Varied slope structures have different landslide initiation mechanisms.However,the role of interfacial asperities in controlling sliding initiation is unclear.This study develops a novel analytical method for interfac...Varied slope structures have different landslide initiation mechanisms.However,the role of interfacial asperities in controlling sliding initiation is unclear.This study develops a novel analytical method for interface mechanisms in practical landslide scenarios.Based on asperity theory,theoretical derivations were conducted,yielding an equilibrium equation grounded in the maximum shear length of asperities(Llimit).A method was proposed to evaluate slope stability by integrating Llimit with monitored displacement data.On-site displacement monitoring and slope state analysis determined the distribution range of asperities,providing theoretical support for slope remediation.Between July 2023 and July 2024,a large landslide located in Shagudu Town,Zhungeer Banner,Ordos,Inner Mongolia,underwent multiple deformation stages.This landslide seriously affected the operations of the Rongwu Expressway.This study initially examined the geological structure of the landslide through geological drilling and surveys.The distribution of asperities in the landslide area was determined through physical and mechanical tests and on-site geological mapping.A layout plan for landslide disposal and monitoring points was developed based on the interface landslide asperity theory.Analysis of 20 days of displacement monitoring data was used to determine asperity distribution and analyze slope movement,informed by asperity theory.This study pioneers the systematic application of asperity theory as the primary framework for analyzing and managing a large-scale interface landslide in engineering practice.Its rationality and effectiveness are rigorously demonstrated through the successful determination of the asperity distribution range within the Rongwu Expressway landslide,leading to effective remediation and favorable monitoring outcomes.This work not only validates the asperity theory for interface landslides but,crucially,establishes a novel,practical method for their stability assessment.Furthermore,a key theoretical advancement is the development of the concept that asperity-controlled main sliding surfaces can induce secondary sliding surfaces,based on field evidence and analysis.展开更多
Elastohydrodynamic lubrication(EHL)point contact occurs between two rough surfaces at the mesoscopic level,while the interaction of rough surfaces involves contact between asperities at the microscale level.In most ca...Elastohydrodynamic lubrication(EHL)point contact occurs between two rough surfaces at the mesoscopic level,while the interaction of rough surfaces involves contact between asperities at the microscale level.In most cases,the contact between asperities within an interface takes the form of lateral contact rather than peak contact.Regions devoid of contact asperities are filled with lubricating oil.However,conventional models often oversimplify lateral contact forms as interactions between asperities and a smooth,rigid plane.These simplifications fail to accurately represent the true contact conditions and can lead to inaccuracies in the analysis of EHL’s contact performance.To address this issue,we have developed a novel EHL interface model comprising two rough surfaces.This model allows us to explore the influence of asperity height,contact angle,and contact azimuth angle on EHL interface performance.展开更多
A hybrid finite-discrete element method was implemented to study the fracture process of rough rock joints under direct shearing. The hybrid method reproduced the joint shear resistance evolution process from asperity...A hybrid finite-discrete element method was implemented to study the fracture process of rough rock joints under direct shearing. The hybrid method reproduced the joint shear resistance evolution process from asperity sliding to degradation and from gouge formation to grinding. It is found that, in the direct shear test of rough rock joints under constant normal displacement loading conditions, higher shearing rate promotes the asperity degradation but constraints the volume dilation, which then results in higher peak shear resistance, more gouge formation and grinding, and smoother new joint surfaces. Moreover, it is found that the joint roughness affects the joint shear resistance evolution through influencing the joint fracture micro mechanism. The asperity degradation and gouge grinding are the main failure micro-mechanism in shearing rougher rock joints with deeper asperities while the asperity sliding is the main failure micro-mechanism in shearing smoother rock joints with shallower asperities. It is concluded that the hybrid finite-discrete element method is a valuable numerical tool better than traditional finite element method and discrete element method for modelling the joint sliding, asperity degradation, gouge formation, and gouge grinding occurred in the direct shear tests of rough rock joints.展开更多
The location and geometry of large-scale asperity present at the foundation of concrete gravity dams and buttress dams affect the shear resistance of the concrete-rock interface.However,the parameters describing the f...The location and geometry of large-scale asperity present at the foundation of concrete gravity dams and buttress dams affect the shear resistance of the concrete-rock interface.However,the parameters describing the frictional resistance of the interface usually do not account for these asperities.This could result in an underestimate of the peak shear stre ngth,which leads to significantly conservative design for new dams or unnecessary stability enhancing measures for existing ones.The aim of this work was to investigate the effect of the location of first-order asperity on the peak shear strength of a concrete-rock interface under eccentric load and the model discrepancy associated with the commonly used rigid body methods for calculating the factor of safety(FS)against sliding.For this,a series of direct and eccentric shear tests under constant normal load(CNL)was carried out on concrete-rock samples.The peak shear strengths measured in the tests were compared in terms of asperity location and with the predicted values from analytical rigid body methods.The results showed that the large-scale asperity under eccentric load significantly affected the peak shear strength.Furthermore,unlike the conventional assumption of sliding or shear failure of an asperity in direct shear,under the effect of eccentric shear load,a tensile failure in the rock or in the concrete could occur,resulting in a lower shear strength compared with that of direct shear tests.These results could have important implications for assessment of the FS against sliding failure in the concrete-rock interface.展开更多
