In the precision cutting of difficult-to-process metals,surface thermal damage to a workpiece is a significant technical challenge.Although clean minimum quantity lubrication(MQL)technology,which replaces traditional ...In the precision cutting of difficult-to-process metals,surface thermal damage to a workpiece is a significant technical challenge.Although clean minimum quantity lubrication(MQL)technology,which replaces traditional pouring cooling,is used,inadequate heat dissipation remains an issue.Cryogenic air MQL(CAMQL),an eco-friendly technology,can enhance the heat transfer performance of the lubricating film in the cutting zone,offering excellent cooling and lubrication effects.However,the influence of jet and temperature parameters on the average particle size and distribution characteristics of atomized droplets is not well understood.This study first analyzes the evolution of lubricant physical properties and establishes a quantitative mapping relationship between cryogenic air temperature and physical parameters of lubricant.Next,the unstable fluctuation in the annular liquid film at the two-phase flow nozzle exit is observed and analyzed.A thickness model of annular liquid film is developed,revealing the effect of airflow field on the annular liquid film.Finally,a model for the average particle size of atomized droplets under CAMQL is established.Numerical analysis and validation experiments under different working conditions show that the measured values align with the theoretical values.Under an air pressure of 0.4 MPa and an air flow temperature of−50℃,the droplet particle size is 133.5μm,with an error of 8.2%.The effect of air pressure on particle size is greater than that of air flow temperature.Additionally,the distribution spans of droplet size under different conditions are analyzed,and the results demonstrated that low temperatures help shorten the interval between particle sizes and improve the relative uniformity of particle size distribution.This research provides a theoretical basis for the application of CAMQL technology in the cutting process.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
The operation of a hoist is not simply constant motion,and different forms of lifting acceleration can cause changes in the tension of the steel wire rope,thereby affecting the strain and friction transmission of the ...The operation of a hoist is not simply constant motion,and different forms of lifting acceleration can cause changes in the tension of the steel wire rope,thereby affecting the strain and friction transmission of the friction lining.The coal mine environment is harsh.During the operation of a friction hoist,different media are often mixed between the friction lining and the steel wire rope.In order to explore the appropriate forms of lifting acceleration under different contact interface media and to investigate the influence of different contact interface media on the strain and friction performance of friction linings under different acceleration forms,this paper simulates the mine environment and conducts four different forms of lifting acceleration friction experiments via a dynamic micro sliding friction experimental platform with a friction lining and steel wire rope.The strain and friction performance changes of friction linings are analyzed through digital image correlation(DIC)technology.The results show that under different contact interface media,the strain change amplitude of the friction lining is the smallest under the trapezoid acceleration form,and the stability of the friction transmission is the best.Under trapezoid acceleration conditions,the friction force,friction coefficient,and strain amplitude of the friction-enhancing grease medium are the smallest,the maximum strain value decreases by 45.6%,and the friction force decreases by 64.3%,which has the greatest impact on the friction transmission performance of the friction lining.This paper provides guidance for the safe operation of friction type hoists.展开更多
Fused filament fabrication(FFF)is one of the additive manufacturing processes which has gained more interest because of its simplicity and low-cost.This technology is similar to the conventional metal injection mouldi...Fused filament fabrication(FFF)is one of the additive manufacturing processes which has gained more interest because of its simplicity and low-cost.This technology is similar to the conventional metal injection moulding(MIM)process,consisting of the feedstock preparation of metal powder and polymer binders,followed by layer-by-layer 3D printing(FFF)or injection(MIM)to create green parts and,finally,debinding and sintering.Moreover,both technologies provide near-dense parts.This work presents an in-depth study of the processing method’s influence.The porosity,microstructure,hardness,corrosion,and tribocorrosion behaviour are compared for 17-4 PH SS samples processed from powder by additive manufacturing using FFF and MIM,as well as conventional powder metallurgy(PM)samples.MIM samples exhibited the highest macro and microhardness,while corrosion behaviour was similar for both MIM and FFF samples,but superior in comparison to conventional PM samples.However,the FFF-as fabricated samples displayed a significant improvement in tribocorrosion resistance that could be explained by the higher proportion of delta ferrite and retained austenite in their microstructure.展开更多
Servo press forming machines are advanced forming systems that are capable of imparting interrupted punch motion,resulting in enhanced room temperature formability.The exact mechanism of the formability improvement is...Servo press forming machines are advanced forming systems that are capable of imparting interrupted punch motion,resulting in enhanced room temperature formability.The exact mechanism of the formability improvement is not yet established.The contribution of interrupted motion in the ductility improvement has been studied through stress relaxation phenomena in uniaxial tensile(UT)tests.However,the reason for improved formability observed when employing servo press is complicated due to the additional contribution from frictional effects.In the present work,an attempt is made to decouple the friction effect on formability improvement numerically.The improved formability is studied using a hole expansion test(HET).The limit of forming during hole expansion is modeled using the Hosford–Coulomb(HC)damage criteria,which is implemented as a user subroutine in a commercial explicit finite element(FE)software.Only the contribution of stress relaxation is accounted for in the evolution of the damage variable during interrupted loading.Therefore,the difference between simulation and experimental hole expansion ratio(HER)can be used to decouple the friction effect from the overall formability improvement during hole expansion.The improvement in HER due to stress relaxation and friction effect is different.The study showed that the model effectively captures the hole expansion deformation process in both monotonic and interrupted loading conditions.Compared to stress relaxation,friction effect played a major role during interrupted HET.展开更多
