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
The models constructed by particle flow simulation method can effectively simulate the heterogeneous substance characteristics and failure behaviors of rocks.However,existing contact models overlook the rock cracks,an...The models constructed by particle flow simulation method can effectively simulate the heterogeneous substance characteristics and failure behaviors of rocks.However,existing contact models overlook the rock cracks,and the various simulation methods that do consider cracks still exhibit certain limitations.In this paper,based on Flat-Joint model and Linear Parallel Bond model,a crack contact model considering linked substance in the crack is proposed by splitting the crack contact into two portions:linked portion and unlinked portion for calculation.The new contact model considers the influence of crack closure on the contact force-displacement law.And a better compressive tensile strength ratio(UCS/T)was obtained by limiting the failure of the contact bond to be solely controlled by the contact force and moment of the linked portion.Then,by employing the FISH Model tool within the Particle Flow Code,the contact model was constructed and verified through contact force–displacement experiments and loading-unloading tests with cracked model.Finally,the contact model was tested through simulations of rock mechanics experiments.The results indicate that the contact model can effectively simulate the axial and lateral strain laws of rocks simultaneously and has a relatively good reproduction of the bi-modularity of rocks.展开更多
Rolling contact fatigue performance is among the most important issues for applications of bearing steels.In this work,a recently developed surface modification technique,surface mechanical rolling treatment,was appli...Rolling contact fatigue performance is among the most important issues for applications of bearing steels.In this work,a recently developed surface modification technique,surface mechanical rolling treatment,was applied on a rare-earth addition bearing steel.And rolling contact fatigue behavior of treated samples was compared with that of as-received counterparts at different contacting stresses.The results demonstrated that a 700μm-thick gradient nanostructured surface layer is produced on samples by surface mechanical rolling treatment.The grain size decreases while the microhardness increases gradually with decreasing depth,reaching~23 nm and~10.2 GPa,respectively,at the top surface.Consequently,the rolling contact fatigue property is significantly enhanced.The characteristic life of treated samples is~3.2 times that of untreated counterparts according to Weibull curves at 5.6 GPa.Analyses of fatigue mechanisms demonstrated that the gradient nanostructured surface layer might not only retard material degradation and microcrack formation,but also prolong the steady-state elastic response stage under rolling contact fatigue.展开更多
All-solid-state lithium batteries(ASSLBs)are strongly considered as the next-generation energy storage devices for their high energy density and intrinsic safety.The solid-solid contact between lithium metal and solid...All-solid-state lithium batteries(ASSLBs)are strongly considered as the next-generation energy storage devices for their high energy density and intrinsic safety.The solid-solid contact between lithium metal and solid electrolyte plays a vital role in the performance of working ASSLBs,which is challenging to investigate quantitatively by experimental approach.This work proposed a quantitative model based on the finite element method for electrochemical impedance spectroscopy simulation of different solid-solid contact states in ASSLBs.With the assistance of an equivalent circuit model and distribution of relaxation times,it is discovered that as the number of voids and the sharpness of cracks increase,the contact resistance Rcgrows and ultimately dominates the battery impedance.Through accurate fitting,inverse proportional relations between contact resistance Rcand(1-porosity)as well as crack angle was disclosed.This contribution affords a fresh insight into clarifying solid-solid contact states in ASSLBs.展开更多
In this paper,an incremental contact model is developed for the elastic self-affine fractal rough surfaces under plane strain condition.The contact between a rough surface and a rigid plane is simplified by the accumu...In this paper,an incremental contact model is developed for the elastic self-affine fractal rough surfaces under plane strain condition.The contact between a rough surface and a rigid plane is simplified by the accumulation of identical line contacts with half-width given by the truncated area divided by the contact patch number at varying heights.Based on the contact stiffness of two-dimensional flat punch,the total stiffness of rough surface is estimated,and then the normal load is calculated by an incremental method.For various rough surfaces,the approximately linear load-area relationships predicted by the proposed model agree well with the results of finite element simulations.It is found that the real average contact pressure depends significantly on profile properties.展开更多
