Simple and efficient nanofabrication technology with low cost and high flexibility is indispensable for fundamental nanoscale research and prototyping.Lithography in the near field using the surface plasmon polariton(...Simple and efficient nanofabrication technology with low cost and high flexibility is indispensable for fundamental nanoscale research and prototyping.Lithography in the near field using the surface plasmon polariton(i.e.,plasmonic lithography)provides a promising solution.The system with high stiffness passive nanogap control strategy on a high-speed rotating substrate is one of the most attractive highthroughput methods.However,a smaller and steadier plasmonic nanogap,new scheme of plasmonic lens,and parallel processing should be explored to achieve a new generation high resolution and reliable efficient nanofabrication.Herein,a parallel plasmonic direct-writing nanolithography system is established in which a novel plasmonic flying head is systematically designed to achieve around 15 nm minimum flying-height with high parallelism at the rotating speed of 8–18 m·s^(-1).A multi-stage metasurface-based polarization insensitive plasmonic lens is proposed to couple more power and realize a more confined spot compared with conventional plasmonic lenses.Parallel lithography of the nanostructures with the smallest(around 26 nm)linewidth is obtained with the prototyping system.The proposed system holds great potential for high-freedom nanofabrication with low cost,such as planar optical elements and nano-electromechanical systems.展开更多
State Key Laboratory of New Ceramics and Fine Processing,School of Materials Science and Engineering,Tsinghua University,Beijing 100084,China Precise and effective control of light has always been pursued.For thousand...State Key Laboratory of New Ceramics and Fine Processing,School of Materials Science and Engineering,Tsinghua University,Beijing 100084,China Precise and effective control of light has always been pursued.For thousands of years,people展开更多
Polyether-etherketone(PEEK)is a corrosion-resistant material that has been widely used in aqueous lubrication.However,its anti-wear performance must be improved for its application in the industry.In this study,to imp...Polyether-etherketone(PEEK)is a corrosion-resistant material that has been widely used in aqueous lubrication.However,its anti-wear performance must be improved for its application in the industry.In this study,to improve the anti-wear performance of PEEK for aqueous boundary lubrication,PEEK/MoS_(2)composites were prepared by ball-milling and spark plasma sintering processes.A competitive MoS_(2)mechanism between the low shear strength property and the role of promoting wear debris generation influences the anti-wear performance of PEEK/MoS_(2)composites.Experiments demonstrated that the coefficients of friction(COF)and wear rate of PEEK composite with 0.25 wt%MoS_(2)were significantly reduced 68%and 94%,respectively.Furthermore,this was the first time that a PEEK composite could achieve a COF of less than 0.05 in aqueous boundary lubrication.Its anti-wear performance was verified to be better than that of PEEK/carbon fiber(CF)and Thordon composites.The PEEK/MoS_(2)composite may be a potential material for underwater equipment because of its outstanding anti-wear performance in aqueous boundary lubrication.展开更多
Corrosion and corrosive wear occur commonly on metals surface in aqueous solutions.External electric field is usually considered as one of the factors to accelerate corrosion or corrosive wear of materials in the pres...Corrosion and corrosive wear occur commonly on metals surface in aqueous solutions.External electric field is usually considered as one of the factors to accelerate corrosion or corrosive wear of materials in the presence of conventional electrolytes.This work aims to reposition widely believed perspective by experimental justification which have been conducted in aqueous solutions containing surfactants.Electric potential of metal surfaces was modulated externally within the electrochemical potential window of the metal electrode-solution-counter electrode system,which actively regulated the adsorption or desorption of surfactant molecule in the aqueous solution over the electrodes to form a molecular barrier of electron transportation across the electrode–electrolyte interface.The advantage of the approach over the anodic passivation is negligible redox reactions on the protected electrode surface while a better lubricious and wear resistant film than oxide is maintained in the meantime.Tribopairs of several metal/metal and metal/ceramic were tested by employing a ball-on-disc tribometer with anionic and cationic surfactants solutions.For anionic surfactant as the modifier,positive surface potential enables coefficient of friction to be decreased by promoting the formation of adsorption film on metal surface in aqueous solutions.For cationic surfactant,negative surface potential plays a role in decreasing the coefficient of friction.Phase diagrams of friction and wear in wide ranges of surfactant concentration and surface potential were plotted for the tested metal/metal and metal/ceramic tribopairs.These results indicate that the adsorption behavior of molecules or ions at the metal–aqueous interface can be well regulated when an external electric field is present without inducing corrosion or corrosive wear.展开更多
