High Friction Research Articles

Investigation on the mechanism and measures of derailment of empty freight train passing a turnout in the diverging route

The derailment of railway vehicles at a turnout is a worldwide concern. However, the derailment of empty freight trains in the switch section of a turnout in the diverging route is rarely concerned. Therefore, in order to analyse the derailment mechanism of empty freight trains in the turnout switch area and to propose appropriate preventive measures, field investigation and dynamic simulation of the derailment are carried out on the basis of an empty freight train derailment in the turnout switch area of the diverging route. Firstly, the background of the derailment is presented and the potential influencing factors of the derailment are analysed according to the field investigation. Secondly, a detailed train-turnout dynamic model is established, taking into account the variable cross-sections of the turnout switch rail and the effect of the longitudinal coupler force. Thirdly, based on the model, the derailment mechanism of the empty freight train is revealed through theoretical analysis and simulation calculation. Finally, the effect of the potential derailment influencing factors is analysed and preventive measures are proposed to reduce the derailment risk of the empty freight train at the turnout switch area in the diverging route. The results indicate that this derailment is caused by the combined effect of the inherent structural characteristics of the switch, the large longitudinal coupler force, and the high wheel rail friction coefficient. The possibility of derailment can be reduced by reducing the longitudinal coupler force and the wheel rail friction coefficient. In addition, the installation of a guard rail in front of the turnout can effectively prevent empty freight train derailment in the turnout area.

Effect of thermal oxidation on the dry sliding friction and wear behaviour of CP-Ti on CP-Ti tribopairs

Thermal oxidation (TO) has proven to be a cost-effective and efficient technique to engineer the surfaces of titanium and its alloys to achieve enhanced surface properties. The benefits of TO treatment in enhancing the tribological properties of titanium have been demonstrated by many investigators. However, most of the reported tribological studies have been based on the contact between a TO treated titanium specimen and a counter-body made of other materials, mainly ceramics, steels and polymers. Very few studies have been reported on the friction and wear behaviour of TO treated titanium sliding against TO treated titanium. In this work, the effect of thermal oxidation on the dry sliding friction and wear behaviour of commercially pure Ti (CP-Ti) on CP-Ti tribopairs was investigated under loading conditions ranging from elastic contact to plastic contact. Comparisons were made among three contact pairs: (1) untreated Ti on untreated Ti (Ti–Ti), (2) untreated Ti on TO treated Ti (Ti-TO) and (3) TO treated Ti on TO treated Ti (TO-TO). The results show that the TO-TO contact pair presents an ideal material combination to achieve the best tribological performance in terms of low friction and superior wear resistance. On the other hand, the Ti–Ti pair presents the worst combination in terms of tribological performance. While the Ti-TO pair performs better than the Ti–Ti pair tribologically, it is not as good as the TO-TO pair. It is essential to thermally oxidize both specimens in order to achieve optimal tribological performance. It is the oxide layer-on-oxide layer contact that imparts the excellent tribological performance. Failure of the oxide layer in one of the contact bodies can lead to high and unstable friction and increased wear from both contacting bodies. The tribological performance of the three contact pairs and the failure mechanism of the oxide layer are discussed in the paper. The results of this work suggest that the TO treated Ti on TO treated Ti contact pair would have potential tribological applications in engineering.

Numerical study on influence of particle shape and deformation on friction behavior of flexible cylindrical particle flows

AbstractA discrete element method (DEM) model for deformable particles is established and adopted to investigate the Jenike shear process of flexible cylindrical particles with different aspect ratios (4 < < 6). The DEM model is firstly validated against both experimental data and analytic solutions. Then, numerical simulations are carried out and the effects of particles shape and deformation on their friction behavior are investigated through a particle‐scale analysis on particle deformation, coordinate number, contact forces, orientation and internal friction angle. Comparative results between flexible and rigid particles under the same conditions show that the shear stress increases almost linearly with the normal load regardless of particle stiffness or shape. For both rigid and flexible particles, the shear stress and internal friction angle increase with . The shear stress and internal friction angle of the flexible particles are higher than those of the rigid ones especially when = 6. The latter has more inter‐particle contacts but the former has stronger contact forces. When = 4 and 5, the flexible particles without many initial deformations will deform significantly during the shear process with a complex reconfiguration taking place. However, when = 6, the initial deformation and internal forces of the flexible particles only change slightly during the shear process. It is thus believed that the high shear stress and internal friction angle of the flexible particles with = 6 are caused by their solid packing structure which strongly enhances the capability of the particle flow to resist shear. The current knowledge will be helpful for improving the kinetic theories for granular flow for complex irregular particle flows.