The wear condition of the piston/cylinder pair is crucial to the performance and reliability of the axial piston pump.The hard piston surface,the soft cylinder bore surface,and the interface oil film affects each othe...The wear condition of the piston/cylinder pair is crucial to the performance and reliability of the axial piston pump.The hard piston surface,the soft cylinder bore surface,and the interface oil film affects each other during the wear process.Specifically,in the mixed lubrication region,the geometry of the hard piston surface asperity directly affects the wear of soft cylinder bore surface,while the asperities may deform or even degrade when penetrating and sliding against the cylinder bore.So far,there is no suitable method to simulate their coupled evolution.This paper proposed a wear process simulation model considering the real-time interaction between the elasto-plastic deformation of the piston surface asperity,the wear contour of the cylinder bore,and the lubrication condition of the interface.An offline library of the elasto-plastic constitutive behavior of the asperity based on the finite element method(FEM)is established as a part of the simulation model to precisely analyze the deformation and degradation of the asperity and quickly invoke them in the numerical wear process simulation.The simulation and experimental results show that the piston asperity and the cylinder bore contour converge to a steady state after running-in for about 0.5 h.The distribution of the simulated asperity degradation and wear depth is also verified by the experiment.展开更多
A precise tangential contact damping model is proposed,which includes the lateral contact of the upper-lower asperities and the interaction of adjacent asperities.The effects of the normal static preload,frequency,and...A precise tangential contact damping model is proposed,which includes the lateral contact of the upper-lower asperities and the interaction of adjacent asperities.The effects of the normal static preload,frequency,and amplitude of tangential displacement on the tangential contact damping were analyzed by simulation,respectively.Furthermore,the results of simulation are verified by experiment.The tangential contact damping of considering the interaction and lateral contact of asperity is very close to the experimental results.展开更多
The peak identification scheme based method(three-point definition)and the spectral moments based method(spectral moment approach)are both widely used for asperity peak modeling in tribology.To discover the difference...The peak identification scheme based method(three-point definition)and the spectral moments based method(spectral moment approach)are both widely used for asperity peak modeling in tribology.To discover the differences between the two methods,a great number of rough surface profile samples with various statistical distributions are first randomly generated using FFT.Then the distribution parameters of asperity peaks are calculated for the generated samples with both methods.The obtained results are compared and verified by experiment.The variation rules of the differences between the two methods with statistical characteristics of rough surfaces are investigated.To explain for the discovered differences,the assumptions by spectral moment approach that the joint distribution of surface height,slope and curvature is normal and that the height distribution of asperities is Gaussian,are examined.The results show that it is unreasonable to assume a joint normal distribution without inspecting the correlation pattern of[z],[z′]and[z′′],and that the height distribution of asperities is not exactly Gaussian before correlation length of rough surface increases to a certain extent,20 for instance.展开更多
A new hybrid numerical method that couples the dynamic slider-crank mechanism(SCM)and crankpin bearing(CB)lubrication models is proposed to analyze the effect of micro asperity contact on the tribological properties o...A new hybrid numerical method that couples the dynamic slider-crank mechanism(SCM)and crankpin bearing(CB)lubrication models is proposed to analyze the effect of micro asperity contact on the tribological properties of a CB.In the hybrid model,the dynamic equations of the SCM are established based on the Newton method,while the lubrication equations of the CB are established on the basis of the Reynolds equation.Experimental data of the engine are also used in simulation analyses to enhance the reliability of the results.The load-bearing capacity(LBC)and friction force of the CB are selected as objective functions.Results show that the LBC has a negligible effect on the tribological properties of the CB,but the friction force greatly affects the resistance of the bearing under different radial clearances and surface roughness values.In particular,the maximum friction force in the asperity contact region accounts for 40.5%of the maximum total friction force at a radial clearance of 5μm and 77.7%of the maximum total friction of the CB with a surface roughness of 10μm.展开更多
As an important model for explaining the seismic rupture mode,the asperity model plays an important role in studying the stress accumulation of faults and the location of earthquake initiation.Taking Qilian-Haiyuan fa...As an important model for explaining the seismic rupture mode,the asperity model plays an important role in studying the stress accumulation of faults and the location of earthquake initiation.Taking Qilian-Haiyuan fault as an example,this paper combines geodetic method and b-value method to propose a multi-source observation data fusion detection method that accurately determines the asperity boundary named dual threshold search method.The method is based on the criterion that the b-value asperity boundary should be most consistent with the slip deficit rate asperity boundary.Then the optimal threshold combination of slip deficit rate and b-value is obtained through threshold search,which can be used to determine the boundary of the asperity.Based on this method,the study finds that there are four potential asperities on the Qilian-Haiyuan fault:two asperities(A1 and A2)are on the Tuolaishan segment and the other two asperities(B and C)are on Lenglongling segment and Jinqianghe segment,respectively.Among them,the lengths of asperities A1 and A2 on Tuolaishan segment are 17.0 km and 64.8 km,respectively.And the lower boundaries are 5.5 km and 15.5 km,respectively;The length of asperity B on Lenglongling segment is 70.7 km,and the lower boundary is 10.2 km.The length of asperity C on Jinqianghe segment is 42.3 km,and the lower boundary is 8.3 km.展开更多
