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In view of the wear problem of key parts of magnetic fluid seal device, epoxy resin (EP) composite coatings reinforced with Fe3O4 and fly ash cenospheres (FACs) were fabricated successfully. The structural and morphological features of the fillers and the composite coatings were characterized by Fourier transform infrared and scanning electron microscopy. CFT‐I material surface performance comprehensive tester was used to investigate the tribological behaviors of the as‐prepared composite coatings. Vibrating sample magnetometer was used to investigate the coatings' magnetic property. The formation mechanism of the composite coating was analyzed by the infrared spectrum results combined with molecular dynamics simulations. The results demonstrated that adding a certain amount of double fillers will have a synergistic effect, and its mechanical properties are better than those of single fillers. The tribological property of the m‐FACs/f‐Fe3O4/EP composite coatings was optimal under magnetic fluid friction, which is about an order of magnitude lower than the wear rate under dry friction. The saturation magnetization of the m‐FACs/f‐Fe3O4/EP composite coating is 2.77 emu/g, and the magnetic susceptibility reaches 4.64 × 10−4 m3/kg. Therefore, the m‐FACs/f‐Fe3O4/EP composite coating will be expected to solve the wear problem of equipment components in complex environments of magnetic field and friction. [ABSTRACT FROM AUTHOR]

[Display omitted] • A HEMA hydrogel was coated with a chitosan/hyaluronic acid layer and loaded with diclofenac. • It was non-cytotoxic, non-irritant, presented antibacterial properties and low friction coefficient. • Diclofenac was sustainedly released for 24 h with concentrations > IC50 of COX-1 and COX-2. • Its physico-chemical properties were suitable to be used in contact lenses. • Overall, it seems to be a promising material for dry eye therapeutic contact lenses. When placed in the eye, contact lenses (CLs) disturb the tear fluid and affect the natural tribological behaviour of the eye. The disruption in the contact mechanics between the ocular tissues can increase frictional shear stress and ocular dryness, causing discomfort. Ultimately, continuous CLs wear can trigger inflammation which is particularly critical for people suffering from dry eye. In this work, a double strategy was followed to obtain therapeutic daily disposable CLs for dry eye: a hydroxyethyl methacrylate (HEMA) based hydrogel was coated with two natural polysaccharides, chitosan (CHI) and hyaluronic acid (HA) and posteriorly loaded with an anti-inflammatory drug (diclofenac, DCF). Material sterilisation was carried out by high hydrostatic pressure (HHP) combined with moderate temperature. The friction coefficient (μ) was determined in the presence of different tear biomolecules (cholesterol, lysozyme and albumin) using a nanotribometer. Drug release experiments were performed in static and in hydrodynamic conditions. The material was extensively characterised, regarding surface morphology/topography, optical properties, water content and swelling behaviour, wettability, ionic and oxygen permeability and mechanical properties. It was found that the coating did not impair the physico-chemical properties relevant for the material's application in CLs. Besides, it also ensured a sustained release of DCF for 24 h in tests performed in hydrodynamic conditions that simulate those found in the eye, increasing significantly the amount of drug released. It reduced friction, improving the lubrication ability of the hydrogel, and presented antibacterial properties against S. aureus , P. aeruginosa and B. Cereus. The coated samples did not reveal any signs of cytotoxicity or potential eye irritation. Overall, the coating of the hydrogel may be useful to produce daily CLs able to alleviate dry eye symptoms and the discomfort of CLs wearers. [ABSTRACT FROM AUTHOR]

This study investigates the use of FeMnSiCrNi shape-memory alloy coatings on 316 stainless steel surfaces to harness the stress-induced γ ↔ ε martensitic transformation, enhancing fatigue strength and wear resistance and reducing residual stresses and microcracks. Utilizing laser alloying for fabrication, we optimized the process parameters with ANSYS software to achieve precise melt pool dimensions. We employed SEM, XRD, stress analyzers, microhardness, and friction testers to assess the coatings' microstructure and mechanical properties. The predominant γ austenite phase in the coatings, enriched with martensite because of laser-induced residual stress, shows a transition in residual stress from compressive in the central area to tensile along the edges. The coatings demonstrated significantly higher hardness, approximately 1.5 times that of the substrate, with a microhardness average of 290.14. They also exhibited reduced friction coefficients and enhanced wear resistance compared to the substrate under varying loads. Under dry friction with 10 N, 15 N, and 20 N loads, the Fe17Mn5Si10Cr5Ni coating has friction coefficients of 0.46, 0.57, and 0.97, while the 316 stainless steel substrate shows higher coefficients of 0.57, 0.98, and 1.33. [ABSTRACT FROM AUTHOR]

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Purpose: Recent progress in aero-engine technologies has led to the widespread adoption of Nickel-based Single Crystal (SC) blades in turbine blade design. Firstly, this study explores the influence law of crystal orientation on the nonlinear dynamics of the nickel-based single-crystal shrouded bladed disk. Secondly, the research pays attention to the intricate changes in resonance amplitude corresponding to different crystal orientation angles. Ultimately, the surrogate models with different excitation forces are presented to achieve accurate prediction of the nonlinear dynamic response for a single-crystal bladed disk with arbitrary crystal orientations. Methods: An innovative approach has been proposed for predicting the nonlinear dynamics of the single crystal shrouded bladed disk. The method employs the multi-harmonic balance method to compute the nonlinear dynamics of the single-crystal shrouded bladed disk. Furthermore, dynamic response prediction method based on Kriging method is implemented to develop the surrogate models, which can predicts the nonlinear dynamics of the single crystal bladed disks under arbitrary crystal orientation accurately. Results: Firstly, the numerical simulation indicates that the angles of crystal orientation play important roles in the nonlinear dynamics of the single crystal shrouded bladed disk. Then the surrogate model is constructed on the basis of the numerical results. Finally, the reliability of the surrogate models has been confirmed through various samples. The calculation results show that the effect of crystal orientation on nonlinear dynamic properties for single crystal bladed disk should be considered during the casting process. Conclusions: In this research, the significant influence of crystal orientation on the nonlinear behaviors of the single crystal shrouded bladed disk is analyzed. The primary objective of this work is to investigate the effect of the crystal orientations on the nonlinear responses and predict the responses amplitude for different crystal orientations. Unlike previous studies that have primarily focused on strength of single-crystal blades or bladed disks, this paper provides a comprehensive exploration of the nonlinear dynamic properties and the advanced predictive methodologies of tuned bladed disks under arbitrary crystal orientations. The results show that the effect of crystal orientation on the nonlinear response amplitude should be considered when casting the bladed disk to avoid high cycle fatigue. [ABSTRACT FROM AUTHOR]

