Water friction in nanoconfinement is of great importance in water lubrication and membrane-based applications,yet remains fraught with doubts despite great efforts.Our molecular dynamics simulations demonstrate that t...Water friction in nanoconfinement is of great importance in water lubrication and membrane-based applications,yet remains fraught with doubts despite great efforts.Our molecular dynamics simulations demonstrate that the first water layer adjacent to the surface plays an important role in interfacial friction.Applying a uniform strain to the surface(changing the lattice constant)can induce a significant change in friction and is quite different for the hydrophilic and hydrophobic cases.Specifically,in the hydrophilic case,there is maximum friction when the lattice constant approaches the preferential oxygen‒oxygen distance of the first water layer(a constant value),and the further it deviates,the smaller the friction.The maximum friction corresponds to the most ordered first water layer.While in the hydrophobic case,the friction increases monotonically with increasing lattice constant,which hardly changes the first water layer structure but only increases the difficulty of water molecular jump(meaning jump from one equilibrium position to another).Starting from the molecular jump in the first water layer,theoretical dependence of friction on the molecular activation barrier and shear velocity is established,which provides a reasonable explanation for the friction behavior.Moreover,the water transport behavior in nanochannels supports the finding of the friction dependence on the lattice constant,suggesting great potential for improving and controlling water transport.Our results not only provide a novel understanding of nanoconfined water friction but are also instructive for friction control and water transport.展开更多
Friction energy consumption is the primary cause of energy loss in rolling bearings,and friction characteristics are critical indicators of rolling bearing quality.To comprehensively understand the friction characteri...Friction energy consumption is the primary cause of energy loss in rolling bearings,and friction characteristics are critical indicators of rolling bearing quality.To comprehensively understand the friction characteristics of ball bearings,the equivalent friction coefficient was proposed,and a reliable measurement method was studied.This new solution addressed the difficulty of measuring the friction characteristics of ball bearings highlighted by friction torque.The angular speeds of various components in the rolling bearings were derived using a quasistatic approach.The angular speed relationships among various components of the rolling bearings were subsequently analyzed.A kinetic energy dissipation model for the measuring system was ultimately obtained.A novel apparatus for measuring the rolling bearing equivalent friction coefficient was established.The spindle only underwent angular speed attenuation due to friction of the tested bearing without the use of power,and the variation in kinetic energy was monitored in real time with a highprecision speed sensor.After that,the equivalent friction coefficients of the measured bearings were examined.The effects of speed,load,and lubrication on the equivalent friction coefficient of the tested bearing were studied.The findings demonstrated that,to some extent,the equivalent friction coefficient increased with an increase in spindle speed and decreased with increasing load.The equivalent friction coefficient also increased with increasing kinematic viscosity of the lubrication oil,and the friction coefficient for dry friction was greater than that with 50 oil(with a kinematic viscosity of 50 mm^(2)/s)but slightly lower than that with 70 oil(with a kinematic viscosity of 70 mm^(2)/s).With this method,an accurate and comprehensive understanding of the friction characteristics of ball bearings is achieved.展开更多
Traditionally,the friction force has been the benchmark for quantifying energy dissipation in frictional phenomena.In this study,we introduce an atomic chain friction model that illuminates the conversion of kinetic e...Traditionally,the friction force has been the benchmark for quantifying energy dissipation in frictional phenomena.In this study,we introduce an atomic chain friction model that illuminates the conversion of kinetic energy into potential energy through interfacial forces.The energy dissipation process is characterized by the release of partial potential energy in the form of phonons,quantifiable by a frictional damping coefficient.We have determined that this damping coefficient is significantly influenced by the intrinsic dynamic properties of the friction system.To expand on this foundation,we formulate an advanced phononic friction model that accurately predicts the friction forces measured using an atomic force microscope(AFM).Our model reveals that energy dissipation is caused by vibrations occurring both parallel and perpendicular to the sliding motion.These findings profoundly enhance our understanding of the basic mechanics of friction and open new avenues for innovative strategies for the active management and reduction of energy dissipation in diverse mechanical systems.展开更多
The stable operation of friction pairs is one of the most critical factors to maintain the stable operation of mechanical equipment.The real-time monitoring of lubrication state of the friction pair is very important ...The stable operation of friction pairs is one of the most critical factors to maintain the stable operation of mechanical equipment.The real-time monitoring of lubrication state of the friction pair is very important to ensure the normal operation of machinery and realize early warning of wear failure,but it is also a big challenge.In this article,a new lubrication insitu monitoring system is designed,which can monitor the lubrication and wear state of friction pairs through triboelectrification.The current acquisition module and friction coefficient acquisition module are integrated into a high vacuum hydrodynamic oil film thickness measuring instrument to explore the intrinsic relationship between triboelectricity and friction coefficient curves.When severe wear occurs,the oil film at the interface of the friction pair is no longer complete,and the accumulated triboelectric charge at the interface of the friction pair breaks down the air and causes discharge,the friction current suddenly increases from nanoampere level to microampere level.The time node when discharge occurs at the steel ball interface is well consistent with the time node when the friction pair suffers serious wear.According to the corresponding relationship between the triboelectric current and the friction and wear status of the friction pair,an early wear warning monitoring system is designed to monitor the operating status of the friction pair in real time through triboelectric signals.When the mechanical friction pair is worn,the early warning system will send out sound and light alarm signals and send real-time warnings to the mobile terminal through the Internet of Things,providing a new and reliable method for real-time monitoring of friction and wear of grease-lubricated machinery.展开更多
Recently,the focus of materials research has shifted toward intelligent materials and structures with customizable properties and stimulus-responsive functions.Here,a recyclable thermosetting epoxy resin with self-rep...Recently,the focus of materials research has shifted toward intelligent materials and structures with customizable properties and stimulus-responsive functions.Here,a recyclable thermosetting epoxy resin with self-reported wear and customizable friction is achieved through dynamic and reversible molecular structure design.The epoxy vitrimer displays exceptional mechanical properties,with a Young's modulus of 2.3 GPa,elongation at break of 7.1%,and tensile strength of 79.25 MPa.Based on the reversible exchange of dynamic covalent bonds,the epoxy vitrimer can be fully recovered through hot pressing without the need for additional adhesives or catalysts,and even self-healing can be achieved.Furthermore,by utilizing the reversibility of dynamic covalent bonds,nanofillers(graphene oxide(GO)and polytetrafluoroethylene(PTFE))with specific tribological properties are incorporated into the recovery process to achieve customizable friction coefficients and wear rates.The self-reported characteristics of wear based on sulfur radicals are realized by exploiting the dynamic nature of disulfide bonds.The correlation between wear time and wear state is investigated.The molecular structure design of epoxy based on dynamic covalent bonds has resulted in a versatile thermosetting material with self-reporting and customizable friction properties that is ideal for sustainable engineering and friction applications.This enables intelligent manufacturing while reducing resource waste.展开更多