The contact problem of deformed rough surfaces exists widely in complex engineering structures.How to reveal the influence mechanism of surface deformation on the contact properties is a key issue in evaluating the in...The contact problem of deformed rough surfaces exists widely in complex engineering structures.How to reveal the influence mechanism of surface deformation on the contact properties is a key issue in evaluating the interface performances of the engineering structures.In this paper,a contact model is established,which is suitable for tensile and bending deformed contact surfaces.Four contact forms of asperities are proposed,and their distribution characteristics are analyzed.This model reveals the mechanism of friction generation from the perspective of the force balance of asperity.The results show the contact behaviors of the deformed contact surface are significantly different from that of the plane contact,which is mainly reflected in the change in the number of contact asperities and the real contact area.This study suggests that the real contact area of the interface can be altered by applying tensile and bending strains,thereby regulating its contact mechanics and conductive behavior.展开更多
Understanding the rate-dependent shear behavior of rough joints is crucial.This study explores the ratedependent shear behavior of rough joints through direct shear tests conducted under constant normal stiffness(CNS)...Understanding the rate-dependent shear behavior of rough joints is crucial.This study explores the ratedependent shear behavior of rough joints through direct shear tests conducted under constant normal stiffness(CNS)boundary conditions,with the shear failure process monitored using acoustic emission(AE)technology.As the shear rate increases,both the peak and ultimate shear stresses of rough joints exhibit a decrease,highlighting a pronounced rate-dependent behavior.Asperity degradation under different shear rates is effectively characterized by normalized AE counts,exhibiting a three-stage Sshaped trend:Stage I(quiescent),Stage II(growth),and Stage III(stable).The simultaneous occurrence of the lowest AE b-value and the highest AE amplitude closely aligns with the moment of peak shear stress.This synchronization suggests that AE events of significant energy are predominantly clustered around the peak shear stress,which critically influences the overall progression of failure.Three failure modes of asperities were categorized,including the biting-off failure mode(BFM),the climbing-sliding failure mode(CFM),and the hybrid biting-off and climbing-sliding failure mode(HFM).Analysis of the multifractal spectra reveals that both the multifractal spectrum width(Δα)and the fractal dimension variability(Δf)diminish as the shear rate increases,suggesting that the complexity of the failure modes is inversely related to the shear rate.With increasing shear rates,the dominant failure mode evolves from BFM to CFM.The research findings facilitate a comprehensive understanding of the ratedependent shear behavior of rough joints,providing valuable guidance for rational support in underground engineering.展开更多
We present a grid-growth method to reconstruct 3D rock joints with arbitrary joint roughness and persistence.In the first step of this workflow,the joint model is divided into uniform grids.Then by adjusting the posit...We present a grid-growth method to reconstruct 3D rock joints with arbitrary joint roughness and persistence.In the first step of this workflow,the joint model is divided into uniform grids.Then by adjusting the positions of the grids,the joint morphology can be modified to construct models with desired joint roughness and persistence.Accordingly,numerous joint models with different joint roughness and persistence were built.The effects of relevant parameters(such as the number,height,slope of asperities,and the number,area of rock bridges)on the joint roughness coefficient(JRC)and joint persistence were investigated.Finally,an artificially split joint was reconstructed using the method,and the method's accuracy was evaluated by comparing the JRC of the models with that of the artificially split joint.The results showed that the proposed method can effectively control the JRC of joint models by adjusting the number,height,and slope of asperities.The method can also modify the joint persistence of joint models by adjusting the number and area of rock bridges.Additionally,the JRC of models obtained by our method agrees with that of the artificially split surface.Overall,the method demonstrated high accuracy for 3D rock joint reconstruction.展开更多
This paper introduces a model for characterizing the contact behavior of irregular asperities,transforming it into a superposition of sinusoidal asperity contact behaviors.A new sinusoidal asperity model is developed ...This paper introduces a model for characterizing the contact behavior of irregular asperities,transforming it into a superposition of sinusoidal asperity contact behaviors.A new sinusoidal asperity model is developed for bilin-ear hardening under plane strain conditions.Empirical equations are proposed,considering geometric shapes,tangent modulus,and Young’s modulus.The frequency of asperity height is extracted through Fourier transform for irregular asperities.Contact area and pressure are predicted using the sinusoidal asperity model,and the behavior of irregular asperities is obtained by superimposing those with the first three frequencies.Experimen-tal validation is conducted with milling and knurling-formed asperities,showing good alignment between the model and experimental results.In rough surface models,the proposed irregular asperity model exhibits greater accuracy in predicting contact behavior than a single sinusoidal asperity when interference exceeds 10%of the amplitude.展开更多