A low-wear synergistic protection system integrating titanium nitride coatings and high-performance layered double hydroxides lubricant. [Display omitted] Given the notoriously poor wear performance of Ti6Al4V (TC4) alloys, two types of MgAl layered double hydroxides (LDHs) were synthesized as lubrication additives. Systematic tribological tests were conducted to explore the performance of the TC4 alloy with these MgAl LDHs at varying concentrations in oil. It was found that, with increasing additive concentration, the wear resistance of TC4 significantly improved. Notably, MgAl LDHs with a hexagonal nanosheet structure exhibited superior lubrication performance, reducing the coefficient of friction (COF) by approximately 67.94 % compared to dry friction, and markedly enhancing the anti-wear characteristics of the TC4 alloy. Furthermore, to improve the utility of TC4 alloy in industrial applications, titanium nitride (TiN) coatings with excellent mechanical properties were deposited onto the TC4 substrate using arc ion deposition. A comprehensive analysis of the tribological behavior and wear mechanisms of TiN coating with the two MgAl LDHs additives was also conducted. Results indicated that the combination of TiN hard coatings and MgAl LDHs lubricants achieved high wear resistance for the TC4 substrate. In conclusion, a low-wear synergistic protection system integrating TiN coatings and high-performance MgAl LDHs lubricants was developed, demonstrating effective protection for TC4 alloys. This strategy not only presents a novel approach for reducing wear in TC4 alloys but also provides a reliable method for safeguarding and ensuring the long-term stability of titanium alloys mechanical components under demanding conditions. [ABSTRACT FROM AUTHOR]

This article investigates a class of Duffing nonlinear dynamic systems with fractional‐order dry friction and conducts in‐depth research on the stability, chaotic characteristics, and erosion of the safety basin of this system; the results are verified through numerical simulation. First, the average method is used to approximate the amplitude–frequency relationship of the system, and the accuracy of the analytical results is verified through numerical experiments. Second, the Melnikov method is used to obtain the conditions for the system to enter chaos in the Smale horseshoe sense, and the Melnikov curve is drawn for further verification. Then, bifurcation diagrams are drawn for the changes in various parameters in the system, with a focus on analyzing the influence of friction factors on chaotic bifurcation. By applying the definition and calculation principle of the maximum Lyapunov exponent, and drawing and utilizing the maximum Lyapunov exponent graph, the chaotic state that the system enters under different parameters is more clearly defined. Finally, the evolution law of the safety basin under various parameter changes, especially dry friction changes, is analyzed, and the erosion and bifurcation mechanism of the safety basin is studied. Comparing with the bifurcation diagram, it reveals that chaos primarily contributes to the erosion of the safety basin. [ABSTRACT FROM AUTHOR]

The bio-based flame-retardant treatment for lyocell fabrics is often characterized by low flame-retardant efficiency and deterioration of wearing property. In this study, the modified lyocell fabrics (APDP/Lyocell) with excellent fire safety and wearing property were designed and obtained via hydrogen bonding. The well-coordinated bio-based APDP was evenly distributed on the surface of lyocell fibers. In addition, water solvent was used in the preparation of APDP and the whole treatment process of the resulting lyocell fabrics. The self-extinguishing property of APDP/Lyocell was obtained using the vertical burning test with the APDP loading of 13.0%. Compared with pure lyocell fabrics, the peak of heat release rate and total heat release of APDP/Lyocell decreased by 69.2% and 57.1%, respectively. The fire safety of APDP/Lyocell was attributed to effective synergistic charring, flammable gas dilution, and free radical capture. Additionally, after 100 dry friction cycles, the APDP/Lyocell retained its self-extinguishing property, and its limited oxygen index value was still 27.5%, illustrating excellent friction durability. Furthermore, the wearing properties of APDP/Lyocell, such as air permeability, whiteness, moisture regain, and handle, were not inferior to those of pure lyocell fabrics, making it a promising flame-retardant material. [ABSTRACT FROM AUTHOR]

The study of various celestial bodies is of great interest at the present time. Soil studies are being conducted. Vibrating robots could be possible tools for implementing the missions involving moving on the surface of celestial bodies. At the same time, such missions must be safe and sustainable. Such missions are very expensive. And they require high-quality modeling. The dynamics of a vibrating robot is investigated in this work. These structures can move on the surface of various celestial bodies, such as Mars, the Moon or asteroids. Various models can be used as a model of the contact interaction of bodies with a surface, in particular the Amonton-Coulomb law of friction. This paper is aimed at studying a mechanical system consisting of a rigid body (outer body) placed on a horizontal rough plane and of an internal moving mass moving inside the outer body in a circle lying in a vertical plane, so that the radius vector of the point has a constant angular velocity. Based on the general properties of the solutions, possible periodic modes and their features depending on the parameters of the problem are considered. All qualitatively different solutions in this case are described. • The equations of motion of a vibrating robot on a horizontal plane with anisotropic friction are obtained. • Conditions for the parameters of a system with different behavior of periodic motions are obtained. • A qualitative description of all robot movements when entering the periodic mode is given. [ABSTRACT FROM AUTHOR]

In this work, we investigate a dynamic internal dissipation mechanism in the context of cement-based materials by introducing a 1D-enhanced micromorphic beam model with a dynamic internal friction term. Here, we consider an inherent feature in concrete-like materials arising from the multi-scale structure, namely, microcracks. Thus, we assume that the internal dissipation of the energy depends on the overall relative sliding displacement of the opposite faces in the microcracks under the effects of an applied cyclic load whenever no significant phenomena related to damage occur at the macroscopic level. The dynamic friction term is based on a well-known model for dry friction in solids due to P. R. Dahl, where the friction force depends only on the sliding displacement and evolves in time, reproducing an elastoplastic behavior. The model proposed in this paper takes into account a mechanical energy interchange between both bending and shear distortion in the beam with the sliding occurring at the microcracks, a storage of mechanical energy because of the asperities inside the faces of the microcracks, and the dissipation of the energy that follows from the interaction between the bending and the microcracks. Numerical simulations of the kinematic descriptors and the dissipative cycles are also provided by using the Finite Element Method and the commercial software COMSOL Multiphysics®. [ABSTRACT FROM AUTHOR]