High friction surface treatment with silicone resin materials (HFST-S): A preventive maintenance method of asphalt pavements

The skid resistance of asphalt pavements is the key to ensuring traffic safety. Silicone resin is often used as a maintenance material for fog seal because of its waterproof performance and weather resistance, but it is rarely mentioned in the field of skid resistance. In this paper, a high friction surface treatment with silicone resin (HFST-S) was prepared by adding skid-resistance aggregates to improve the skid resistance of pavements. Firstly, the curing time, chemical composition, group content, and hydrophobic performance of silicone resin were studied. Then the morphology characteristics and mechanical performance of skid-resistance aggregates were investigated. Finally, the type and particle size of skid-resistance aggregates, the ratio of silicone resin to skid-resistance aggregates (RSA), and silicone resin dosage were optimized by laboratory tests. The results indicate that silicone resin cured basically at 60 °C for 24 h and Si-OH content decreased during curing. The cured silicone resin was mainly composed of C, O, and Si elements and had remarkable hydrophobicity. In addition, emery sands had richer angularity and better mechanical performance than basalt sands. Therefore, the HFST-S prepared by silicone resin and emery sands has outstanding waterproof performance and skid resistance. The optimum formula of HFST-S was determined as 0.60 – 1.18 mm particle size of emery sands, 40:60 of RSA, and 800 g/m2 of silicone resin.

Tribological behavior of diamond coated reaction-bonded silicon carbide under dry and seawater environment

Ceramic seal materials such as Silicon carbide (SiC) and Reaction-Bonded SiC (89%SiC and 11 % free Silicon) are widely used in mechanical pumps, compressors, and feed water pumps to prevent the fluid leakage between the two rotating shafts. In a continuously harsh environment, these mechanical seal materials undergo high friction and wear due to the high asperity-to-asperity contact between the two mating parts and generate high frictional heat at the interface. This scenario induces seal failure under high operating conditions. Especially in corrosive mediums such as acids, high pH value solutions, and hard abrasive media can cause aggressive seal failure. To reduce production downtime and improve the longevity of the mechanical seal, the surface of the seal material needs to be engineered with a suitable coating that will satisfy the required properties of high hardness, chemically inertness, and low friction coefficient. In this regard, we have come up with a super hard coating material such as diamond (Micro-crystalline) on the surface of Reaction-Bonded SiC using the hot filament CVD (HFCVD) method to meet the above-required properties. In this work, we have carried out a systematic study on the tribological effect of uncoated, and diamond-coated seal material against silicon nitride ceramic under a dry and seawater environment. The initial physical characteristics such as surface morphology, surface roughness, and Raman analysis were performed on the samples before and after coating. To understand the friction and wear characteristics, the linear reciprocating tribometer test (Ball on Flat) was conducted on the uncoated and diamond-coated samples using a universal tribometer for an operating period of 36,000 cycles. The experimental results show that the diamond-coated sample exhibits a low friction coefficient (0.05 ± 0.01) compared to the uncoated sample (Friction coefficient (CoF) = 0.24 ± 0.037) at a normal load of 10 N with a frequency of 10 Hz under a seawater environment. Similarly, under dry conditions for the same tribo-test parameters, the diamond-coated sample (CoF = 0.06 ± 0.02) outperforms compared with the uncoated sample (CoF = 0.42 ± 0.17) at a percentage improvement of 85 %. From the observed results, we conclude that diamond-coated ceramic seals are considered a suitable alternative to commercially available seals in terms of high operating conditions and durability under both wet (seawater) and dry running operations.