A macroscopically nominal flat surface is rough at the nanoscale level and consists of nanoasperities.Therefore,the frictional properties of the macroscale-level rough surface are determined by the mechanical behavior...A macroscopically nominal flat surface is rough at the nanoscale level and consists of nanoasperities.Therefore,the frictional properties of the macroscale-level rough surface are determined by the mechanical behaviors of nanoasperity contact pairs under shear.In this work,we first used molecular dynamics simulations to study the non-adhesive shear between single contact pairs.Subsequently,to estimate the friction coefficient of rough surfaces,we implemented the frictional behavior of a single contact pair into a Greenwood-Williamson-type statistical model.By employing the present multiscale approach,we used the size,rate,and orientation effects,which originated from nanoscale dislocation plasticity,to determine the dependence of the macroscale friction coefficient on system parameters,such as the surface roughness,separation,loading velocity,and direction.Our model predicts an unconventional dependence of the friction coefficient on the normal contact load,which has been observed in nanoscale frictional tests.Therefore,this model represents one step toward understanding some of the relevant macroscopic phenomena of surface friction at the nanoscale level.展开更多
When assessing the sliding stability of a concrete dam,the influence of large-scale asperities in the sliding plane is often ignored due to limitations of the analytical rigid body assessment methods provided by curre...When assessing the sliding stability of a concrete dam,the influence of large-scale asperities in the sliding plane is often ignored due to limitations of the analytical rigid body assessment methods provided by current dam assessment guidelines.However,these asperities can potentially improve the load capacity of a concrete dam in terms of sliding stability.Although their influence in a sliding plane has been thoroughly studied for direct shear,their influence under eccentric loading,as in the case of dams,is unknown.This paper presents the results of a parametric study that used finite element analysis(FEA)to investigate the influence of large-scale asperities on the load capacity of small buttress dams.By varying the inclination and location of an asperity located in the concrete-rock interface along with the strength of the rock foundation material,transitions between different failure modes and correlations between the load capacity and the varied parameters were observed.The results indicated that the inclination of the asperity had a significant impact on the failure mode.When the inclinationwas 30and greater,interlocking occurred between the dam and foundation and the governing failure modes were either rupture of the dam body or asperity.When the asperity inclination was significant enough to provide interlocking,the load capacity of the dam was impacted by the strength of the rock in the foundation through influencing the load capacity of the asperity.The location of the asperity along the concrete-rock interface did not affect the failure mode,except for when the asperity was located at the toe of the dam,but had an influence on the load capacity when the failure occurred by rupture of the buttress or by sliding.By accounting for a single large-scale asperity in the concrete-rock interface of the analysed dam,a horizontal load capacity increase of 30%e160%was obtained,depending on the inclination and location of the asperity and the strength of the foundation material.展开更多
The geometric properties of fracture surfaces significantly influence shear-seepage in rock fractures,introducing complexities to fracture modelling.The present study focuses on the hydro-mechanical behaviours of roug...The geometric properties of fracture surfaces significantly influence shear-seepage in rock fractures,introducing complexities to fracture modelling.The present study focuses on the hydro-mechanical behaviours of rough rock fractures during shear-seepage processes to reveal how dilatancy and fracture asperities affect these phenomena.To achieve this,an improved shear-flow model(SFM)is proposed with the incorporation of dilatancy effect and asperities.In particular,shear dilatancy is accounted for in both the elastic and plastic stages,in contrast to some existing models that only consider it in the elastic stage.Depending on the computation approaches for the peak dilatancy angle,three different versions of the SFM are derived based on Mohr-Coulomb,joint roughness coefficient-joint compressive strength(JRC-JCS),and Grasselli’s theories.Notably,this is a new attempt that utilizes Grasselli’s model in shearseepage analysis.An advanced parameter optimization method is introduced to accurately determine model parameters,addressing the issue of local optima inherent in some conventional methods.Then,model performance is evaluated against existing experimental results.The findings demonstrate that the SFM effectively reproduces the shear-seepage characteristics of rock fracture across a wide range of stress levels.Further sensitivity analysis reveals how dilatancy and asperity affect hydraulic properties.The relation between hydro-mechanical properties(dilatancy displacement and hydraulic conductivity)and asperity parameters is analysed.Several profound understandings of the shear-seepage process are obtained by exploring the phenomenon under various conditions.展开更多
It is clear from the literature data that the geometric characteristics of the seismogenic source are directly related to the nucleation of their strong earthquakes. Our study starts from the observation of the proxim...It is clear from the literature data that the geometric characteristics of the seismogenic source are directly related to the nucleation of their strong earthquakes. Our study starts from the observation of the proximity relationship between the epicenter of a strong earthquake and the surface trace of the seismogenic source. The proposed model is based on the mathematical analysis of seismicity falling within an area, through a polynomial function to determine a curve. The experimental results of our model confirm that 97% of the epicenters of strong earthquakes are located near the concavities or at the inflection points of the polynomial curve. Only 3% of strong earthquakes are located at the edges of the analyzed areas, where the number of data is not significant. The proposed model makes it possible to locate, with good approximation, the areas most likely to be the site of future strong earthquakes.展开更多
基金supported by the National Natural Science Foundation of China(Grant No:12362034)the Science and Technology Plan Project of Inner Mongolia Autonomous Region(Grant No:2022YFSH0047)Talent Project of Inner Mongolia Autonomous Region(DC2300001439,DC2200000913).