Friction is an unfavourable phenomenon in deep-drawing forming processes because it hinders the deformation processes and causes deterioration of the surface quality of drawpieces. One way to reduce the unfavourable effect of friction in deep-drawing processes is to use lubricants with the addition of hard particles. For this reason, this article presents the results of friction tests of dual-phase HCT600X+Z steel sheets using the flat die strip drawing test. Sunflower oil and rapeseed oil with the addition of 1, 5 and 10 wt.% of silicon dioxide (SiO2) particles were used as lubricants. Tests were also carried out in dry friction conditions and lubricated conditions using SiO2-modified oils and oils without the addition of particles, as a reference. Tests were carried out at different pressure values between 2 and 8 MPa. The effect of friction on the change in sheet surface roughness was also examined. For the entire range of pressures analysed, pure sunflower oil showed lower efficiency in reducing the coefficient of friction compared to pure rapeseed oil. In the pressure range of 4–8 MPa, the lubricants with 5 wt.% and 10 wt.% of particles were more effective in reducing friction than the biolubricant with the addition of 1 wt.% of SiO2. The lowest average roughness was observed for lubrication with sunflower oil containing 5 wt.% of particles. In relation to rapeseed oil, the addition of 10 wt.% of SiO2 provided a sheet surface with the lowest average roughness. [ABSTRACT FROM AUTHOR]

In order to investigate the impact of micro‐textured surfaces with varying surface density on coating properties, the bionic leaf vein micro‐texture with different surface densities were prepared on the substrate surface by laser processing. Bi2S3 soft coatings were deposited on the textured surfaces by electrohydrodynamic atomization. The influence of textured surface density on the adhesion and tribological properties of the coatings was analysed and discussed by scratch tests and friction wear tests. The results showed a significant increase in the friction coefficient as the surface density increased. However, after reaching a certain point, the friction coefficient tended to decrease. The coatings deposited on the lower surface density (13.9%, 14.5%) have better tribological performance compared with the higher surface density (35.6%, 36.2%). Meanwhile, the adhesion of coatings on the textured substrate enhanced compared with coatings deposited on the polished substrate. A reasonable textured surface density can effectively improve the adhesion and tribological properties of the coating. [ABSTRACT FROM AUTHOR]

We present a mathematical model describing the equilibrium of a viscoelastic body with long-term memory in frictional contact with a sliding foundation. The process is quasistatic, and material damage resulting from excessive stress or strain is captured by a damage function. We assume the material is inhomogeneous, leading to multiple contact boundary conditions. The contact interface is partitioned into two segments: One part takes into account the wear of the contact surface, utilizing Archard's law. Here, contact is modeled with a normal compliance condition with unilateral constraints, coupled with a sliding version of Coulomb's law of dry friction. In the other part, contact is modeled with a nonmonotone condition involving normal compliance and a subdifferential frictional boundary condition. Variational formulation of the model is governed by a coupled system consisting of a variational–hemivariational inequality for the displacement field, a parabolic variational inequality for the damage field and an integral equation for the wear function. We study a fully discrete scheme for numerical approximation with an error estimation of the solution to this problem. Optimal error estimates for the linear finite element method are derived, followed by numerical simulations illustrating the behavior of the model. [ABSTRACT FROM AUTHOR]

In this study, a chaos theory-based characterization method is proposed to address the nonlinear behavior of acoustic emission (AE) signals during the startup and shutdown phases of dry gas seals. AE signals were collected through a controlled experiment at three distinct phases: startup, normal operation, and shutdown. Analysis of these signals identified a transition speed of 350 r/min between the mixed lubrication (ML) and hydrodynamic lubrication (HL) states. The maximum Lyapunov exponent, correlation dimension, K-entropy, and attractors of the AE signals throughout the operation of the dry gas seal are calculated and analyzed. The findings indicate that the chaotic features of these signals reflect the friction state of the seal system. Specifically, when the maximum Lyapunov exponent is greater than zero, the system exhibits chaotic behavior. The correlation dimension and K-entropy first increase and then decrease in boundary and hybrid lubrication states, while remaining stable in the hydrodynamic lubrication state. Attractors exhibit clustering in boundary lubrication and dispersion in mixed lubrication states. The proposed method achieves an accuracy of 98.6% in recognizing the friction states of dry gas seals. Therefore, the maximum Lyapunov exponent, correlation dimension, and K-entropy are reliable tools for characterizing friction states, while attractors serve as a complementary diagnostic feature. This approach provides a novel framework for utilizing AE signals to evaluate the friction states of dry gas seals. [ABSTRACT FROM AUTHOR]

The objective of this study is to analyze a quasistatic frictional contact problem involving the interaction between a thermo-viscoelastic body and a thermally conductive foundation. The constitutive relation in our investigation is constructed using a fractional Kelvin–Voigt model to describe displacement behavior. Additionally, the heat conduction aspect is governed by a time-fractional derivative parameter that is associated with temperature. The contact is modeled using the Signorini condition, which is a version of Coulomb's law for dry friction. We develop a variational formulation for the problem and establish the existence of its weak solution using a combination of techniques, including the theory of monotone operators, Caputo derivative, Galerkin method, and the Banach fixed point theorem. To demonstrate the effectiveness of our approach, we include several numerical simulations that showcase the performance of the method. [ABSTRACT FROM AUTHOR]

Fe-based amorphous coatings (AMCs) were applied onto 316L stainless steel using the detonation spraying technique. Friction and wear experiments were conducted under varying normal loads (5N and 10N) and sliding speeds (0.1-0.3 m/s) to investigate the microstructure, as well as the dry sliding friction and wear behavior of the coating. The findings reveal that the Fe-based AMC exhibits a fully amorphous structure, with measured thickness, porosity, and surface hardness values of 174 ± 10 μm, 1.2 vol.% and 783 ± 8 Hv0.1, respectively. When subjected to dry sliding wear conditions, the coating demonstrates favorable wear resistance, with a wear rate ranging from (0.16-2.53) × 10−6mm3N−1m−1. As the normal load and sliding velocity increase, the wear mechanism of the coating gradually transitions from oxidation wear to delamination wear, with minimal abrasive wear observed. Furthermore, the results indicate that the impact of the applied normal load on the wear rate of Fe-based AMCs is more pronounced than that of the sliding speed, particularly at higher sliding speeds. [ABSTRACT FROM AUTHOR]