This study investigates the effect of various tread designs to enhance grip on both dry and wet friction,aiming to reduce slip and fall accidents,especially in slipprone workplaces and among the elderly.The research i...This study investigates the effect of various tread designs to enhance grip on both dry and wet friction,aiming to reduce slip and fall accidents,especially in slipprone workplaces and among the elderly.The research involves analyzing frictional performance and deformation characteristics through dry and wet friction testing.Computeraided design(CAD)software was used to create digital models of various tread patterns,and two different additive manufacturing(AM)techniques,fused filament fabrication(FFF)and stereolithography(SLA)printing,were used for three-dimensional(3D)print block samples with tread patterns,and the materials used were thermoplastic rubber(TPR)filament and photocurable elastomeric resin.A specialized friction testing machine was used to measure the friction force of the treads on a glass surface under dry and wet conditions.A high-speed camera recorded the treads’deformation and water drainage during testing.The results revealed the influence of tread pattern designs with two different rubber-like materials on friction and deformation,as well as performance on various contact surfaces.展开更多
In the Olympic winter sports cross-country skiing and the biathlon,athletes aim to minimise resistive forces such as aerodynamic drag,gravity,and ski–snow friction to enhance performance.Ski-snow friction is complex,...In the Olympic winter sports cross-country skiing and the biathlon,athletes aim to minimise resistive forces such as aerodynamic drag,gravity,and ski–snow friction to enhance performance.Ski-snow friction is complex,involving multiple friction mechanisms that vary depending on snow conditions.In cold environments,where the moisture and water content are minimal,friction is presumably influenced primarily by dry interactions between the ski and snow,particularly through adhesion and abrasion at the micro-scale.Here,we examined ski-snow friction under cold conditions using eight pairs of cross-country skis,with different apparent contact lengths and real contact areas.Our findings revealed that apparent contact length,a macro-scale parameter,had the greatest impact on friction,followed by total real contact area,which is a multi-scale parameter.For snow temperatures below approximately−10℃,longer apparent contact lengths reduced friction,whereas shorter lengths are more effective above−10℃.In addition,at−3℃,minimising the total real contact area was advantageous for reducing friction,while this effect diminished at−8.5℃.At the coldest tested temperature of−13℃,a larger total real contact area resulted in the lowest friction.These findings highlight the importance of considering both macro-and micro-scale contact properties for optimising ski performance in different cold conditions.展开更多
This paper presents an overview of the role of adhesion in various tribological phenomena.We discuss(1)adhesion and adhesive hysteresis in rough contacts,(2)adhesive contribution to dry friction,(3)properties of adhes...This paper presents an overview of the role of adhesion in various tribological phenomena.We discuss(1)adhesion and adhesive hysteresis in rough contacts,(2)adhesive contribution to dry friction,(3)properties of adhesive contacts under tangential loading,(4)“negative adhesion”and superlubricity,and(5)adhesive wear.Based on theoretical considerations,simulations with the boundary element method and experiments,we argue that the key process underlying all these phenomena is jump-like changes of the contact boundary.These jumps are an essential property of adhesive contacts and are solely responsible for energy dissipation in both adhesive hysteresis and adhesive friction.On the mesoscale,the aforementioned instabilities give rise to boundary line friction,which forms a convenient tool for understanding the properties of adhesive contacts both under normal and tangential loading,including changes of contact area and the phenomenon of the“sticking zone”.On the macroscale,the concept of boundary line friction can be approximated by simple adhesive contact with two different works of adhesion—a smaller one for closing the adhesive crack(attachment)and a larger one for opening it(detachment).The well-known equivalence between the adhesive contact boundary and the Griffith crack also leads to the application of the same ideas to wear.In this context,we discuss the modified Rabinowicz criterion for wear particle formation and argue that the adhesive nature of wear all but rule out Archard’s law.Finally,we note that adhesive forces are not necessarily attractive and discuss how“negative”,i.e.,repulsive,adhesion can account for the phenomenon of superlubricity.展开更多
In cross-country skiing,athletes expend large amounts of energy to overcome friction as their skis interact with snow.Even minor reductions in the friction can significantly influence race outcomes.Over the years,rese...In cross-country skiing,athletes expend large amounts of energy to overcome friction as their skis interact with snow.Even minor reductions in the friction can significantly influence race outcomes.Over the years,researchers have found many ways of quantifying ski–snow friction,but there are only a few methods that consider the glide of real-sized skis under natural conditions during both accelerating and decelerating movements.This study introduces a novel experimental setup,consisting of a sled equipped with authentic cross-country skis and a base station that uses satellite receivers to communicate via radio,constituting a real-time kinematic positioning system with centimetre accuracy.While the sled was running on a classic ski track with natural height variations,altitude and velocity data were recorded for quantification of the coefficient of friction(COF),both for accelerating and decelerating motion,employing a model based on Newton’s second law.The results show that the COF during acceleration was more than 20%higher than during deceleration,demonstrating dynamic changes in the frictional behaviour between these phases.This finding is crucial for the execution of all types of cross-country skiing techniques,where the athlete either accelerates or decelerates while moving forward.The ability of the current experimental set-up to distinguish between the COF during acceleration and deceleration has considerable implications for further developments.展开更多
Monolayer MoS_(2)has garnered significant interest because of its exceptional optoelectronic and tribological properties and potential application as a lubrication layer in micro-and nanoelectromechanical systems.Alth...Monolayer MoS_(2)has garnered significant interest because of its exceptional optoelectronic and tribological properties and potential application as a lubrication layer in micro-and nanoelectromechanical systems.Although the nanotribological performance of chemical vapor deposition(CVD)-grown MoS_(2)and the characteristics associated with CVD growth have been extensively studied,challenges remain in designing specific regions on the monolayer MoS_(2)surface with reduced friction.Here,we develop nuclei with an onion-shell structure on CVD-grown monolayer MoS_(2)to achieve remarkable friction and adhesion reduction.These nuclei,dispersed on high-quality and crystalline MoS_(2),consist of an oxi-sulfide core surrounded by a multilayer MoS_(2)shell.Lateral force microscopy results indicate that onion-shell nuclei create an ensemble effect that decreases friction and adhesion by up to 45%and 20%,respectively,compared with those of MoS_(2)because of the multilayer structure and in-plane tensile strain,both of which minimize out-of-plane deformation.Derjaguin–Müller–Toporov(DMT)model calculations and step-down load‒friction correlations illustrate that the work of adhesion,shear strength,and coefficient of friction on the nucleus decrease by more than 22%,19%,and 34%,respectively,compared with those on MoS_(2).The onion-shell nucleus presents a novel lubrication strategy to mitigate friction and adhesion in CVD-grown two-dimensional(2D)materials,with potential applications in lubricating nanoscale friction pairs.展开更多
