In order to solve the problem of poor formability caused by different materials and properties in the process of tailor-welded sheets forming,a forming method was proposed to change the stress state of tailor-welded s...In order to solve the problem of poor formability caused by different materials and properties in the process of tailor-welded sheets forming,a forming method was proposed to change the stress state of tailor-welded sheets by covering the tailor-welded sheets with better plastic properties overlapping sheets.At the same time,the interface friction effect between the overlapping and tailor-welded sheets was utilized to control the stress magnitude and further improve the formability and quality of the tailor-welded sheets.In this work,the bulging process of the tailor-welded overlapping sheets was taken as the research object.Aluminum alloy tailor-welded overlapping sheets bulging specimens were studied by a combination of finite element analysis and experimental verification.The results show that the appropriate use of interface friction between tailor-welded and overlapping sheets can improve the formability of tailor-welded sheets and control the flow of weld seam to improve the forming quality.When increasing the interface friction coefficient on the side of tailor-welded sheets with higher strength and decreasing that on the side of tailor-welded sheets with lower strength,the deformation of the tailor-welded sheets are more uniform,the offset of the weld seam is minimal,the limit bulging height is maximal,and the forming quality is optimal.展开更多
Understanding frictional anisotropy,which refers to the variation in frictional resistance based on the shear direction,is crucial for optimizing the friction angle between a bio-inspired structure and the surrounding...Understanding frictional anisotropy,which refers to the variation in frictional resistance based on the shear direction,is crucial for optimizing the friction angle between a bio-inspired structure and the surrounding soil.Previous studies focused on estimating the interface frictional anisotropy mobilized by snakeskin-inspired textured surfaces and sand under monotonic shear loading conditions.However,there is a need to estimate interface frictional anisotropy under repetitive shear loads.In this study,a series of repetitive direct shear(DS)tests are performed with snakeskin-inspired textured surfaces under a constant vertical stress and two shear directions(cranial first half→caudal second half or caudal first half→cranial second half).The results show that(1)mobilized shear stress increases with the number of shearing cycles,(2)cranial shearing(shearing against the scales)consistently produces a higher shear resistance and less contractive behavior than caudal shearing(shearing along the scales),and(3)a higher scale height or smaller scale length of the surface yields a higher interface friction angle across all shearing cycles.Further analysis reveals that the gap between the cranial and caudal shear zones of the interface friction angle as a function of L/H(i.e.the ratio of scale length L to scale height H)continues to decrease as the number of shearing cycles approaches asymptotic values.The directional frictional resistance(DFR)decreases as the number of shearing cycles increases.Furthermore,the discussion covers the impact of initial relative density,vertical stress,and the number of shearing cycles on interface frictional anisotropy.展开更多
Ti-6Al-4V is widely used in the aviation industry because of its high strength, and good heat resistance. However, severe tool wear on the rake face occurs during the milling of Ti-6Al-4V,which is caused by intense fr...Ti-6Al-4V is widely used in the aviation industry because of its high strength, and good heat resistance. However, severe tool wear on the rake face occurs during the milling of Ti-6Al-4V,which is caused by intense friction between the tool rake face and the chips. To investigate tool wear in the milling of Ti-6Al-4V, ultrasonic vibration is introduced, and a cutting force prediction model that considers tool-chip contact interface friction behavior in Ultrasonic Longitudinal-Torsional Vibration-Assisted Milling(ULTVAM) is proposed in this paper. First, the tool tip motion trajectory and dynamic cutting thickness under ULTVAM were analyzed calculated, and compared with those in Common Milling(CM). Subsequently, the effects of ultrasonic vibration on the shear force under the ultrasonic softening effect, the friction force, and the friction reversal force on the toolchip contact interface were investigated. A dynamic milling force model under ULTVAM was established before and after friction force reversal caused by ultrasonic longitudinal-torsional vibration. Finally, numerous experiments were conducted to validate the proposed model, and the experimental results indicated that the calculated dynamic milling forces agreed well with the measured values, with errors in the X and Y directions of 5.51% and 10.23%, respectively. In addition, the average roughness of the workpiece surface also decreased(1.08, 0.9, 0.6, 0.7 μm under ultrasonic amplitudes of 0, 1, 2, and 3 μm) and the tool wear state improved on the rake face under ULTVAM.展开更多