Selective laser melting (SLM) is a rapid prototyping additive manufacturing technology that has been widely utilized in the biomedical field. Surface texturing is an effective surface treatment used to improve tribological performance. In this work, both SLM and surface texturing were applied to prepare textured 316L stainless steel (SS) samples with different parameters. The tribological performance of the SLM-prepared textured 316L SS under dry and phosphate buffer solution (PBS)-lubricated friction conditions was investigated. The results show that the circular textured sample has the smallest percentage reduction in texture characteristic size and hence has a larger volume to store more wear debris generated during the friction process. Moreover, reducing the texture area ratio and characteristic size increase the friction coefficient of the 316L SS textured samples under the two friction conditions. The friction coefficient and wear loss of the textured samples are larger than those of the untextured sample under dry friction conditions. Under the PBS-lubricated friction conditions, the friction coefficient and wear loss of the textured samples decrease significantly compared to the untextured sample, except for the wear loss of textured samples prepared with a small characteristic size. Simultaneously, the triangular textured sample has better wear resistance than the circular textured samples. Therefore, 316L SS textured samples prepared by SLM technology can achieve stable friction and less wear loss under simulated body fluid conditions by selecting reasonable texturing parameters. [ABSTRACT FROM AUTHOR]

The article describes the possibility of determining the damping coefficient of a support with an elastic ring based on dry friction forces using a special test bench. The forced excitation force is set by the oscillations of a compact speaker installed on top of the oscillating mass through a U-shaped crossbar. The object of the study is a damper with an elastic ring, that is a thin-walled ring with evenly distributed bulges inside and outside, arranged in a checkerboard pattern. The damping coefficient is estimated using a device for simulating a rotor support, an acceleration sensor, an exciter speaker, a controller and a processing station. The amount of damping is estimated according to the width of the peak at the resonant frequency. A comparison is given of the magnitude of the damping coefficient obtained from the analysis of the resonance peak and from the decay rate during the impact experiment.

The purpose of this study was to investigate the dry friction and wear behavior of WC-4.3 wt%MgO-2wt.%ZrO 2 (WM2Z) composite. WM2Z composite prepared by high-energy ball milling and spark plasma sintering (SPS) technology exhibited excellent comprehensive mechanical properties and dense microstructure. Dry friction test results indicated that the increase of sliding speed will lead to the decrease of friction coefficient, while at the same sliding speed, the extension of sliding time has no significant effect on the friction coefficient. The wear volume increased proportionally with the sliding time, while the wear rate stabilized after reaching a certain duration. The wear mechanism was mainly slight abrasive wear. Additionally, some oxidation occurred on both the WM2Z composite and the Si 3 N 4 ball during friction, forming an oxide film that contributed to the reduction of the friction coefficient. The novelty of this study lies in the first systematic investigation of the effects of sliding speed and time on the wear performance of WM2Z composite, and the revelation that in high-speed sliding environments, even with shorter sliding times, the material experiences faster wear. This discovery emphasizes the important role of sliding speed in the wear process and provides new insights into understanding the wear mechanism of materials in practical applications. This study not only enriches the friction and wear theory of binderless WC matrix composites, but also provides important experimental data and theoretical support for the design and application of related materials, laying a solid foundation for wear resistance optimization and industrial applications. [ABSTRACT FROM AUTHOR]

Currently, few studies have been conducted on the use of fluorocarbon resin (FEVE) and polytetrafluoroethylene (PTFE) as adhesive substrates and lubricating and anti-corrosion fillers, respectively, for the fabrication of PTFE-reinforced fluorocarbon composite coatings. In this paper, the tribological properties of polytetrafluoroethylene-reinforced fluorocarbon composite coatings were investigated through orthogonal tests under various operating conditions. The optimal configuration for coating preparation under dry friction and aqueous lubrication was thus obtained: the optimal filler particle size, mass ratio of FEVE to PTFE, spraying pressure, and curing agent content were 50 μm, 3:4.5, 0.3 MPa, and 0.3, respectively. Under oil lubrication, the corresponding optimal values were 5 μm, 3:4.5, 0.3 MPa, and 0.3, respectively. Tribological tests revealed that the best overall performance of the FEVE/PTFE coating was obtained when the mass ratio of FEVE to PTFE was 3:4.5, and the filler particle size also significantly affected the tribological properties under different environments, including the friction coefficients of the FEVE/50 μm-PTFE coating under both dry friction and aqueous lubrication, as well as the friction coefficient of the FEVE/5 μm-PTFE coating under oil lubrication. These coefficients were 0.067, 0.062, and 0.055, representing decreases of 86%, 92%, and 56%, respectively, compared to those of the pure FEVE coating under the same working conditions. This research was conducted with the goal of expanding the application of fluorocarbon coatings in the field of tribology. [ABSTRACT FROM AUTHOR]

The article compares the properties of coatings (cataphoretic, hot-dip zinc, and thermo-diffusion zinc) applied to steel components used in the automotive industry. The research focused on the analysis of corrosion resistance, hardness measurements, and tribological properties conducted on steel guides used in trailer and truck body structures as well as fasteners (M12 × 40 bolts). The base surfaces were cleaned chemically. Corrosion resistance was tested in a salt chamber, while coating thickness was measured using the magnetic induction method. Coating hardness (HV 0.02) was assessed with a microhardness tester, and tribological properties were tested under dry friction conditions. The results showed that the zinc coatings demonstrated corrosion resistance far superior to paint coatings. [ABSTRACT FROM AUTHOR]

This article investigates the dynamic features of domain walls in a bilayer piezoelectric-magnetostrictive heterostructure under the influence of piezo-induced strains, inertial damping, and dry friction dissipation. We assume that the magnetostrictive material belongs to the transversely isotropic hexagonal crystal. The analysis is carried out within the framework of the inertial Landau-Lifshitz-Gilbert equation, which describes the ultrafast evolution of magnetization inside the magnetostrictive materials. By employing the classical traveling wave ansatz, the study explores how various factors such as magnetoelasticity, dry friction, inertial damping, crystal symmetry, and a tunable external magnetic field characterize the motion of the magnetic domain walls in both steady-state and precessional dynamic regimes. The results present valuable insights into how these key parameters can effectively modulate dynamic features such as domain wall width, threshold, Walker breakdown, and domain wall velocity. The obtained analytical results are further numerically illustrated, and a qualitative comparison with recent observations is also presented. [ABSTRACT FROM AUTHOR]

The article explores the assumption in introductory physics courses that dry sliding friction is independent of the relative speed of contact surfaces. The authors conducted experiments to determine if sliding friction force depends on sliding speed, using different materials and padding to minimize surface damage. Results showed that friction force can be considered independent of sliding speed, with the friction coefficient dependent on the normal force. The study provides valuable insights for physics education and suggests further research possibilities in the field of sliding friction. [Extracted from the article]