Wearless sliding friction in the lack of lubrication remains one of the primary goals of scientific research,as wear greatly reduces the life of mechanical components.While ultralow wear is achievable in sliding frict...Wearless sliding friction in the lack of lubrication remains one of the primary goals of scientific research,as wear greatly reduces the life of mechanical components.While ultralow wear is achievable in sliding friction with proper hydrodynamic lubrication or at microscale normal loads,it remains a significant challenge to overcome wear under high normal loads,high sliding speeds,and in boundary lubrication or dry sliding friction.This paper introduces an approach to significantly mitigate wear in plain bearings operating under boundary lubrication at high normal forces and sliding speeds.The plain bearings were constructed from steel shafts tested against different materials.The surfaces of the steel shafts were alloyed with bismuth oxide using a novel high-energy short-pulse laser treatment.In order to incorporate the bismuth oxide into the surface layers of the steel,MnO_(2)was utilized as a carrier.Ultralow wear was observed for the Bi-alloyed steel disk sliding against aluminum countersurface at normal loads up to 250 N(~5 MPa)and a sliding speed up to 9 m/s under extreme lack of lubrication.Achieving ultralow coefficient of friction(COF)and ultralow wear depends on eliminating adhesion between sliding surfaces,reducing the mechanical component of friction through diamond burnishing,and ensuring high fatigue endurance.The results of tribological tests demonstrate an exception to the Frenkel–Kontorova–Tomlinson model for wearless friction.The test results for Bi-alloyed steel–aluminum pair offer a new approach for a wide range of applications.展开更多
Modifying the surface properties of energetic materials with coating has theoretical and practical significance in the field of their application.Wax,in its role as a functional lubrication layer,has extensive utility...Modifying the surface properties of energetic materials with coating has theoretical and practical significance in the field of their application.Wax,in its role as a functional lubrication layer,has extensive utility in mitigating the sensitivity of explosives to external stimuli.This study aims to investigate the friction behavior and temperature rise ofβ-octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine(β-cyclotetramethylenetetranitramine,orβ-HMX)crystals with and without the wax coating,and the friction coefficient,frictional temperature rise,and frictional work-heat conversion rate were systematically analyzed.The experimental results show that regardless of single and reciprocating scratch conditions,the wax coating significantly reduced the coefficient of friction of theβ-HMX surface by up to 63%and effectively suppressed the temperature rise during friction by up to 83%.Further analyses reveal that under single scratch conditions,the frictional work-heat conversion rate of the pristineβ-HMX surface is approximately 42%,whereas that of the wax-coated surface increases to about 30%with the frictional power density,which involves the contact pressure,sliding speed,and friction coefficient.In contrast,under reciprocating scratch conditions,the frictional work-heat conversion rate of the uncoatedβ-HMX surface decreases with increasing number of sliding cycles,which is related to the increase in surface temperature and potential surface damage.The frictional work-heat conversion rate of wax-coated surfaces increases with increasing number of sliding cycles until the contact pressure is high enough that the lubricating effect of the wax layer diminish and the conversion rate begin to decrease.The obtained results not only pave the way for understanding the friction energy regulation and desensitization mechanism of wax on the surface of energetic crystals at the micro and quantitative levels but also provide a necessary basis for establishing friction hotspot models under dry friction and wax lubrication conditions from the aspects of friction characteristic parameters,frictional temperature rise,and the work-heat conversion rate.展开更多
Driven by the potential applications of ionic liquid(IL)flow for charging graphene-based surfaces in many emerging technologies,recent research efforts have focused on understanding ion dynamics and structuring at IL...Driven by the potential applications of ionic liquid(IL)flow for charging graphene-based surfaces in many emerging technologies,recent research efforts have focused on understanding ion dynamics and structuring at IL–graphene interfaces.Here,graphene colloid probe(GrP)atomic force microscopy(AFM)was used to probe the dynamics and ion structuring of 1-butyl-3-methylimidazolium tetrafluoroborate at graphene surfaces under various bias voltages.In particular,the AFM-measured nanofriction provides a good measure of the dynamic properties of the ILs at graphene surfaces.Compared with the IL at the unbiased graphene surface(0 V),the charged graphene surfaces with either negative(-1,-2 V)or positive(+1,+2 V)voltages favor a reduction in the friction coefficient by the IL.A higher magnitude of the bias voltage applied on the graphene surface with either sign(-2 or+2 V)results in a smaller friction coefficient than that at -1 and+1 V.In combination with the AFM-probed contact stiffness,adhesion forces,and ion structuring force curves with an ion orientational distribution according to molecular dynamics(MD)simulations,we discovered that the unbiased graphene surface(0 V)possesses randomly structured IL ions and that the graphene colloid probe is more likely to become stuck,resulting in more energy dissipation to contribute to a larger friction coefficient.Biasing of the graphene surface under either negative or positive voltages resulted in uniformly arranged ions,which produced a more ordered ion structure and,thus,a smoother sliding plane to reduce the friction coefficient.Electrochemical impedance spectroscopy(EIS)for the IL with graphene as an electrode demonstrated a greater ionic conductivity in the IL paired with the biased graphene than in the unbiased one,implying faster ion movement at the charged graphene,which is beneficial for reducing the friction coefficient.展开更多
Changes in the components of synovial fluid in the human body have an important influence on the tribological behavior of artificial joints.Based on the concentration of components in the synovial fluid after arthropl...Changes in the components of synovial fluid in the human body have an important influence on the tribological behavior of artificial joints.Based on the concentration of components in the synovial fluid after arthroplasty,“hard−soft”joint pair materials composed of cobalt‒chrome‒molybdenum(CoCrMo)and highly crosslinked polyethylene(XLPE)were used as the research objects.Composite synovial fluid containing different concentrations of albumin(Alb),γ-globulin(γ-Glo),hyaluronic acid(HA),and phospholipids(PLs)was prepared.By studying the influence mechanism of single component concentration changes on the tribological properties of joint pair materials,the friction and wear behavior of joint pair materials in different composite synovial fluids are systematically explored.The coupling mechanism among the components is clarified,and the wear mechanism of the joint pair materials under different composite synovial fluids is revealed.In addition,the results of 2 million in vitro simulated wear experiments of CoCrMo‒XLPE artificial joints in composite synovial fluid were further studied.Furthermore,this study validated the influence of the concentration of the composite synovial fluid on the friction and wear properties of artificial joints under actual working conditions.The results show that the four main components in the composite synovial fluid have a great influence on the friction and wear properties of the“hard–soft”joint pair materials.When the concentration of PL increased from 0 to 0.45 mg/mL,the wear rate decreased by 69.6%,and the coefficient of friction(COF)decreased by 63.3%.The coupling mechanism between PLs,HA,and proteins significantly affects the adsorption of the membrane and affects the tribological behavior of the artificial joint.In addition,the simulated wear results of artificial joints in composite synovial fluid are consistent with those of friction and wear testers.The concentration of each component in the composite synovial fluid significantly affects the lubrication of the artificial joint,and the degree of influence becomes more obvious during long-term service.In summary,this study provides a theoretical basis for the study of composite synovial fluid and the improvement of the lubrication performance of artificial joints and is highly important for prolonging the service life of artificial joints.展开更多