This study evaluated dry-in-place lubricants used for cold forging.A group of isothermal compression tests with a strain rate(ε)e&range of 0.001–1 s^(−1) and temperature(T)range of 30–400℃ were completed.The f...This study evaluated dry-in-place lubricants used for cold forging.A group of isothermal compression tests with a strain rate(ε)e&range of 0.001–1 s^(−1) and temperature(T)range of 30–400℃ were completed.The flow stress(σ)curves of annealed steel S45C were obtained,and a corresponding Hensel–Spittel model was developed to support finite element(FE)simulation.The sensitivity of the steady combined forward and backward extrusion(SCFBE)test proposed in another study was improved by approximately 20%after it was optimized using the results of the FE simulations.Key parameters were identified,and the calibration curves after optimization were obtained.On the basis of the optimized test,a friction testing setup with a heating system was developed,in which the die temperature could be adjusted from room temperature(RT)to 230℃.Three dry-in-place lubricants and conventional phosphating lubricant were tested,and the friction factors(m),forming loads,and ejection loads were measured.The surface features of the specimens after testing were also investigated.According to the testing results,of the three tested dry-in-place lubricants,the mica type was the best.In addition,the optimized friction testing design was verified as effective.展开更多
A thermal model of kinetic friction is assigned to a classical loaded particle moving on a fluctuating smooth surface.A sinusoidal wave resembles surface fluctuations with a relaxation time.The Hamiltonian is approxim...A thermal model of kinetic friction is assigned to a classical loaded particle moving on a fluctuating smooth surface.A sinusoidal wave resembles surface fluctuations with a relaxation time.The Hamiltonian is approximated to the mean energy of the wave describing a system of Harmonic oscillators.The quantization of amplitudes yields in terms of annihilation and creation operators multiplied by a quantum phase.Further,we consider acoustic dispersion relation and evaluate the friction coefficient from the force autocorrelation function.While the sliding particle remains classical describing a nano-particle or a tip with negligible quantum effects like tunneling or delocalization in the wave function,the quantized model of the surface fluctuations results in the temperature dependence of the kinetic friction coefficient.It follows an asymptotic value for higher temperatures and supper-slipperiness at low temperatures.展开更多
Non-dimensional similarity groups and analytically solvable proximity equations can be used to estimate integral fluid film parameters of elastohydrodynamically lubricated(EHL)contacts.In this contribution,we demonstr...Non-dimensional similarity groups and analytically solvable proximity equations can be used to estimate integral fluid film parameters of elastohydrodynamically lubricated(EHL)contacts.In this contribution,we demonstrate that machine learning(ML)and artificial intelligence(AI)approaches(support vector machines,Gaussian process regressions,and artificial neural networks)can predict relevant film parameters more efficiently and with higher accuracy and flexibility compared to sophisticated EHL simulations and analytically solvable proximity equations,respectively.For this purpose,we use data from EHL simulations based upon the full-system finite element(FE)solution and a Latin hypercube sampling.We verify that the original input data are required to train ML approaches to achieve coefficients of determination above 0.99.It is revealed that the architecture of artificial neural networks(neurons per layer and number of hidden layers)and activation functions influence the prediction accuracy.The impact of the number of training data is exemplified,and recommendations for a minimum database size are given.We ultimately demonstrate that artificial neural networks can predict the locally-resolved film thickness values over the contact domain 25-times faster than FE-based EHL simulations(R^(2) values above 0.999).We assume that this will boost the use of ML approaches to predict EHL parameters and traction losses in multibody system dynamics simulations.展开更多
Relationship between contact size(A)and static friction(f)has been studied for rigid crystalline systems.We built a series of systems with two identical surfaces but different orientations and investigated the effects...Relationship between contact size(A)and static friction(f)has been studied for rigid crystalline systems.We built a series of systems with two identical surfaces but different orientations and investigated the effects of the size and shape of the contact area on static friction.In these systems,there are numerous nontrivial commensurate contacts.Our results confirmed that the relationship between A and f was determined by both commensurability and shape of the contact.For commensurate contacts,f∝A independent of the shape.For incommensurate contacts,generally f∝A^(0) for regular shapes or f∝A^(1/4) for irregular shapes;however,in very few cases of regular shapes,f∝A^(1/2).Moreover,in above systems,commensurability of a contact can be easily changed by a perturbation of the misfit angle.Therefore,if the perturbation caused by the lateral force and the deformation of the surface are considered(as is the case in real systems),further research is necessary.展开更多
Electronic content:friction.tsinghuajournals.com,1.Manuscript submission The following types of manuscripts on all topics within the scope of the journal are welcomed:·Original research articles.