The Sommerfeld Effect pertains to the non-linear jump phenomenon near the resonance frequency of an excited structure powered by a non-ideal drive that is incapable to supply the required power to the oscillating sub-system. Often this situation is dealt with by increasing the viscous damping present in the system at the expense of considerable power loss. However, the use of non-viscous damping for the attenuation of the Sommerfeld Effect is considered in very few articles. In this paper, the dynamics of a non-ideal DC motor-driven vibrating system with frictional slip as the dissipation element is presented. Use of the method of multiple time scales is employed to find the response of the system semi-analytically. The non-linear dynamical characteristics of the response as the motor speed crosses the resonance condition is analyzed using the linear stability analysis and subsequently, the obtained response is verified using numerical results. The transition of the operating condition between stable and unstable zones and the post-resonance dynamic behavior of such systems indicated that under proper parametric condition, it is possible to achieve a smooth variation of operating speed via a combination of stick and slip motion. Furthermore, the rate of voltage increment is also found to play a pivotal role in surpassing the critical speed of the system. [ABSTRACT FROM AUTHOR]

Under dry friction conditions, wear of the C-ring mating surface and excessive contact pressure of the Stirling engine piston rod cap seal can reduce its sealing performance and service life. Based on the modified Archard wear model, its thermal coupling-wear mathematical model was established and performance analysis was carried out. Based on the established simulation model, the model's predictions were first made using a BP neural network (BPNN) optimized by a particle swarm optimization (PSO). On this basis, the grey relational method was used to optimize the design of the working condition parameters with the minimum average wear rate Wr and the maximum contact pressure Pcmax as the optimization objectives, and the best optimization combination scheme was derived. Finally, the optimized design method presented in this paper was verified to exhibit superior performance using the seal test bench. The results show that the BPNN optimized by PSO the coefficient of determination R2 of Wr and Pcmax higher than 90 %, the root mean square error (RMSE) lower than 0.5, the model prediction accuracy high and the combination of regression design verifies that the BPNN prediction is real and effective. Through the grey relational method, it is found that the work pressure A1 is the most significant for the multi-objective response, and the significance of the relative operating speed B1, ambient temperature D1, and friction factor C1 decreases in the order of significance: when A1 = 7 MPa, B1 = 2.5 m/s, C1 = 0.11, and D1 = 120 °C, the Wr is 5.07e−6 (mm3/s), and the Pcmax is 22.406 MPa, which is higher than that of orthogonal experimental method and the original data, Wr decreases by 8.75 % and 18.33 %, and Pcmax increases by 15.50 % and 35.88 %, respectively, indicating that the grey relational method is superior in terms of comprehensive performance, and the sealing performance and service life of the optimized design method in this paper are verified by the experiment. [ABSTRACT FROM AUTHOR]

This study investigates how laser-induced surface modifications influence key properties such as wear resistance, hardness, and friction in dry and lubricated conditions. The research applies nanosecond pulsed laser treatment to create random, quasi-random, quasi-periodic, and periodic surface structures on the steel surface, aiming to enhance the wear resistance and reduce the coefficient of friction (COF). The frictional performance between the carbon steel ball and the texturized surface was evaluated, including an analysis of the initial friction phase contact (single, double, and multi-contact), with the surface topography assessed before and after wear. The results of the pin-on-plate tests indicate that laser texturing improves the hardness by transforming austenite into martensite, modifies the wettability by periodizing the surface, reduces the COF, and enhances the wear resistance. Periodic surface structures allow for better lubricant retention and change in the lubrication regime, contributing to lower friction and a longer surface lifespan. Minimizing ball–surface contact through appropriate surface periodization significantly affects the load transfer. The primary wear phenomena are the adhesive and abrasion wear of a two-body nature, transforming into a three-body one. The study concludes that laser surface texturing is an effective method for enhancing the tribological performance of AISI 321 steel, with potential applications in industries requiring high wear resistance. [ABSTRACT FROM AUTHOR]

Non-lubricated jacking will be predominantly employed to achieve cost reduction and efficiency during the initial stages of rock pipe jacking. However, a lack of comprehensive scientific understanding regarding dry friction characteristics may significantly elevate the probability of major engineering accidents. The pivotal determinant for these characteristics lies in the dynamic friction coefficient, which inevitably undergoes substantial variations due to changes in jacking distance, speed, and pipe weight. Therefore, in this work, a developed dynamic friction coefficient prediction model with a correlation between the shear velocity (representing the speed of pipe jacking), test times (indicating the distance covered during pipe jacking), and normal pressure (reflecting variations in pipe jacking weight) have been proposed. The results consistently demonstrate that the order of grey relational degree for the test numbers, shear velocity, and normal pressure is determined as V < Nt < Fn. When the jacking distance is less than 25 m (500 tests), the dynamic friction coefficient ranges from 0.412 to 0.453; and when exceeding 500 tests, it can be considered that the dynamic friction coefficient stabilizes at approximately 0.404 with negligible variation. In addition, considering the variable dynamic friction coefficient allows for a more precise evaluation of the jacking force, providing a crucial scientific foundation for cost reduction and efficiency engineering development. Highlights: The dynamic friction coefficient prediction model (DFPM) has been established. The grey relational order of the 3TI factors has been determined as V< Nt< Fn. The DFPM with shear velocity, test times and normal force has been analyzed. The DFPM with jacking speed, distance and pipe weight has been established. The reliability of DFPM has been finally validated. [ABSTRACT FROM AUTHOR]

The vibration of turbine blades during the operation of jet engines is a serious and complex issue that has garnered significant attention. In practical jet engines, dry friction damping is commonly used to suppress blade vibrations due to its reliability and efficiency. The equivalent damping ratio of dry friction dampers is a crucial metric for evaluating their performance. However, calculating dry friction dampers' damping ratio for actual structures involves nonlinear vibration calculations, which are challenging and often lack precision. A method combining simulation and experimentation to calculate the equivalent damping ratio of a structure is proposed. In a laboratory setting, the vibration response of turbine blades under centrifugal load and the damping effect of under-platform dampers were analyzed using oil excitation. The research results indicate that this method can effectively calculate the equivalent damping ratio of actual structures. The findings provide robust support for the design of under-platform dampers and the vibration analysis of turbine blades. [ABSTRACT FROM AUTHOR]

In various applications, dry friction could induce vibrations. A well-known example is frictional braking systems in ground transportation vehicles involving a sliding contact between a rotating and a stationary part. In such scenarios, the emission of high-intensity noise, commonly known as squeal, can present human health risks based on the noise's intensity, frequency, and occurrences. Despite the importance of squeal in the context of advancing urbanization, the parameters determining its occurrence remain uncertain due to the complexity of the involved phenomena. This study aims to identify a relevant operando indicator for predicting squeal occurrences. To this end, a pin-on-disc test rig was developed to replicate various contact conditions found in road profiles and investigate resulting squealing. Each test involves a multimodal instrumentation, complemented by surface observations. It is illustrated that the enhanced thermal indicator identified is relevant because it is sensitive to the thermomechanical and tribological phenomena involved in squealing. [ABSTRACT FROM AUTHOR]