The importance of reducing energy-related environmental and economic issues by extending the lifetime and efficiency of mechanical systems has increased.The use of ultralow friction composite materials is one approach...The importance of reducing energy-related environmental and economic issues by extending the lifetime and efficiency of mechanical systems has increased.The use of ultralow friction composite materials is one approach to eliminate frictional wear.Polytetrafluoroethylene(PTFE)has excellent low friction properties and has been used to reduce frictional wear in various industrial fields.However,degradation of PTFE in natural environments poses challenges owing to its stable chemical structure,which is characterized by strong C-F bonds.Furthermore,PTFE can accumulate in the living body and environment over a long period of time.Consequently,it is resistant to physiological filtration or decomposition.Hence,it is sometimes called a"forever chemical".Therefore,PTFE,which is a type of poly-and perfluoroalkyl substance(PFAS),is increasingly being adopted as a regulated substance.This review focuses on several aspects of PTFE and PFAS,reasons for their adoption as regulated chemicals,and research onalternatives toPTFE,particularlytheuseof liquid lubricants.展开更多
Nickel foam(NF)-polytetrafluoroethylene(PTFE)interpenetrating phase composites(IPCs)were prepared via vacuum-assisted emulsion impregnation and free sintering.The effects of the pores per inch(PPI)of the NFs on the mi...Nickel foam(NF)-polytetrafluoroethylene(PTFE)interpenetrating phase composites(IPCs)were prepared via vacuum-assisted emulsion impregnation and free sintering.The effects of the pores per inch(PPI)of the NFs on the microstructure,mechanical properties,thermal conductivity,and tribological properties were investigated.The results indicated that the incorporation of a three-dimensional Ni skeleton inhibited heat accumulation at the friction interface,and the thermal conductivity and wear resistance of the composite significantly improved with increasing PPI.Compared with those of the PTFE matrix,the thermal conductivity of the 80 PPI NF-PTFE IPCs improved by~394%and the wear rate decreased by up to~66%.展开更多
Surface graphitization is an effective method for improving the friction performance of amorphous carbon(a-C)films.However,traditional modified methods,such as metal catalysis,addition of extra graphite or graphene,an...Surface graphitization is an effective method for improving the friction performance of amorphous carbon(a-C)films.However,traditional modified methods,such as metal catalysis,addition of extra graphite or graphene,and annealing,often have drawbacks,such as complex operation,structural damage to the graphitized layer and intrinsic a-C films.In this study,a novel approach is explored to achieve in-situ surface graphitization of a-C films by short-term laser irradiation.In particular,as a key parameter,the influence of laser irradiation power on the surface graphitization structure and the mechanical and tribological properties of a-C films was emphasized.The results indicate that surface in-situ graphitization is successfully obtained on the surface of a-C films by laser irradiation and the surface graphitization degree is positively correlated with the laser irradiation power.Importantly,an obviously curled graphene structure is formed on the a-C films after laser irradiation.Compared with those of the intrinsic a-C film,the hardness and elastic modulus of the graphitized film surface obviously decrease after laser irradiation but without significantly deteriorated internal mechanical properties of the a-C film and also decrease gradually with increasing laser power,which is related to the increase in the sp2-C structure.Notably,in-situ surface graphitization induced by laser irradiation obviously reduces friction,which can be reduced by 25.41%compared with the intrinsic a-C film.This is attributed to the fast formation of the graphitized transfer film,which facilitates the transition of the friction interface from graphitized a-C surface/Al2O3 to graphitized a-C surface/graphitized transfer film.展开更多
Frictional contact between biological tissues is of critical importance in biomechanics and clinical treatment strategies,which is particularly relevant to diarthrodial joints,where articular cartilage surfaces underg...Frictional contact between biological tissues is of critical importance in biomechanics and clinical treatment strategies,which is particularly relevant to diarthrodial joints,where articular cartilage surfaces undergo reciprocal contact loading for thousands of cycles per day.Taking the temporomandibular joint(TMJ)as an example,mandibular resection and reconstruction significantly alter the masticatory system and impact its biomechanical conditions.Clinical evidence indicates that pain is more frequent in the contralateral TMJ after this kind of surgery.However,there has been limited analysis of TMJ biomechanics following reconstructive surgery to date.Therefore,our study aimed to investigate the effects of masticatory muscle loss on stress distribution in the TMJs,determine an optimum loading region to mitigate excessive stress in the contralateral TMJ,and explore how the frictional change influences the biomechanics of the TMJ.The results demonstrate that the loss of masticatory muscles on the ipsilateral side due to resection can increase contact pressure in the contralateral TMJ and that incisor and ipsilateral dental implant occlusal loading generates the most desired stress patterns in the contralateral TMJ.This study reveals that the excessive contact pressure could increase the real contact area in the joint and further cause a transition from fluid film lubrication to solid contact,leading to increased friction and wear.This work sheds some light on asymmetric anatomy and frictional condition changes arising from surgery,which contribute to stress concentration in the contralateral TMJ and may be associated with degenerative changes.These findings hold significant clinical implications for selecting an optimal and patient-specific occlusal loading to mitigate excessive contact pressure and potential damage in the articular joint.展开更多
A detailed review of various fractal models used in tribology is presented.The analysis of the models is based on the use of the Cantor–Borodich(CB)profile and its modifications.This profile and related models may be...A detailed review of various fractal models used in tribology is presented.The analysis of the models is based on the use of the Cantor–Borodich(CB)profile and its modifications.This profile and related models may be studied analytically and,therefore,they provide us with tools for rigorous analysis of fractal approaches to description of surface roughness and corresponding contact problems.In turn,this allows us to present a critical review of current fractal approaches to tribology.It will be demonstrated that fractal dimension alone cannot give a full description of surface roughness,however,some of these models may reflect the multilevel hierarchical structure of real surface roughness.This review helps to avoid the repetition of common erroneous statements about the use of fractal concepts in tribology.展开更多
Hydrogels with high water content,excellent permeability,and biocompatibility are widely used in the biomedical field.In this study,an ordered structure-reinforced hydroxyapatite(HA)composite hydrogel with high water ...Hydrogels with high water content,excellent permeability,and biocompatibility are widely used in the biomedical field.In this study,an ordered structure-reinforced hydroxyapatite(HA)composite hydrogel with high water content,high strength,low friction,and fatigue resistance was developed through a molecular network design combined with temperature field-induced orientation and nano-reinforcement technology.The hydrogel has a honeycomb network with a vertically ordered orientation,showing greater network regularity,greater freedom of network cross-linking points,and enhanced flexibility and rigidity of the polymer chain.Its compressive strength is 11 MPa,compressive modulus is 5.2 MPa,friction coefficient is 0.05,and it also has excellent crack propagation and compressive fatigue resistance,exhibiting greater mechanical strength and better tribological properties.Thus,new applications of hydrogels in the biomedical field and soft biological equipment have expanded.展开更多
基金financial support from the National Natural Science Foundation of China(No.22032006)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB047020104).