Superlubricity,or structural lubricity,is a state that has two contacting surfaces exhibiting no resistance to sliding.This effect has been theoretically described to be possible between two completely clean single cr...Superlubricity,or structural lubricity,is a state that has two contacting surfaces exhibiting no resistance to sliding.This effect has been theoretically described to be possible between two completely clean single crystalline solid surfaces.However,experimental observations of superlubricity were limited to nanoscale and under high vacuum or inert gas environments even after twenty years since the concept of superlubricity has been suggested in 1990.In the last two years,remarkable advances have been achieved in experimental observations of superlubricity ranging from micro-scale to centimeters and in ambient environment.This study aims to report a comprehensive understanding of the superlubricity phenomenon.展开更多
The mechanisms of energy dissipation are discussed in this paper by reviewing the models and research in atomic-scale friction.The study is undertaken to answer a fundamental question in the study of friction:How is f...The mechanisms of energy dissipation are discussed in this paper by reviewing the models and research in atomic-scale friction.The study is undertaken to answer a fundamental question in the study of friction:How is frictional work dissipated,particularly in cases where material damage and wear are not involved.The initiation of energy dissipation,the role of structural commensurability,and the estimation of the interfacial shear strength have been examined in detail by introducing the Tomlinson model,the Frenkel-Kontorova model,and the cobblestone model,respectively.The discussion is extended to energy dissipation progress described in terms of phononic and electronic damping.The contributions from other mechanisms of dissipation such as viscoelastic relaxation and material wear are also included.As an example,we analyzed a specific process of dissipation in multilayer graphene,on the basis of results of molecular dynamics(MD)simulations,which reveal a reversible part of energy that circulates between the system and the external driver.This leads us to emphasize that it is crucial in future studies to clearly define the coefficient of dissipation.展开更多
The mixed lubricant prepared by mixing 1-(4-ethylphenyl)-nonane-1,3-dione(0206)and chelate(0206-Fe)in a ratio of 4:6 had better tribological properties than 0206.In this study,it was found that the mixed lubricant pre...The mixed lubricant prepared by mixing 1-(4-ethylphenyl)-nonane-1,3-dione(0206)and chelate(0206-Fe)in a ratio of 4:6 had better tribological properties than 0206.In this study,it was found that the mixed lubricant prepared by mixing alkane lubricants with 0206-Fe(60%)at a ratio of 2:8 can not only achieve superlubricity,but also reduce the wear scar diameter(WSD)of the friction pairs.The mixed solution prepared by the four polar solutions with 0206-Fe(60%)cannot achieve superlubricity.The results of surface analysis and molecular dynamics(MD)simulation showed that the four polar molecules were preferentially adsorbed on the metal surface,occupying the diketone adsorption sites,and the adsorption layer formed by them cannot produce synergistic lubrication with the chelates.展开更多
Friction is a peer-reviewed international journal for the publication of theoretical and experimental research works related to the friction,lubrication and wear.Original,high quality research papers and review articl...Friction is a peer-reviewed international journal for the publication of theoretical and experimental research works related to the friction,lubrication and wear.Original,high quality research papers and review articles on all aspects of tribology are welcome,including,but are not limited to,a variety of topics,such as:Friction:Origin of friction,Friction theories,New phenomena of friction,Nano-friction,Ultra-low friction,Molecular friction,Ultra-high friction,Friction at high speed,Friction at high temperature or low temperature,Friction at solid/liquid interfaces,Bio-friction,Adhesion,etc.展开更多
Electronic content:https://www.springer.com/journal/405441.Manuscriptsubmission The following types of manuscripts on all topics within the scope of the journal are welcomed:·Original research articles.Short comm...Electronic content:https://www.springer.com/journal/405441.Manuscriptsubmission The following types of manuscripts on all topics within the scope of the journal are welcomed:·Original research articles.Short communications on topics of immediate interest.·Reviews(with the prior approval of the Editorin-Chief)Authors should submit their manuscripts using the Online Manuscript Submission,Review and Tracking System at http://mc03.manuscriptcentral.com/friction/.When submitting your manuscript,please provide names and email addresses of two suggested reviewers.展开更多
Copper,permalloy,cobalt,and silicon are the materials that have been widely utilised in magnetic devices.When the size of interest is down to the nanoscale,the inter-diffusion between certain materials becomes influen...Copper,permalloy,cobalt,and silicon are the materials that have been widely utilised in magnetic devices.When the size of interest is down to the nanoscale,the inter-diffusion between certain materials becomes influential.This paper studies the nanoscale friction characteristics between frictional pairs with and without inter-diffusion properties through the atomic force microscope.The distinct evolution features of nanoscale friction force when inter-diffusion is involved are discovered experimentally,which is also confirmed through theoretical analysis.Firstly,through the thin film deposition method,four pairs of contact materials(Cu–Ni_(81)Fe_(19),Si–Ni_(81)Fe_(19),Cu–Co,Cu–Si)are designed for friction tests,in which diffusion occurs at the interface of Cu–Ni_(81)Fe_(19)pair.Then,the effects of sliding velocity and loading force on the nano friction of each pair are measured.It is found that regardless of the diffusion phenomenon:(1)the adhesion force values exhibit a notable correlation to the values of the friction force;(2)the friction force in all four material pairs consistently increases with the growth of the normal loading force,although the growth rate may differ.In terms of the sliding velocity effect,the friction forces of immiscible materials(Si–Ni_(81)Fe_(19),Cu–Co,and Cu–Si)are found to increase with the increasing sliding velocity.However,the friction force of Cu–Ni_(81)Fe_(19),decreases with the increasing sliding velocity.Furthermore,a compositive friction model considering both the velocity and the normal force effect was proposed,which shows good agreement with the experimental results and explains the nano friction behaviour of both miscible and immiscible metals.展开更多
