, low density and excellent thermal stability, carbon fiber reinforced ceramic composites have a very wide range of applications in aerospace, military, energy, chemical industries and transportation. Short carbon fiber reinforced ceramic composites are characterized by simple processes, low manufacturing costs, short preparation times and automated production, can be used in fields such as friction materials and thermal protection system. This paper reviews the current status and recent advances in research on homogenization techniques, mechanical properties, thermal properties and frictional properties of short carbon fiber reinforce ceramic composites. Different processing routes for short carbon fiber reinforced ceramic composites, including reactive melt infiltration (RMI), hot pressing (HP), spark plasma sintering (SPS) and pressureless sintering, the advantages and drawbacks of each method are briefly discussed. The future development direction of low-cost manufacturing short carbon fiber reinforced ceramic composites is prospected. [ABSTRACT FROM AUTHOR]

The tribological behavior of ultra-high temperature ceramic matrix composites (UHTCMCs) was investigated to understand these materials in friction applications. Samples consisting of pitch-based randomly orientated chopped carbon fiber (CF) reinforced ZrB 2 -10 vol% SiC were prepared (ZS). The tribological behavior was tested on a self-designed dynamometer, coupling the UHTCMC pads with either carbon fiber reinforced carbon−silicon carbide (C/C-SiC) or steel disks, with two applied contact pressures (1 and 3 MPa) and the surface microstructures were analyzed to unravel the wear mechanisms. Even at high mechanical stresses, tests against the C/C-SiC disk showed stable braking performance and wear. The abraded material from a steel disk formed a stable friction film by fusing together harder pad particles with abraded steel, which reduced wear and stabilized the braking performance. The high values of coefficient of friction obtained (0.5–0.7), their stability during the braking and the acceptable wear rate make these materials appealing for automotive brake applications. [ABSTRACT FROM AUTHOR]

The application of Cu-graphite composites in the field of friction materials is limited by the poor wettability between Cu and graphite and weakened mechanical properties. In this work, in-situ TiC layers were generated by interfacial resistance sintering with direct current to manipulate the interfacial bonding of the composites and enhance their comprehensive properties. The Ti added to the composites would react with graphite at the interface to generate TiC layers and form strong Cu–TiC-graphite interfaces due to interfacial reactions. When the added Ti content is 6 wt%, the composite demonstrates the most excellent mechanical properties and tribological characteristics, i.e., yield strength (168 MPa) and wear rate (2.7 × 10−10 m2/N) are 93.1% higher and 29.7% lower than those of the Cu-graphite composite without Ti addition, respectively. The dense TiC layer induces the strengthening of the Cu matrix and serves as the reinforcing phase to optimize the interfacial bonding and stress transfer, which not only greatly enhances the mechanical properties of the composite but also enables the composite to take full advantage of the hard TiC and graphite phases to obtain stable friction coefficient and low wear rate. This work provides a simpler technique to prepare modified Cu-graphite composites with excellent performance and contributes to the in-depth understanding of the enhancement mechanism of hard ceramic layers on the mechanical and tribological properties of composites. [ABSTRACT FROM AUTHOR]

In this research, an upper bound (UB) analysis of channel angular pressing process was carried out considering die geometric characteristics including die angle, thicknesses of the inlet and the outlet channels, radiuses of outer and inner corners, length of the outlet channel, as well as the length of initial billet, friction and strain-hardening of material, under cold conditions and for a billet with a rectangular cross-section. To validate the results of the UB analysis, the result of the analytical equations was compared with that of the numerical simulation and actual process. The results revealed that the total plastic strain and the process force were augmented by reducing the die angle, the outlet channel thickness, and the outer corner radius, as well as by increasing the inlet channel thickness and the inner corner radius. It was also shown that the process force increased with augmenting the initial billet length. A very good agreement was obtained between the results of the analytical method and numerical and experimental methods. [ABSTRACT FROM AUTHOR]

This study explores the friction and wear performance of brake materials for new energy micro logistics vans under different ambient temperature (3 °C, 23 °C, 43 °C) and humidity conditions (35 %, 65 %, 95 %) using pin-disc experimental device. The findings reveal that at 3 °C, the friction coefficient exhibits extreme sensitivity to changes in humidity, with a significant reduction as humidity increases. Simultaneously, the increase of humidity leads to the transition from adhesive wear to abrasive wear and fatigue wear. At room temperature (23 °C) and 43 °C, humidity has minimal impact on the friction coefficient; however, higher humidity promotes oxidation film formation on the friction surface leading to dominant oxidation wear. Notably, in low-humidity environments, temperatures at 3 °C and 43 °C cause severe brake pad wear. The severity is greater at 43 °C because the resin-based components within the brake pad material decompose at elevated temperatures. Under such circumstances, appropriately increased humidity helps mitigate brake pad wear rates. However, too much humidity can increase fatigue wear of brake pad materials. • At 3 °C, the friction coefficient is extremely sensitive to humidity, significantly decreasing as humidity rises. • In high humidity (95 %) environments, moisture plays a dual role in wear. • At room temperature (23 °C) and medium humidity (65 %), the brake material has good friction and wear properties. [ABSTRACT FROM AUTHOR]

A granular vibration pumping system leverages the phenomenon wherein particles ascend within a vertically vibrating pipe. This study aims to experimentally clarify the lifting performance of the system against millimeter-sized particles. The results indicated that this unique transporting mechanism can lift particles larger than 1 mm. All the particles used in this study, with size distributions of 1.0–1.4 mm, 1.5–2.5 mm, and 2.5–3.5 mm, reached approximately 1 m in height. An increase in vibration frequency enabled the millimeter particles to climb and reach higher up to a certain point in the frequency, while an excessively higher frequency decreased the climbing height. The climbing behavior was considerably affected by the inertia of the constituent particles. In addition, the climbing speed decreased as the particle size increased, and the ratio of the particle diameter to the pipe diameter, as well as the particle size itself, impacted the lifting performance. [Display omitted] • The granular vibration pumping system can lift particles larger than 1 mm. • Particles of 1 mm, 2 mm, and 3 mm types reached approximately 1 m in height. • A vibration frequency largely influenced climbing heights of millimeter particles. • The climbing behavior of millimeter particles was affected by the particle inertia. [ABSTRACT FROM AUTHOR]