文摘Water friction in nanoconfinement is of great importance in water lubrication and membrane-based applications,yet remains fraught with doubts despite great efforts.Our molecular dynamics simulations demonstrate that the first water layer adjacent to the surface plays an important role in interfacial friction.Applying a uniform strain to the surface(changing the lattice constant)can induce a significant change in friction and is quite different for the hydrophilic and hydrophobic cases.Specifically,in the hydrophilic case,there is maximum friction when the lattice constant approaches the preferential oxygen‒oxygen distance of the first water layer(a constant value),and the further it deviates,the smaller the friction.The maximum friction corresponds to the most ordered first water layer.While in the hydrophobic case,the friction increases monotonically with increasing lattice constant,which hardly changes the first water layer structure but only increases the difficulty of water molecular jump(meaning jump from one equilibrium position to another).Starting from the molecular jump in the first water layer,theoretical dependence of friction on the molecular activation barrier and shear velocity is established,which provides a reasonable explanation for the friction behavior.Moreover,the water transport behavior in nanochannels supports the finding of the friction dependence on the lattice constant,suggesting great potential for improving and controlling water transport.Our results not only provide a novel understanding of nanoconfined water friction but are also instructive for friction control and water transport.
基金supported by the National Natural Science Foundation of China(Nos.52175430 and 52105478)the Graduate Innovation Foundation Program of Tianjin(No.2021YJSB178).
文摘Friction energy consumption is the primary cause of energy loss in rolling bearings,and friction characteristics are critical indicators of rolling bearing quality.To comprehensively understand the friction characteristics of ball bearings,the equivalent friction coefficient was proposed,and a reliable measurement method was studied.This new solution addressed the difficulty of measuring the friction characteristics of ball bearings highlighted by friction torque.The angular speeds of various components in the rolling bearings were derived using a quasistatic approach.The angular speed relationships among various components of the rolling bearings were subsequently analyzed.A kinetic energy dissipation model for the measuring system was ultimately obtained.A novel apparatus for measuring the rolling bearing equivalent friction coefficient was established.The spindle only underwent angular speed attenuation due to friction of the tested bearing without the use of power,and the variation in kinetic energy was monitored in real time with a highprecision speed sensor.After that,the equivalent friction coefficients of the measured bearings were examined.The effects of speed,load,and lubrication on the equivalent friction coefficient of the tested bearing were studied.The findings demonstrated that,to some extent,the equivalent friction coefficient increased with an increase in spindle speed and decreased with increasing load.The equivalent friction coefficient also increased with increasing kinematic viscosity of the lubrication oil,and the friction coefficient for dry friction was greater than that with 50 oil(with a kinematic viscosity of 50 mm^(2)/s)but slightly lower than that with 70 oil(with a kinematic viscosity of 70 mm^(2)/s).With this method,an accurate and comprehensive understanding of the friction characteristics of ball bearings is achieved.
基金the National Natural Science Foundation of China(Nos.52127811,52035003,51575104,51705074,52175161,and T2321002)the Natural Science Foundation of Jiangsu Province(No.BK20222005)for financial supportthe Southeast University“Zhongying Young Scholars”Project.
文摘Traditionally,the friction force has been the benchmark for quantifying energy dissipation in frictional phenomena.In this study,we introduce an atomic chain friction model that illuminates the conversion of kinetic energy into potential energy through interfacial forces.The energy dissipation process is characterized by the release of partial potential energy in the form of phonons,quantifiable by a frictional damping coefficient.We have determined that this damping coefficient is significantly influenced by the intrinsic dynamic properties of the friction system.To expand on this foundation,we formulate an advanced phononic friction model that accurately predicts the friction forces measured using an atomic force microscope(AFM).Our model reveals that energy dissipation is caused by vibrations occurring both parallel and perpendicular to the sliding motion.These findings profoundly enhance our understanding of the basic mechanics of friction and open new avenues for innovative strategies for the active management and reduction of energy dissipation in diverse mechanical systems.
基金the financial support of the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB0470103)the Key Research and Development Program in Shandong Province(No.SYS202203)+5 种基金the National Natural Science Foundation of China(Nos.52275219,U21A2046,52205230,52205233)the Program for Taishan Scholars of Shandong Province(No.ts20190965)the Key Research Program of the Chinese Academy of Sciences(No.ZDBS-ZRKJZ-TLC010)the Western Light Project of CAS(No.xbzg-zdsys-202118)Major Science and Technology Projects in Gansu Province(No.22ZD6GA002)the Major Program of the Lanzhou Institute of Chemical Physics,CAS(No.ZYFZFX-5).
文摘The stable operation of friction pairs is one of the most critical factors to maintain the stable operation of mechanical equipment.The real-time monitoring of lubrication state of the friction pair is very important to ensure the normal operation of machinery and realize early warning of wear failure,but it is also a big challenge.In this article,a new lubrication insitu monitoring system is designed,which can monitor the lubrication and wear state of friction pairs through triboelectrification.The current acquisition module and friction coefficient acquisition module are integrated into a high vacuum hydrodynamic oil film thickness measuring instrument to explore the intrinsic relationship between triboelectricity and friction coefficient curves.When severe wear occurs,the oil film at the interface of the friction pair is no longer complete,and the accumulated triboelectric charge at the interface of the friction pair breaks down the air and causes discharge,the friction current suddenly increases from nanoampere level to microampere level.The time node when discharge occurs at the steel ball interface is well consistent with the time node when the friction pair suffers serious wear.According to the corresponding relationship between the triboelectric current and the friction and wear status of the friction pair,an early wear warning monitoring system is designed to monitor the operating status of the friction pair in real time through triboelectric signals.When the mechanical friction pair is worn,the early warning system will send out sound and light alarm signals and send real-time warnings to the mobile terminal through the Internet of Things,providing a new and reliable method for real-time monitoring of friction and wear of grease-lubricated machinery.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB 0470303)the National Natural Science Foundation of China(No.52305225 and 51935012)the Chinese Academy of Sciences Project for Young Scientists in Basic Research(No.YSBR-023).
文摘Recently,the focus of materials research has shifted toward intelligent materials and structures with customizable properties and stimulus-responsive functions.Here,a recyclable thermosetting epoxy resin with self-reported wear and customizable friction is achieved through dynamic and reversible molecular structure design.The epoxy vitrimer displays exceptional mechanical properties,with a Young's modulus of 2.3 GPa,elongation at break of 7.1%,and tensile strength of 79.25 MPa.Based on the reversible exchange of dynamic covalent bonds,the epoxy vitrimer can be fully recovered through hot pressing without the need for additional adhesives or catalysts,and even self-healing can be achieved.Furthermore,by utilizing the reversibility of dynamic covalent bonds,nanofillers(graphene oxide(GO)and polytetrafluoroethylene(PTFE))with specific tribological properties are incorporated into the recovery process to achieve customizable friction coefficients and wear rates.The self-reported characteristics of wear based on sulfur radicals are realized by exploiting the dynamic nature of disulfide bonds.The correlation between wear time and wear state is investigated.The molecular structure design of epoxy based on dynamic covalent bonds has resulted in a versatile thermosetting material with self-reporting and customizable friction properties that is ideal for sustainable engineering and friction applications.This enables intelligent manufacturing while reducing resource waste.