When the interface of a multilayered saturated soil is rough with noticeable gaps, heat flow lines converge towards the actual contact points, causing thermal flow contraction. Conversely, in the interface between two...When the interface of a multilayered saturated soil is rough with noticeable gaps, heat flow lines converge towards the actual contact points, causing thermal flow contraction. Conversely, in the interface between two layers of soil with different properties, pore water flows slowly along the pore channels, demonstrating laminar flow phenomenon. To predict the thermal contact resistance and flow contact resistance at the interface, this paper constructs general imperfect thermal contact model and general imperfect flow contact model, respectively. Utilizing a thermo-hydro- mechanical coupling model, the thermal consolidation behavior of multilayered saturated soil under two-dimensional conditions is investigated. Fourier and Laplace transformations are applied to decouple the governing equations, yielding expressions for the temperature increment, pore water pressure, and displacement in multilayered saturated soil. The inverse Fourier-Laplace transformation is then used to obtain numerical solutions, which are compared with degeneration solutions to validate the computational accuracy. The differences in the thermal consolidation process under various thermal contact and flow contact resistance models are discussed. Furthermore, the impact of parameters such as the thermal resistance coefficient, partition thermal contact coefficient, flow contact resistance coefficient, and partition flow contact coefficient on thermal consolidation are investigated. Results indicate that thermal contact resistance creates a relative thermal gradient at the interface, leading to increased pore water pressure and reduced displacement nearby. In contrast, flow contact resistance generates a relative pore pressure gradient at the interface, resulting in increased displacement within the saturated soil with minimal effect on temperature increment distribution.展开更多
The contact characteristics between cycloidal gear teeth and pinwheel teeth significantly impact the operational performance of cycloidal pinwheel mechanisms.Current research methods tend to rely primarily on theoreti...The contact characteristics between cycloidal gear teeth and pinwheel teeth significantly impact the operational performance of cycloidal pinwheel mechanisms.Current research methods tend to rely primarily on theoretical calculations,with limited use of experimental methods for detecting dynamic contact properties.We propose a novel method for testing the dynamic contact characteristics of cycloidal pinwheel mechanisms.By combining Hertzian contact theory and contact strength theory,we establish a force and meshing stiffness model for the cycloidal and pinwheel gears,and determine the maximum contact stress and variations in pinwheel gear force and meshing stiffness.Based on the principle of photoelasticity,we built a testing platform for the cycloidal pinwheel mechanism to assess its contact characteristics.This platform provides the stress distribution of the cycloidal pinwheel mechanism and allows us to deduce key parameters such as the number of meshing teeth and the meshing interval.This study provides an experimental method for investigating the contact characteristics of cycloidal pinwheel mechanisms.展开更多
This paper investigates interfacial heat transfer characteristics in amulti-layer structure under ultra-high heat flux conditions,focusing on thermal contact resistance(TCR)between adjacent layers.Athree-layer computa...This paper investigates interfacial heat transfer characteristics in amulti-layer structure under ultra-high heat flux conditions,focusing on thermal contact resistance(TCR)between adjacent layers.Athree-layer computational model with dual rough interfaces was developed to systematically analyze the synergistic effects of interfacial pressure,surface emissivity,and thermal interface materials(TIMs).Surface reconstruction using experimental measurement data generated two representative roughness models to quantify the impact of surface roughness on heat dissipation.Numerical simulations demonstrate that the absence of TIMs leads to insufficient thermal dissipation capacity under ultra-high heat flux conditions.Compared to TIMapplication,merely increasing the convective heat transfer coefficient shows limited effectiveness in enhancing heat dissipation efficiency.展开更多
This study proposes a general imperfect thermal contact model to predict the thermal contact resistance at the interface among multi-layered composite structures.Based on the Green-Lindsay(GL)thermoelastic theory,semi...This study proposes a general imperfect thermal contact model to predict the thermal contact resistance at the interface among multi-layered composite structures.Based on the Green-Lindsay(GL)thermoelastic theory,semi analytical solutions of temperature increment and displacement of multi-layered composite structures are obtained by using the Laplace transform method,upon which the effects of thermal resistance coefficient,partition coefficient,thermal conductivity ratio and heat capacity ratio on the responses are studied.The results show that the generalized imperfect thermal contact model can realistically describe the imperfect thermal contact problem.Accordingly,it may degenerate into other thermal contact models by adjusting the thermal resistance coefficient and partition coefficient.展开更多