Efficient cooperative lubrication can be achieved via the introduction of core‒shell structure lubricant additives with hard core and soft shell,for obtaining the expected anti-wear performance from the structural cha...Efficient cooperative lubrication can be achieved via the introduction of core‒shell structure lubricant additives with hard core and soft shell,for obtaining the expected anti-wear performance from the structural changes in the friction process.In this study,C@Ag microspheres with a core‒shell structure were prepared by the redox method with carbon spheres as the core and Ag nanoparticles as the shell.Their tribological behaviors as base oil(G1830)additive with different concentrations were investigated in detail.Compared with base oil,the addition of C@Ag particles at 0.5 wt%can reduce the coefficient of friction(COF)and wear volume(Wv)up to 15.5%and 88%,respectively.More importantly,C@Ag particles provide superior lubrication performance to single additive(like carbon sphere(CS)and Ag nanoparticle).C@Ag core‒shell particles contribute to the formation of tribo-film by melt bonding of flexible Ag and carbon sphere(CS)toward excellent self-repair performance and high-efficiency lubrication.Hence,core‒shell structural nanoparticles with hard-core and soft-shell hold bright future for high-performance lubrication application.展开更多
In this paper,a semi-analytical calculation model for the coefficient of friction(COF)of single spherical protrusions is presented.It allows the prediction of the deformative friction part(μ_(def))and adhesive fricti...In this paper,a semi-analytical calculation model for the coefficient of friction(COF)of single spherical protrusions is presented.It allows the prediction of the deformative friction part(μ_(def))and adhesive friction part(μ_(def))of the friction pairings steel|polyethylene with ultra-high molecular weight(PE-UHMW)and polyoxymethylene(POM)|PE-UHMW.The experimental studies included unlubricated friction tests,which served to determine the total COF(μ_(def)),as well as tests being lubricated with silicone oil,from whichμ_(def)is obtained.Based on the verification tests,it could be shown that both states of lubrication result in the same deformation and that the relationship between the rear angle(w)andμ_(def)postulated in the calculation model is valid.Therefore,friction tests with segmented spheres were carried out,which allow a specific variation of thew.It can be concluded that for both pairings theμ_(def)is generally of minor significance(approx.1/3μ_(tot))and the influence of theμ_(adh)predominates(approx.2/3μ_(tot))the friction process.Furthermore themtot decreases with increasing contact pressure especially in the low pressure range and depends on the form of motion(continuous and discontinuous).展开更多
Surface textures with micro-scale feature dimensions still hold great potential to enhance the frictional performance of tribological systems.Apart from the ability of surface texturing to reduce friction,surface text...Surface textures with micro-scale feature dimensions still hold great potential to enhance the frictional performance of tribological systems.Apart from the ability of surface texturing to reduce friction,surface textures can also be used to intentionally increase friction in various applications that rely on friction for their adequate functioning.Therefore,this review aims at presenting the state-of-the-art regarding textured surfaces for high-friction purposes.After a brief general introduction,the recent trends and future paths in laser surface texturing are summarized.Then,the potential of surface textures to increase friction in different applications including adhesion,movement transmission and control,biomimetic applications,and road-tire contacts is critically discussed.Special emphasis in this section is laid on the involved mechanisms responsible for friction increase.Finally,current short-comings and future research directions are pointed out thus emphasizing the great potential of(laser-based)surface texturing methods for innovations in modern surface engineering.展开更多
Modeling the real contact area plays a key role in every tribological process,such as friction,adhesion,and wear.Contact between two solids does not necessarily occur everywhere within the apparent contact area.Consid...Modeling the real contact area plays a key role in every tribological process,such as friction,adhesion,and wear.Contact between two solids does not necessarily occur everywhere within the apparent contact area.Considering the multiscale nature of roughness,Persson proposed a theory of contact mechanics for a soft and smooth solid in contact with a rigid rough surface.In this theory,he assumed that the vertical displacement on the soft surface could be approximated by the height profile of the substrate surface.Although this assumption gives an accurate pressure distribution at the interface for complete contact,when no gap exists between two surfaces,it results in an overestimation of elastic energy stored in the material for partial contact,which typically occurs in many practical applications.This issue was later addressed by Persson by including a correction factor obtained from the comparison of the theoretical results with molecular dynamics simulation.This paper proposes a different approach to correct the overestimation of vertical displacement in Persson’s contact theory for rough surfaces with self-affine fractal properties.The results are compared with the correction factor proposed by Persson.The main advantage of the proposed method is that it uses physical parameters such as the surface roughness characteristics,material properties,sliding velocity,and normal load to correct the model.This method is also implemented in the theory of rubber friction.The results of the corrected friction model are compared with experiments.The results confirm that the modified model predicts the friction coefficient as a function of sliding velocity more accurately than the original model.展开更多
基金supported by the following foundation items:the National Natural Science Foundation of China(Nos.52375447 and 52205481)the Shandong Provincial Natural Science Foundation of General Program(No.ZR2024ME205)+1 种基金the Special Fund of Taishan Scholars Project(No.tsqn202408220)the Shandong Provincial Natural Science Foundation of Youth Fund(No.ZR2021QE116).