Bumps in coal mines have been recognized as a major hazard for many years. These sudden and violent failures around mine openings have compromised safety, ventilation and access to mine workings.Previous studies showe...Bumps in coal mines have been recognized as a major hazard for many years. These sudden and violent failures around mine openings have compromised safety, ventilation and access to mine workings.Previous studies showed that the violence of coal specimen failure depends on both the interface friction and width-to-height（W/H） ratio of coal specimen. The mode of failure for a uniaxially loaded coal specimen or a coal pillar is a combination of both shear failure along the interface and compressive failure in the coal. The shear failure along the interface triggered the compressive failure in coal. The compressive failure of a coal specimen or a coal pillar can be controlled by changing its W/H ratio. As the W/H ratio increases, the ultimate strength increases. Hence, with a proper combination of interface friction and the W/H ratio of pillar or coal specimen, the mode of failure will change from sudden violent failure which is brittle failure to non-violent failure which is ductile failure. The main objective of this paper is to determine at what W/H ratio and interface friction the mode of failure changes from violent to non-violent. In this research, coal specimens of W/H ratio ranging from 1 to 10 were uniaxially tested under two interface frictions of 0.1 and 0.25, and the results are presented and discussed.展开更多
The stress wave profile at the frictional interface is crucial for investigating the frictional process.This study modeled a brittle material interface with a micro-contact to analyze the fine stress wave structure as...The stress wave profile at the frictional interface is crucial for investigating the frictional process.This study modeled a brittle material interface with a micro-contact to analyze the fine stress wave structure associated with frictional slip.Employing the finite element simulation alongside the related wave theory and experiments,two new wave structures were indentified:A Mach cone symmetric to the frictional interface associated with incident plane wave propagation,and a new plane longitudinal wave generated across the entire frictional interface at the moment when the incident wave began to propagate.The time and space of its appearance implies that the overall response of the frictional interface precedes the local wave response of the medium.Consequently,a model involving characteristic line theory and the idea of Green’s function has been proposed for its occurrence.The analysis results show that these two new wave phenomena are independent of the fracture of micro-contacts at the interface;instead,the frictional interface effect may be responsible for the generation of such new wave structures.The measured wave profiles provide a proof for the existence of the new wave structures.These results display new wave phenomena,and suggest a wave profile for investigating the dynamic mechanical properties of the frictional interface.展开更多
The scaled suction caisson repre sents an innovative design featuring a bio-inspired sidewall modeled after snake skin,commonly utilized in offshore mooring platforms.In comparison with traditional suction caissons,th...The scaled suction caisson repre sents an innovative design featuring a bio-inspired sidewall modeled after snake skin,commonly utilized in offshore mooring platforms.In comparison with traditional suction caissons,this bio-inspired design demonstrates reduced penetration resistance and enhanced pull-out capacity due to the anisotropic shear behaviors of its sidewall.To investigate the shear behavior of the bio-inspired sidewall under pull-out load,direct shear tests were conducted between the bio-inspired surface and sand.The research demonstrates that the interface shear strength of the bio-inspired surface significantly surpasses that of the smooth surface due to interlocking effects.Additionally,the interface shear strength correlates with the aspect ratio of the bio-inspired surface,shear angle,and particle diameter distribution,with values increasing as the uniformity coefficient Cudecreases,while initially increasing and subsequently decreasing with increases in both aspect ratio and shear angle.The ratio between the interface friction angleδand internal friction angle δ_(s) defines the interface effect factor k.For the bio-inspired surface,the interface effect factor k varies with shear angleβ,ranging from 0.9 to 1.12.The peak value occurs at a shear angleβof 60°,substantially exceeding that of the smooth surface.A method for calculating the relative roughness R_(N) is employed to evaluate the interface roughness of the bio-inspired surface,taking into account scale dimension and particle diameter distribution effects.展开更多
Structure-soil interface friction characteristics is of importance to investigate the interaction between engineering structures and soils,especially for offshore structures.The interface friction behavior between mar...Structure-soil interface friction characteristics is of importance to investigate the interaction between engineering structures and soils,especially for offshore structures.The interface friction behavior between marine clay and structural materials with different roughness was studied in this paper by using 3D optical scanning tests,a modified direct shear device and numerical simulation.Relationships between the surface roughness of structures,water content and interface friction angle were presented by model tests.The increase of water contents decreased the interface friction angles.For interfaces with different roughness,the interface friction angles will be smaller than that of the soil when the water content exceeds a certain value.The roughness of the interface and the water content of the soil are mutually coupled to influence the coefficient of friction(COF).This paper proposed a Finite Element Method(FEM)to simulate the interface direct shear tests of structures with different roughness.The surface models with different roughness are established based on the structure data obtained by 3D scanning.The Coupled Eulerian-Lagrangian(CEL)approach was employed to analyse soils sheared by irregular surfaces.The interface behavior for interfaces with different roughness under cyclic shear stresses was analyzed by FEM.展开更多