This research comprehensively analyzes the friction and wear behavior of composite friction materials when dry sliding against grey cast iron and laser-clad nickel-based (LC1) and iron-based (LC2) alloy discs. The composite friction materials (P 1 , P 2 , P 3 , P 4 , P 5 , and P 6) under investigation contain graphite, MoS 2, and hBN-based solid lubricant synthesized through the powder metallurgy technique. Tribological tests were conducted using a pin-on-disc configuration to simulate the dynamic interaction between the composite materials and the laser-clad grey cast iron discs. The tests were performed at a 60 N load, 6283.19 m sliding distance, and 2.094 m/s sliding velocity under dry sliding conditions. The results provide valuable insights into the effectiveness of MoS 2 and hBN-based solid lubricant composites in reducing friction and wear when in contact with iron and nickel alloy-based laser-clad grey cast iron surfaces. The study elucidates the mechanisms governing tribological behavior, including the formation of friction plateaus and the role of laser-clad counter-discs in reducing wear. The specific wear rate of the nickel-based laser-clad counter disc (LC1) and iron-based laser-clad (LC2) system improved by 63.76 % and 48.32 %, respectively, compared to the conventional grey cast iron disc system when using the hBN-based pin (P 6). Additionally, the specific wear rate of the hBN-based pin was 38.49 % lower than the conventional graphite-based pin when sliding against the grey cast iron counter-disc. Artificial Neural Network (ANN) was used to validate the wear rate of the best-performing tribological pair, namely the hBN-based pin (P 6) and LC2 counter discs, through supervised learning. [Display omitted] ● Friction and wear study of composite friction materials against grey cast iron and laser-clad LC1 and LC2 discs. ● MoS 2 and hBN-based composites reduce friction and wear against GCI and laser-clad surfaces. ● ANN validated wear rate predictions for the hBN-based pin P 6 and LC2 disc pair. ● LC1 and LC2 discs with MoS 2 and hBN-based pins offer enhanced performance and can be utilized in automotive braking systems. [ABSTRACT FROM AUTHOR]

Friction stir processing (FSP) is an energy-efficient and environmentally friendly technique that provides tailored manufacturing possibilities for surface composites in solid-state conditions. This study focuses on manufacturing solid lubricant-reinforced aluminum matrix surface composite (AMSC) through FSP, which can be used as a journal-bearing material. Composite fabrications are performed utilizing Sn, Cu, and graphite particles (hybrid powder) with four passes of FSP. The cross-sectional macro and microstructures of obtained surface composites are investigated via optical microscopy (OM) and scanning electron microscopy (SEM). The stir zone (SZ) chemistry is analyzed with energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The microhardness measurements show the effects of hybrid powder as reinforcement and FSP parameters on the mechanical features of the composite cross-sections. Wettability and tribological tests are also conducted to determine the surface properties of the fabricated composites. According to the findings, the wear rate is decreased by 8 % with the reduction of average CoF to 0.75, while a hardness increment is achieved over ∼35 % in manufactured surface composites compared to the base material. It is observed that the content and amount of the hybrid powder and FSP parameters employed can ensure the fabrication of desired characteristics compatible with the aim in surface composites. • Solid lubricant-reinforced aluminum matrix composites are manufactured via four passes of FSP. • The mechanisms affecting the mechanical property of stir zone are investigated. • Lower CoF is achieved with Sn/Cu/Graphite hybrid powder reinforcement. • FSP enhances surface wettability by grain refinement. • Fabricated surface composites exhibit synergic mechanical, wetting, and tribological properties. [ABSTRACT FROM AUTHOR]

The last few decades have witnessed the great progress in surface modification through the use of functional polymer coatings. Surface-grafted polymers with thickness ranging from several nanometers to micrometers have been proven to significantly improve the surface properties of materials, thus enabling diverse, customizable, and controllable performances. Consequently, surface-grafting has become a key tool in scientific research on surface/interface and in surface engineering applications. The interface adhesion and friction between materials and their environments can be precisely controlled by grafting specially designed polymer coatings on material surfaces. As a result, the use of surface-grafted polymers to control the adhesion and friction of materials has attracted extensive attention across various disciplines, from polymer chemistry, physics, and materials science to biology and medical science. This review starts with a discussion of functional surfaces in nature that exhibit unique adhesion and friction phenomena. It then introduces the fundamental principles of tribology and the adhesion and friction behaviors of polymer surfaces. It covers different methods for producing polymer coatings and the corresponding strategies for controlling adhesion and friction. Finally, the challenges and barriers that prevent broader application of surface-grafted polymers are discussed and an outlook of future opportunities is presented. [Display omitted] [ABSTRACT FROM AUTHOR]

Although refractory high entropy films exhibit excellent strength and hardness, their high brittleness often leads to cracking upon frictional contact, resulting in wear resistance that falls short of expectations. This limitation severely restricts their application in industries such as aerospace. In order to address this issue, the development of high entropy composite films has emerged as a viable approach to mitigate friction and enhance reliability. In this paper, a series of (NbMoWTa) 1−x Ag x films were prepared by introducing nano phase Ag into the NbMoWTa system by magnetron sputtering co-deposition. Despite the soft second phase potentially deteriorating the mechanical performance of the composite films, our study demonstrates that the unique chemical nanolayering in the NbMoWTa/Ag can lead to a significant reduction in friction while maintain a high hardness. Compared with the monolithic NbMoWTa film, the (NbMoWTa) 75 Ag 25 film exhibited a 54.3 % reduction in friction coefficient and an 81.6 % decrease in wear rate, demonstrating superior tribological behavior compared to most Ag-containing composite films. The present work provides an effective strategy and facile route, through self-assembling of layered phase, for developing high performance refractory high entropy alloy films. [ABSTRACT FROM AUTHOR]