文摘This study investigates the effect of various tread designs to enhance grip on both dry and wet friction,aiming to reduce slip and fall accidents,especially in slipprone workplaces and among the elderly.The research involves analyzing frictional performance and deformation characteristics through dry and wet friction testing.Computeraided design(CAD)software was used to create digital models of various tread patterns,and two different additive manufacturing(AM)techniques,fused filament fabrication(FFF)and stereolithography(SLA)printing,were used for three-dimensional(3D)print block samples with tread patterns,and the materials used were thermoplastic rubber(TPR)filament and photocurable elastomeric resin.A specialized friction testing machine was used to measure the friction force of the treads on a glass surface under dry and wet conditions.A high-speed camera recorded the treads’deformation and water drainage during testing.The results revealed the influence of tread pattern designs with two different rubber-like materials on friction and deformation,as well as performance on various contact surfaces.
基金supported by the Swedish Olympic Committee(SOK)and the Kempe Foundation#JCK-2107.
文摘In the Olympic winter sports cross-country skiing and the biathlon,athletes aim to minimise resistive forces such as aerodynamic drag,gravity,and ski–snow friction to enhance performance.Ski-snow friction is complex,involving multiple friction mechanisms that vary depending on snow conditions.In cold environments,where the moisture and water content are minimal,friction is presumably influenced primarily by dry interactions between the ski and snow,particularly through adhesion and abrasion at the micro-scale.Here,we examined ski-snow friction under cold conditions using eight pairs of cross-country skis,with different apparent contact lengths and real contact areas.Our findings revealed that apparent contact length,a macro-scale parameter,had the greatest impact on friction,followed by total real contact area,which is a multi-scale parameter.For snow temperatures below approximately−10℃,longer apparent contact lengths reduced friction,whereas shorter lengths are more effective above−10℃.In addition,at−3℃,minimising the total real contact area was advantageous for reducing friction,while this effect diminished at−8.5℃.At the coldest tested temperature of−13℃,a larger total real contact area resulted in the lowest friction.These findings highlight the importance of considering both macro-and micro-scale contact properties for optimising ski performance in different cold conditions.
基金support from Deutsche Forschungsgemeinschaft(DFG)(Grant Nos.PO 810/55-3,PO 810/63-2,PO 810/69-1,and PO 810/71-1).
文摘This paper presents an overview of the role of adhesion in various tribological phenomena.We discuss(1)adhesion and adhesive hysteresis in rough contacts,(2)adhesive contribution to dry friction,(3)properties of adhesive contacts under tangential loading,(4)“negative adhesion”and superlubricity,and(5)adhesive wear.Based on theoretical considerations,simulations with the boundary element method and experiments,we argue that the key process underlying all these phenomena is jump-like changes of the contact boundary.These jumps are an essential property of adhesive contacts and are solely responsible for energy dissipation in both adhesive hysteresis and adhesive friction.On the mesoscale,the aforementioned instabilities give rise to boundary line friction,which forms a convenient tool for understanding the properties of adhesive contacts both under normal and tangential loading,including changes of contact area and the phenomenon of the“sticking zone”.On the macroscale,the concept of boundary line friction can be approximated by simple adhesive contact with two different works of adhesion—a smaller one for closing the adhesive crack(attachment)and a larger one for opening it(detachment).The well-known equivalence between the adhesive contact boundary and the Griffith crack also leads to the application of the same ideas to wear.In this context,we discuss the modified Rabinowicz criterion for wear particle formation and argue that the adhesive nature of wear all but rule out Archard’s law.Finally,we note that adhesive forces are not necessarily attractive and discuss how“negative”,i.e.,repulsive,adhesion can account for the phenomenon of superlubricity.
基金supported by the Swedish Olympic Committee(SOK)and the Kempe Foundation#JCK-2107.
文摘In cross-country skiing,athletes expend large amounts of energy to overcome friction as their skis interact with snow.Even minor reductions in the friction can significantly influence race outcomes.Over the years,researchers have found many ways of quantifying ski–snow friction,but there are only a few methods that consider the glide of real-sized skis under natural conditions during both accelerating and decelerating movements.This study introduces a novel experimental setup,consisting of a sled equipped with authentic cross-country skis and a base station that uses satellite receivers to communicate via radio,constituting a real-time kinematic positioning system with centimetre accuracy.While the sled was running on a classic ski track with natural height variations,altitude and velocity data were recorded for quantification of the coefficient of friction(COF),both for accelerating and decelerating motion,employing a model based on Newton’s second law.The results show that the COF during acceleration was more than 20%higher than during deceleration,demonstrating dynamic changes in the frictional behaviour between these phases.This finding is crucial for the execution of all types of cross-country skiing techniques,where the athlete either accelerates or decelerates while moving forward.The ability of the current experimental set-up to distinguish between the COF during acceleration and deceleration has considerable implications for further developments.
基金support from the National Natural Science Foundation of China(No.52475216)the National Key R&D Program of China(No.2023YFE0206300)+1 种基金the Natural Science Foundation of Shaanxi Province(No.2024RSCXTD-62)the Research Fund of the State Key Laboratory of Solidification Processing(NPU)(No.2022-QZ-04).
文摘Monolayer MoS_(2)has garnered significant interest because of its exceptional optoelectronic and tribological properties and potential application as a lubrication layer in micro-and nanoelectromechanical systems.Although the nanotribological performance of chemical vapor deposition(CVD)-grown MoS_(2)and the characteristics associated with CVD growth have been extensively studied,challenges remain in designing specific regions on the monolayer MoS_(2)surface with reduced friction.Here,we develop nuclei with an onion-shell structure on CVD-grown monolayer MoS_(2)to achieve remarkable friction and adhesion reduction.These nuclei,dispersed on high-quality and crystalline MoS_(2),consist of an oxi-sulfide core surrounded by a multilayer MoS_(2)shell.Lateral force microscopy results indicate that onion-shell nuclei create an ensemble effect that decreases friction and adhesion by up to 45%and 20%,respectively,compared with those of MoS_(2)because of the multilayer structure and in-plane tensile strain,both of which minimize out-of-plane deformation.Derjaguin–Müller–Toporov(DMT)model calculations and step-down load‒friction correlations illustrate that the work of adhesion,shear strength,and coefficient of friction on the nucleus decrease by more than 22%,19%,and 34%,respectively,compared with those on MoS_(2).The onion-shell nucleus presents a novel lubrication strategy to mitigate friction and adhesion in CVD-grown two-dimensional(2D)materials,with potential applications in lubricating nanoscale friction pairs.
基金supported by the Russian Science Foundation(No.19-79-20012).