The friction interface matching plays a deterministic role in the motor efficiency,and the microcosmic contact status of friction interface should be investigated to improve the ultrasonic motor performance.The main p...The friction interface matching plays a deterministic role in the motor efficiency,and the microcosmic contact status of friction interface should be investigated to improve the ultrasonic motor performance.The main purpose is to improve the effective output power of ultrasonic motor.Hence,one studies the contact condition of the friction interface of the ultrasonic motor,analyzes the micro condition of contact interface through finite element analysis,optimizes unreasonable structures,and compares the two different-structure ultrasonic motors through experiments.The results reflect the necessity of optimization.After optimization,the stator and rotor deform after pre-pressure and the contact interface of them full contact theoretically.When reaching heat balance the effective output of the motor is 37%,and the average effective output efficiency is 2.384 times higher than that of the unoptimized.It can be seen that the total consumption of the ultrasonic motor system decreases significantly.Therefore,when using in certain system the consumption taken from the system will decreases largely,especially in the system with a strict consumption control.展开更多
A 2D time domain boundary element method(BEM)is developed to solve the transient scattering of plane waves by a unilaterally frictionally constrained inclusion.Coulomb friction is assumed along the contact interface.T...A 2D time domain boundary element method(BEM)is developed to solve the transient scattering of plane waves by a unilaterally frictionally constrained inclusion.Coulomb friction is assumed along the contact interface.The incident wave is assumed strong enough so that localized slip and separation take place along the interface.The present problem is in effect a nonlinear boundary value problem since the mixed boundary conditions involve unknown intervals (slip,separation and stick regions).In order to determine the unknown intervals,an iterative technique is developed.As an example,we consider the scattering of a circular cylinder embedded in an infinite solid.展开更多
High-temperature ablation is a common failure phenomenon that limits the service life of the transmission parts on heavy-duty machines used in heavy load,high temperature,high shock conditions due to in-sufficient sup...High-temperature ablation is a common failure phenomenon that limits the service life of the transmission parts on heavy-duty machines used in heavy load,high temperature,high shock conditions due to in-sufficient supply of lubricating oil and grease.Traditional self-lubricating coatings prepared by inorganic,organic or organic-inorganic hybrid methods are prone to be oxidated at high temperatures to lose their friction reducing function,so that it is difficult to meet the engineering requirements of high-temperature lubrication.We design viscoelastic polymer coatings by a high-temperature self-lubricating and wear-resistant strategy.Polytetrafluoroethylene(PTFE,T_(m)=329℃)and polyphenylene sulfide(PPS,T_(g)=84℃,T_(m)=283℃)are used to prepare a PTFE/PPS polymer alloy coating.As the temperature increases from 25 to 300℃,the PTFE/PPS coating softens from glass state to viscoelastic state and viscous flow state,which is owing to the thermodynamic transformation characteristic of the PPS component.Additionally the friction coefficient(μ)decreased from 0.096 to 0.042 with the increasing of temperature from 25 to 300℃.The mechanism of mechanical deformation and surface morphology evolution for the PTFE/PPS coating under the multi-field coupling action of temperature(T),temperature–centrifugal force(T–F_(ω)),temperature–centrifugal force–shearing force(T–F_(ω)–F_(τ))were investigated.The physical model of“thermoviscoelasticity driven solid–liquid interface reducing friction”is proposed to clarify the self-lubricating mechanism determined by the high-temperature viscoelastic properties of polymers.The high-temperature adjusts the viscosity(η)of the coating,increases interface slipping and intensifies shear deformation(τ),reducing the friction coefficient.The result is expected to provide a new idea for designing anti-ablation coatings served in high temperature friction and wear conditions.展开更多