The reach of tribology has expanded in diverse fields and tribology related research activities have seen immense growth during the last decade.This review takes stock of the recent advances in research pertaining to ...The reach of tribology has expanded in diverse fields and tribology related research activities have seen immense growth during the last decade.This review takes stock of the recent advances in research pertaining to different aspects of tribology within the last 2 to 3 years.Different aspects of tribology that have been reviewed including lubrication,wear and surface engineering,biotribology,high tem perature tribology,and computational tribology.This review attempts to highlight recent research and also presents future outlook pertaining to these aspects.It may however be noted that there are limitations of this review.One of the most important of these is that tribology being a highly multidisciplinary field,the research results are widely spread across various disciplines and there can be omissions because of this.Secondly,the topics dealt with in the field of tribology include only some of the salient topics(such as lubrication,wear,surface engineering,biotribology,high tem perature tribology,and computational tribology)but there are many more aspects of tribology that have not been covered in this review.Despite these limitations it is hoped that such a review will bring the most recent salient research in focus and will be beneficial for the growing community of tribology researchers.展开更多
A complete understanding of the mechanism of boundary lubrication is a goal that scientists have been striving to achieve over the past century.Although this complicated process has been far from fully revealed,a gene...A complete understanding of the mechanism of boundary lubrication is a goal that scientists have been striving to achieve over the past century.Although this complicated process has been far from fully revealed,a general picture and its influencing factors have been elucidated,not only at the macroscopic scale but also at the nanoscale,which is sufficiently clear to provide effective instructions for a lubrication design in engineering and even to efficiently control the boundary lubrication properties.Herein,we provide a review on the main advances,especially the breakthroughs in uncovering the mysterious but useful process of boundary lubrication by adsorption film.Despite the existence of an enormous amount of knowledge,albeit unsystematic,acquired in this area,in the present review,an effort was made to clarify the mainline of leading perspectives and methodologies in revealing the fundamental problems inherent to boundary lubrication.The main content of this review includes the formation of boundary film,the effects of boundary film on the adhesion and friction of rough surfaces,the behavior of adsorption film in boundary lubrication,boundary lubrication at the nanoscale,and the active control of boundary lubrication,generally sequenced based on the real history of our understanding of this process over the past century,incorporated by related modern concepts and prospects.展开更多
The combined effect of boundary layer formation and surface smoothing on friction and wear rate of metallic surfaces under lubricated point contact condition was investigated. The double trend of friction coefficient ...The combined effect of boundary layer formation and surface smoothing on friction and wear rate of metallic surfaces under lubricated point contact condition was investigated. The double trend of friction coefficient variations was revealed during running-in and sub-running-in processes. The evolution of surface topography was measured on-site using white-light interference profilometer and analyzed using bearing area curves. Comprehensive theoretical equations that explicitly express the contributions of boundary friction, adhesive friction and wear have been derived, and results obtained by these equations were compared with experimental observations. It is concluded that the theoretical models are quantitatively adequate to describe the combined effect of surface smoothing due to mechanical wear and formation of boundary films on the changes in friction and wear rate during normal running-in processes.展开更多
A multi-physical signal correlation analysis method is proposed to identify the different tribological properties of materials.The acoustic emission(AE),contact resistance,and frictional force behaviors during dry sli...A multi-physical signal correlation analysis method is proposed to identify the different tribological properties of materials.The acoustic emission(AE),contact resistance,and frictional force behaviors during dry sliding between four metals,45#carbon steel,YG12 carbide,2A12 aluminum alloy,and H62 brass,have been studied.Both positive and negative correlations between the root mean square of the amplified AE(AE RMS)signal and the frictional coefficient have been found in the experiments.In addition,the AE RMS signal and the contact resistance changed with changing sliding speed and normal load in different ways.The different correlation behaviors have been attributed to diverse tribological states under different experimental conditions due to different material characteristics.The correlation analysis provides a new method of quantitatively identifying the tribological states and the AE sources during frictional interaction.The observed anomalous correlations between the AE signal and frictional coefficient should be properly considered according to the different material properties during industrial friction condition monitoring using AE technology.展开更多