文摘Wearless sliding friction in the lack of lubrication remains one of the primary goals of scientific research,as wear greatly reduces the life of mechanical components.While ultralow wear is achievable in sliding friction with proper hydrodynamic lubrication or at microscale normal loads,it remains a significant challenge to overcome wear under high normal loads,high sliding speeds,and in boundary lubrication or dry sliding friction.This paper introduces an approach to significantly mitigate wear in plain bearings operating under boundary lubrication at high normal forces and sliding speeds.The plain bearings were constructed from steel shafts tested against different materials.The surfaces of the steel shafts were alloyed with bismuth oxide using a novel high-energy short-pulse laser treatment.In order to incorporate the bismuth oxide into the surface layers of the steel,MnO_(2)was utilized as a carrier.Ultralow wear was observed for the Bi-alloyed steel disk sliding against aluminum countersurface at normal loads up to 250 N(~5 MPa)and a sliding speed up to 9 m/s under extreme lack of lubrication.Achieving ultralow coefficient of friction(COF)and ultralow wear depends on eliminating adhesion between sliding surfaces,reducing the mechanical component of friction through diamond burnishing,and ensuring high fatigue endurance.The results of tribological tests demonstrate an exception to the Frenkel–Kontorova–Tomlinson model for wearless friction.The test results for Bi-alloyed steel–aluminum pair offer a new approach for a wide range of applications.
基金supported by the National Natural Science Foundation of China(Nos.52575239,12472372,and 12272051)the Science Challenge Project(No.TZ20250001)+1 种基金the Tribology Science Fund of the State Key Laboratory of Tribology in Advanced Equipment(No.SKLTKF22A01)the funding from the Sichuan Science and Technology Program(Nos.2024NSFSC0147 and 2024NSFTD0019).
文摘Modifying the surface properties of energetic materials with coating has theoretical and practical significance in the field of their application.Wax,in its role as a functional lubrication layer,has extensive utility in mitigating the sensitivity of explosives to external stimuli.This study aims to investigate the friction behavior and temperature rise ofβ-octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine(β-cyclotetramethylenetetranitramine,orβ-HMX)crystals with and without the wax coating,and the friction coefficient,frictional temperature rise,and frictional work-heat conversion rate were systematically analyzed.The experimental results show that regardless of single and reciprocating scratch conditions,the wax coating significantly reduced the coefficient of friction of theβ-HMX surface by up to 63%and effectively suppressed the temperature rise during friction by up to 83%.Further analyses reveal that under single scratch conditions,the frictional work-heat conversion rate of the pristineβ-HMX surface is approximately 42%,whereas that of the wax-coated surface increases to about 30%with the frictional power density,which involves the contact pressure,sliding speed,and friction coefficient.In contrast,under reciprocating scratch conditions,the frictional work-heat conversion rate of the uncoatedβ-HMX surface decreases with increasing number of sliding cycles,which is related to the increase in surface temperature and potential surface damage.The frictional work-heat conversion rate of wax-coated surfaces increases with increasing number of sliding cycles until the contact pressure is high enough that the lubricating effect of the wax layer diminish and the conversion rate begin to decrease.The obtained results not only pave the way for understanding the friction energy regulation and desensitization mechanism of wax on the surface of energetic crystals at the micro and quantitative levels but also provide a necessary basis for establishing friction hotspot models under dry friction and wax lubrication conditions from the aspects of friction characteristic parameters,frictional temperature rise,and the work-heat conversion rate.
基金the Science Fund of Shandong Laboratory of Advanced Materials and Green Manufacturing at Yantai(No.AMGM2024F18)funding from the China Postdoctoral Science Foundation and the National Natural Science Foundation of China(No.21838004)+2 种基金the Center of Analytical Facilities,Nanjing University of Science and Technology,for supporting the AFM measurementssupport from the Postgraduate Research&Practice Innovation Program of Jiangsu Provincethe financial support from the Swedish Research Council(No.2018-04133).
文摘Driven by the potential applications of ionic liquid(IL)flow for charging graphene-based surfaces in many emerging technologies,recent research efforts have focused on understanding ion dynamics and structuring at IL–graphene interfaces.Here,graphene colloid probe(GrP)atomic force microscopy(AFM)was used to probe the dynamics and ion structuring of 1-butyl-3-methylimidazolium tetrafluoroborate at graphene surfaces under various bias voltages.In particular,the AFM-measured nanofriction provides a good measure of the dynamic properties of the ILs at graphene surfaces.Compared with the IL at the unbiased graphene surface(0 V),the charged graphene surfaces with either negative(-1,-2 V)or positive(+1,+2 V)voltages favor a reduction in the friction coefficient by the IL.A higher magnitude of the bias voltage applied on the graphene surface with either sign(-2 or+2 V)results in a smaller friction coefficient than that at -1 and+1 V.In combination with the AFM-probed contact stiffness,adhesion forces,and ion structuring force curves with an ion orientational distribution according to molecular dynamics(MD)simulations,we discovered that the unbiased graphene surface(0 V)possesses randomly structured IL ions and that the graphene colloid probe is more likely to become stuck,resulting in more energy dissipation to contribute to a larger friction coefficient.Biasing of the graphene surface under either negative or positive voltages resulted in uniformly arranged ions,which produced a more ordered ion structure and,thus,a smoother sliding plane to reduce the friction coefficient.Electrochemical impedance spectroscopy(EIS)for the IL with graphene as an electrode demonstrated a greater ionic conductivity in the IL paired with the biased graphene than in the unbiased one,implying faster ion movement at the charged graphene,which is beneficial for reducing the friction coefficient.
基金supported by the National Natural Science Foundation of China(No.52335004).
文摘Changes in the components of synovial fluid in the human body have an important influence on the tribological behavior of artificial joints.Based on the concentration of components in the synovial fluid after arthroplasty,“hard−soft”joint pair materials composed of cobalt‒chrome‒molybdenum(CoCrMo)and highly crosslinked polyethylene(XLPE)were used as the research objects.Composite synovial fluid containing different concentrations of albumin(Alb),γ-globulin(γ-Glo),hyaluronic acid(HA),and phospholipids(PLs)was prepared.By studying the influence mechanism of single component concentration changes on the tribological properties of joint pair materials,the friction and wear behavior of joint pair materials in different composite synovial fluids are systematically explored.The coupling mechanism among the components is clarified,and the wear mechanism of the joint pair materials under different composite synovial fluids is revealed.In addition,the results of 2 million in vitro simulated wear experiments of CoCrMo‒XLPE artificial joints in composite synovial fluid were further studied.Furthermore,this study validated the influence of the concentration of the composite synovial fluid on the friction and wear properties of artificial joints under actual working conditions.The results show that the four main components in the composite synovial fluid have a great influence on the friction and wear properties of the“hard–soft”joint pair materials.When the concentration of PL increased from 0 to 0.45 mg/mL,the wear rate decreased by 69.6%,and the coefficient of friction(COF)decreased by 63.3%.The coupling mechanism between PLs,HA,and proteins significantly affects the adsorption of the membrane and affects the tribological behavior of the artificial joint.In addition,the simulated wear results of artificial joints in composite synovial fluid are consistent with those of friction and wear testers.The concentration of each component in the composite synovial fluid significantly affects the lubrication of the artificial joint,and the degree of influence becomes more obvious during long-term service.In summary,this study provides a theoretical basis for the study of composite synovial fluid and the improvement of the lubrication performance of artificial joints and is highly important for prolonging the service life of artificial joints.