This paper presents the results of the shear strength（frictional strength） of cemented paste backfillcemented paste backfill（CPB-CPB） and cemented paste backfillerock wall（CPB-rock） interfaces. The frictional be...This paper presents the results of the shear strength（frictional strength） of cemented paste backfillcemented paste backfill（CPB-CPB） and cemented paste backfillerock wall（CPB-rock） interfaces. The frictional behaviors of these interfaces were assessed for the short-term curing times（3 d and 7 d） using a direct shear apparatus RDS-200 from GCTS（Geotechnical Consulting ＆ Testing Systems）. The shear（friction） tests were performed at three different constant normal stress levels on flat and smooth interfaces. These tests aimed at understanding the mobilized shear strength at the CPB-rock and CPB-CPB interfaces during and/or after open stope filling（no exposed face）. The applied normal stress levels were varied in a range corresponding to the usually measured in-situ horizontal pressures（longitudinal or transverse） developed within paste-filled stopes（uniaxial compressive strength, s c 150 k Pa）. Results show that the mobilized shear strength is higher at the CPB-CPB interface than that at the CPB-rock interface. Also, the perfect elastoplastic behaviors observed for the CPB-rock interfaces were not observed for the CPB-CPB interfaces with low cement content which exhibits a strain-hardening behavior. These results are useful to estimate or validate numerical model for pressures determination in cemented backfill stope at short term. The tests were performed on real backfill and granite. The results may help understanding the mechanical behavior of the cemented paste backfill in general and, in particular, analyzing the shear strength at backfillebackfill and backfill-rock interfaces.展开更多
Friction exists wherever relative motion occurs and is the main source of energy consumption.Lubrication plays a significant role in improving fuel efficiency,reducing emissions,and prolonging the service life of mach...Friction exists wherever relative motion occurs and is the main source of energy consumption.Lubrication plays a significant role in improving fuel efficiency,reducing emissions,and prolonging the service life of machines.Surface interactions between two moving solid surfaces or the flow of a fluid (and/or environment) on a solid surface are the primary causes of friction.Apart from the mechanical design of moving parts,surface physicochemistry is of crucial importance to lubrication.This review deals with the frontier research on controlling friction and lubrication,highlights the importance of physicochemistry aspects,and enumerates the state-of-the-art chemistry solutions to tribological issues.It aims at inspiring talented young scientists from different fields to make significant contributions to the area.展开更多
Motor-pump assembly is the core component of the Aerospace Electro-hydrostatic Actuator(EHA).Thus,the design of the motor pump can be very challenging under conditions of high speed and wide pressure range,especially ...Motor-pump assembly is the core component of the Aerospace Electro-hydrostatic Actuator(EHA).Thus,the design of the motor pump can be very challenging under conditions of high speed and wide pressure range,especially in particular working mediums.Our ultimate goal is to pursue better flow characteristics under a wide range of working conditions.In this paper,we built a sub-model of the main friction interfaces and a model of single-shaft coaxial motor-pump assembly adopting the method of hierarchical modeling.The experimental investigation of the output characteristics was mainly carried out in a phosphate ester medium environment.Then,the flow characteristics were compared and analyzed with the simulation results.Results indicated that the flow characteristics of the motor-pump assembly could be accurately simulated by the model and quite severe in a low speed and high-pressure environment.展开更多
Assessment of the reinforcement behavior of soil under cyclic and monotonic loads is of great impor- tance in the safe design of mechanically stabilized earth walls, In this article, the method of conducting a multist...Assessment of the reinforcement behavior of soil under cyclic and monotonic loads is of great impor- tance in the safe design of mechanically stabilized earth walls, In this article, the method of conducting a multistage pullout （MSP） test on the polymeric strip （PS） is presented, The post-cyclic behavior of the reinforcement can be evaluated using a large-scale pullout apparatus adopting MSP test and one-stage pullout （OSP） test procedures, This research investigates the effects of various factors including load amplitude, load frequency, number of load cycles and vertical effective stress on the peak apparent coefficient of friction mobilized at the soil-PS interface and the pullout resistance of the PS buried in dry sandy soil. The results illustrate that changing the cyclic tensile load frequency from 0,1 Hz to 0,5 Hz does not affect the pullout resistance. Moreover, the influence of increasing the number of load cycles from 30 to 250 on the peak pullout resistance is negligible. Finally, the effect of increasing the cyclic tensile load amplitude from 20% to 40% on the monotonic pullout resistance can be ignored. The peak apparent coefficient of friction mobilized at the soil-PS interface under monotonic and cyclic load conditions decreases with the increase in vertical effective stress.展开更多
The process of lubricant penetration into frictional interfaces has not been fully established,hence compromising their tribological performance.In this study,the penetration characteristics of deionized water(DI wate...The process of lubricant penetration into frictional interfaces has not been fully established,hence compromising their tribological performance.In this study,the penetration characteristics of deionized water(DI water)containing an electroosmotic suppressant(cetyltrimethylammonium bromide(CTAB))and an electroosmotic promoter(sodium lauriminodipropionate(SLI)),were investigated using steel-onsteel friction pairs.The results indicated that the lubricant with electroosmotic promoter reduced the coefficient of friction and wear scar diameter,whereas that with an electroosmotic suppressant exhibited an opposite behavior compared with DI water.The addition of SLI promoted the penetration of the DI water solution,thus resulting in the formation of a thick lubricating film of iron oxide at the sliding surface.This effectively reduced the abrasion damage,leading to a lower coefficient of friction and wear loss.展开更多