Adhesive and corrosive wear at microscales are quantitatively distinguished in lifetime tests of resonant bulk-fabricated silicon microelectromechanical systems(MEMS).By analyzing the oscillation decay characteristics...Adhesive and corrosive wear at microscales are quantitatively distinguished in lifetime tests of resonant bulk-fabricated silicon microelectromechanical systems(MEMS).By analyzing the oscillation decay characteristics in different vapor environments,we find that wear is dominated by asperity adhesion during the initial stages of rubbing in dry N2 or O2/N2 mixtures;in these situations the transient wear rate is inversely proportional to the wear depth.But in water or ethanol vapors,chemical reactions between the corrosive adsorbed layer and the silicon substrate limit the wear rate to a constant.These observations are consistent with atomic explanations.The differences between adhesive and corrosive wear explain the advantages offered by lubricating with alcohol vapors rather than using dry environments for tribo-MEMS devices.Compared to ethanol,the relatively poor anti-wear effect of water vapor is explained by aggressive and rapid tribo-reactions.展开更多
Around 1,000 peer-reviewed papers were selected from 3,450 articles published during 2020–2021,and reviewed as the representative advances in tribology research worldwide.The survey highlights the development in lubr...Around 1,000 peer-reviewed papers were selected from 3,450 articles published during 2020–2021,and reviewed as the representative advances in tribology research worldwide.The survey highlights the development in lubrication,wear and surface engineering,biotribology,high temperature tribology,and computational tribology,providing a show window of the achievements of recent fundamental and application researches in the field of tribology.展开更多
Different from direct impact damage exerted by limbs of most organisms,mantis shrimps’appendages can carry out ultra-fast,powerful underwater strikes with cavitation superimposed damage to harvest hard-shelled prey.T...Different from direct impact damage exerted by limbs of most organisms,mantis shrimps’appendages can carry out ultra-fast,powerful underwater strikes with cavitation superimposed damage to harvest hard-shelled prey.The power amplification systems and cavitation generation of mantis shrimp have attracted vast attention of researchers.Much effort has been paid to developing mantis shrimp-inspired striking robots;however,none of them are capable of generating cavitation during impacting hard objects yet.In this paper,an underwater striking robot named Shrimpbot was developed to reproduce the cavitation phenomenon when striking hard objects.Shrimpbot incorporates a Latch-Mediated Spring Actuation(LaMSA)to slowly store energy and release it instantaneously.A Diamond-Shaped Four-bar Linkage(DSFL)stretches springs to more effectively store elastic energy by reducing the maximum torque requirement of the motor.This design promised an average power amplification of over 30 times of the motor.Shape optimization and hydrophobic coating on the hammerhead and hand of Shrimpbot helped to reduce the water drag.The accomplished Shrimpbot reached an impact speed of over 12 m/s,at an acceleration of 2×10^(3) m/s^(2),an impact force of more than 1200 N in water,very close to the performance of mantis shrimp.More importantly,cavitation bubbles accompanied with the impacts were observed for the first time in mantis shrimp-inspired robots.Shrimpbot ingeniously employs only one motor to accomplish the striking automatically and repeatedly for practical purposes.Shrimpbot mimics the cavitation generation skills of mantis shrimp,which could facilitate the understanding of its mechanical principles and fluid dynamics of ultra-fast power-amplified systems of mantis shrimp and even those energy storage mechanisms of jumping robots or exoskeleton robots.展开更多
Rotary near-field lithography(RNFL) technology provides a route to overcome the diffraction limit with a high throughput and low cost for nanomanufacturing. Utilizing the advantage of the passive flying of a plasmonic...Rotary near-field lithography(RNFL) technology provides a route to overcome the diffraction limit with a high throughput and low cost for nanomanufacturing. Utilizing the advantage of the passive flying of a plasmonic head, RNFL can achieve a 10 m/s processing speed with a perfect near-field condition at dozens of nanometers. The flying performance of the plasmonic flying head(PFH) is the pivotal issue in the system. The linewidth has a strong correlation with the near-field gap, and the manufacturing uniformity is directly influenced by the dynamic performance. A more serious issue is that the unexpected contact between the PFH and substrate will result in system failure. Therefore, it is important to model and analyze the flying process of the PFH at the system level. In this study, a novel full-coupled suspension-PFH-air-substrate(SPAS) model that integrates a six-degree of freedom suspension-PFH dynamics, PFH-air-substrate air bearing lubrication, and substrate vibration, is established. The pressure distribution of the air bearing is governed by the molecular gas lubrication equation that is solved by the finite element method(FEM) with a local pressure gradient based adaptive mesh refinement algorithm using the COMSOL Multiphysics software. Based on this model, three designs of the air bearing surface are chosen to study the static, dynamic, and load/unload performance to verify whether it satisfies the design requirements of RNFL. Finally, a PFH analysis solver SKLY.app is developed based on the proposed model.展开更多