Tribological Property of Al3BC3 Ceramic: A Lightweight Material

Lightweight materials with a density less than 3 g/cm3 as potential tribo-materials for tribological applications (e.g., space tribology) are always desired. Al3BC3 ceramic, a kind of ternary material, is one of the lightweight materials. In this study, dense Al3BC3 ceramic is prepared via a reactive hot-pressing process in a vacuum furnace. Its tribological properties are investigated in two unlubricated conditions (one is at elevated temperature up to 700 °C in air, and another is in a vacuum chamber of back pressures from 105 Pa to 10−2 Pa at room temperature) and lubricated conditions (i.e., water and ethanol as low-viscosity fluids). At 400 °C and lower temperatures in air, as well as in vacuum, the tribological property of Al3BC3 ceramic is poor due to the fracture of grains and formation of a mechanically mixed layer. The beneficial influence of adsorbed gas species on reducing friction is very limited. Due to the formation of lubricious tribo-oxide at 600 °C and 700 °C, the friction coefficient is reduced from ca. 0.9 at room temperature and 400 °C to ca. 0.4. In the presence of low-viscosity fluids, a high friction coefficient and wear but a polished surface are observed in water, while a low friction coefficient and wear occur in ethanol. A lubricious carbide-derived carbon (CDC) coating on top of Al3BC3 ceramic through high-temperature chlorination can be fabricated and the wear resistance of CDC can be improved by adjusting the chlorination parameters. The above results suggest that Al3BC3 ceramic is a potential lubricating material for some tribological applications.

The heating effect on tribological behaviour in the hot rolling process using TiO2 oil-in-water emulsion - A comparative study

The tribological investigations were performed at various nanoparticle concentrations (TiO2 wt%) of 0.05, 0.1, 0.3, 0.5, and 1.0 in oil-water (O/W) emulsions. The materials used for the pin and disc are IS 2062 E250 and 2% chromium-forged steel respectively. IS 2062 E250 is used for good mechanical properties, excellent resistance to corrosion at elevated temperatures, and superior tensile strength and hardness. The tribological tests were performed at the optimised concentration (0.1%) from normal temperature to 150 °C. Excellent tribological efficacy and surface characteristics were observed for optimised concentration. Relatively high friction, wear, and surface roughness were observed at a high temperature. The high-temperature test showed 40% higher frictional force than the low-temperature test. The Wear Scar Diameter increased to 2.76 mm from 2.28 mm. Surface roughness of 0.246 μm from 0.212 μm was detected from low to high-temperature tests. Hence, the nano-additive O/W emulsion could substitute O/W emulsions in the near future for high-temperature applications.

Mechanisms controlling friction and material transfer in sliding contacts between cemented carbide and aluminum during metal forming

Cold forming of aluminum alloys is frequently associated with problems related to severe adhesion and material transfer onto the forming tools which results in high friction forces and negatively affects the surface quality of the formed parts, a phenomenon frequently named galling. In the present study, well controlled laboratory tests using a scratch testing equipment have been performed to evaluate the friction characteristics and investigate the mechanisms controlling the initial transfer of aluminum in dry sliding contact with five different cemented carbide grades. In the tests, an aluminum pin (representing the work material) with a conical tip slides against a flat, fine-polished, cemented carbide surface (representing the tool). During sliding, the mechanical contact results in plastic deformation and flattening of the work material against the tool surface, thus simulating a metal forming contact. The small scale and well-defined tribo contact in combination with post-test surface characterization using optical surface profilometry, high resolution SEM and EDS makes it possible to evaluate the influence of material transfer on the friction characteristics.The results show that sub-μm surface irregularities in the cemented carbide surface trigger mechanical interaction with the softer aluminum surface which promotes aluminum transfer to the cemented carbide surface resulting in high friction. Common surface irregularities, promoting aluminum transfer, are sharp edges of slightly protruding carbide grains, surface steps in connection to binder phase pockets, surface steps in connection to surface pores, etc. It should be noted that even very small surface steps, < 20 nm in height, constitute efficient cutting edges able to effectively cut off the passing aluminum material and thus have a very strong impact on material transfer. In contrast, the effect of carbide composition, e.g. the presence of cubic carbides of different composition, seems to be of minor importance to reduce the adhesion and the tendency to material transfer.

Construction and Properties of High-Toughness Soft-Soft Interfaces Based on the Adhesion of Natural Polyphenols.