基金Funded by the National Natural Science Foundation of China(Nos.52075347,51575364)and the Natural Science Foundation of Liaoning Provincial(No.2022-MS-295)。
文摘In order to solve the problem of poor formability caused by different materials and properties in the process of tailor-welded sheets forming,a forming method was proposed to change the stress state of tailor-welded sheets by covering the tailor-welded sheets with better plastic properties overlapping sheets.At the same time,the interface friction effect between the overlapping and tailor-welded sheets was utilized to control the stress magnitude and further improve the formability and quality of the tailor-welded sheets.In this work,the bulging process of the tailor-welded overlapping sheets was taken as the research object.Aluminum alloy tailor-welded overlapping sheets bulging specimens were studied by a combination of finite element analysis and experimental verification.The results show that the appropriate use of interface friction between tailor-welded and overlapping sheets can improve the formability of tailor-welded sheets and control the flow of weld seam to improve the forming quality.When increasing the interface friction coefficient on the side of tailor-welded sheets with higher strength and decreasing that on the side of tailor-welded sheets with lower strength,the deformation of the tailor-welded sheets are more uniform,the offset of the weld seam is minimal,the limit bulging height is maximal,and the forming quality is optimal.
基金the funding supported from the National Research Foundation of Korea(NRF)grant funded by the Korea Government MSIT(No.2021R1C1C1006003).
文摘Understanding frictional anisotropy,which refers to the variation in frictional resistance based on the shear direction,is crucial for optimizing the friction angle between a bio-inspired structure and the surrounding soil.Previous studies focused on estimating the interface frictional anisotropy mobilized by snakeskin-inspired textured surfaces and sand under monotonic shear loading conditions.However,there is a need to estimate interface frictional anisotropy under repetitive shear loads.In this study,a series of repetitive direct shear(DS)tests are performed with snakeskin-inspired textured surfaces under a constant vertical stress and two shear directions(cranial first half→caudal second half or caudal first half→cranial second half).The results show that(1)mobilized shear stress increases with the number of shearing cycles,(2)cranial shearing(shearing against the scales)consistently produces a higher shear resistance and less contractive behavior than caudal shearing(shearing along the scales),and(3)a higher scale height or smaller scale length of the surface yields a higher interface friction angle across all shearing cycles.Further analysis reveals that the gap between the cranial and caudal shear zones of the interface friction angle as a function of L/H(i.e.the ratio of scale length L to scale height H)continues to decrease as the number of shearing cycles approaches asymptotic values.The directional frictional resistance(DFR)decreases as the number of shearing cycles increases.Furthermore,the discussion covers the impact of initial relative density,vertical stress,and the number of shearing cycles on interface frictional anisotropy.
基金the National Natural Science Foundation of China(No.52475516,52005166,91960203)the Young Core Instructor Project in the Higher Education Institutions of Henan Province(No.2023GGJS051)the National Science Fund for Distinguished Young Scholars of Henan Polytechnic University(No.J2022-5).
文摘Ti-6Al-4V is widely used in the aviation industry because of its high strength, and good heat resistance. However, severe tool wear on the rake face occurs during the milling of Ti-6Al-4V,which is caused by intense friction between the tool rake face and the chips. To investigate tool wear in the milling of Ti-6Al-4V, ultrasonic vibration is introduced, and a cutting force prediction model that considers tool-chip contact interface friction behavior in Ultrasonic Longitudinal-Torsional Vibration-Assisted Milling(ULTVAM) is proposed in this paper. First, the tool tip motion trajectory and dynamic cutting thickness under ULTVAM were analyzed calculated, and compared with those in Common Milling(CM). Subsequently, the effects of ultrasonic vibration on the shear force under the ultrasonic softening effect, the friction force, and the friction reversal force on the toolchip contact interface were investigated. A dynamic milling force model under ULTVAM was established before and after friction force reversal caused by ultrasonic longitudinal-torsional vibration. Finally, numerous experiments were conducted to validate the proposed model, and the experimental results indicated that the calculated dynamic milling forces agreed well with the measured values, with errors in the X and Y directions of 5.51% and 10.23%, respectively. In addition, the average roughness of the workpiece surface also decreased(1.08, 0.9, 0.6, 0.7 μm under ultrasonic amplitudes of 0, 1, 2, and 3 μm) and the tool wear state improved on the rake face under ULTVAM.