Bio-inspired reversible adhesion has significant potential in many fields requiring flexible grasping and manipulation,such as precision manufacturing,flexible electronics,and intelligent robotics.Despite extensive ef...Bio-inspired reversible adhesion has significant potential in many fields requiring flexible grasping and manipulation,such as precision manufacturing,flexible electronics,and intelligent robotics.Despite extensive efforts for adhesive synthesis with a high adhesion strength at the interface,an effective strategy to actively tune the adhesion capacity between a strong attachment and an easy detachment spanning a wide range of scales has been lagged.Herein,we report a novel soft-hard-soft sandwiched composite design to achieve a stable,repeatable,and reversible strong adhesion with an easily scalable performance for a large area ranging from~1.5 to 150 cm2 and a high load ranging from~20 to 700 N.Theoretical studies indicate that this design can enhance the uniform loading for attachment by restraining the lateral shrinkage in the natural state,while facilitate a flexible peeling for detachment by causing stress concentration in the bending state,yielding an adhesion switching ratio of~54 and a switching time of less than~0.2 s.This design is further integrated into versatile grippers,climbing robots,and human climbing grippers,demonstrating its robust scalability for a reversible strong adhesion.This biomimetic design bridges microscopic interfacial interactions with macroscopic controllable applications,providing a universal and feasible paradigm for adhesion design and control.展开更多
With the development of surface and interface science and technology,methods for the online modulation of interfacial performance by external stimuli are in high demand.Switching between ultra-low and high friction st...With the development of surface and interface science and technology,methods for the online modulation of interfacial performance by external stimuli are in high demand.Switching between ultra-low and high friction states is a particular goal owing to its applicability to the development of precision machines and nano/micro-electromechanical systems.In this study,reversible switching between superlubricity and high friction is realized by controlling the electric potential of a gold surface in aqueous salt solution sliding against a SiO_(2) microsphere.Applying positive potential results creates an ice-like water layer with high hydrogen bonding and adhesion at the interface,leading to nonlinear high friction.However,applying negative potential results in free water on the gold surface and negligible adhesion at the interface,causing linear ultra-low friction(friction coefficient of about 0.004,superlubricity state).A quantitative description of how the external load and interfacial adhesion affected friction force was developed,which agrees well with the experimental results.Thus,this work quantitatively reveals the mechanism of potential-controlled switching between superlubricity and high-friction states.Controlling the interfacial behavior via the electric potential could inspire novel design strategies for nano/micro-electromechanical and nano/micro-fluidic systems.展开更多
Among the basic tribological phenomena of contact,adhesion, friction, lubrication and wear, wear remains the least scientifically understood. At the same time,wear remains one of the most important tribological phenom...Among the basic tribological phenomena of contact,adhesion, friction, lubrication and wear, wear remains the least scientifically understood. At the same time,wear remains one of the most important tribological phenomena in practice, affecting all aspects of our lives and current technologies. The impact of wear展开更多
The year 2022 marks the 10th anniversary of the founding of Friction.Friction was launched on 26 March 2013,with an aim to promote the development in tribology by publishing theoretical and experimental research works...The year 2022 marks the 10th anniversary of the founding of Friction.Friction was launched on 26 March 2013,with an aim to promote the development in tribology by publishing theoretical and experimental research works as well as monographic review articles related to surface contact,friction,wear,lubrication,adhesion,and interface science.展开更多
It is with great regret that we have to inform the readers of our journal Friction that professor Duncan Dowson has passed away.He had not been feeling well in the last few years and his condition was worsened after a...It is with great regret that we have to inform the readers of our journal Friction that professor Duncan Dowson has passed away.He had not been feeling well in the last few years and his condition was worsened after a fall.He died in hospital on 6 January 2020.This is a great loss to all of us in the tribology community and we will remember him as one of the greatest tribologists,an eminent scientist and a visionary engineer of our time.展开更多
Friction causes wear and energy dissipation of all moving parts under various operating conditions and environments.Approximately one third of the world’s primary energy consumption is attributed to friction.Friction...Friction causes wear and energy dissipation of all moving parts under various operating conditions and environments.Approximately one third of the world’s primary energy consumption is attributed to friction.Friction,as a decisive factor of energy efficiency,attracts vital interest of scientists and engineers trying to understand its origin and develop means to control friction through predictive models.Therefore,under-standing the fundamental origins and mechanisms of friction is one of the great challenges in tribology.展开更多
A short commentary on the two research articles published in Friction in 2021 is presented.Both articles reported experimental results of applications of laser surface texturing technology to the raceway of rolling el...A short commentary on the two research articles published in Friction in 2021 is presented.Both articles reported experimental results of applications of laser surface texturing technology to the raceway of rolling element bearings.After briefly reviewing the main findings of the articles,the arguable problems and distinctions between the two articles are pointed out.展开更多
基金We acknowledge the financial support by the National Natural Science Foundation of China(91623105 and 52005175)Natural Science Foundation of Hunan Province of China(2020JJ5059).