This article provides information on the processing of chromium-containing waste from the Aktobe ferroalloy compounds plant using chemical reagents followed by high-temperature heat treatment for the synthesis of a composite chromite pigment used in the textile industry. This technology was developed for the first time for the purpose of recycling industrial waste and rational use of natural resources. The obtained pigments were analyzed by the X-ray phase of a D878-PC75-17.0 incident beam monochromator and the phase composition of the composite chromite pigment was studied. The thermogravimetric analysis of the composite chromite pigments was performed using a TGA/DSC 1HT/319 analyzer to determine the change in mass with time and temperature. According to the TGA results, the mass loss was determined to be 0.18% of the total mass. The elemental composition of the composite chromite pigment was determined using a JEOL JSM-6490 LV SEM device and the content of chromium oxide (Cr2O3) was determined, which reached up to 50%. The thermodynamic patterns of the processes occurring during the production of chromite pigments were studied using the integrated Chemistry software pack HSC-6. The results of testing printed and processed cotton and composite fabrics by the proposed method showed that the color fastness to washing and wet and dry friction is 4 points and the wear resistance assessment is 4860 and 6485 cycles, respectively. Composite chromite pigment based on technogenic wastes is recommended for use in various coloring compositions, including those used for printing on cotton and composite fabrics. [ABSTRACT FROM AUTHOR]

In order to study the wear failure mechanism and structure evolution law of bearings under different speeds and contact loads, an elastoplastic model of a 7009AC bearing was established in this paper. The stress, temperature rise and grain size during dry friction and wear of the bearing inner ring were simulated with the finite element method. The effects of the inner ring speed, load pressure and other parameters on the wear rate were studied. The relationship between the grain size and yield strength of GCr15 bearing steel was obtained. The effects of the initial grain size, rotational speed and load pressure on the bearing wear failure were studied. The evolutions of the grain size during service were predicted by means of the dynamic grain recrystallization (DRX), static grain recrystallization (SRX) and grain growth (GG) subprogram. The results show that the contact stress has a more significant effect on the early failure wear than the bearing speed, and the increase in the contact stress will aggravate the wear rate of the bearing inner ring. Under the same working conditions, the smaller the grain size, the more significant the influence of the cycle times on wear was. The heat-affected zone produced a local high temperature in the contact area, temperature flashes of up to 580 °C could occur in the central contact area, and the temperature decreased gradually with the increase in the depth from the contact area. It is noteworthy that both the surface and the subsurface of the material produced grain refinement; the grain size was refined from 20 μm to 0.4–12 μm under different working conditions. And the degree of refinement of the subsurface was higher than that of the surface. [ABSTRACT FROM AUTHOR]

Predictive assessments of the performance characteristics of metal-polymer (MP) plain bearings at the design stage are necessary and important for engineering practice. They include assessments of bearing capacity, linear wear of the bushing, and bearing life. However, no method for their calculation has been developed. The authors created a generalized analytical method for the mathematical modeling of MP sliding bearings as a classical science-based method to study the contact mechanics of conformal cylindrical bodies with consideration of polymer bushing wear. The contact problem of the theory of elasticity takes into account the significant difference in the elasticity characteristics of polymeric materials from those of steel: their Young's modulus is 60–250 times smaller, and Poisson's ratio is 1.27–1.37 times larger. The method was used to study MP bearings with bushings made from several common groups of tribopolymers: polyamides (PAs), polytetrafluoroethylenes (PTFEs), polyethylene terephthalates (PETs), and polyetheretherketones (PEEKs). The maximum contact pressures and durability of the dry friction bearings were calculated while taking into account the load; radial clearance; bushing thickness; the tribopolymers' elasticity characteristics and wear resistance; the sliding friction coefficient; and the type of tribopolymer material. The Young's modulus of a polymer material had a significant impact on the level of maximum contact pressures. Polymer fillers, depending on their type and the type of polymer, had very different effects on pressure changes (increase, no change, or decrease). An increase in pressure caused an increase in contact pressures. The durability of a mechanical bearing depended not only on the contact pressure but also on the polymer's wear resistance, Young's modulus, and friction coefficient. This study determined the quantitative and qualitative effects of these factors on the maximum contact pressures and bearing durability. The presented analytical method provides an effective and reasonable assessment of the specified service characteristics of sliding bearings with consideration of the multifactorial influence of the above factors. [ABSTRACT FROM AUTHOR]

Purpose: This paper proposes the application of Recurrence Plot (RP) to analyze dry friction on mechanical rotating systems. Method: The construction of Recurrence Plots is based on the evaluation of the system dynamics represented in a phase plane. The phase plane represents the relationship between displacement and velocity; but in this case, the vibration signals are measured with accelerometers; thus the displacement and velocity function must be obtained integrating the field data. In this paper, a comparison of two integration methods is included, one of the methods is based on the Simpson's integration, and the other is based on the empirical model decomposition (EMD) and the shifting principle of harmonic functions. The experiment consisted of a flexible rotor with an unbalance disk that rub a fixed plate. The tests included different operating speeds, keeping the unbalance constant. The vibrations were recorded with an accelerometer mounted on the rotor's support and a laser vibrometer (LV) that measured the lateral displacements of the disk. Results: The results indicated that the RP patterns show significant differences when the friction load is applied, but only some quantification parameters reflect these differences. The RP were evaluated using quantitative parameters that highlighted the nonlinear effect caused by friction. [ABSTRACT FROM AUTHOR]

AbstractAs an important pipeline support component, metal rubber clamp is mainly used for pipeline connection, fixation and vibration isolation. At present, the researches on hysteretic and stiffness characteristics of metal rubber clamps in aero engines are still in their infancy. This work aims to develop a nonlinear mechanical calculation model for metal rubber clamps to effectively capture the nonlinear mechanical properties, such as hysteresis characteristics and variable stiffness behavior. The equivalent stiffness model of metal rubber clamps was established by introducing tightening torque and friction between metal wires as control variables, and the mechanical behavior under repeated loads is analyzed by combining the force and deformation relations of typical hysteretic curves. By comparing the measured hysteretic curve and natural frequencies, the proposed equivalent stiffness model of a metal rubber clamp is verified. This also suggests that the proposed model can effectively simulate the dry friction damping characteristics of metal rubber. In addition, the effects of tightening torque and friction coefficient on hysteretic characteristics and stiffness are also analyzed. The aim of this study is to develop mechanical anisotropy tests integrated with equivalent numerical simulation techniques to elucidate the mechanical characteristics of the aero engine clamp. The research can provide theoretical support for the structural design of metal rubber clamps. [ABSTRACT FROM AUTHOR]