基金sponsored by Coal and Energy Research Bureau and CDC-NIOSH under Grant No.R01OH009532
文摘Bumps in coal mines have been recognized as a major hazard for many years. These sudden and violent failures around mine openings have compromised safety, ventilation and access to mine workings.Previous studies showed that the violence of coal specimen failure depends on both the interface friction and width-to-height（W/H） ratio of coal specimen. The mode of failure for a uniaxially loaded coal specimen or a coal pillar is a combination of both shear failure along the interface and compressive failure in the coal. The shear failure along the interface triggered the compressive failure in coal. The compressive failure of a coal specimen or a coal pillar can be controlled by changing its W/H ratio. As the W/H ratio increases, the ultimate strength increases. Hence, with a proper combination of interface friction and the W/H ratio of pillar or coal specimen, the mode of failure will change from sudden violent failure which is brittle failure to non-violent failure which is ductile failure. The main objective of this paper is to determine at what W/H ratio and interface friction the mode of failure changes from violent to non-violent. In this research, coal specimens of W/H ratio ranging from 1 to 10 were uniaxially tested under two interface frictions of 0.1 and 0.25, and the results are presented and discussed.
基金supported by the National Natural Science Foundation of China(Grant No.12272127)the Construction Project of Double First Class in Safety Discipline of the Universities of Henan Province(Grant No.AQ20230751).
文摘The stress wave profile at the frictional interface is crucial for investigating the frictional process.This study modeled a brittle material interface with a micro-contact to analyze the fine stress wave structure associated with frictional slip.Employing the finite element simulation alongside the related wave theory and experiments,two new wave structures were indentified:A Mach cone symmetric to the frictional interface associated with incident plane wave propagation,and a new plane longitudinal wave generated across the entire frictional interface at the moment when the incident wave began to propagate.The time and space of its appearance implies that the overall response of the frictional interface precedes the local wave response of the medium.Consequently,a model involving characteristic line theory and the idea of Green’s function has been proposed for its occurrence.The analysis results show that these two new wave phenomena are independent of the fracture of micro-contacts at the interface;instead,the frictional interface effect may be responsible for the generation of such new wave structures.The measured wave profiles provide a proof for the existence of the new wave structures.These results display new wave phenomena,and suggest a wave profile for investigating the dynamic mechanical properties of the frictional interface.
基金supported by the National Natural Science Foundation of China(Grant Nos.52371301 and 52471289)。
文摘The scaled suction caisson repre sents an innovative design featuring a bio-inspired sidewall modeled after snake skin,commonly utilized in offshore mooring platforms.In comparison with traditional suction caissons,this bio-inspired design demonstrates reduced penetration resistance and enhanced pull-out capacity due to the anisotropic shear behaviors of its sidewall.To investigate the shear behavior of the bio-inspired sidewall under pull-out load,direct shear tests were conducted between the bio-inspired surface and sand.The research demonstrates that the interface shear strength of the bio-inspired surface significantly surpasses that of the smooth surface due to interlocking effects.Additionally,the interface shear strength correlates with the aspect ratio of the bio-inspired surface,shear angle,and particle diameter distribution,with values increasing as the uniformity coefficient Cudecreases,while initially increasing and subsequently decreasing with increases in both aspect ratio and shear angle.The ratio between the interface friction angleδand internal friction angle δ_(s) defines the interface effect factor k.For the bio-inspired surface,the interface effect factor k varies with shear angleβ,ranging from 0.9 to 1.12.The peak value occurs at a shear angleβof 60°,substantially exceeding that of the smooth surface.A method for calculating the relative roughness R_(N) is employed to evaluate the interface roughness of the bio-inspired surface,taking into account scale dimension and particle diameter distribution effects.
基金supported by a grant from the National Natural Science Foundations of China(No.52171282)supported by Taishan Scholars Program of Shandong Province,China(No.tsqn202306098)the Shandong Provincial Key Research and Development Plan,China(No.2021ZLGX04).