文摘In the precision cutting of difficult-to-process metals,surface thermal damage to a workpiece is a significant technical challenge.Although clean minimum quantity lubrication(MQL)technology,which replaces traditional pouring cooling,is used,inadequate heat dissipation remains an issue.Cryogenic air MQL(CAMQL),an eco-friendly technology,can enhance the heat transfer performance of the lubricating film in the cutting zone,offering excellent cooling and lubrication effects.However,the influence of jet and temperature parameters on the average particle size and distribution characteristics of atomized droplets is not well understood.This study first analyzes the evolution of lubricant physical properties and establishes a quantitative mapping relationship between cryogenic air temperature and physical parameters of lubricant.Next,the unstable fluctuation in the annular liquid film at the two-phase flow nozzle exit is observed and analyzed.A thickness model of annular liquid film is developed,revealing the effect of airflow field on the annular liquid film.Finally,a model for the average particle size of atomized droplets under CAMQL is established.Numerical analysis and validation experiments under different working conditions show that the measured values align with the theoretical values.Under an air pressure of 0.4 MPa and an air flow temperature of−50℃,the droplet particle size is 133.5μm,with an error of 8.2%.The effect of air pressure on particle size is greater than that of air flow temperature.Additionally,the distribution spans of droplet size under different conditions are analyzed,and the results demonstrated that low temperatures help shorten the interval between particle sizes and improve the relative uniformity of particle size distribution.This research provides a theoretical basis for the application of CAMQL technology in the cutting process.
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supported by the National Natural Science Foundation of China(Grant No.52105231).
文摘The operation of a hoist is not simply constant motion,and different forms of lifting acceleration can cause changes in the tension of the steel wire rope,thereby affecting the strain and friction transmission of the friction lining.The coal mine environment is harsh.During the operation of a friction hoist,different media are often mixed between the friction lining and the steel wire rope.In order to explore the appropriate forms of lifting acceleration under different contact interface media and to investigate the influence of different contact interface media on the strain and friction performance of friction linings under different acceleration forms,this paper simulates the mine environment and conducts four different forms of lifting acceleration friction experiments via a dynamic micro sliding friction experimental platform with a friction lining and steel wire rope.The strain and friction performance changes of friction linings are analyzed through digital image correlation(DIC)technology.The results show that under different contact interface media,the strain change amplitude of the friction lining is the smallest under the trapezoid acceleration form,and the stability of the friction transmission is the best.Under trapezoid acceleration conditions,the friction force,friction coefficient,and strain amplitude of the friction-enhancing grease medium are the smallest,the maximum strain value decreases by 45.6%,and the friction force decreases by 64.3%,which has the greatest impact on the friction transmission performance of the friction lining.This paper provides guidance for the safe operation of friction type hoists.
基金supported by the Ministry of Science and Innovation of Spain under the grant PID2019-109371GB-I00,and by the Junta de Castilla y Leon(VA044G19 y VA2020P20)the funding received from the pre-doctoral grant(2018/12504)with cofinancing from the Government of Castilla-La Mancha and the European Union through the European Social Fund.
文摘Fused filament fabrication(FFF)is one of the additive manufacturing processes which has gained more interest because of its simplicity and low-cost.This technology is similar to the conventional metal injection moulding(MIM)process,consisting of the feedstock preparation of metal powder and polymer binders,followed by layer-by-layer 3D printing(FFF)or injection(MIM)to create green parts and,finally,debinding and sintering.Moreover,both technologies provide near-dense parts.This work presents an in-depth study of the processing method’s influence.The porosity,microstructure,hardness,corrosion,and tribocorrosion behaviour are compared for 17-4 PH SS samples processed from powder by additive manufacturing using FFF and MIM,as well as conventional powder metallurgy(PM)samples.MIM samples exhibited the highest macro and microhardness,while corrosion behaviour was similar for both MIM and FFF samples,but superior in comparison to conventional PM samples.However,the FFF-as fabricated samples displayed a significant improvement in tribocorrosion resistance that could be explained by the higher proportion of delta ferrite and retained austenite in their microstructure.
文摘Servo press forming machines are advanced forming systems that are capable of imparting interrupted punch motion,resulting in enhanced room temperature formability.The exact mechanism of the formability improvement is not yet established.The contribution of interrupted motion in the ductility improvement has been studied through stress relaxation phenomena in uniaxial tensile(UT)tests.However,the reason for improved formability observed when employing servo press is complicated due to the additional contribution from frictional effects.In the present work,an attempt is made to decouple the friction effect on formability improvement numerically.The improved formability is studied using a hole expansion test(HET).The limit of forming during hole expansion is modeled using the Hosford–Coulomb(HC)damage criteria,which is implemented as a user subroutine in a commercial explicit finite element(FE)software.Only the contribution of stress relaxation is accounted for in the evolution of the damage variable during interrupted loading.Therefore,the difference between simulation and experimental hole expansion ratio(HER)can be used to decouple the friction effect from the overall formability improvement during hole expansion.The improvement in HER due to stress relaxation and friction effect is different.The study showed that the model effectively captures the hole expansion deformation process in both monotonic and interrupted loading conditions.Compared to stress relaxation,friction effect played a major role during interrupted HET.