Grain comminution is commonly observed in numerous geological settings. To elucidate the role of grain comminution in dry granular friction, we sheared breakable halite (NaCl) grains using a ring‐shear configuration at a constant slip rate under various normal stresses. We observed transient frictional behaviors: a constant regime exhibiting a high friction coefficient at small slip displacements, and a weakening regime showing a substantial decay in friction at large slip displacements. The characteristic slip lengths for both regimes decreased with normal stress and were characterized by similar exponents. Micro‐X‐ray tomography revealed the evolution of microstructure from distributed grain comminution to progressive shear localization for these two regimes. We propose that the filling processes of comminuted fine particles, during which fine particles saturate and then overflow the shear zone, define transient frictional behaviors. This study may hold significant implications for natural shear systems, given the ubiquity of comminution and localization phenomena. Plain Language Summary: Grain comminution and structural evolution are common phenomena in natural settings, including earthquake faults and landslides. However, their role in granular friction remains unclear. To investigate this, we experimentally sheared breakable NaCl grains to simulate the processes within growing fault zones and visualized microstructural evolution using micro‐X‐ray computed tomography (CT). We observed two distinct frictional behaviors: a constant regime exhibiting a high friction coefficient at small slip displacements, and a weakening regime showing a substantial decay in friction at large slip displacements. The characteristic slip lengths for both regimes decreased with normal stress. Micro‐observations revealed drastic grain comminution and segregation processes in the constant regime, while the weakening regime showed progressive shear localization evolving from multiple discontinuous shear planes to one extremely localized shear plane. The higher constant friction appeared to result from large grain contacts, while the substantially lower steady‐state friction arose from comminuted fine particle contacts. We propose that grain comminution generates fine particles, gradually filling the pores within the shear zone in the constant regime, ultimately leading to frictional weakening by effectively reducing large grain contacts. The characteristic lengths defining transient behavior may be influenced by geometrical complexities and boundary conditions in various geological settings. Key Points: Sheared granular halite exhibits constant friction at small slip displacement and substantial weakening at large displacementCharacteristic slip lengths for constant friction and weakening decrease with normal stress and are characterized by similar exponentsThe production, saturation, and overflow of comminuted fines in the shear zone are key factors determining transient frictional behavior [ABSTRACT FROM AUTHOR]

Owing to their high producibility and resistance to corrosion, austenitic chromium–nickel steels are widely used in the chemical, petroleum, and food industries. However, their significant disadvantage lies in their poor structural performance, which cannot be improved by heat treatment. This significantly limits the usability of these steels in parts of machines that operate under friction loads. Hardening can be achieved by decreasing the size of grains and applying deformation-induced martensitic transformation. Nanostructuring burnishing (NSB) may be one of the technologies suited for producing parts of tribological assemblies with enhanced operating characteristics. Nanostructuring burnishing using a sliding indenter is being developed as a method of industrial surface nanocrystallization through severe plastic deformation used in the mechanical machining of various types of parts. This article investigates the possibility of enhancing the mechanical and tribological properties of nanocrystallized surfaces of austenitic steels, which are formed through nanostructuring burnishing using a tool with a natural diamond spherical indenter and a change in sliding speed from 40 to 280 m/min with one, three, and five passes. Increasing the tool sliding speed makes surface nanostructuring machining of big parts highly effective. This paper aims to establish the influence exerted by the sliding speed and number of indenter passes on the formation of a nanocrystalline structure, as well as on the modification of microhardness and residual stresses, texture, and tribological properties of the surface layer in the nanostructuring burnishing of AISI 304 steel. Transmission microscopy and microdurometry, 3D-profilometry, and tribological tests of surfaces nanocrystallized with the "ball-on-disk" scheme with dry and lubricated friction established the optimal values of speed and number of passes for a spherical indenter in nanostructuring burnishing. [ABSTRACT FROM AUTHOR]

The working conditions of tools during plastic working operations are determined by, among other things, temperature, loads, loading method, and processing speed. In sheet metal forming processes, additionally, lubricant and tool surface roughness play a key role in changing the surface topography of the drawpieces. This article presents the results of friction analysis on the edge of the punch in a deep drawing process using the bending under tension test. A DC04 steel sheet was used as the test material. The influence of various types of titanium nitride and titanium coatings applied on the surface of countersamples made of 145Cr6 cold-work tool steel was tested by means of high-intensity plasma pulses, magnetron sputtering, and electron pulse irradiation. The influence of the type of tool coating on the evolution of the coefficient of friction, the change in the sheet surface topography, and the temperature in the contact zone is presented in this paper. An increase in the coefficient of friction with sample elongation was observed. Countersamples modified with protective coatings provided a more stable coefficient value during the entire friction test compared to dry friction conditions. The electron pulse irradiated countersample provided the highest stability of the coefficient of friction in the entire range of sample elongation until fracture. The skewness Ssk of the sheet metal tested against the coated countersamples was characterized by negative value, which indicates a plateau-like shape of their surface. The highest temperature in the contact zone during friction with all types of countersamples was observed for the uncoated countersample. [ABSTRACT FROM AUTHOR]

A Babbitt alloy SnSb11Cu6 with 0–2.0 wt.% Co was synthesized using the induction melting process. This study examined the effect of cobalt (Co) on the microstructure, tensile properties, compressive properties, Brinell hardness, and wear properties of SnSb11Cu6 using optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), a universal tensile testing machine, a Brinell hardness tester, and a wear testing machine. The results indicate that the optimal quantity of Co can enhance the microstructure of the Babbitt alloy and promote microstructure uniformity, with presence of Co3Sn2 in the matrix. With the increase in Co content, the tensile and compressive strength of the Babbitt alloy first increased and then decreased, and the Brinell hardness gradually increased with the increase in Co content. The presence of trace Co has a minimal effect on the dry friction coefficient of the Babbitt alloy. When the Co content exceeds 1.5 wt.%, the friction properties of the Babbitt alloy deteriorate significantly. The optimized Babbitt alloy SnSb11Cu6-1.5Co was subsequently fabricated into wires, followed by conducting cold metal transfer (CMT) surfacing experiments. The Co element can promote the growth of interfacial compounds. The microstructure at the interface of the Babbitt alloy/steel is dense, and there is element diffusion between it. The metallurgical bonding is good, and there are serrated compounds relying on the diffusion layer to extend to the direction of the additive layer with serrated compounds extending and growing from the diffusion layer to the additive layer. Overall, Babbitt alloys such as SnSb11Cu6 exhibit improved comprehensive properties when containing 1.5 wt.% Co. [ABSTRACT FROM AUTHOR]