文摘Simple and efficient nanofabrication technology with low cost and high flexibility is indispensable for fundamental nanoscale research and prototyping.Lithography in the near field using the surface plasmon polariton(i.e.,plasmonic lithography)provides a promising solution.The system with high stiffness passive nanogap control strategy on a high-speed rotating substrate is one of the most attractive highthroughput methods.However,a smaller and steadier plasmonic nanogap,new scheme of plasmonic lens,and parallel processing should be explored to achieve a new generation high resolution and reliable efficient nanofabrication.Herein,a parallel plasmonic direct-writing nanolithography system is established in which a novel plasmonic flying head is systematically designed to achieve around 15 nm minimum flying-height with high parallelism at the rotating speed of 8–18 m·s^(-1).A multi-stage metasurface-based polarization insensitive plasmonic lens is proposed to couple more power and realize a more confined spot compared with conventional plasmonic lenses.Parallel lithography of the nanostructures with the smallest(around 26 nm)linewidth is obtained with the prototyping system.The proposed system holds great potential for high-freedom nanofabrication with low cost,such as planar optical elements and nano-electromechanical systems.
文摘State Key Laboratory of New Ceramics and Fine Processing,School of Materials Science and Engineering,Tsinghua University,Beijing 100084,China Precise and effective control of light has always been pursued.For thousands of years,people
基金This work was financially supported by the National Natural Science Foundation of China(Grant No.51425502).
文摘Polyether-etherketone(PEEK)is a corrosion-resistant material that has been widely used in aqueous lubrication.However,its anti-wear performance must be improved for its application in the industry.In this study,to improve the anti-wear performance of PEEK for aqueous boundary lubrication,PEEK/MoS_(2)composites were prepared by ball-milling and spark plasma sintering processes.A competitive MoS_(2)mechanism between the low shear strength property and the role of promoting wear debris generation influences the anti-wear performance of PEEK/MoS_(2)composites.Experiments demonstrated that the coefficients of friction(COF)and wear rate of PEEK composite with 0.25 wt%MoS_(2)were significantly reduced 68%and 94%,respectively.Furthermore,this was the first time that a PEEK composite could achieve a COF of less than 0.05 in aqueous boundary lubrication.Its anti-wear performance was verified to be better than that of PEEK/carbon fiber(CF)and Thordon composites.The PEEK/MoS_(2)composite may be a potential material for underwater equipment because of its outstanding anti-wear performance in aqueous boundary lubrication.
基金supported by National Natural Science Foundation of China(Grant Nos.51961145303,5191101008,and 52105193.)China Postdoctoral Science Foundation(Grant No.2021TQ0175).
文摘Corrosion and corrosive wear occur commonly on metals surface in aqueous solutions.External electric field is usually considered as one of the factors to accelerate corrosion or corrosive wear of materials in the presence of conventional electrolytes.This work aims to reposition widely believed perspective by experimental justification which have been conducted in aqueous solutions containing surfactants.Electric potential of metal surfaces was modulated externally within the electrochemical potential window of the metal electrode-solution-counter electrode system,which actively regulated the adsorption or desorption of surfactant molecule in the aqueous solution over the electrodes to form a molecular barrier of electron transportation across the electrode–electrolyte interface.The advantage of the approach over the anodic passivation is negligible redox reactions on the protected electrode surface while a better lubricious and wear resistant film than oxide is maintained in the meantime.Tribopairs of several metal/metal and metal/ceramic were tested by employing a ball-on-disc tribometer with anionic and cationic surfactants solutions.For anionic surfactant as the modifier,positive surface potential enables coefficient of friction to be decreased by promoting the formation of adsorption film on metal surface in aqueous solutions.For cationic surfactant,negative surface potential plays a role in decreasing the coefficient of friction.Phase diagrams of friction and wear in wide ranges of surfactant concentration and surface potential were plotted for the tested metal/metal and metal/ceramic tribopairs.These results indicate that the adsorption behavior of molecules or ions at the metal–aqueous interface can be well regulated when an external electric field is present without inducing corrosion or corrosive wear.