Self-powered flexible electronic devices are being rapidly developed rapidly for the field of sensing and motion monitoring, posing greater challenges to friction electrical materials. Triboelectric hydrogels must be enhanced in terms of their electrical conductivity and mechanical strength to address the poor stability, low sensitivity, and susceptibility to unpredictable physical damage of conventional hydrogels. In this study, multinetwork polyacrylamide (PAM)-agar (AG)/nanofibrillar cellulose (CNF)-MXene triboelectric hydrogels with homogeneous structures were prepared. By adopting AG and CNF as "sacrificial bonding" modes and utilizing the high conductivity of MXene, triboelectric hydrogels were found to have good electrical conductivity, high tensile properties, high tensile strength, and high sensitivity. Single-electrode triboelectric nanogenerators made of triboelectric hydrogels were used as self-powered wearable sensors for accurately detecting the amplitude of movement in different parts of the human body during exercise. The results obtained in this study have positive implications for promoting the design of high-performance hydrogel materials and their application in flexible wearable sensors. • Construction of PACM multinetwork hydrogels by AG and CNF "sacrificial bond" mode. • PACM Multinetwork Hydrogel with excellent mechanical strength. • Flexible strain sensors based on PACM multinetwork hydrogels exhibit high sensitivity. • PACM multinetwork hydrogel-based TENG can be used as a self-powered pressure sensor and to monitor human motion. [ABSTRACT FROM AUTHOR]

• Cu-VC-Al 2 O 3 -graphite composites were prepared with copper-coated graphite and V 2 AlC. • A VC interface transition layer was formed between the copper matrix and graphite. • The microstructure of the composites was analyzed by XRD, SEM and EDS. Cu-graphite composites play an important role as friction materials used in many fields. However, weak bonding of copper with graphite and low strength of copper are significant limitations. In this study, our focus on fabricating high-density Cu-VC-Al 2 O 3 -graphite composites by using V 2 AlC as a modifier for the Cu-graphite systems. The microstructure and interface properties of the composites were thoroughly examined by SEM, EDS, and XRD techniques. The results indicate the in-situ synthesis of VC and Al 2 O 3 , which exhibit good compatibility with the copper matrix in the composites. Furthermore, the formation of a VC layer facilitates enhanced interfacial bonding between the copper matrix and graphite. In addition, the resulting composite materials show desirable density and hardness, boasting a relative density of 94.5 % and a hardness of 80.6 HV. [ABSTRACT FROM AUTHOR]

Research shows that there is an increasing interest in alternative friction materials that do not harm human health and the environment, especially after the harmful effects of asbestos were revealed and its use was banned. This study evaluates the potential of apricot kernel shell, an agricultural waste, to be used as a bio-material in brake pad compositions. Composites containing different granule sizes and amounts of apricot kernel shell were experimentally tested for friction performance using a dynamometer. The addition of apricot kernel shell to the brake pad compositions slightly increased the noise level but improved the coefficient of friction. These findings reveal the potential of using apricot kernel shells as an economical and environmentally friendly material in brake pad compositions. [ABSTRACT FROM AUTHOR]

In this study, laser surface structuring (LSS) of titanium alloy (Ti-6Al-4 V) using pulsed Nd: YLF laser with 100 ns pulse duration at various laser powers, scan speeds, and line-spacings has been undertaken for improving the tribocorrosion property. Due to LSS, there is an increment in nano hardness (4.9 GPa - 6.3 GPa) and Young's modulus (140 GPa − 153 GPa) when compared to untreated Ti-6Al-4 V (3.9 GPa, 123 GPa). The tribocorrosion behavior in simulated body fluid against the ZrO 2 ball in fretting mode shows that due to LSS, the degradation rate was significantly reduced (5.3–67.2%) when compared to the untreated one. With an increase in load, the coefficient of friction and material removal rate increases. The mechanism of tribocorrosion is established. [Display omitted] • Development of periodic structured surface on Ti6Al4V using Nd: YLF laser. • Improved nano hardness and Young's modulus of the structured surface. • Improved tribocorrosion resistance of Ti6Al4V due to laser surface structuring. • The mechanism of improved tribocorrosion behavior on laser-structured Ti6Al4V surface is proposed. [ABSTRACT FROM AUTHOR]

Air-cooled blast furnace slag is a metallurgical waste that can be used to produce the slag aggregate for pavement subbase. Slag aggregate is much cheaper than natural stone aggregate, but differs in heterogeneity in strength (from 2 to 40 MPa), tendency to absorb water, and low resistance to freezing-thawing. The paper suggests the use of methods of enrichment by friction properties, selective crushing, and hydrophobization to increase slag aggregate resistance to freezing-thawing cycles, crushing, and water penetration. Selection of the most strength (low porous) 75 % slag aggregate grains due to enrichment by friction properties decreases the total water absorption of the sample from 4.45 % to 3.64 %, decreases the sample mass loss after tests for resistance to freezing-thawing cycles from 5.05 % to 2.82 %, reduces the aggregate crushing value (ACV) from 30.71 % up to 23.80 %. Hydrophobization of the pre-enriched slag aggregate additionally reduces its water absorption to 1.08–––1.3 %. [ABSTRACT FROM AUTHOR]

Graphene and graphite are generally considered as materials exhibiting friction anisotropy. However, it was demonstrated by friction force microscopy experiments that friction anisotropy most likely originates from adsorbates aligning in well-ordered stripes on graphitic surfaces. In this study, we analyzed the evolution of adsorbates on a few-layer graphene-/graphite-flake on top of a Si/SiO 2 -substrate after different times of storage using a multifrequency force microscopy approach. The method allows for the simultaneous in-plane and out-of-plane sample analysis as well as the discrimination of conservative and dissipative tip-sample interactions directed parallel and perpendicular to the surface and thus offers a myriad of complementary physical information. We found that friction anisotropy was observable at distinct areas of the graphene-/graphite-flake after 14 days of storage when exposed to air, albeit not throughout the whole flake, indicating different types of adsorbates. High-resolution imaging revealed that friction anisotropy occurred not only at positions where stripe-like structures were visible, but also on areas which were completely covered with adsorbates. Additionally, we demonstrated that after removal of the adsorbate material by oxygen-plasma treatment, no friction anisotropy was observable on the graphene-/graphite-flake, corroborating adsorbate driven nature of friction anisotropy on graphitic surfaces. [Display omitted] • Combined in-plane and out-of-plane force microscopy for interpretation of ordered adsorbate formation on graphite/graphene. • Discrimination of different types of adsorbates by tip-sample interactions parallel and perpendicular to the surface. • 90° rotation of the graphene/graphite flake revealed that friction anisotropy is only caused by certain types of adsorbates. [ABSTRACT FROM AUTHOR]