基金This research was partially supported by the National Natural Science Foundation of China(NSFC,No.51875348).
文摘This study evaluated dry-in-place lubricants used for cold forging.A group of isothermal compression tests with a strain rate(ε)e&range of 0.001–1 s^(−1) and temperature(T)range of 30–400℃ were completed.The flow stress(σ)curves of annealed steel S45C were obtained,and a corresponding Hensel–Spittel model was developed to support finite element(FE)simulation.The sensitivity of the steady combined forward and backward extrusion(SCFBE)test proposed in another study was improved by approximately 20%after it was optimized using the results of the FE simulations.Key parameters were identified,and the calibration curves after optimization were obtained.On the basis of the optimized test,a friction testing setup with a heating system was developed,in which the die temperature could be adjusted from room temperature(RT)to 230℃.Three dry-in-place lubricants and conventional phosphating lubricant were tested,and the friction factors(m),forming loads,and ejection loads were measured.The surface features of the specimens after testing were also investigated.According to the testing results,of the three tested dry-in-place lubricants,the mica type was the best.In addition,the optimized friction testing design was verified as effective.
文摘A thermal model of kinetic friction is assigned to a classical loaded particle moving on a fluctuating smooth surface.A sinusoidal wave resembles surface fluctuations with a relaxation time.The Hamiltonian is approximated to the mean energy of the wave describing a system of Harmonic oscillators.The quantization of amplitudes yields in terms of annihilation and creation operators multiplied by a quantum phase.Further,we consider acoustic dispersion relation and evaluate the friction coefficient from the force autocorrelation function.While the sliding particle remains classical describing a nano-particle or a tip with negligible quantum effects like tunneling or delocalization in the wave function,the quantized model of the surface fluctuations results in the temperature dependence of the kinetic friction coefficient.It follows an asymptotic value for higher temperatures and supper-slipperiness at low temperatures.
基金support from Pontificia Universidad Católica de Chile.A.Rosenkranz gratefully acknowledges the financial support given by ANID(Chile)in the framework of the Fondecyt projects(Nos.11180121 and EQM190057)Additionally,A.Rosenkranz acknowledges the financial support given by the VID of the University of Chile within the project U-Moderniza(No.UM-04/19).
文摘Non-dimensional similarity groups and analytically solvable proximity equations can be used to estimate integral fluid film parameters of elastohydrodynamically lubricated(EHL)contacts.In this contribution,we demonstrate that machine learning(ML)and artificial intelligence(AI)approaches(support vector machines,Gaussian process regressions,and artificial neural networks)can predict relevant film parameters more efficiently and with higher accuracy and flexibility compared to sophisticated EHL simulations and analytically solvable proximity equations,respectively.For this purpose,we use data from EHL simulations based upon the full-system finite element(FE)solution and a Latin hypercube sampling.We verify that the original input data are required to train ML approaches to achieve coefficients of determination above 0.99.It is revealed that the architecture of artificial neural networks(neurons per layer and number of hidden layers)and activation functions influence the prediction accuracy.The impact of the number of training data is exemplified,and recommendations for a minimum database size are given.We ultimately demonstrate that artificial neural networks can predict the locally-resolved film thickness values over the contact domain 25-times faster than FE-based EHL simulations(R^(2) values above 0.999).We assume that this will boost the use of ML approaches to predict EHL parameters and traction losses in multibody system dynamics simulations.
基金supported by National Natural Science Foundation of China(No.51675395)Special Fund for Outstanding Young and Middle-aged Scientific and Technological Innovation Team in the University from Hubei Province(No.T201709)Doctoral Startup Fund for Scientific Research at Wuhan Polytechnic University(2014RZ31).
文摘Relationship between contact size(A)and static friction(f)has been studied for rigid crystalline systems.We built a series of systems with two identical surfaces but different orientations and investigated the effects of the size and shape of the contact area on static friction.In these systems,there are numerous nontrivial commensurate contacts.Our results confirmed that the relationship between A and f was determined by both commensurability and shape of the contact.For commensurate contacts,f∝A independent of the shape.For incommensurate contacts,generally f∝A^(0) for regular shapes or f∝A^(1/4) for irregular shapes;however,in very few cases of regular shapes,f∝A^(1/2).Moreover,in above systems,commensurability of a contact can be easily changed by a perturbation of the misfit angle.Therefore,if the perturbation caused by the lateral force and the deformation of the surface are considered(as is the case in real systems),further research is necessary.
文摘Electronic content:friction.tsinghuajournals.com,1.Manuscript submission The following types of manuscripts on all topics within the scope of the journal are welcomed:·Original research articles.
基金supports from the National Natural Science Foundation of China(NSFC)(Grant No.10832005)the the National Key Basic Research(973)Program of China(Grants Nos.2007CB936803 and 2013CB934200)are acknowledged.