文摘Structure-soil interface friction characteristics is of importance to investigate the interaction between engineering structures and soils,especially for offshore structures.The interface friction behavior between marine clay and structural materials with different roughness was studied in this paper by using 3D optical scanning tests,a modified direct shear device and numerical simulation.Relationships between the surface roughness of structures,water content and interface friction angle were presented by model tests.The increase of water contents decreased the interface friction angles.For interfaces with different roughness,the interface friction angles will be smaller than that of the soil when the water content exceeds a certain value.The roughness of the interface and the water content of the soil are mutually coupled to influence the coefficient of friction(COF).This paper proposed a Finite Element Method(FEM)to simulate the interface direct shear tests of structures with different roughness.The surface models with different roughness are established based on the structure data obtained by 3D scanning.The Coupled Eulerian-Lagrangian(CEL)approach was employed to analyse soils sheared by irregular surfaces.The interface behavior for interfaces with different roughness under cyclic shear stresses was analyzed by FEM.
文摘The friction interface matching plays a deterministic role in the motor efficiency,and the microcosmic contact status of friction interface should be investigated to improve the ultrasonic motor performance.The main purpose is to improve the effective output power of ultrasonic motor.Hence,one studies the contact condition of the friction interface of the ultrasonic motor,analyzes the micro condition of contact interface through finite element analysis,optimizes unreasonable structures,and compares the two different-structure ultrasonic motors through experiments.The results reflect the necessity of optimization.After optimization,the stator and rotor deform after pre-pressure and the contact interface of them full contact theoretically.When reaching heat balance the effective output of the motor is 37%,and the average effective output efficiency is 2.384 times higher than that of the unoptimized.It can be seen that the total consumption of the ultrasonic motor system decreases significantly.Therefore,when using in certain system the consumption taken from the system will decreases largely,especially in the system with a strict consumption control.
基金Project supported by the National Natural Science Foundation of China(Nos.19872001 and 59878004)the National Natural Science Foundation for Distinguished Young Scholars(No.10025211).
文摘A 2D time domain boundary element method(BEM)is developed to solve the transient scattering of plane waves by a unilaterally frictionally constrained inclusion.Coulomb friction is assumed along the contact interface.The incident wave is assumed strong enough so that localized slip and separation take place along the interface.The present problem is in effect a nonlinear boundary value problem since the mixed boundary conditions involve unknown intervals (slip,separation and stick regions).In order to determine the unknown intervals,an iterative technique is developed.As an example,we consider the scattering of a circular cylinder embedded in an infinite solid.
基金The authors are grateful for the financial support from National Natural Science Foundation of China(No.52075560).
文摘High-temperature ablation is a common failure phenomenon that limits the service life of the transmission parts on heavy-duty machines used in heavy load,high temperature,high shock conditions due to in-sufficient supply of lubricating oil and grease.Traditional self-lubricating coatings prepared by inorganic,organic or organic-inorganic hybrid methods are prone to be oxidated at high temperatures to lose their friction reducing function,so that it is difficult to meet the engineering requirements of high-temperature lubrication.We design viscoelastic polymer coatings by a high-temperature self-lubricating and wear-resistant strategy.Polytetrafluoroethylene(PTFE,T_(m)=329℃)and polyphenylene sulfide(PPS,T_(g)=84℃,T_(m)=283℃)are used to prepare a PTFE/PPS polymer alloy coating.As the temperature increases from 25 to 300℃,the PTFE/PPS coating softens from glass state to viscoelastic state and viscous flow state,which is owing to the thermodynamic transformation characteristic of the PPS component.Additionally the friction coefficient(μ)decreased from 0.096 to 0.042 with the increasing of temperature from 25 to 300℃.The mechanism of mechanical deformation and surface morphology evolution for the PTFE/PPS coating under the multi-field coupling action of temperature(T),temperature–centrifugal force(T–F_(ω)),temperature–centrifugal force–shearing force(T–F_(ω)–F_(τ))were investigated.The physical model of“thermoviscoelasticity driven solid–liquid interface reducing friction”is proposed to clarify the self-lubricating mechanism determined by the high-temperature viscoelastic properties of polymers.The high-temperature adjusts the viscosity(η)of the coating,increases interface slipping and intensifies shear deformation(τ),reducing the friction coefficient.The result is expected to provide a new idea for designing anti-ablation coatings served in high temperature friction and wear conditions.