Artificial joint replacement is the most effective way to treat osteoarthritis. However, these artificial joints are too stiff with high interfacial contact stress and poor surface lubrication, resulting in stress shielding and severe wear and tear lead to an extremely high failure rate. At present, hydrogels are considered the most promising substitute for artificial joint prostheses owing to their good biocompatibility, adjustable mechanical properties, and excellent flexibility. Nevertheless, a traditional single-layer hydrogel has poor bearing capacity and lubrication, which are far from the properties of natural articular cartilage. The high strength and low friction properties of natural articular cartilage are based on its own multilayer fibrous structure. Therefore, by simulating the multilayer structure of natural cartilage, a bilayer bionic cartilage hydrogel was prepared; that is, the upper hydrogel realized excellent lubrication and the lower hydrogel realized high load-bearing capacity. However, the interface binding of bilayer hydrogels is a challenge at present. Therefore, the interfacial adhesion of the bilayer hydrogel is improved by adding tannic acid (TA) based on the adhesion of the natural polyphenol structure. The average interfacial toughness reaches 3650 J/m2, and the average interfacial shear force reaches 800 kPa. In the preparation of the bilayer hydrogel, taking advantage of the coordination reaction between TA and metal cations, Fe3+ is further added to endow the bilayer hydrogel with excellent mechanical properties and good sliding friction performance. Therefore, this work opens up a new way to construct cartilage-like materials with high toughness and a soft-soft interface.

Influence of the Friction Coefficient on the Stress Distributions and Contact Pressure in Press-Fits via Finite Element Analysis

Press fits are a simple and effective method for assembling a shaft into a hub for different applications in the mechanical engineering field. This method consists of forcing to pass a shaft into a hub via axial insertion. As a result of the difference in the diameters of both components of the shaft and hub, a radial interference is generated, causing a contact pressure at the interface shaft–hub. Contact pressure and the friction coefficient are key factors influencing the maximum transmitted torque. So, in this study, different scenarios for the assembly of a press fit were simulated using finite elements (FE) in order to reveal the influence of this key parameter on the manufacturing-induced stresses in the hub. This way, different friction conditions were considered in terms of the friction coefficient from the frictionless case to a case of high dry friction. In addition, different hub geometries were analyzed including conventional hubs and chamfer hubs with optimal geometry that allows lowering the localized stress concentrations at the hub edges. This way, a more realistic estimation of the final stress state of a press fit is obtained. According to the obtained results, the friction coefficient is revealed as a key parameter in the resulting stress field, causing a non-uniform distribution of stress that can affect the mechanical performance of the press-fit assembly.

Effect of irregular silicon carbide and tackifying phenolic resin on friction coefficients of rubber compounds

AbstractRubber compounds with high friction coefficients are widely used in safety shoes, functional shoes, etc. However, in the presence of a liquid lubrication layer, friction coefficients between rubber compounds and the opposing surface are generally very low. In this work, friction coefficients of rubber compounds are improved by a two‐pronged method. First, micron silicon carbides (SiC) with irregular shape and knife‐edge are selected as fillers to improve the plowing friction in dry state, and to improve the adhesive friction in wet state via piercing the liquid lubrication layer. Second, tackifying phenolic resin is added to increase the damping performance of rubber compounds, so as to improve the hysteresis friction in both dry and wet states. The results show that the comprehensive static and dynamic friction properties of rubber compounds are the best in both dry and wet states (0.5 wt% sodium dodecyl sulfate solution or 90 wt% glycerol solution), when SiC size is 7–14 μm and SiC content is 75–90 phr. Phenolic resin can increase the loss factor (tanδ) and loss modulus (E") of rubber compounds, and improve the static and dynamic friction coefficients in wet state (90 wt% glycerol solution). At the same time, it can improve the hardness of rubber compounds and reduce the relative content of SiC, thus reducing the static and dynamic friction coefficients of rubber compounds in dry and wet states (0.5 wt% sodium lauryl sulfate aqueous solution). In general, the optimal content of phenolic resin is 10–15 phr.Highlights Rubber friction coefficients improved via both adhesion and hysteresis friction. Irregular silicon carbides pierce liquid layer to improve adhesive friction of rubber. Phenolic resin increases hysteresis friction of rubber via damping property.