The complex geometrical features of mechanical components significantly influence contact interactions and system dynamics.However,directly modeling contact forces on surfaces with intricate geometries presents consid...The complex geometrical features of mechanical components significantly influence contact interactions and system dynamics.However,directly modeling contact forces on surfaces with intricate geometries presents considerable challenges.This study focuses on the helically twisted wire rope-sheave contact and proposes a contact force model that incorporates complex geometric features through a parameter identification approach.The model's impact on contact forces and system dynamics is thoroughly investigated.Leveraging a point contact model and an elliptic integral approximation,a loss function is formulated using the finite element(FE)contact model results as the reference data.Geometric parameters are subsequently determined by optimizing this loss function via a genetic algorithm(GA).The findings reveal that the contact stiffness increases with the wire rope pitch length,the radius of principal curvature,and the elliptic eccentricity of the contact zone.The proposed contact force model is integrated into a rigid-flexible coupled dynamics model,developed by the absolute node coordinate formulation,to examine the effects of contact geometry on system dynamics.The results demonstrate that the variations in wire rope geometry alter the contact stiffness,which in turn affects dynamic rope tension through frictional energy dissipation.The enhanced model's predictions exhibit superior alignment with the experimental data,thereby validating the methodology.This approach provides new insights for deducing the contact geometry from kinetic parameters and monitoring the performance degradation of mechanical components.展开更多
As the performance of the box-type multiple launch rocket system(BMLRS)improves,its mechanical structures,particularly the plane clearance design between the slider on the rocket and the guide inside the launch canist...As the performance of the box-type multiple launch rocket system(BMLRS)improves,its mechanical structures,particularly the plane clearance design between the slider on the rocket and the guide inside the launch canister,have grown increasingly complex.However,deficiencies still exist in the current launch modeling theory for BMLRS.In this study,a multi-rigid-flexible-body launch dynamics model coupling the launch platform and rocket was established using the multibody system transfer matrix method and the Newton-Euler formulation.Furthermore,considering the bending of the launch canister,a detection algorithm for slider-guide plane clearance contact was proposed.To quantify the contact force and friction effect between the slider and guide,the contact force model and modified Coulomb model were introduced.Both the modal and launch tests were conducted.Additionally,the modal convergence was verified.By comparing the modal experiments and simulation results,the maximum relative error of the eigenfrequency is 3.29%.thereby verifying the accuracy of the developed BMLRS dynamics model.Furthermore,the launch test validated the proposed plane clearance contact model.Moreover,the study investigated the influence of various model parameters on the dynamic characteristics of BMLRS,including launch canister bending stiffness,slider and guide material,slider-guide clearance,slider length and layout.This analysis of influencing factors provides a foundation for future optimization in BMLRS design.展开更多
Ohmic contacts are fundamental components in semiconductor technology,facilitating efficient electrical connection and excellent device performance.We employ first-principles calculations to show that semimetallic gra...Ohmic contacts are fundamental components in semiconductor technology,facilitating efficient electrical connection and excellent device performance.We employ first-principles calculations to show that semimetallic graphene is a natural Ohmic contact partner of monolayer semiconducting black arsenic(BAs),for which the top of the valence band is below the Fermi energy of the order of 10~2 meV.The Ohmic contact arises from the giant Stark effect induced by van der Waals electron transfer from BAs to graphene,which does not destroy their respective band features.Remarkably,we show that this intrinsic Ohmic contact remains robust across a wide range of interlayer distances(adjustable by strain)or vertical electric fields,whereas the weak spin splitting of the order of 1 meV induced by symmetry breaking plays little part in Ohmic contact.These findings reveal the potential applications of graphene–BAs in ultralow dissipation transistors.展开更多