文摘Varied slope structures have different landslide initiation mechanisms.However,the role of interfacial asperities in controlling sliding initiation is unclear.This study develops a novel analytical method for interface mechanisms in practical landslide scenarios.Based on asperity theory,theoretical derivations were conducted,yielding an equilibrium equation grounded in the maximum shear length of asperities(Llimit).A method was proposed to evaluate slope stability by integrating Llimit with monitored displacement data.On-site displacement monitoring and slope state analysis determined the distribution range of asperities,providing theoretical support for slope remediation.Between July 2023 and July 2024,a large landslide located in Shagudu Town,Zhungeer Banner,Ordos,Inner Mongolia,underwent multiple deformation stages.This landslide seriously affected the operations of the Rongwu Expressway.This study initially examined the geological structure of the landslide through geological drilling and surveys.The distribution of asperities in the landslide area was determined through physical and mechanical tests and on-site geological mapping.A layout plan for landslide disposal and monitoring points was developed based on the interface landslide asperity theory.Analysis of 20 days of displacement monitoring data was used to determine asperity distribution and analyze slope movement,informed by asperity theory.This study pioneers the systematic application of asperity theory as the primary framework for analyzing and managing a large-scale interface landslide in engineering practice.Its rationality and effectiveness are rigorously demonstrated through the successful determination of the asperity distribution range within the Rongwu Expressway landslide,leading to effective remediation and favorable monitoring outcomes.This work not only validates the asperity theory for interface landslides but,crucially,establishes a novel,practical method for their stability assessment.Furthermore,a key theoretical advancement is the development of the concept that asperity-controlled main sliding surfaces can induce secondary sliding surfaces,based on field evidence and analysis.
基金supported by the National Natural Science Foundation of China(No.52005401,No.52375127)the Cultivation Scientific Research Project of Panzhihua University(2021PY001)+1 种基金the Opening Project of Material Corrosion and Protection Key Laboratory of Sichuan province(2022CL15)the Project for Science and Technology Plan of Henan Province(212102210445).
文摘Elastohydrodynamic lubrication(EHL)point contact occurs between two rough surfaces at the mesoscopic level,while the interaction of rough surfaces involves contact between asperities at the microscale level.In most cases,the contact between asperities within an interface takes the form of lateral contact rather than peak contact.Regions devoid of contact asperities are filled with lubricating oil.However,conventional models often oversimplify lateral contact forms as interactions between asperities and a smooth,rigid plane.These simplifications fail to accurately represent the true contact conditions and can lead to inaccuracies in the analysis of EHL’s contact performance.To address this issue,we have developed a novel EHL interface model comprising two rough surfaces.This model allows us to explore the influence of asperity height,contact angle,and contact azimuth angle on EHL interface performance.
基金The first author would like to thank the supports of the NARGS, IRGS and AAS grants of Australia, and the National Science Foundation grants （No. 51574060 and No. 51079017） of China, in which the first author is the intemational collaborator. The academic visits of the third and fourth authors to the University of Tasmania are partly supported by a PhD visiting scholarship and an academic visiting scholarship, respectively, provided by the China Scholarship Council, which are greatly appreciated.
文摘A hybrid finite-discrete element method was implemented to study the fracture process of rough rock joints under direct shearing. The hybrid method reproduced the joint shear resistance evolution process from asperity sliding to degradation and from gouge formation to grinding. It is found that, in the direct shear test of rough rock joints under constant normal displacement loading conditions, higher shearing rate promotes the asperity degradation but constraints the volume dilation, which then results in higher peak shear resistance, more gouge formation and grinding, and smoother new joint surfaces. Moreover, it is found that the joint roughness affects the joint shear resistance evolution through influencing the joint fracture micro mechanism. The asperity degradation and gouge grinding are the main failure micro-mechanism in shearing rougher rock joints with deeper asperities while the asperity sliding is the main failure micro-mechanism in shearing smoother rock joints with shallower asperities. It is concluded that the hybrid finite-discrete element method is a valuable numerical tool better than traditional finite element method and discrete element method for modelling the joint sliding, asperity degradation, gouge formation, and gouge grinding occurred in the direct shear tests of rough rock joints.
基金funded by the Research Council of Norway(Grant No.244029)。
文摘The location and geometry of large-scale asperity present at the foundation of concrete gravity dams and buttress dams affect the shear resistance of the concrete-rock interface.However,the parameters describing the frictional resistance of the interface usually do not account for these asperities.This could result in an underestimate of the peak shear stre ngth,which leads to significantly conservative design for new dams or unnecessary stability enhancing measures for existing ones.The aim of this work was to investigate the effect of the location of first-order asperity on the peak shear strength of a concrete-rock interface under eccentric load and the model discrepancy associated with the commonly used rigid body methods for calculating the factor of safety(FS)against sliding.For this,a series of direct and eccentric shear tests under constant normal load(CNL)was carried out on concrete-rock samples.The peak shear strengths measured in the tests were compared in terms of asperity location and with the predicted values from analytical rigid body methods.The results showed that the large-scale asperity under eccentric load significantly affected the peak shear strength.Furthermore,unlike the conventional assumption of sliding or shear failure of an asperity in direct shear,under the effect of eccentric shear load,a tensile failure in the rock or in the concrete could occur,resulting in a lower shear strength compared with that of direct shear tests.These results could have important implications for assessment of the FS against sliding failure in the concrete-rock interface.