Sliding wear behaviors of atmospheric plasma-sprayed Yttria Stabilized Zirconia (YSZ) coating mated with four metallic or ceramic counterparts (Si 3 N 4 , Al 2 O 3 , GCr15 and ZrO 2) were investigated. It has been found that YSZ coatings in contact with Si 3 N 4 and GCr15 show better tribological performances than the other cases, which is due to the formation of the tribolayer mainly consisting of Si 3 N 4 and Fe 2 O 3 respectively on the worn surfaces. In the case of YSZ coating-Al 2 O 3 and YSZ coating-ZrO 2 tribopairs, the wear debris are more irregular and larger in size, resulting in severe abrasive wear and brittle fracture of debris particles. In particular, the specific wear rate of YSZ coating sliding against GCr15 is negative due to the significant material transfer of the tribo-oxide layer, while that of YSZ coating sliding against ZrO 2 is the highest. Amorphization of the wear particles appears in the four cases due to the repeated mechanical action. It has been demonstrated that the wear of YSZ coating deteriorates with the increased flash temperature between the contact surfaces during rubbing process. • YSZ coating is prepared by atmospheric plasma spraying. • The wear behavior depends strongly on the counterpart materials. • Wear particle characteristics is well recognized for clarifying wear mechanism. • Flash temperature correlates with the specific wear rate of YSZ coating. [ABSTRACT FROM AUTHOR]

C f /SiC composites are used as advanced thermal protection and friction materials. However, machining these materials is difficult because of their hard, brittle, anisotropic, and heterogeneous characteristics. This study investigated the removal behavior and surface integrity of C f /SiC composites during abrasive belt grinding using rubber contact wheels of various hardness. Additionally, detailed analysis was performed on their thermal-mechanical coupling characteristics, surface integrity (that is, surface roughness, surface micro morphology, and subsurface damages), and the grinding chips produced. Results revealed that with decreasing hardness of the contact wheel, the surface roughness in all directions, grinding force, and temperature decreased significantly. Moreover, the surface removal morphology of the C f /SiC composites changed from macro-fracture to micro-fracture, and the subsurface morphology changed from SiC matrix cracking and carbon fibers pull-out to matrix plastic flow and fiber micro-fracture, respectively. Furthermore, strip chips with plastically squeezed and cut surfaces were visible in the grinding chips obtained under the 40-HA contact wheel. Therefore, the ductile removal behavior of the C f /SiC composites was enhanced, and the surface quality in abrasive belt grinding with low-hardness contact wheels was markedly improved. [ABSTRACT FROM AUTHOR]

C f /C–SiC composites were fabricated via liquid silicon infiltration with 2.5D needle-punched carbon fiber reinforced C f /C composites. The effect of surface topography and carbon content of the C f /C–SiC composites on the tribological properties was researched by the ball-on-disk reciprocating tribometer. The results indicate that different fiber layers and cross-section of the composites have various surface topography and show significant differences in the friction and wear properties. By the wear morphology and model analyses, the reason for the tribological anisotropy of the composites is that the distribution of carbon and SiC phases in the composites are inhomogeneous caused by the difference of the carbon fiber orientation and the relative content in each layer. Moreover, the wear rate of the short-cut fiber web layer was the lowest and there is an obvious linear decrease in coefficient of friction with increase of carbon content. The present work explains why the tribological properties of the composites are inconsistent and provides a way to adjust the friction properties of composite materials by optimizing the friction surface. [ABSTRACT FROM AUTHOR]

• Sinter- brazing technique involves sintering and brazing in a single heat cycle. • The joining was established between the Fe- FGM to the backing plate (mild steel). • The cross-section microstructure of the sinter-brazed specimen is defect free. • The elemental mapping establishes the distribution of Ni- filler on both sides. • The interface microhardness was 133.2HV with shear strength of 74.3 N/mm2. This study explores the sinter brazing of friction materials to the backing plate, aiming to enhance the bonding strength of the wind turbine mechanical braking system. Sinter brazing, a hybrid process of integrating sintering and brazing in a single heat cycle to offer a robust method for joining friction materials to backing plates under high temperatures. The microstructure establishes the evidence of strong metallurgical bond between the friction material and the backing plate. An average hardness of 133.2HV was obtained at the interface and the shear strength obtained was 74.3 N/mm2. [ABSTRACT FROM AUTHOR]

In this study, advanced aluminium metal matrix hybrid surface composites were synthesized using the five-pass friction stir processing (FSP) technique. A blend of Hybrid reinforcement particles, silicon carbide and cerium oxide, were incorporated into the Al-5052 matrix at varying SiC: CeO 2 ratios of 100:0, 75:25, 50:50, 25:75, and 0:100. The multi-pass FSP methodology ensured thorough mixing and uniform nanoparticle distribution, resulting in tailored microstructures. The optimal 75:25 SiC: CeO 2 ratio exhibited superior microstructural, anti-corrosion, and tribological properties, with the lowest wear rates of 8.3 × 10−9 and 8.8 × 10−9 mm3/m at 15 N and 25 N loads, respectively, and the lowest corrosion rate of 8.06 mm per year compared to other hybrid blends. [Display omitted] [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) layered materials such as transition metal dichalcogenides (e.g., MoS 2 , WS 2) and MXenes (e.g., Ti 3 C 2 T x), as well as hybrids of these materials are the focus of current research in solid lubrication due to their outstanding performance. Transition metal carbo-chalcogenides (TMCCs), consisting of an MXene core and a TMD-like surface, represent an inherent combination of TMDs and MXenes without the need to construct hybrids out of the individual layers. Due to their layered structure and surface chemistry, favorable tribological properties can be expected from these novel materials. Here, multilayer Ta 2 S 2 C and Nb 2 S 2 C TMCCs are deposited solely as a powder onto a steel substrate and their tribological properties under linear sliding against different counterbodies, i.e., Al 2 O 3 , SiC, 100Cr6, and polytetrafluoroethylene (PTFE) are discussed. Advanced materials characterization techniques are used to detect the presence of TMCCs inside the wear tracks and to reveal their 2D structure within the tribofilm. Finally, density functional theory (DFT) simulations are used to unravel the easy shearability of TMCCs at the nanoscale. The results demonstrate the great potential of this new 2D material family, which also offers many possibilities for defined tuning of the solid-solid interface. [Display omitted] [ABSTRACT FROM AUTHOR]