The contact stiffness of the tool-holder assembly interface affects the overall dynamic performance of the milling system.Currently,the contact parameters are primarily established by minimizing the frequency response...The contact stiffness of the tool-holder assembly interface affects the overall dynamic performance of the milling system.Currently,the contact parameters are primarily established by minimizing the frequency response in modal tests and through dynamic simulation results.However,alterations in the structure or material of the tool-holder system necessitate multiple modal tests,thereby increasing computational costs.This study aims to streamline the process of determining contact stiffness and enhance accuracy by developing an analytical model that considers tool-holder contact properties.Initially,the microstructure of the contact surface is characterized via fractal theory to determine its fractal parameters.Then the contact coefficient is introduced to precisely depict the area distribution function of the microcontact.Building upon this,a contact stiffness model is established which is verified by the modal tests.The test results indicate that utilizing this model can reduce the structural modal frequency calculation error to 0.56%.Finally,the Monte Carlo algorithm is employed to investigate the sensitivity of fractal parameters and radial interference on contact characteristics.The findings demonstrate that the fractal dimension has the greatest influence on the dynamic behavior of the tool-holder structure.This study proposes a milling tool-holder contact stiffness modeling method from a microscopic perspective,which offers sufficient computational accuracy to provide a theoretical basis for the selection of milling tool-holder structures in practical machining.展开更多
This paper investigates the frictional adhesive contact of a rigid,electrically/magnetically conductive spherical indenter sliding past a multiferroic coating deposed onto a rigid substrate,based on the hybrid element...This paper investigates the frictional adhesive contact of a rigid,electrically/magnetically conductive spherical indenter sliding past a multiferroic coating deposed onto a rigid substrate,based on the hybrid element method.The adhesion behavior is described based on the Maugis-Dugdale model.The adhesion-driven conjugate gradient method is employed to calculate the distribution of unknown pressures,while the discrete convolution-fast Fourier transform is utilized to compute the deformations,surface electric and magnetic potentials as well as the subsurface stresses,electric displacements,and magnetic inductions.The goal of this study is to investigate the influences of adhesion parameter,friction coefficient,coating thickness,and surface electric and magnetic charge densities on contact behaviors,such as contact area and pressures,electric and magnetic potentials,and subsurface stresses.展开更多
AIM:To gain insight into the future research directions in scleral contact lenses(SCLs)through a comprehensive bibliometrics study.METHODS:The publications related to SCLs were screened from the Web of Science Core Co...AIM:To gain insight into the future research directions in scleral contact lenses(SCLs)through a comprehensive bibliometrics study.METHODS:The publications related to SCLs were screened from the Web of Science Core Collection(WOSCC)database.All bibliographic information was extracted and used to conduct a performance analysis.CiteSpace and VOSviewer were employed to visualize annual publication counts,journals,authors,countries,institutions,collaboration networks,keywords,and references.RESULTS:A total of 498 articles were included in our analysis and the number of publications about SCLs showed a significant yearly increase.These publications predominantly emanated from 523 institutions across 38 countries,with the United States and Australia leading in frequency.Totally 1361 authors were identified,among whom Vincent J.Stephen exhibited the highest number of publications,while Jacobs S.Deborah received the most citations.Notably,the journal Contact Lens&Anterior Eye emerged as the primary publisher of studies,and it also boasted the highest citation rate.“Fluid-ventilated,gas-permeable scleral contact lens is an effective option for managing severe ocular surface disease and many corneal disorders that would otherwise require penetrating keratoplasty”was the most cited paper published in eye&contact lens in 2005.The most prevalent keywords encompassed“keratoconus”,“scleral contact lenses”,“management”,“contact lenses”,“scleral contact lens”,“ocular surface disease”,“dry eye”,and“contact lens”.CONCLUSION:Although SCLs have demonstrated significant potential in ophthalmological care,the results offer valuable insights pertinent to future research directions and clinical practice.Greater emphasis should be placed on developing enhancements in design,materials,and fitting technique,as well as on reducing the complications associated with SCLs.展开更多