基金National N atural Science Foundation of China(Grant Nos.51635009 and 51775460)the funding of State Key Laboratory of Tribology,China(SKLT2018C05).
文摘The reach of tribology has expanded in diverse fields and tribology related research activities have seen immense growth during the last decade.This review takes stock of the recent advances in research pertaining to different aspects of tribology within the last 2 to 3 years.Different aspects of tribology that have been reviewed including lubrication,wear and surface engineering,biotribology,high tem perature tribology,and computational tribology.This review attempts to highlight recent research and also presents future outlook pertaining to these aspects.It may however be noted that there are limitations of this review.One of the most important of these is that tribology being a highly multidisciplinary field,the research results are widely spread across various disciplines and there can be omissions because of this.Secondly,the topics dealt with in the field of tribology include only some of the salient topics(such as lubrication,wear,surface engineering,biotribology,high tem perature tribology,and computational tribology)but there are many more aspects of tribology that have not been covered in this review.Despite these limitations it is hoped that such a review will bring the most recent salient research in focus and will be beneficial for the growing community of tribology researchers.
基金supported by the National Natural Science Foundation of China(NSFC)with the grant No.91123033.
文摘A complete understanding of the mechanism of boundary lubrication is a goal that scientists have been striving to achieve over the past century.Although this complicated process has been far from fully revealed,a general picture and its influencing factors have been elucidated,not only at the macroscopic scale but also at the nanoscale,which is sufficiently clear to provide effective instructions for a lubrication design in engineering and even to efficiently control the boundary lubrication properties.Herein,we provide a review on the main advances,especially the breakthroughs in uncovering the mysterious but useful process of boundary lubrication by adsorption film.Despite the existence of an enormous amount of knowledge,albeit unsystematic,acquired in this area,in the present review,an effort was made to clarify the mainline of leading perspectives and methodologies in revealing the fundamental problems inherent to boundary lubrication.The main content of this review includes the formation of boundary film,the effects of boundary film on the adhesion and friction of rough surfaces,the behavior of adsorption film in boundary lubrication,boundary lubrication at the nanoscale,and the active control of boundary lubrication,generally sequenced based on the real history of our understanding of this process over the past century,incorporated by related modern concepts and prospects.
基金partially supported by NSFC under grant No. 51635009by the State Administra-tion of Foreign Expert Affairs under grant No. DL2017QHDX001
文摘The combined effect of boundary layer formation and surface smoothing on friction and wear rate of metallic surfaces under lubricated point contact condition was investigated. The double trend of friction coefficient variations was revealed during running-in and sub-running-in processes. The evolution of surface topography was measured on-site using white-light interference profilometer and analyzed using bearing area curves. Comprehensive theoretical equations that explicitly express the contributions of boundary friction, adhesive friction and wear have been derived, and results obtained by these equations were compared with experimental observations. It is concluded that the theoretical models are quantitatively adequate to describe the combined effect of surface smoothing due to mechanical wear and formation of boundary films on the changes in friction and wear rate during normal running-in processes.
基金supported by the National Basic Research Program of China with Grant 2011CB707603the National Natural Science Foundation of China(Grant Nos.51175281 and 51323006).
文摘A multi-physical signal correlation analysis method is proposed to identify the different tribological properties of materials.The acoustic emission(AE),contact resistance,and frictional force behaviors during dry sliding between four metals,45#carbon steel,YG12 carbide,2A12 aluminum alloy,and H62 brass,have been studied.Both positive and negative correlations between the root mean square of the amplified AE(AE RMS)signal and the frictional coefficient have been found in the experiments.In addition,the AE RMS signal and the contact resistance changed with changing sliding speed and normal load in different ways.The different correlation behaviors have been attributed to diverse tribological states under different experimental conditions due to different material characteristics.The correlation analysis provides a new method of quantitatively identifying the tribological states and the AE sources during frictional interaction.The observed anomalous correlations between the AE signal and frictional coefficient should be properly considered according to the different material properties during industrial friction condition monitoring using AE technology.