The development of modern brake systems requires the assessment of multiple aspects. Among these, parameters related to the tribological behaviour, vibration, and particulate matter emission are typically evaluated using inertia dynamometers and tribometers. While these two testing systems have been previously compared regarding emissions and tribological behaviours, vibrations were not compared, nor have all these aspects been examined simultaneously. This study investigates the scale effects between a pin-on-disc tribometer and a reduced-scale dynamometer operating under dragging conditions with two levels of pressure and velocity, and a disc temperature not exceeding 260 °C. Regarding the vibration, the pin-on-disc exhibited higher and broader values in the normal direction, 1.3–15.5 m/s2, than the reduced-scale dynamometer, 0.37–0.42 m/s2, while the tangential vibrations exceeded those in the normal direction in both systems. The wear rates in the two systems were overall similar, in the range of 1–4 e−14 m2/N. During the tests the disc temperature in the dynamometer increased at a higher rate compared to the pin-on-disc, affecting the tribological and emission behaviours: steady state values were obtained only in the pin-on-disc tests. The particulate concentration values observed during dynamometer tests better correlated with the peak values from pin-on-disc tests rather than with the steady-state values. This study highlights the importance of including transient values in the evaluation of pin-on-disc testing. • Influence of the thermal behaviour on the PoD and dynamometer results. • CoF: higher PV sensitivity in the PoD than in the dynamometer scale. • Specific wear rate: comparable range for the two scales, but different PV sensitivity. • PNC: The PoD peaks correlate well with the final values of the dynamometer. • Higher vibrations in the PoD: RMS values 1–3 m/s2 (dynamometer), 3–90 m/s2 (PoD). [ABSTRACT FROM AUTHOR]

• Nano-sized primary cementite particles in the bainite plus martensite matrix (NCBM) were produced. • Higher proportion of bainitic areas among the martensite phases in the matrix structure in the NCBM sample. • The wear rate and friction coefficient in the NCBM sample is dramatically reduced. The production of nano-sized primary cementite in bainite/martensite matrix (NCBM) microstructure was designed to improve the dry sliding wear properties of high carbon PM parts. A different heat treatment cycle was carried out for the production of novel the NCBM microstructure. High purity iron powder 1.5 wt%. natural graphite powder was added and it was compacted in the form of a dry sliding wear test specimen in a mold and sintered at 1200 °C in a pure Ar gas atmosphere. The novel NCBM microstructure in the PM material was produced by quenching at 950 °C, then annealing at 600 °C for 12 min, then quickly cooling from 730 °C to 250 °C in a salt bath and keeping it isothermal for 100 s. The friction coefficient of materials with NCBM microstructure was less than other samples. It was found that while the wear coefficient were higher in the tempered martensitic microstructure sample having higher hardness, they were less than in the sample having bainitic/martensitic microstructure with similar hardness. [ABSTRACT FROM AUTHOR]

Friction dampers are widely used energy dissipators for the seismic fortification of engineering structures, due to their efficiency, reliability, and cost-effectiveness. Since the friction force is proportional to the normal load applied on the sliding interfaces for given friction materials, increasing the applied normal load is always the only approach to enhance the energy dissipation capacity of friction dampers. However, a large applied normal load may result in serious wear problems at the interfaces, which in turn affects the functionality of the damper. To address the above issue, a novel rotary amplification friction damper (RAFD) is proposed in the present study, which can realize several times amplified friction force for a given normal load due to the adopted amplification system. The conceptual design and working mechanism of the proposed RAFD are first introduced. Subsequently, a damper prototype was manufactured and experimental studies were carried out to examine the behaviors of RAFD. Then, a nonlinear mechanical model considering the gap between the gear and rack is developed based on the experimental results. Finally, an analytical model of a single-degree-of-freedom (SDOF) system equipped with RAFD is established to investigate the control performance of RAFD in reducing the structural seismic responses and evaluate the influences of various parameters including gap and earthquake types (far-field and near-field ground motions). The analytical and experimental results demonstrate that the proposed RAFD showcases superior seismic control effectiveness compared to the traditional friction damper; the presence of a gap would reduce the control effectiveness of RAFD to some extent, while earthquake types have minimal impact. • A more effective rotary amplification friction damper (RAFD) is proposed. • A mechanical model considering gap is developed and validated through tests. • Seismic effectiveness of RAFD is comprehensively evaluated. [ABSTRACT FROM AUTHOR]

Cu-based friction materials (CBFMs) are widely used in brake system such as High-Speed Trains and Wind Power Generation, its mechanical and tribological properties are of vital importance for the stable and safe operation. In this study, CBFMs holding 3D mesh structure were designed and fabricated by wet granulation and particle coating technology. Stress and temperature fields were obtained by finite element simulation. After that, the mechanical and tribological properties were investigated. The results showed that 3D mesh structure can enhance the compressive strength of CBFMs to 34.56 % and reduce wear rate to a large extent. This study was expected to open up a new direction in enhancing comprehensive performances of CBFMs without changing its composition. [ABSTRACT FROM AUTHOR]

Self-lubricating ceramic materials are mainly achieved through the addition of lubrication phases. Although incorporating lubrication phases can improve their tribological performances, the mechanical properties are consistently compromised. Thus, designing and fabricating single-phase ceramic with favorable self-lubricity is the relentless pursuit of researchers. In this study, the single-phase high-entropy ceramic of (Hf 0.2 Mo 0.2 Nb 0.2 Ta 0.2 Ti 0.2)C exhibits self-lubricating properties and which closely relates to the testing condition. The wear rate and friction coefficient decrease with the increasing of loads (not above 30 N). And the friction coefficient of (Hf 0.2 Mo 0.2 Nb 0.2 Ta 0.2 Ti 0.2)C samples against Si 3 N 4 balls is as low as 0.3 under 30 N and 5 Hz. This originates from the carbon-rich tribo-film with self-lubricity, which is generated through diffusion and enrichment under the effect of tribo-induced. Single-phase self-lubricating ceramics—using own constituent elements to form a lubricating tribo-film—are expected to open up a new research field on the high-performance friction materials. [ABSTRACT FROM AUTHOR]