文摘Superlubricity,or structural lubricity,is a state that has two contacting surfaces exhibiting no resistance to sliding.This effect has been theoretically described to be possible between two completely clean single crystalline solid surfaces.However,experimental observations of superlubricity were limited to nanoscale and under high vacuum or inert gas environments even after twenty years since the concept of superlubricity has been suggested in 1990.In the last two years,remarkable advances have been achieved in experimental observations of superlubricity ranging from micro-scale to centimeters and in ambient environment.This study aims to report a comprehensive understanding of the superlubricity phenomenon.
基金The authors would like to express their appreciations to the financial support from the National Natural Science Foundation of China under the grant Nos.of 51075526,51005129,and 51021064.
文摘The mechanisms of energy dissipation are discussed in this paper by reviewing the models and research in atomic-scale friction.The study is undertaken to answer a fundamental question in the study of friction:How is frictional work dissipated,particularly in cases where material damage and wear are not involved.The initiation of energy dissipation,the role of structural commensurability,and the estimation of the interfacial shear strength have been examined in detail by introducing the Tomlinson model,the Frenkel-Kontorova model,and the cobblestone model,respectively.The discussion is extended to energy dissipation progress described in terms of phononic and electronic damping.The contributions from other mechanisms of dissipation such as viscoelastic relaxation and material wear are also included.As an example,we analyzed a specific process of dissipation in multilayer graphene,on the basis of results of molecular dynamics(MD)simulations,which reveal a reversible part of energy that circulates between the system and the external driver.This leads us to emphasize that it is crucial in future studies to clearly define the coefficient of dissipation.
基金financially supported by National Key R&D Program of China(Grant No.2020YFA0711003)the National Natural Science Foundation of China(Grant Nos.51925506 and 52305178)the XPLORER PRIZE.
文摘The mixed lubricant prepared by mixing 1-(4-ethylphenyl)-nonane-1,3-dione(0206)and chelate(0206-Fe)in a ratio of 4:6 had better tribological properties than 0206.In this study,it was found that the mixed lubricant prepared by mixing alkane lubricants with 0206-Fe(60%)at a ratio of 2:8 can not only achieve superlubricity,but also reduce the wear scar diameter(WSD)of the friction pairs.The mixed solution prepared by the four polar solutions with 0206-Fe(60%)cannot achieve superlubricity.The results of surface analysis and molecular dynamics(MD)simulation showed that the four polar molecules were preferentially adsorbed on the metal surface,occupying the diketone adsorption sites,and the adsorption layer formed by them cannot produce synergistic lubrication with the chelates.
文摘Friction is a peer-reviewed international journal for the publication of theoretical and experimental research works related to the friction,lubrication and wear.Original,high quality research papers and review articles on all aspects of tribology are welcome,including,but are not limited to,a variety of topics,such as:Friction:Origin of friction,Friction theories,New phenomena of friction,Nano-friction,Ultra-low friction,Molecular friction,Ultra-high friction,Friction at high speed,Friction at high temperature or low temperature,Friction at solid/liquid interfaces,Bio-friction,Adhesion,etc.
文摘Electronic content:https://www.springer.com/journal/405441.Manuscriptsubmission The following types of manuscripts on all topics within the scope of the journal are welcomed:·Original research articles.Short communications on topics of immediate interest.·Reviews(with the prior approval of the Editorin-Chief)Authors should submit their manuscripts using the Online Manuscript Submission,Review and Tracking System at http://mc03.manuscriptcentral.com/friction/.When submitting your manuscript,please provide names and email addresses of two suggested reviewers.
基金the National Natural Science Foundation of China(No.52171193)China Postdoctoral Science Foundation(No.2019M652564)Henan Postdoctoral Science Foundation(No.19030013)。
文摘Copper,permalloy,cobalt,and silicon are the materials that have been widely utilised in magnetic devices.When the size of interest is down to the nanoscale,the inter-diffusion between certain materials becomes influential.This paper studies the nanoscale friction characteristics between frictional pairs with and without inter-diffusion properties through the atomic force microscope.The distinct evolution features of nanoscale friction force when inter-diffusion is involved are discovered experimentally,which is also confirmed through theoretical analysis.Firstly,through the thin film deposition method,four pairs of contact materials(Cu–Ni_(81)Fe_(19),Si–Ni_(81)Fe_(19),Cu–Co,Cu–Si)are designed for friction tests,in which diffusion occurs at the interface of Cu–Ni_(81)Fe_(19)pair.Then,the effects of sliding velocity and loading force on the nano friction of each pair are measured.It is found that regardless of the diffusion phenomenon:(1)the adhesion force values exhibit a notable correlation to the values of the friction force;(2)the friction force in all four material pairs consistently increases with the growth of the normal loading force,although the growth rate may differ.In terms of the sliding velocity effect,the friction forces of immiscible materials(Si–Ni_(81)Fe_(19),Cu–Co,and Cu–Si)are found to increase with the increasing sliding velocity.However,the friction force of Cu–Ni_(81)Fe_(19),decreases with the increasing sliding velocity.Furthermore,a compositive friction model considering both the velocity and the normal force effect was proposed,which shows good agreement with the experimental results and explains the nano friction behaviour of both miscible and immiscible metals.