基金financially supported by the National Key Research and Development Program of China(No.2018YFB2001101)the National Outstanding Youth Science Foundation of China(No.51922093)the National Natural Science Foundation of China(No.51890882).
文摘The wear condition of the piston/cylinder pair is crucial to the performance and reliability of the axial piston pump.The hard piston surface,the soft cylinder bore surface,and the interface oil film affects each other during the wear process.Specifically,in the mixed lubrication region,the geometry of the hard piston surface asperity directly affects the wear of soft cylinder bore surface,while the asperities may deform or even degrade when penetrating and sliding against the cylinder bore.So far,there is no suitable method to simulate their coupled evolution.This paper proposed a wear process simulation model considering the real-time interaction between the elasto-plastic deformation of the piston surface asperity,the wear contour of the cylinder bore,and the lubrication condition of the interface.An offline library of the elasto-plastic constitutive behavior of the asperity based on the finite element method(FEM)is established as a part of the simulation model to precisely analyze the deformation and degradation of the asperity and quickly invoke them in the numerical wear process simulation.The simulation and experimental results show that the piston asperity and the cylinder bore contour converge to a steady state after running-in for about 0.5 h.The distribution of the simulated asperity degradation and wear depth is also verified by the experiment.
基金National Natural Science Foundation of China under Grant Nos. 51275407,51475363.The authors gratefully acknowledge financial support provided by NNSF.
文摘A precise tangential contact damping model is proposed,which includes the lateral contact of the upper-lower asperities and the interaction of adjacent asperities.The effects of the normal static preload,frequency,and amplitude of tangential displacement on the tangential contact damping were analyzed by simulation,respectively.Furthermore,the results of simulation are verified by experiment.The tangential contact damping of considering the interaction and lateral contact of asperity is very close to the experimental results.
基金Supported by National Natural Science Foundation of China(Grant Nos.51705142,51535012)Hunan Provincial Natural Science Foundation of China(Grant No.2018JJ3162).
文摘The peak identification scheme based method(three-point definition)and the spectral moments based method(spectral moment approach)are both widely used for asperity peak modeling in tribology.To discover the differences between the two methods,a great number of rough surface profile samples with various statistical distributions are first randomly generated using FFT.Then the distribution parameters of asperity peaks are calculated for the generated samples with both methods.The obtained results are compared and verified by experiment.The variation rules of the differences between the two methods with statistical characteristics of rough surfaces are investigated.To explain for the discovered differences,the assumptions by spectral moment approach that the joint distribution of surface height,slope and curvature is normal and that the height distribution of asperities is Gaussian,are examined.The results show that it is unreasonable to assume a joint normal distribution without inspecting the correlation pattern of[z],[z′]and[z′′],and that the height distribution of asperities is not exactly Gaussian before correlation length of rough surface increases to a certain extent,20 for instance.
基金The National Key Research and Development Project(No.2019YFB2006402)the Open Fund Project of Key Laboratory of Intelligent Conveying Technology and Device,Hubei Polytechnic University.
文摘A new hybrid numerical method that couples the dynamic slider-crank mechanism(SCM)and crankpin bearing(CB)lubrication models is proposed to analyze the effect of micro asperity contact on the tribological properties of a CB.In the hybrid model,the dynamic equations of the SCM are established based on the Newton method,while the lubrication equations of the CB are established on the basis of the Reynolds equation.Experimental data of the engine are also used in simulation analyses to enhance the reliability of the results.The load-bearing capacity(LBC)and friction force of the CB are selected as objective functions.Results show that the LBC has a negligible effect on the tribological properties of the CB,but the friction force greatly affects the resistance of the bearing under different radial clearances and surface roughness values.In particular,the maximum friction force in the asperity contact region accounts for 40.5%of the maximum total friction force at a radial clearance of 5μm and 77.7%of the maximum total friction of the CB with a surface roughness of 10μm.