The scales of Xenopeltis hainanensis , a snake that can crawl in fields, valleys, and other places, can serve as inspiration for the design of scale-like bionic materials. We present a systematic morphological, microstructural, chemical, and mechanical analysis, including elastic modulus, hardness, and wear morphology of the scales to understand the friction basis for achieving the reptile requirements. At the surface level, a comb-like arrangement of microstructures on the ventral scales provides more surface area and reduces pressure. The separation of microstructures, along with the bending and delamination of collagen fibrils could contribute to energy dissipation, which helps prevent catastrophic failure at deeper structural levels. At the cross-sectional level, a greater thickness provides more distribution of stresses over a larger volume, reducing local deformation and increasing the resistance to damage. At the material level, the ventral scales show higher modulus (E = 384.65 ± 19.03 MPa, H = 58.67 ± 6.15 MPa) than other regions of snake scales, which is attributed to the increased thickness of the scales and the higher concentration of sulfur (S). The experimental results, combined with Energy-dispersive X-ray spectroscopy and SEM characterization, provide a complete picture of the fiction properties influenced by surface morphology and chemical composition during scratch extension of the Xenopeltis hainanensis scales. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) of ferrous alloys has achieved a technological maturity level that allows for the production of high-performance steel components. Among these alloys, tool steels and maraging steels can be used in die manufacturing for different hot forming processes as both materials have good mechanical properties and thermal stability. In recent years, several works have successfully produced these alloys through selective laser melting, focusing on the optimization and characterization of their microstructure and mechanical properties. However, few studies look into the tribological aspects of these newly produced materials and even fewer consider high temperature friction and wear performance. Therefore, there is a need to understand the high temperature tribological response of tool materials produced by additive manufacturing. In this context, the aim of this work is to investigate the tribological behavior of a tool steel and a maraging steel, both produced by selective laser melting, at different elevated temperatures. A conventionally produced tool steel was used as reference. A reciprocating sliding tribometer was used to perform tests at 40 °C, 200 °C and 400 °C. The counter-body was a WC-Co cemented carbide. Friction and wear of the AM tool steel and reference tool steel were very similar, thus no signs of the AM route having an impact on the tribological behavior were observed. Both tool steels showed reduced wear volume with increasing temperature, while the opposite was observed for their respective WC-Co counter-bodies. Higher temperature also resulted in increased amount of W transferred onto the tool steel wear scars. AM maraging steel showed higher and more unstable friction level, as well as a much larger wear volume at all temperatures; material transfer onto WC-Co was observed at certain temperatures. Overall, tribolayer formation (or lack thereof) was the dominant aspect in the tribological responses. • High temperature tribological behavior of additively manufactured tool materials was investigated. • Additively manufactured tool steel and reference tool steel showed very similar friction and wear behavior. • For the tool steel materials, large reduction in wear volume was observed at higher temperatures. • Additively manufactured low-nickel maraging steel showed an overall poorer tribological response at all temperatures. • Tribolayer formation (or lack thereof) was the dominant aspect in determining the tribological response of the system. [ABSTRACT FROM AUTHOR]

The copper-based powder metallurgy friction material, modified with dual ceramic components (WC/B 4 C), underwent friction experiments paired with custom-made carbon ceramic discs. The overall findings are as follows: The judicious addition of dual ceramic components (WC/B 4 C) can enhance the mechanical, thermal, and frictional performance of copper-based powder metallurgy friction materials. When the WC/B 4 C ratio is 5:3, the material exhibits the optimal mechanical, thermal, and frictional properties. B 4 C and WC, after braking, form friction films of B 2 O 3 and WO 3. Additionally, the friction film of copper-based powder metallurgy friction materials can be categorized into an oxide layer, a deformation layer, and a matrix layer. The oxide layer primarily consists of Fe 2 O 3 , the deformation layer is mainly composed of WO 3 and B 2 O 3 , and the matrix layer is primarily composed of CuO and Cu 2 O. With the increase in the WC/B 4 C ratio, the primary wear mechanisms of copper-based powder metallurgy friction materials shift from abrasive wear to mild fatigue wear, mild fatigue wear progressing to severe fatigue wear, adhesive wear, and fatigue wear, accompanied by a gradual intensification of oxidative wear. • The judicious addition of WC/B 4 C (5:3) facilitates the improvement of frictional, mechanical, and thermal properties. • The friction film comprises WO 3 , B 2 O 3 , and metallic oxide films. • The wear mechanism of the WC/B 4 C ceramic components can be more effectively understood. [ABSTRACT FROM AUTHOR]

The purpose of this work is to optimize the penetration temperature to obtain 316 L honeycomb-filled tube/aluminum matrix composite (HFT/AMC) with good wear resistance. Utilized selective laser melting technology to fabricate honeycomb-filled tubes as reinforcement for the composite material. HFT/AMC was prepared by filling aluminum into honeycomb-filled tubes under three different temperatures of 800 °C, 850 °C, and 900 °C through vacuum infiltration casting. And performed tissue characterization and performance testing. Microstructure, hardness, XRD, and EDS studies showed that the composite materials generate intermetallic compound transition layers of over 100 μm, and the overall strength of the interface was improved. A large number of intermetallic compounds and honeycomb-filled tubes distributed in the aluminum matrix inside the cells jointly strengthen the aluminum-based material. Inspection of worn surfaces of HFT/AMCs revealed abrasive and oxidative wear as the main wear mechanisms. Considering the wear of the produced HFT/AMC under certain conditions, the most suitable infiltration temperature is 850 °C (wear rate: 0.52 ± 0.16 [(mm3/N·m) × 10−3]). This study confirmed that honeycomb-filled tubes can significantly improve the tribological properties of aluminum-based materials. [Display omitted] • HFT/AMCs at different temperatures can achieve good metallurgical bonding. • The IMC layer of HFT/AMC at different temperatures exceeds 100 μm. • The Al matrix hardness of HFT/AMCs at different temperatures is enhanced. • HFT/AMC at different temperatures have excellent tribological properties. • HFT/AMC-stabilized CoF has potential applications in the field of friction materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • TLM electrodes ensure superior conductivity-friction material interfacing in DF, even during intense deformation. • The SEBS sheath confers super-elasticity to the DF (strain at break of 862.3%). • The dual-structure variable design significantly enhances the triboelectric output performance of the DF. • DF has an excellent open-circuit voltage (265.8 V/m) while maintaining 60 % open-circuit voltage at 300 % elongation. Fibrous triboelectric nanogenerators (FTENGs) are highly desirable nano-energy harvesting devices due to largely available contact area and convenience in integration, which enables more efficient conversion of randomly disordered low-mass mechanical energy into electrical energy. Unfortunately, the high triboelectric output of existing FTENGs under mechanical deformations is considerably limited due to their inherently low stretchability of conductive or friction materials. Therefore, simplified equivalent models are established by mimicking the core–shell structure of natural silk, which discuss the influence of different structural variables of fibers on the electrical energy output, thus guiding the design of construction as well as enhancing the triboelectric behaviors. Herein, we successfully constructed a dual-structure variable FTENG (DF) (dual-channel electrode, twisting) that combines excellent stretch and electric performance by utilizing an efficient and scalable thermal stretching, twisting, and injection process. The twisting process assigns the FTENG a larger effective contact area to enhance the surface charge density of the friction material, while the dual-channel electrode enable faster charge transfer, resulting in a significant improvement in the triboelectric output performance. The open-circuit voltage (V oc) of the DF is up to 265.8 V/m, far surpassing the non-structure variable, single electrode-structure variable and single twisting-structure variable counterpart FTENGs, providing remarkable durability. Also, a single DF has a strain at break of up to 862.3 %, exhibiting excellent mechanical stretchability. Moreover, multiple DFs can achieve more significant electrical output characteristics. The dual-structure variable design and the facile manufacturing method will bring inspiration for the preparation of high-performance energy production devices. [ABSTRACT FROM AUTHOR]