文摘This paper presents the results of the shear strength（frictional strength） of cemented paste backfillcemented paste backfill（CPB-CPB） and cemented paste backfillerock wall（CPB-rock） interfaces. The frictional behaviors of these interfaces were assessed for the short-term curing times（3 d and 7 d） using a direct shear apparatus RDS-200 from GCTS（Geotechnical Consulting ＆ Testing Systems）. The shear（friction） tests were performed at three different constant normal stress levels on flat and smooth interfaces. These tests aimed at understanding the mobilized shear strength at the CPB-rock and CPB-CPB interfaces during and/or after open stope filling（no exposed face）. The applied normal stress levels were varied in a range corresponding to the usually measured in-situ horizontal pressures（longitudinal or transverse） developed within paste-filled stopes（uniaxial compressive strength, s c 150 k Pa）. Results show that the mobilized shear strength is higher at the CPB-CPB interface than that at the CPB-rock interface. Also, the perfect elastoplastic behaviors observed for the CPB-rock interfaces were not observed for the CPB-CPB interfaces with low cement content which exhibits a strain-hardening behavior. These results are useful to estimate or validate numerical model for pressures determination in cemented backfill stope at short term. The tests were performed on real backfill and granite. The results may help understanding the mechanical behavior of the cemented paste backfill in general and, in particular, analyzing the shear strength at backfillebackfill and backfill-rock interfaces.
基金The work is financially supported by the National Natural Science Foundation of China (NSFC)，the National Key Basic Research and Development (973) Program of China，Natural Science Foundation of Gansu Province
文摘Friction exists wherever relative motion occurs and is the main source of energy consumption.Lubrication plays a significant role in improving fuel efficiency,reducing emissions,and prolonging the service life of machines.Surface interactions between two moving solid surfaces or the flow of a fluid (and/or environment) on a solid surface are the primary causes of friction.Apart from the mechanical design of moving parts,surface physicochemistry is of crucial importance to lubrication.This review deals with the frontier research on controlling friction and lubrication,highlights the importance of physicochemistry aspects,and enumerates the state-of-the-art chemistry solutions to tribological issues.It aims at inspiring talented young scientists from different fields to make significant contributions to the area.
基金This study was co-supported by the Chinese Civil Aircraft Project(No.MJ-2017-S49)China Postdoctoral Science Foundation(No.2021M700331).
文摘Motor-pump assembly is the core component of the Aerospace Electro-hydrostatic Actuator(EHA).Thus,the design of the motor pump can be very challenging under conditions of high speed and wide pressure range,especially in particular working mediums.Our ultimate goal is to pursue better flow characteristics under a wide range of working conditions.In this paper,we built a sub-model of the main friction interfaces and a model of single-shaft coaxial motor-pump assembly adopting the method of hierarchical modeling.The experimental investigation of the output characteristics was mainly carried out in a phosphate ester medium environment.Then,the flow characteristics were compared and analyzed with the simulation results.Results indicated that the flow characteristics of the motor-pump assembly could be accurately simulated by the model and quite severe in a low speed and high-pressure environment.
文摘Assessment of the reinforcement behavior of soil under cyclic and monotonic loads is of great impor- tance in the safe design of mechanically stabilized earth walls, In this article, the method of conducting a multistage pullout （MSP） test on the polymeric strip （PS） is presented, The post-cyclic behavior of the reinforcement can be evaluated using a large-scale pullout apparatus adopting MSP test and one-stage pullout （OSP） test procedures, This research investigates the effects of various factors including load amplitude, load frequency, number of load cycles and vertical effective stress on the peak apparent coefficient of friction mobilized at the soil-PS interface and the pullout resistance of the PS buried in dry sandy soil. The results illustrate that changing the cyclic tensile load frequency from 0,1 Hz to 0,5 Hz does not affect the pullout resistance. Moreover, the influence of increasing the number of load cycles from 30 to 250 on the peak pullout resistance is negligible. Finally, the effect of increasing the cyclic tensile load amplitude from 20% to 40% on the monotonic pullout resistance can be ignored. The peak apparent coefficient of friction mobilized at the soil-PS interface under monotonic and cyclic load conditions decreases with the increase in vertical effective stress.
基金The authors gratefully acknowledge the support of the National Natural Science Foundation of China(No.51775507)the Natural Science Foundation of Zhejiang Province(No.LY19E050006).
文摘The process of lubricant penetration into frictional interfaces has not been fully established,hence compromising their tribological performance.In this study,the penetration characteristics of deionized water(DI water)containing an electroosmotic suppressant(cetyltrimethylammonium bromide(CTAB))and an electroosmotic promoter(sodium lauriminodipropionate(SLI)),were investigated using steel-onsteel friction pairs.The results indicated that the lubricant with electroosmotic promoter reduced the coefficient of friction and wear scar diameter,whereas that with an electroosmotic suppressant exhibited an opposite behavior compared with DI water.The addition of SLI promoted the penetration of the DI water solution,thus resulting in the formation of a thick lubricating film of iron oxide at the sliding surface.This effectively reduced the abrasion damage,leading to a lower coefficient of friction and wear loss.