Gravitational baryogenesis in non-minimal kinetic coupling model

In this work, we consider the gravitational baryogenesis in the framework of non-minimal derivative coupling model. A mechanism to generate the baryon asymmetry based on the coupling between the derivative of the Ricci scalar curvature and the baryon current in context of non-minimal derivative coupling model is investigated. We show that, in this model, the temperature increases during the reheating periods to the end of reheating period or beginning of radiation dominated era. Therefore the reheating temperature is larger then decoupling temperature. It can be demonstrated that, the evaluation of baryon asymmetry is not depends on coupling constant. In this model we can generate baryon asymmetry at low and high reheating temperature, by considering the high friction constraint.

Adhesive wear mechanism of coated tools and its influence on cutting performance during machining of Zr-based bulk metallic glass

Adhesive wear is the primary failure form of coated tools in zirconium-based bulk metallic glasses (Zr-based BMGs) machining. This work investigated the adhesion formation and failure of TiN/Al2O3/Ti(C,N), Al2O3/Ti(C,N), and TiAlN-coated tools when machining Zr41.2Ti13.8Cu10Ni12.5Be22.5 BMG. Characterization of tool-chip interfacial material responses revealed the mechanism of adhesive wear. The relationship between the wear resistance and micro-mechanical properties of coatings was established. The cutting performance of coated tools is also discussed. According to the results, the adhesive wear of coated tools results because the temperature at the tool-chip interface is above the glass transition temperature, reducing the viscosity of chips. Low-viscosity chips were welded to the tool surface under high pressure. Subsequently, high interfacial friction tore the adhesive interface, causing coatings to peel off layer by layer. The exposed tool substrate also generated secondary adhesion, which triggered the diffusion of tungsten and cobalt atoms towards the chip. This was accompanied by redox reactions that exacerbated tool failure. The wear resistance of coatings depended on the elastic modulus (E) and the ratio of nano hardness to elastic modulus (H/E). The TiAlN coating had a lower E of ∼410 GPa and higher H/E of 0.064, and it exhibited better wear resistance than the TiN/Al2O3/Ti(C,N) (E ∼ 436 GPa, H/E = 0.051) and Al2O3/Ti(C,N) (E ∼ 469 GPa, H/E = 0.061) coatings. The lifespan of the TiAlN-coated tool was more than three times longer that of the other two, and the obtained machined surface roughness was less than half that of the others.

Instantaneous formation of covalently bonded diamond–graphite–graphene with synergistic properties

Diamond and graphene are the most widely used carbon allotropes and offer great potential for developing mechanical, electronic, energy-storage, and sensor applications. Their combination, especially interfacial covalent bonding, can impart excellent properties. However, achieving interfacial covalent bonding with superior performance using flexible and low-power strategies remains challenging. This study developed a novel instantaneous transformation method from diamond to graphene to prepare a new covalent structure of diamond–nano-graphite–graphene (CDGG). That is, a nanosecond-pulse laser induces sp3-to-sp2 instantaneous transformations from diamond to graphite in air, and the subsequent mechanical cleavage overcomes the weak van der Waals forces to achieve the final transformation of graphite to graphene. First, the key factors influencing laser-induced graphitization and mechanical cleavage were investigated, and a covalent carbon structure with multidirectional graphene was obtained. Furthermore, the mechanisms encompassing the lattice transformation, interface relationships, transformation time, and interface bonding were elucidated. The obtained new structure synergized the excellent properties of diamond, nano-graphite, and graphene, exhibiting superior lubrication, mechanochemical wear resistance, durability, and load-capacity. Compared to polished diamond, the obtained structure exhibited a significant decrease in the stable coefficient of friction by 49–59 % and a reduction of more than one order of magnitude in the relative wear rate under high friction against ferrous metals with a normal load of 1–9 N. Even under a heavy load of 100 N, it still exhibited superior lubrication and mechanochemical wear resistance. Finally, the preparation and patterning of covalent carbon structures were achieved on various diamond surfaces with high efficiency, environmental friendliness, and low power. This study is expected to broaden the scope of developing and applying diamond, diamond films, and graphene devices.