基金the National Natural Science Foundation of China(NSFC,Nos.91123033 and 51021064).
文摘Adhesive and corrosive wear at microscales are quantitatively distinguished in lifetime tests of resonant bulk-fabricated silicon microelectromechanical systems(MEMS).By analyzing the oscillation decay characteristics in different vapor environments,we find that wear is dominated by asperity adhesion during the initial stages of rubbing in dry N2 or O2/N2 mixtures;in these situations the transient wear rate is inversely proportional to the wear depth.But in water or ethanol vapors,chemical reactions between the corrosive adsorbed layer and the silicon substrate limit the wear rate to a constant.These observations are consistent with atomic explanations.The differences between adhesive and corrosive wear explain the advantages offered by lubricating with alcohol vapors rather than using dry environments for tribo-MEMS devices.Compared to ethanol,the relatively poor anti-wear effect of water vapor is explained by aggressive and rapid tribo-reactions.
基金This work was financially supported by the National Natural Science Foundation of China(Nos.52225502,51922058,52035012,and U2141243).
文摘Around 1,000 peer-reviewed papers were selected from 3,450 articles published during 2020–2021,and reviewed as the representative advances in tribology research worldwide.The survey highlights the development in lubrication,wear and surface engineering,biotribology,high temperature tribology,and computational tribology,providing a show window of the achievements of recent fundamental and application researches in the field of tribology.
基金National Natural Science Foundation of China under Grant 51425502.
文摘Different from direct impact damage exerted by limbs of most organisms,mantis shrimps’appendages can carry out ultra-fast,powerful underwater strikes with cavitation superimposed damage to harvest hard-shelled prey.The power amplification systems and cavitation generation of mantis shrimp have attracted vast attention of researchers.Much effort has been paid to developing mantis shrimp-inspired striking robots;however,none of them are capable of generating cavitation during impacting hard objects yet.In this paper,an underwater striking robot named Shrimpbot was developed to reproduce the cavitation phenomenon when striking hard objects.Shrimpbot incorporates a Latch-Mediated Spring Actuation(LaMSA)to slowly store energy and release it instantaneously.A Diamond-Shaped Four-bar Linkage(DSFL)stretches springs to more effectively store elastic energy by reducing the maximum torque requirement of the motor.This design promised an average power amplification of over 30 times of the motor.Shape optimization and hydrophobic coating on the hammerhead and hand of Shrimpbot helped to reduce the water drag.The accomplished Shrimpbot reached an impact speed of over 12 m/s,at an acceleration of 2×10^(3) m/s^(2),an impact force of more than 1200 N in water,very close to the performance of mantis shrimp.More importantly,cavitation bubbles accompanied with the impacts were observed for the first time in mantis shrimp-inspired robots.Shrimpbot ingeniously employs only one motor to accomplish the striking automatically and repeatedly for practical purposes.Shrimpbot mimics the cavitation generation skills of mantis shrimp,which could facilitate the understanding of its mechanical principles and fluid dynamics of ultra-fast power-amplified systems of mantis shrimp and even those energy storage mechanisms of jumping robots or exoskeleton robots.
基金financially supported by the National Natural Science Foundation of China (NSFC) with Grant No. 51635009
文摘Rotary near-field lithography(RNFL) technology provides a route to overcome the diffraction limit with a high throughput and low cost for nanomanufacturing. Utilizing the advantage of the passive flying of a plasmonic head, RNFL can achieve a 10 m/s processing speed with a perfect near-field condition at dozens of nanometers. The flying performance of the plasmonic flying head(PFH) is the pivotal issue in the system. The linewidth has a strong correlation with the near-field gap, and the manufacturing uniformity is directly influenced by the dynamic performance. A more serious issue is that the unexpected contact between the PFH and substrate will result in system failure. Therefore, it is important to model and analyze the flying process of the PFH at the system level. In this study, a novel full-coupled suspension-PFH-air-substrate(SPAS) model that integrates a six-degree of freedom suspension-PFH dynamics, PFH-air-substrate air bearing lubrication, and substrate vibration, is established. The pressure distribution of the air bearing is governed by the molecular gas lubrication equation that is solved by the finite element method(FEM) with a local pressure gradient based adaptive mesh refinement algorithm using the COMSOL Multiphysics software. Based on this model, three designs of the air bearing surface are chosen to study the static, dynamic, and load/unload performance to verify whether it satisfies the design requirements of RNFL. Finally, a PFH analysis solver SKLY.app is developed based on the proposed model.