基金funded by the Commercialization Promotion Agency for R&D Outcomes(2023-21040102-00)conducted with the support of the Korea Institute of Industrial Technology as Regional Bearing Industrial Development&Competitiveness Support on Manufacturing Technology(Kitech-UR-24-0015).
文摘The importance of reducing energy-related environmental and economic issues by extending the lifetime and efficiency of mechanical systems has increased.The use of ultralow friction composite materials is one approach to eliminate frictional wear.Polytetrafluoroethylene(PTFE)has excellent low friction properties and has been used to reduce frictional wear in various industrial fields.However,degradation of PTFE in natural environments poses challenges owing to its stable chemical structure,which is characterized by strong C-F bonds.Furthermore,PTFE can accumulate in the living body and environment over a long period of time.Consequently,it is resistant to physiological filtration or decomposition.Hence,it is sometimes called a"forever chemical".Therefore,PTFE,which is a type of poly-and perfluoroalkyl substance(PFAS),is increasingly being adopted as a regulated substance.This review focuses on several aspects of PTFE and PFAS,reasons for their adoption as regulated chemicals,and research onalternatives toPTFE,particularlytheuseof liquid lubricants.
基金supported by the National Key R&D Program of China(No.2022YFB3708000).
文摘Nickel foam(NF)-polytetrafluoroethylene(PTFE)interpenetrating phase composites(IPCs)were prepared via vacuum-assisted emulsion impregnation and free sintering.The effects of the pores per inch(PPI)of the NFs on the microstructure,mechanical properties,thermal conductivity,and tribological properties were investigated.The results indicated that the incorporation of a three-dimensional Ni skeleton inhibited heat accumulation at the friction interface,and the thermal conductivity and wear resistance of the composite significantly improved with increasing PPI.Compared with those of the PTFE matrix,the thermal conductivity of the 80 PPI NF-PTFE IPCs improved by~394%and the wear rate decreased by up to~66%.
基金financially supported by the National Natural Science Foundation of China(Nos.52175204 and 52305237)the Innovation Team of Jiangsu Province(No.JSSCTD202241)+1 种基金the Foreign Expert Program of the Ministry of Science and Technology of China(No.G2023142001L)the Open Fund of the State Key Laboratory of Solid Lubrication,Lanzhou Institute of Chemical Physics,Chinese Academy of Sciences(No.LSL-2310).
文摘Surface graphitization is an effective method for improving the friction performance of amorphous carbon(a-C)films.However,traditional modified methods,such as metal catalysis,addition of extra graphite or graphene,and annealing,often have drawbacks,such as complex operation,structural damage to the graphitized layer and intrinsic a-C films.In this study,a novel approach is explored to achieve in-situ surface graphitization of a-C films by short-term laser irradiation.In particular,as a key parameter,the influence of laser irradiation power on the surface graphitization structure and the mechanical and tribological properties of a-C films was emphasized.The results indicate that surface in-situ graphitization is successfully obtained on the surface of a-C films by laser irradiation and the surface graphitization degree is positively correlated with the laser irradiation power.Importantly,an obviously curled graphene structure is formed on the a-C films after laser irradiation.Compared with those of the intrinsic a-C film,the hardness and elastic modulus of the graphitized film surface obviously decrease after laser irradiation but without significantly deteriorated internal mechanical properties of the a-C film and also decrease gradually with increasing laser power,which is related to the increase in the sp2-C structure.Notably,in-situ surface graphitization induced by laser irradiation obviously reduces friction,which can be reduced by 25.41%compared with the intrinsic a-C film.This is attributed to the fast formation of the graphitized transfer film,which facilitates the transition of the friction interface from graphitized a-C surface/Al2O3 to graphitized a-C surface/graphitized transfer film.
文摘Frictional contact between biological tissues is of critical importance in biomechanics and clinical treatment strategies,which is particularly relevant to diarthrodial joints,where articular cartilage surfaces undergo reciprocal contact loading for thousands of cycles per day.Taking the temporomandibular joint(TMJ)as an example,mandibular resection and reconstruction significantly alter the masticatory system and impact its biomechanical conditions.Clinical evidence indicates that pain is more frequent in the contralateral TMJ after this kind of surgery.However,there has been limited analysis of TMJ biomechanics following reconstructive surgery to date.Therefore,our study aimed to investigate the effects of masticatory muscle loss on stress distribution in the TMJs,determine an optimum loading region to mitigate excessive stress in the contralateral TMJ,and explore how the frictional change influences the biomechanics of the TMJ.The results demonstrate that the loss of masticatory muscles on the ipsilateral side due to resection can increase contact pressure in the contralateral TMJ and that incisor and ipsilateral dental implant occlusal loading generates the most desired stress patterns in the contralateral TMJ.This study reveals that the excessive contact pressure could increase the real contact area in the joint and further cause a transition from fluid film lubrication to solid contact,leading to increased friction and wear.This work sheds some light on asymmetric anatomy and frictional condition changes arising from surgery,which contribute to stress concentration in the contralateral TMJ and may be associated with degenerative changes.These findings hold significant clinical implications for selecting an optimal and patient-specific occlusal loading to mitigate excessive contact pressure and potential damage in the articular joint.
基金supported by National Science Foundation of China(Grant Nos.11932004 and HWG2022001)Opening Fund of State Key Laboratory of Nonlinear Mechanics.
文摘A detailed review of various fractal models used in tribology is presented.The analysis of the models is based on the use of the Cantor–Borodich(CB)profile and its modifications.This profile and related models may be studied analytically and,therefore,they provide us with tools for rigorous analysis of fractal approaches to description of surface roughness and corresponding contact problems.In turn,this allows us to present a critical review of current fractal approaches to tribology.It will be demonstrated that fractal dimension alone cannot give a full description of surface roughness,however,some of these models may reflect the multilevel hierarchical structure of real surface roughness.This review helps to avoid the repetition of common erroneous statements about the use of fractal concepts in tribology.
基金supported by National Natural Science Foundation of China(Nos.52405239,52335004,and 52475233)the Open Fund of State Key Laboratory of Solid Lubrication,Lanzhou Institute of Chemical Physics(No.LSL-2402)+1 种基金the Fundamental Research Funds for the Central Universities(No.2024QN11044)the Jiangsu Funding Program for Excellent Postdoctoral Talent.
文摘Hydrogels with high water content,excellent permeability,and biocompatibility are widely used in the biomedical field.In this study,an ordered structure-reinforced hydroxyapatite(HA)composite hydrogel with high water content,high strength,low friction,and fatigue resistance was developed through a molecular network design combined with temperature field-induced orientation and nano-reinforcement technology.The hydrogel has a honeycomb network with a vertically ordered orientation,showing greater network regularity,greater freedom of network cross-linking points,and enhanced flexibility and rigidity of the polymer chain.Its compressive strength is 11 MPa,compressive modulus is 5.2 MPa,friction coefficient is 0.05,and it also has excellent crack propagation and compressive fatigue resistance,exhibiting greater mechanical strength and better tribological properties.Thus,new applications of hydrogels in the biomedical field and soft biological equipment have expanded.