Frictional strength, electrical conductivity, and microstructure of calcite–graphite mixtures sheared at a subseismic slip rate

Calcite is a common mineral found in carbonate-bearing fault zones. Crystalline graphite (Gr) can be generated within calcite-bearing fault zones, which may contribute to their low strength and high electrical conductivity. To investigate the mixed effects of Gr on calcite gouges, a dedicated assembly was employed in a rotary-shear friction experiment, which enabled simultaneous measurement of friction and electrical conductivity. The experiments were conducted on synthetic dry calcite–Gr mixtures with 0–50 wt% Gr under a fixed normal stress of approximately 2 MPa at approximately 20 °C. A constant equivalent slip rate of 1 mm/s was imposed, with displacements ranging from 0.8 to 4.6 m. To resolve the microstructure evolution, four additional displacement-controlled experiments were performed on the 6 wt% Gr-bearing specimens under the same conditions. Following high peak friction, all Gr-bearing mixtures experienced dramatic slip weakening. The steady-state electrical conductivity of the specimens increased by over eight orders of magnitude when the Gr content exceeded 6 wt%. Microstructures indicated that the calcite particles initially formed a strong framework with distributed Gr, followed by the gradual development of conductive strain-localization zones (SLZs) and Gr-lubricated slip surfaces with increasing displacement. Even the mixtures with low-Gr content (< 2.4 vol%) developed smooth slip surfaces, sustaining low-level electrical conductivities throughout the experiments. For specimens with high electrical conductivities (Gr > 5.3 vol%), abundant Gr flakes were present in the SLZs, forming an interconnected structure. Combined with our companion study on quartz-Gr mixtures, we propose that the conductivity and frictional strength trends with displacement for Gr-bearing mixtures are not always consistent. Mineral crystal properties (e.g., hardness and crystal structure) may influence the frictional properties of these mixtures significantly, while the level of electrical conductivity of a fault zone cannot be used to infer its frictional strength.

Optimization and Performance Evaluation of an Atomized Acid System for the Expansion of Carbonate Gas Injection

The conventional liquid acid has several shortcomings in the acidizing process of fractured-vuggy carbonate reservoirs, including high filtration loss, fast reaction rate, high friction resistance, and difficult flowback. To address these issues, a new atomizing acid acidizing technology is proposed, combining the gas injection development practice from the fractured-vuggy carbonate reservoir in the Tahe oilfield. The laboratory experiments were conducted to optimize the type and concentration of atomized acid, iron ion stabilizer, corrosion inhibitor, and atomization stabilizer. The acid atomization rate was evaluated under different combinations of gas and liquid injection flows using a self-made atomized acid well migration simulator, and the best atomization scheme was selected. Furthermore, a kinetic experiment for the acid–rock reaction was carried out to evaluate the retarding performance of the atomized acid. The optimized formula for the atomizing acid system consists of 15~25% hydrochloric acid, 0.005% atomizing stabilizer (AEO-7), 1% iron ion stabilizer (EET), 1.5% corrosion inhibitor (EEH-160), and water. The optimal gas and acid injection scheme is gas injection at 2m3/min and acid injection at 10 mL/min, which maintains an atomization rate of over 80% after the acid mist migrates through the wellbore. Compared with gelling acid, the acid–rock reaction rate of atomized acid is 8.5, 9.1, and 10.6 times slower under acid concentrations of 15%, 20%, and 25% respectively. The retarding effect of atomized acid is superior, facilitating etching and initiating underdeveloped gas drive channels and thereby increasing the probability of gas communication with new reservoirs. The research findings presented in this paper establish a theoretical foundation for the practical implementation of the atomized acid acidizing process in the field.

Proactive Fault Diagnosis of a Radiator: A Combination of Gaussian Mixture Model and LSTM Autoencoder.

Radiator reliability is crucial in environments characterized by high temperatures and friction, where prompt interventions are often required to prevent system failures. This study introduces a proactive approach to radiator fault diagnosis, leveraging the integration of the Gaussian Mixture Model and Long-Short Term Memory autoencoders. Vibration signals from radiators were systematically collected through randomized durability vibration bench tests, resulting in four operating states-two normal, one unknown, and one faulty. Time-domain statistical features of these signals were extracted and subjected to Principal Component Analysis to facilitate efficient data interpretation. Subsequently, this study discusses the comparative effectiveness of the Gaussian Mixture Model and Long Short-Term Memory in fault detection. Gaussian Mixture Models are deployed for initial fault classification, leveraging their clustering capabilities, while Long-Short Term Memory autoencoders excel in capturing time-dependent sequences, facilitating advanced anomaly detection for previously unencountered faults. This alignment offers a potent and adaptable solution for radiator fault diagnosis, particularly in challenging high-temperature or high-friction environments. Consequently, the proposed methodology not only provides a robust framework for early-stage fault diagnosis but also effectively balances diagnostic capabilities during operation. Additionally, this study presents the foundation for advancing reliability life assessment in accelerated life testing, achieved through dynamic threshold adjustments using both the absolute log-likelihood distribution of the Gaussian Mixture Model and the reconstruction error distribution of the Long-Short Term Memory autoencoder model.