基金This work was supported by the National Natural Science Foundation of China(Grant No.51425502).
文摘Bio-inspired reversible adhesion has significant potential in many fields requiring flexible grasping and manipulation,such as precision manufacturing,flexible electronics,and intelligent robotics.Despite extensive efforts for adhesive synthesis with a high adhesion strength at the interface,an effective strategy to actively tune the adhesion capacity between a strong attachment and an easy detachment spanning a wide range of scales has been lagged.Herein,we report a novel soft-hard-soft sandwiched composite design to achieve a stable,repeatable,and reversible strong adhesion with an easily scalable performance for a large area ranging from~1.5 to 150 cm2 and a high load ranging from~20 to 700 N.Theoretical studies indicate that this design can enhance the uniform loading for attachment by restraining the lateral shrinkage in the natural state,while facilitate a flexible peeling for detachment by causing stress concentration in the bending state,yielding an adhesion switching ratio of~54 and a switching time of less than~0.2 s.This design is further integrated into versatile grippers,climbing robots,and human climbing grippers,demonstrating its robust scalability for a reversible strong adhesion.This biomimetic design bridges microscopic interfacial interactions with macroscopic controllable applications,providing a universal and feasible paradigm for adhesion design and control.
基金the National Natural Science Foundation of China(Nos.51901112 and 51425502)China Postdoctoral Science Foundation(No.2018M630145)the Major Scientific Research and Development Project in Jiangxi(No.20173ABC28008).
文摘With the development of surface and interface science and technology,methods for the online modulation of interfacial performance by external stimuli are in high demand.Switching between ultra-low and high friction states is a particular goal owing to its applicability to the development of precision machines and nano/micro-electromechanical systems.In this study,reversible switching between superlubricity and high friction is realized by controlling the electric potential of a gold surface in aqueous salt solution sliding against a SiO_(2) microsphere.Applying positive potential results creates an ice-like water layer with high hydrogen bonding and adhesion at the interface,leading to nonlinear high friction.However,applying negative potential results in free water on the gold surface and negligible adhesion at the interface,causing linear ultra-low friction(friction coefficient of about 0.004,superlubricity state).A quantitative description of how the external load and interfacial adhesion affected friction force was developed,which agrees well with the experimental results.Thus,this work quantitatively reveals the mechanism of potential-controlled switching between superlubricity and high-friction states.Controlling the interfacial behavior via the electric potential could inspire novel design strategies for nano/micro-electromechanical and nano/micro-fluidic systems.
文摘Among the basic tribological phenomena of contact,adhesion, friction, lubrication and wear, wear remains the least scientifically understood. At the same time,wear remains one of the most important tribological phenomena in practice, affecting all aspects of our lives and current technologies. The impact of wear
文摘The year 2022 marks the 10th anniversary of the founding of Friction.Friction was launched on 26 March 2013,with an aim to promote the development in tribology by publishing theoretical and experimental research works as well as monographic review articles related to surface contact,friction,wear,lubrication,adhesion,and interface science.
文摘It is with great regret that we have to inform the readers of our journal Friction that professor Duncan Dowson has passed away.He had not been feeling well in the last few years and his condition was worsened after a fall.He died in hospital on 6 January 2020.This is a great loss to all of us in the tribology community and we will remember him as one of the greatest tribologists,an eminent scientist and a visionary engineer of our time.
文摘Friction causes wear and energy dissipation of all moving parts under various operating conditions and environments.Approximately one third of the world’s primary energy consumption is attributed to friction.Friction,as a decisive factor of energy efficiency,attracts vital interest of scientists and engineers trying to understand its origin and develop means to control friction through predictive models.Therefore,under-standing the fundamental origins and mechanisms of friction is one of the great challenges in tribology.
文摘A short commentary on the two research articles published in Friction in 2021 is presented.Both articles reported experimental results of applications of laser surface texturing technology to the raceway of rolling element bearings.After briefly reviewing the main findings of the articles,the arguable problems and distinctions between the two articles are pointed out.