基金This work is supported by the National Key Research and Development Plan of China under Grants No.2018YFC1503604the National Natural Science Foundation of China under Grants No.41721003,No.42074007the Key Laboratory of Geospace Environment and Geodesy,Ministry of Education,Wuhan University,No.19-01-08。
文摘As an important model for explaining the seismic rupture mode,the asperity model plays an important role in studying the stress accumulation of faults and the location of earthquake initiation.Taking Qilian-Haiyuan fault as an example,this paper combines geodetic method and b-value method to propose a multi-source observation data fusion detection method that accurately determines the asperity boundary named dual threshold search method.The method is based on the criterion that the b-value asperity boundary should be most consistent with the slip deficit rate asperity boundary.Then the optimal threshold combination of slip deficit rate and b-value is obtained through threshold search,which can be used to determine the boundary of the asperity.Based on this method,the study finds that there are four potential asperities on the Qilian-Haiyuan fault:two asperities(A1 and A2)are on the Tuolaishan segment and the other two asperities(B and C)are on Lenglongling segment and Jinqianghe segment,respectively.Among them,the lengths of asperities A1 and A2 on Tuolaishan segment are 17.0 km and 64.8 km,respectively.And the lower boundaries are 5.5 km and 15.5 km,respectively;The length of asperity B on Lenglongling segment is 70.7 km,and the lower boundary is 10.2 km.The length of asperity C on Jinqianghe segment is 42.3 km,and the lower boundary is 8.3 km.
基金This work are supported by the Natural Science Foundation of China General Program(Grant No.12272157)the Natural Science Foundation of China Major Program(Grant No.12327901)+1 种基金the Fundamental Research Funds for the Central Universities(Grant No.lzujbky-2023-ey05)the 111 Project(Grant No.B14044).
文摘The contact problem of deformed rough surfaces exists widely in complex engineering structures.How to reveal the influence mechanism of surface deformation on the contact properties is a key issue in evaluating the interface performances of the engineering structures.In this paper,a contact model is established,which is suitable for tensile and bending deformed contact surfaces.Four contact forms of asperities are proposed,and their distribution characteristics are analyzed.This model reveals the mechanism of friction generation from the perspective of the force balance of asperity.The results show the contact behaviors of the deformed contact surface are significantly different from that of the plane contact,which is mainly reflected in the change in the number of contact asperities and the real contact area.This study suggests that the real contact area of the interface can be altered by applying tensile and bending strains,thereby regulating its contact mechanics and conductive behavior.
基金supported by the Nagasaki University Global Human Resource Development Scholarship and the Support for Pioneering Research Initiated by the Next Generation.
文摘Understanding the rate-dependent shear behavior of rough joints is crucial.This study explores the ratedependent shear behavior of rough joints through direct shear tests conducted under constant normal stiffness(CNS)boundary conditions,with the shear failure process monitored using acoustic emission(AE)technology.As the shear rate increases,both the peak and ultimate shear stresses of rough joints exhibit a decrease,highlighting a pronounced rate-dependent behavior.Asperity degradation under different shear rates is effectively characterized by normalized AE counts,exhibiting a three-stage Sshaped trend:Stage I(quiescent),Stage II(growth),and Stage III(stable).The simultaneous occurrence of the lowest AE b-value and the highest AE amplitude closely aligns with the moment of peak shear stress.This synchronization suggests that AE events of significant energy are predominantly clustered around the peak shear stress,which critically influences the overall progression of failure.Three failure modes of asperities were categorized,including the biting-off failure mode(BFM),the climbing-sliding failure mode(CFM),and the hybrid biting-off and climbing-sliding failure mode(HFM).Analysis of the multifractal spectra reveals that both the multifractal spectrum width(Δα)and the fractal dimension variability(Δf)diminish as the shear rate increases,suggesting that the complexity of the failure modes is inversely related to the shear rate.With increasing shear rates,the dominant failure mode evolves from BFM to CFM.The research findings facilitate a comprehensive understanding of the ratedependent shear behavior of rough joints,providing valuable guidance for rational support in underground engineering.
基金supported by the National Natural Science Foundation of China(Nos.12172019 and 42477210).
文摘We present a grid-growth method to reconstruct 3D rock joints with arbitrary joint roughness and persistence.In the first step of this workflow,the joint model is divided into uniform grids.Then by adjusting the positions of the grids,the joint morphology can be modified to construct models with desired joint roughness and persistence.Accordingly,numerous joint models with different joint roughness and persistence were built.The effects of relevant parameters(such as the number,height,slope of asperities,and the number,area of rock bridges)on the joint roughness coefficient(JRC)and joint persistence were investigated.Finally,an artificially split joint was reconstructed using the method,and the method's accuracy was evaluated by comparing the JRC of the models with that of the artificially split joint.The results showed that the proposed method can effectively control the JRC of joint models by adjusting the number,height,and slope of asperities.The method can also modify the joint persistence of joint models by adjusting the number and area of rock bridges.Additionally,the JRC of models obtained by our method agrees with that of the artificially split surface.Overall,the method demonstrated high accuracy for 3D rock joint reconstruction.
基金supported by the National Natural Science Foundation of China(Grant Nos.12272227 and 11732009).
文摘This paper introduces a model for characterizing the contact behavior of irregular asperities,transforming it into a superposition of sinusoidal asperity contact behaviors.A new sinusoidal asperity model is developed for bilin-ear hardening under plane strain conditions.Empirical equations are proposed,considering geometric shapes,tangent modulus,and Young’s modulus.The frequency of asperity height is extracted through Fourier transform for irregular asperities.Contact area and pressure are predicted using the sinusoidal asperity model,and the behavior of irregular asperities is obtained by superimposing those with the first three frequencies.Experimen-tal validation is conducted with milling and knurling-formed asperities,showing good alignment between the model and experimental results.In rough surface models,the proposed irregular asperity model exhibits greater accuracy in predicting contact behavior than a single sinusoidal asperity when interference exceeds 10%of the amplitude.