• Damping components with different deformation capabilities were obtained via perforation design. • A tribology test of high-speed train friction braking was carried out on a test rig. • Finite element simulation of friction-induced vibration considering block wear was carried out. • Effect of damping component deformation on tribological and dynamical behaviours was discussed. Aiming to the issue of the unclear mechanism and lack of design basis for the influence of the deformation of the damping component installed in the brake pads of high-speed train, various perforated configurations were implemented on the damping component to obtain different typical deformation. The damping component was then installed on the back of the friction block and the tests on friction braking were performed using a test rig designed to assess high-speed train braking performance. A finite element model (FEM) was established for wear simulation to obtain block worn surfaces that closely matched the test results, succeeded by conducting both complex eigenvalue analysis (CEA) and implicit dynamic analysis (IDA). The findings indicate that the perforated configurations effectively provided damping components with different deformation capabilities, and increasing the deformation weakened its damping effect on vibration. The damping component deformation not only significantly affected the non-uniform wear on the block surface but also altered the wear patterns. Inappropriate deformation exacerbated the degree of non-uniform wear, leading to complex abrasive wear and adhesive wear, and added to the interface damage. Therefore, the damping component deformation significantly altered the friction-induced vibration and noise (FIVN) characteristics. Enhancing the deformation disrupted the continuity of FIVN but intensified its strength. The major reason is that the damping component deformation determined the time length of its compression and rebound, and inappropriate deformation significantly amplifying the oscillation intensity of contact area and friction force. This posed a challenge in establishing stable contact at the braking interface, ultimately leading to the generation of intense FIVN. Installation of damping components in brake pad to improve interface contact characteristics and suppress FIVN should carefully consider the structural of the braking system, and design damping components with appropriate deformation. Otherwise, it may lead to opposite effects. [ABSTRACT FROM AUTHOR]

Achieving a significant friction reduction is crucial for using thermoplastic materials as substrates in tribological applications and presents an eligible alternative to the use of light metals. In this study, previously developed MoS 2 /graphite/zinc composite coatings, applied by an atmospheric pressure plasma deposition (APPD) process, were investigated to extend the understanding of their characteristics and the influence of the process and environmental parameters on friction behavior. Tribological tests were conducted in ambient conditions and at elevated temperatures (110 °C) to study the friction behavior under application-oriented conditions. The presence of atmospheric oxygen during the deposition process was shown to influence the durability of the coatings, which motivated the application of an inert gas atmosphere for the coating deposition. A novel shrouding plasma nozzle was introduced, which further lowered the friction coefficients. The oxidizing effect of the plasma spray deposition was studied with X-ray photoelectron spectroscopy to investigate the strong impact of the deposition current on the friction behavior and durability of the deposited coatings. Coating composition, morphology, and the effects of the tribological testing were evaluated using optical microscopy, 3D surface measurements, scanning electron microscopy, X-ray diffraction, and nanoindentation. The fabricated coatings with thicknesses in the 10 μm range and good adhesion on the polyamide substrate were stable under extended testing durations and at elevated temperatures and accomplished a significant friction reduction compared to the uncoated polyamide. Thus, APPD-fabricated MoS 2 /graphite/zinc coatings represent an excellent candidate for low-friction applications of thermoplastic substrates. [Display omitted] • MoS 2 -C-Zn coatings significantly improve the friction behavior of PA 4.6. • Durable coatings under extended testing durations (approx. 1200 m sliding distance) • The deposition current determines the coating performance. • Controlled deposition atmosphere to limit the oxidizing effect of the plasma [ABSTRACT FROM AUTHOR]

• A method was proposed to improve interface tribological behavior by modifying the friction block connection. • An evaluation of the mechanical performance of disc springs with varying thicknesses was performed. • A finite element model was established based on the Archard model and the restart method. • The influence mechanism of disc spring connection of friction block on the tribological behavior was discussed. This work aims to improve interface tribological behavior by modifying the friction block connection. The effectiveness of this approach and its underlying mechanisms are evaluated through friction braking test and finite element analysis (FEA). A finite element model (FEM) was established based on the main structure and material parameters of the high-speed train braking performance simulation test setup. The Achard wear formula was used to adequately run-in the friction block. Using a restart analysis to inherit the model post run-in, complex eigenvalue analysis (CEA) and implicit dynamic analysis (IDA) were conducted. Results indicate that the disc spring deformation significantly affects tribological behavior and friction-induced vibration and noise (FIVN) via regulating the contact state at the braking interface. Inappropriate deformation of the disc spring can lead to severe eccentric wear of the friction block, exacerbating the tribological behavior at the braking interface and inducing the brake system to generate high-intensity FIVN. Therefore, rational design of disc spring connection is an effective strategy for improving interface tribological behavior, but the disc spring connection design must provide it appropriate deformation capability. This is essential to ensure that the braking interface exhibits favorable contact state, thereby improving tribological behavior. [ABSTRACT FROM AUTHOR]

To meet the demand for damage optimization of current-carrying friction materials and based on the uneven distribution characteristics of damage, copper-graphite gradient composite materials were prepared using spark plasma sintering technology. These materials were paired with H62 brass, conducting damage optimization studies on copper-graphite gradient composite materials using a self-made current-carrying friction test machine. The results indicate that the copper-graphite gradient composite materials possess excellent current-carrying performance. With an increase of graphite content, the degree of mechanical damage and arc damage on the worn surface is optimized. The friction coefficient and wear rate of the material significantly decrease. When the content of graphite in the material is 5 wt% − 10 wt%, The material's damage optimization reaches the best and the wear rate is 9.7 × 10−4 mg·m−1. At this point, the predominant form of damage to the material is plastic deformation. [ABSTRACT FROM AUTHOR]