基金the National Natural Science Foundation of China(Nos.52075458 and U2141211)the Sichuan Science Foundation for Distinguished Young Scholars(No.2023NSFSC1957)。
文摘Efficient cooperative lubrication can be achieved via the introduction of core‒shell structure lubricant additives with hard core and soft shell,for obtaining the expected anti-wear performance from the structural changes in the friction process.In this study,C@Ag microspheres with a core‒shell structure were prepared by the redox method with carbon spheres as the core and Ag nanoparticles as the shell.Their tribological behaviors as base oil(G1830)additive with different concentrations were investigated in detail.Compared with base oil,the addition of C@Ag particles at 0.5 wt%can reduce the coefficient of friction(COF)and wear volume(Wv)up to 15.5%and 88%,respectively.More importantly,C@Ag particles provide superior lubrication performance to single additive(like carbon sphere(CS)and Ag nanoparticle).C@Ag core‒shell particles contribute to the formation of tribo-film by melt bonding of flexible Ag and carbon sphere(CS)toward excellent self-repair performance and high-efficiency lubrication.Hence,core‒shell structural nanoparticles with hard-core and soft-shell hold bright future for high-performance lubrication application.
基金funded by the Federal Ministry of Economic Affairs and Energy(BMWi)through the“Otto von Guericke”German Federation of Industrial Research Associations(AiF)on the basis of a resolution of the German Bundestag as part of the programme to promote joint industrial research(IGF No.20967 BG).
文摘In this paper,a semi-analytical calculation model for the coefficient of friction(COF)of single spherical protrusions is presented.It allows the prediction of the deformative friction part(μ_(def))and adhesive friction part(μ_(def))of the friction pairings steel|polyethylene with ultra-high molecular weight(PE-UHMW)and polyoxymethylene(POM)|PE-UHMW.The experimental studies included unlubricated friction tests,which served to determine the total COF(μ_(def)),as well as tests being lubricated with silicone oil,from whichμ_(def)is obtained.Based on the verification tests,it could be shown that both states of lubrication result in the same deformation and that the relationship between the rear angle(w)andμ_(def)postulated in the calculation model is valid.Therefore,friction tests with segmented spheres were carried out,which allow a specific variation of thew.It can be concluded that for both pairings theμ_(def)is generally of minor significance(approx.1/3μ_(tot))and the influence of theμ_(adh)predominates(approx.2/3μ_(tot))the friction process.Furthermore themtot decreases with increasing contact pressure especially in the low pressure range and depends on the form of motion(continuous and discontinuous).
基金This work was supported by ANID-CONICYT within the project Fondecyt 11180121 and Fondequip EQM190057 as well as the VID of the University of Chile in the framework of“U-Inicia UI013/2018”HLC acknowledges financial support from Fapergs/Brazil(No.19/2551-0001849-5)+1 种基金CNPq/Brazil(No.305453/2017-3)JS thanks the German Federal Ministry of Education and Research(BMBF)for financial support in the project FH-Europa 2020:MACH-XLT(No.13FH009EX0).
文摘Surface textures with micro-scale feature dimensions still hold great potential to enhance the frictional performance of tribological systems.Apart from the ability of surface texturing to reduce friction,surface textures can also be used to intentionally increase friction in various applications that rely on friction for their adequate functioning.Therefore,this review aims at presenting the state-of-the-art regarding textured surfaces for high-friction purposes.After a brief general introduction,the recent trends and future paths in laser surface texturing are summarized.Then,the potential of surface textures to increase friction in different applications including adhesion,movement transmission and control,biomimetic applications,and road-tire contacts is critically discussed.Special emphasis in this section is laid on the involved mechanisms responsible for friction increase.Finally,current short-comings and future research directions are pointed out thus emphasizing the great potential of(laser-based)surface texturing methods for innovations in modern surface engineering.
文摘Modeling the real contact area plays a key role in every tribological process,such as friction,adhesion,and wear.Contact between two solids does not necessarily occur everywhere within the apparent contact area.Considering the multiscale nature of roughness,Persson proposed a theory of contact mechanics for a soft and smooth solid in contact with a rigid rough surface.In this theory,he assumed that the vertical displacement on the soft surface could be approximated by the height profile of the substrate surface.Although this assumption gives an accurate pressure distribution at the interface for complete contact,when no gap exists between two surfaces,it results in an overestimation of elastic energy stored in the material for partial contact,which typically occurs in many practical applications.This issue was later addressed by Persson by including a correction factor obtained from the comparison of the theoretical results with molecular dynamics simulation.This paper proposes a different approach to correct the overestimation of vertical displacement in Persson’s contact theory for rough surfaces with self-affine fractal properties.The results are compared with the correction factor proposed by Persson.The main advantage of the proposed method is that it uses physical parameters such as the surface roughness characteristics,material properties,sliding velocity,and normal load to correct the model.This method is also implemented in the theory of rubber friction.The results of the corrected friction model are compared with experiments.The results confirm that the modified model predicts the friction coefficient as a function of sliding velocity more accurately than the original model.