The aim of this work was to perform a simulation analysis of the dynamics of a freight wagon with a variant vibration damping: dry friction and viscous damping. The following mathematical models of the damping characteristics are presented: the Maxwell model and the Kolsch model. The differences among the types of damping were first analyzed based on the dynamic responses of the 1 DOF model. Simulation studies were then carried out in a VI-Rail environment with the use of S-curved track models comprising short straight sections connecting the curves. The track models differed in the values of curve radii, cant, and length, which made it possible to run at different speeds. The multibody model of the vehicle represents a typical two-axle freight wagon. The dynamics of the wagon model were investigated for two states: empty and laden. Standard kinematic and dynamic values were compared in order to investigate if the nature of the damping has a significant impact on the dynamic properties of a freight wagon. The analysis of the simulation study showed that replacing dry friction damping with the viscous one can generally reduce forces acting on the wheel–rail contact, which, in turn, can be related to improving the running behavior of wagons while reducing the negative impact on the track. [ABSTRACT FROM AUTHOR]

The positive effect of plasma electrolytic treatment on CrWMn tool steel to increase the wear resistance of its surface is shown. The effect of plasma electrolytic nitriding and subsequent polishing on the structure, phase and elemental composition, microhardness of the surface layer, and surface morphology is established. Steel nitriding leads to the formation of a modified surface layer including Fe2–3N iron nitride and nitrogen martensite, below which hardening martensite is formed, reaching a microhardness value of 1200 HV. Subsequent polishing leads to a decrease in surface roughness by 42–68%. Tribological tests were carried out according to the shaft-bushing scheme. A decrease in the friction coefficient and weight wear of up to 2.6 and 30.1 times, respectively, is shown. The formed structure of the surface layer compensates for the effect of the counter body and determines the destruction of friction bonds by plastic displacement. The wear mechanism has been established and is defined as fatigue wear under dry friction and plastic contact. [ABSTRACT FROM AUTHOR]

Purpose: Machinery operating in a sand-dust environment is more susceptible to sand particles. The purpose of this paper is to investigate the impact of sand particle deposition rate, surface hardness and normal load on the tribological performance. Design/methodology/approach: A predictive model to approximate the number of sand particles within the pin-on-disc contact surface is proposed. The efficacy of the model is validated through experimental method, which replicates a sand environment with two distinct particle deposition rates. Dry sliding friction experiments are also conducted using 45 carbon steel and H90 brass pins against GCr15 bearing steel discs. Findings: When at high particle deposition rate [6.89 × 10–5 g/(s·mm2)], the contact surfaces are separated by particles, resulting in an indirect metal contact. While at low deposition rate [6.08 × 10–8 g/(s·mm2)], there is an alternating occurrence of direct and indirect metal contacts. In sand environment, the specific wear rate of 45 and H90 decreases by 50% and 33%, respectively, compared to non-sand environment when the applied load is 2.45 N. However, it is only 0.18% for 45 but remains significant at 25% for H90 at load of 9.8 N. Originality/value: The predictive model and experimental method used in this paper are helpful for understanding the interaction between particles and sliding surfaces, thereby providing a solid foundation for material selection and load optimization of friction pairs influenced by sand-dust environments. Peer review: The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-05-2024-0155/ [ABSTRACT FROM AUTHOR]

A deep understanding of non-smooth dynamics of vehicle systems, particularly with dry friction damping offer valuable insights into the design and optimization of railway vehicle systems, ultimately enhancing the safety and reliability of railway operations. In this paper, the two-parameter dynamics of a non-smooth railway wheelset system incorporating dry friction damping are investigated. The effect of the crucial parameters on the complexity of the evolution process is comprehensively exposed by identifying different dynamic responses in the two-parameter plane. In addition, the multistability and the various routes transition to chaos for the system are also discussed. It is found that dry friction induces highly complex dynamics in the system, encompassing a range of behaviors such as periodic, quasi-periodic, and chaotic motions. These intricate dynamics are a direct result of the interplay between multiple parameters, such as speed and damping coefficients, which are critical in determining the system's stability and performance. The presence of multistability further complicates the system, resulting in unpredictable transitions between different motion states. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the asymptotic behavior of inertial dynamics with dry friction within the context of a Hilbert framework for convex differentiable optimization. Our study focuses on a doubly nonlinear first-order evolution inclusion that encompasses two potentials. In our analysis, we specifically focus on two main components: the differentiable function f that needs to be minimized, which influences the system's state through its gradient, and the nonsmooth dry friction potential denoted as φ = r ‖ · ‖ . It's important to note that the dry friction term acts on a linear combination of the velocity vector and the gradient of f. Consequently, any stationary point in our system corresponds to a critical point of f, unlike the case where only the velocity vector is involved in the dry friction term, resulting in an approximate critical point of f. To emphasize the crucial role of ∇ f (x) , we also explore the dual formulation of this dynamic, which possesses a Riemannian gradient structure. To address these dynamics, we employ the recently developed generic acceleration approach by Attouch, Bot, and Nguyen. This approach involves the time scaling of a continuous first-order differential equation, followed by the application of the method of averaging. By applying this methodology, we derive fast convergence results for second-order time-evolution systems with dry friction, asymptotically vanishing viscous damping, and implicit Hessian-driven damping. [ABSTRACT FROM AUTHOR]

PTFE coatings were deposited on YT15 carbide substrates using spray technology. A series of examinations were conducted, including the use of surface and cross-section micrographs to analyze the structural integrity of the coatings. The surface roughness, the adhesion force between the PTFE coatings and the carbide substrate, and the micro-hardness of the coated carbide were also evaluated. Additionally, the friction and wear behaviors were assessed through dry sliding friction tests against WC/Co balls. The test results indicated that while the PTFE-coated carbide exhibited a rougher surface and reduced micro-hardness, it also demonstrated a significant reduction in surface friction and adhesive wear. These findings suggest that the PTFE coatings enhance the overall wear resistance of the carbides. The lower surface hardness and shear strength of the coatings influenced the friction performance, leading to specific wear failure mechanisms, such as abrasion wear, coating delamination, and flaking. Overall, the deposition of PTFE coatings on carbide substrates presents a promising strategy to enhance their friction and wear performance. This approach not only improves the durability of carbide materials but also offers potential applications in industries where reduced friction and wear are critical for performance. [ABSTRACT FROM AUTHOR]