文摘A macroscopically nominal flat surface is rough at the nanoscale level and consists of nanoasperities.Therefore,the frictional properties of the macroscale-level rough surface are determined by the mechanical behaviors of nanoasperity contact pairs under shear.In this work,we first used molecular dynamics simulations to study the non-adhesive shear between single contact pairs.Subsequently,to estimate the friction coefficient of rough surfaces,we implemented the frictional behavior of a single contact pair into a Greenwood-Williamson-type statistical model.By employing the present multiscale approach,we used the size,rate,and orientation effects,which originated from nanoscale dislocation plasticity,to determine the dependence of the macroscale friction coefficient on system parameters,such as the surface roughness,separation,loading velocity,and direction.Our model predicts an unconventional dependence of the friction coefficient on the normal contact load,which has been observed in nanoscale frictional tests.Therefore,this model represents one step toward understanding some of the relevant macroscopic phenomena of surface friction at the nanoscale level.
基金the Research Council of Norway(Grant No.244029)the project‘Stable dams’,FORMAS(Grant No.2019e01236)+1 种基金the project‘Improved safety assessment of concrete dams’,and SVC(Grant No.VKU32019)the project‘Safe dams’,that supported the development of the research presented in this article.
文摘When assessing the sliding stability of a concrete dam,the influence of large-scale asperities in the sliding plane is often ignored due to limitations of the analytical rigid body assessment methods provided by current dam assessment guidelines.However,these asperities can potentially improve the load capacity of a concrete dam in terms of sliding stability.Although their influence in a sliding plane has been thoroughly studied for direct shear,their influence under eccentric loading,as in the case of dams,is unknown.This paper presents the results of a parametric study that used finite element analysis(FEA)to investigate the influence of large-scale asperities on the load capacity of small buttress dams.By varying the inclination and location of an asperity located in the concrete-rock interface along with the strength of the rock foundation material,transitions between different failure modes and correlations between the load capacity and the varied parameters were observed.The results indicated that the inclination of the asperity had a significant impact on the failure mode.When the inclinationwas 30and greater,interlocking occurred between the dam and foundation and the governing failure modes were either rupture of the dam body or asperity.When the asperity inclination was significant enough to provide interlocking,the load capacity of the dam was impacted by the strength of the rock in the foundation through influencing the load capacity of the asperity.The location of the asperity along the concrete-rock interface did not affect the failure mode,except for when the asperity was located at the toe of the dam,but had an influence on the load capacity when the failure occurred by rupture of the buttress or by sliding.By accounting for a single large-scale asperity in the concrete-rock interface of the analysed dam,a horizontal load capacity increase of 30%e160%was obtained,depending on the inclination and location of the asperity and the strength of the foundation material.
基金support from the National Natural Science Foundation of China(Grant Nos.51991392 and 42293355).
文摘The geometric properties of fracture surfaces significantly influence shear-seepage in rock fractures,introducing complexities to fracture modelling.The present study focuses on the hydro-mechanical behaviours of rough rock fractures during shear-seepage processes to reveal how dilatancy and fracture asperities affect these phenomena.To achieve this,an improved shear-flow model(SFM)is proposed with the incorporation of dilatancy effect and asperities.In particular,shear dilatancy is accounted for in both the elastic and plastic stages,in contrast to some existing models that only consider it in the elastic stage.Depending on the computation approaches for the peak dilatancy angle,three different versions of the SFM are derived based on Mohr-Coulomb,joint roughness coefficient-joint compressive strength(JRC-JCS),and Grasselli’s theories.Notably,this is a new attempt that utilizes Grasselli’s model in shearseepage analysis.An advanced parameter optimization method is introduced to accurately determine model parameters,addressing the issue of local optima inherent in some conventional methods.Then,model performance is evaluated against existing experimental results.The findings demonstrate that the SFM effectively reproduces the shear-seepage characteristics of rock fracture across a wide range of stress levels.Further sensitivity analysis reveals how dilatancy and asperity affect hydraulic properties.The relation between hydro-mechanical properties(dilatancy displacement and hydraulic conductivity)and asperity parameters is analysed.Several profound understandings of the shear-seepage process are obtained by exploring the phenomenon under various conditions.
文摘It is clear from the literature data that the geometric characteristics of the seismogenic source are directly related to the nucleation of their strong earthquakes. Our study starts from the observation of the proximity relationship between the epicenter of a strong earthquake and the surface trace of the seismogenic source. The proposed model is based on the mathematical analysis of seismicity falling within an area, through a polynomial function to determine a curve. The experimental results of our model confirm that 97% of the epicenters of strong earthquakes are located near the concavities or at the inflection points of the polynomial curve. Only 3% of strong earthquakes are located at the edges of the analyzed areas, where the number of data is not significant. The proposed model makes it possible to locate, with good approximation, the areas most likely to be the site of future strong earthquakes.