Generally, modification of materials by adding multiple types of nano particles could cause dispersion problems, generally limited the performance improvement effect. Herein, we report the modification of UHMWPE materials by organic-inorganic core-shell particles with PTFE as the core and Al(OH) 3 as the shell, which prepared by in-situ polymerization of sodium bicarbonate and aluminum sulfate solution. Core-shell particles were filled in UHMWPE matrix and sintered into composite by spark plasma sintering (SPS). The mechanical and tribological properties of the composites were characterized by tensile compression testing machine, universal micro tribometer (UMT-5), three-dimensional white light interferometer and scanning electron microscope (SEM). The results showed that the addition of core-shell structural materials effectively improved the tribological properties (friction coefficient decreased by 40%, wear rate decreased by 30%) and mechanical properties (compression strength increased by 2.4 times) of the composites. It was demonstrated that the inorganic framework provided strength to improve the mechanical properties and wear resistance of materials, and the organic phase was used as a lubricating phase to reduce the friction coefficient of materials. Surface treatment of core-shell particles both improved the binding between particles and matrix and decreased the formation of agglomerations, thus significantly reducing ploughing phenomena's effect produced by abrasive wear of agglomeration [Display omitted] [ABSTRACT FROM AUTHOR]

In this paper, the experimental, statistical and computational universal analysis methods applicable to most fiber-reinforced friction materials (FMs) are presented for four natural wollastonite fibers (WFs) with different length-to-diameter (L/D) ratios. Machine learning (ML) methods for friction coefficient prediction of friction materials are compared and screened. Numerical statistics and calculations are used in conjunction with the use of finite element (FE) models to determine the performance metrics and friction wear mechanisms of FMs. The experimental and computational results show that the artificial neural network (ANN) model performs the best in COF prediction with an accuracy of 0.961. The friction fluctuation, friction stability and integrated friction performance of the WF-containing samples are better than those of the blank samples. For the first time, the FE model was used to explain the swirling phenomenon on the wear surface of FMs. This study provides new ways and ideas for the design, experimentation, data processing and application of friction composites. [ABSTRACT FROM AUTHOR]

The emission of airborne particulate matter from a train brake depends on the formulation of its friction material. This study investigates the emission and properties of wear particles from train brake friction materials based on straight or resorcinol-modified novolac phenolic resin and nitrile or styrene butadiene rubber used as binding ingredients. The wear particles are generated by a pin-on-disc tribomachine inside an aerodynamic chamber, counted and collected using aerosol measurement techniques, subjected to microscopic and elemental analysis. It has been found that the modification of novolac phenolic resin with resorcinol has no considerable effects on the emission of wear particles and their properties. By contrast, replacing styrene butadiene rubber with nitrile butadiene rubber leads to a significant decrease in the emission of 0.1–10 μm wear particles. • Modifying novolac phenolic resin with resorcinol has no effect on particle emission. • Replacing styrene butadiene rubber with nitrile one reduces particle emission. • Size distribution of wear particles exhibits peaks at 0.15, 0.5 and 1.6 μm. • Wear particles may contain silicon, aluminium and magnesium from mineral fibre. [ABSTRACT FROM AUTHOR]

• We, herein, proposes a surface modification method by replicating the surface morphology of sandpaper to construct microstructure on the surface of chitosan film or by constructing porous structure using electrospinning technology. • Thanks to the significant increase in the effective contact area between the two friction materials, the output performance of the vertical contact-separation TENG with chitosan (Fluorinated ethylene propylene) film being used as a friction positive (negative) material is greatly enhanced. • Based on the excellent electrical output capability of theTENG, it can collect mechanical energy from various human movements and provide power to small electronic devices such as LED, capacitor, and calculator. • In addition, the TENG can demonstrate effective corrosion protection when used for cathodic protection, confirming the enormous potential of TENG in self powered corrosion protection. The triboelectric nanogenerator (TENG) has enormous application prospects and research value in energy collection due to its small size, simple structure, and ability to convert mechanical energy into electrical energy output. The microstructure of TENG's friction layer has a significant impact on its output performance. We, herein, propose a surface modification method by replicating the surface morphology of sandpaper to construct microstructure on the surface of chitosan film or by constructing porous structure using electrospinning technology. Thanks to the significant increase in the effective contact area between the two friction materials, the output performance of the vertical contact-separation TENG with chitosan (Fluorinated ethylene propylene) film being used as a friction positive (negative) material is greatly enhanced. This TENG also exhibits its sensitivity in perceiving human movements and has good power supply capabilities. Our results indicate that surface modification of the friction materials is a facile strategy to boost the performance of TENG. [ABSTRACT FROM AUTHOR]

[Display omitted] • ZnO@SiO 2 have the best tribological properties under light load. • SiO 2 @ZnO exhibit the best anti-friction effect under heavy load conditions. • GCr15-ZnO-SiO 2 surface composite film is the key to improve tribological property. Nano-additives can enhance the tribological properties of greases. In particular, core-shell composite nanoparticles, which combine multiple nanoparticles, have been the subject of recent research due to their superior properties. In this study, based on the friction pairs material, GCr15, by choosing ZnO with low hardness and SiO 2 with high hardness, core-shell composite nanoparticles with soft shell hard core SiO 2 @ZnO and hard shell soft core ZnO@SiO 2 were prepared by chemical deposition and calcination methods. The impact of different structural forms of these composite nanoparticles as grease additives were investigated for the first time by adding them into lithium grease. The results show that ZnO@SiO 2 have good tribological properties under light load, reducing the COF by 18 % and decreasing the WSD by 22 %. SiO 2 @ZnO exhibit the best anti-friction effect under heavy load conditions, reducing the COF by 15 % and decreasing the WSD by 28 %. The GCr15-ZnO-SiO 2 surface composite film structure is the key to improve the performance of grease in the two composite nanoparticles. It not only has good wear resistance, but also can increase the bearing capacity of the oil film. The two core-shell structure nano-additives provide a new idea for the design of lubricants under special conditions. [ABSTRACT FROM AUTHOR]