Ultrahigh grain boundary strengthening ability of VCoNi medium entropy alloy

Tensile tests of VCoNi medium-entropy alloy with different grain sizes were conducted at 77 K, 194 K and 293 K. The results show that the grain boundary strengthening ability characterized by the Hall-Petch slope of the alloy increases with decreasing temperature and is evidently higher than that of FCC pure metals, CuAl alloys, and some common FCC high-entropy alloys/medium-entropy alloys at room temperature. A new model correlated to intrinsic stacking fault energy and lattice friction stress is derived to describe the high grain boundary strengthening ability. The high grain boundary strengthening ability and its temperature dependence of the VCoNi medium-entropy alloy are mainly attributed to the high lattice friction stress of the VCoNi alloy. The findings provide a possibility for designing the single-phase FCC medium-entropy alloy with ultra-high yield strength and considerable plasticity.

Microgel-Modified Bilayered Hydrogels Dramatically Boosting Load-Bearing and Lubrication.

Hydrogel-based articular cartilage replacement materials are promising candidates for their potential to provide both high load-bearing capacity and low friction performance, similar to natural cartilage. Nevertheless, the design of these materials presents a significant challenge in reconciling the conflicting demands of the load-bearing capacity and lubrication. Despite extensive research in this area, there is still room for improvement in the creation of hydrogel-based materials that effectively meet these demands. Herein, a facile strategy is provided to realize simultaneously high load-bearing and low friction properties on the proposed hydrogel by modifying the surface of mechanically strong annealled PVA-PAAc hydrogel with a high hydration potential PAAm-co-PAMPS microgel. Consequently, a bilayer hydrogel with a porous surface and a compact substrate has been obtained. Compressive experiments confirmed that the bilayer hydrogel exhibited excellent mechanical strength with a compressive strength of 32.23 MPa at 90% strain. A high load-bearing (applied load up to 30 N), extremely low friction coefficiency (0.01-0.05) and excellent wear resistance (COF low to 0.03 after a 4 h test at 10 N using a steel ball as the contact pair) are successfully achieved. These findings provide new perspectives for the design of articular cartilage materials.

Metal ion reinforced hydrogel/Ti6Al4V bionic composite joint bearing interface with extraordinary mechanical and biotribological properties

Artificial joints are facing challenges of high friction and severe wear, which limits their application in the high stress-loading conditions of joint bearing interfaces. Inspired by the soft/hard structure of articular cartilage/subchondral bone in a natural joint and the presence of lubricating proteoglycan/lubricin on cartilage surface, a polyanionic hydrogel coating rich in carboxylates/sulfonates was constructed on a porous Ti6Al4V substrate through ultraviolet radiation combined with metal ion bridging method. In addition, metal ions were adopted to form ionic coordination bonds with the polyanionic hydrogel layer to enhance its mechanical properties. Characterization results showed that the hydrogel layer was firmly adhered to the porous Ti6Al4V surface, and the as-obtained metal ion reinforced hydrogel/Ti6Al4V joint bearing interfaces displayed improved hydrophilicity and mechanical properties. Notably, compared with Al3+ and Fe3+, Ca2+ reinforced PVA-PAA-PSPMK/DT-Ti6Al4V joint bearing interface in deionized water exhibited a lower friction coefficient (∼0.068), which was similar to that of fresh porcine cartilage, and only slight scratches on the worn surface. Moreover, after 4 h of lubrication in phosphate buffer (PBS) or calf serum, its stable and low friction coefficient further revealed its great application potential in physiological environments. The lubrication mechanisms were also discussed in detail. This work presents a simple and effective method to develop hydrogel/Ti6Al4V bionic composite joint bearing interfaces with advanced performance.