AIM:To compare the Ishihara test errors scores of colour vision deficiency(CVD)subjects when wearing four different types of red-tinted contact lenses(RCL)that differ in their transmittance as determined using a spect...AIM:To compare the Ishihara test errors scores of colour vision deficiency(CVD)subjects when wearing four different types of red-tinted contact lenses(RCL)that differ in their transmittance as determined using a spectrophotometer.METHODS:Six congenital CVD subjects volunteered to participate in this study.Ishihara plates were used to determine the colour vision errors made,whereas Farnsworth-Munsell 100 Hue test was conducted to determine the total error scores(TES)and type of CVD.Four types of RCL(Types A,B,C and D)were inserted in the non-dominant eye and tested in a randomised manner by a masked operator.Errors scores in Ishihara test were determined at baseline without any contact lens and after wearing the four different RCL.The subjects were then divided into two groups based on the mean TES.RESULTS:Repeated measures ANOVA with Greenhouse-Geisser corrections showed that there was a highly significant effect of RCL type on Ishihara error score[F(2.056,10.282)=30.214,P<0.001].Error scores with RCL Type B were significantly lower than errors made when no lens was worn,and with RCL Type C and Type D(all P<0.001).Error scores with RCL Type B were also lower than those made with RCL Type A,however,they were not significantly different.For subjects with TES values less than 180,RCL type B showed the largest improvement in Ishihara error score(50%)compared to the other three RCLs.RCL type A showed the best performance in TES value of more than 180,with an improvement of 80%in Ishihara score.RCL Type A has the lowest transmittance at the confusion wavelength(450-568 nm),followed by RCL Types B,D and C.CONCLUSION:This study shows that RCL can improve Ishihara error scores.RCL with lower transmission at 450-568 nm and 90%transmittance beyond 637 nm are the most effective.Lenses which could block more light between 550-580 nm are more effective for colour defectives with more severe colour defects.展开更多
AlGaN-based LEDs with peak wavelength below 240 nm(far-UVC)pose no significant harm to human health,thus highlighting their broader application potential.While,there is a significant Schottky barrier between the n-ele...AlGaN-based LEDs with peak wavelength below 240 nm(far-UVC)pose no significant harm to human health,thus highlighting their broader application potential.While,there is a significant Schottky barrier between the n-electrode and Alrich n-AlGaN,adversely impeding electron injection and resulting in considerable heat generation.Here,we fabricate V-based electrodes of V/Al/Ti/Au on n-AlGaN with Al content over 80%and investigate the relationship between the metal diffusion and contact properties during the high-temperature annealing process.Experiments reveal that decreasing V thickness in the electrode promotes the diffusion of Al towards the surface of n-AlGaN,which facilitates the formation of VN and thus the increase of local electron concentration,resulting in lower specific contact resistivity.Then,increasing the Al thickness inhibits the diffusion of Au to the n-AlGaN surface,suppressing the rise of Schottky barrier.Experimentally,an optimized n-electrode of V(10 nm)/Al(240 nm)/Ti(40 nm)/Au(50 nm)on n-Al_(0.81)Ga_(0.19)N is obtained,realizing an optimal specific contact resistivity of 7.30×10^(−4)Ω·cm^(2).Based on the optimal n-electrode preparation scheme for Al-rich n-AlGaN,the work voltage of a far-UVC LED with peak wavelength of 233.5 nm is effectively reduced.展开更多
This study experimentally investigates the oscillatory dynamics of wind-driven droplets using high-speed imaging to capture droplet profiles within the symmetry plane and to characterize their natural oscillation freq...This study experimentally investigates the oscillatory dynamics of wind-driven droplets using high-speed imaging to capture droplet profiles within the symmetry plane and to characterize their natural oscillation frequencies.Results reveal that the eigenfrequencies vary spatially due to distinct oscillation modes occurring at different droplet locations.Notably,the fundamental eigenfrequency decreases with reducing droplet volume,while droplet viscosity exerts minimal influence on this frequency.Prior to the onset of motion,the dynamic contact angle consistently remains between the advancing and receding angles.The inertial forces generated by droplet oscillation are found to be significantly greater than the adhesion forces,indicating that classical static models are inadequate for capturing inertial contributions to droplet motion.These findings offer new insights into the role of oscillatory behavior in influencing the dynamics of droplet motion,and contribute to a more detailed understanding of wind-driven droplet transport phenomena.展开更多
MXene-based smart contact lenses demonstrate a cutting-edge advancement in wearable ophthalmic technology,combining real-time biosensing,therapeutic capabilities,and user comfort in a single platform.These devices tak...MXene-based smart contact lenses demonstrate a cutting-edge advancement in wearable ophthalmic technology,combining real-time biosensing,therapeutic capabilities,and user comfort in a single platform.These devices take the advantage of the exceptional electrical conductivity,mechanical flexibility,and biocompatibility of two-dimensional MXenes to enable noninvasive,tear-based monitoring of key physiological markers such as intraocular pressure and glucose levels.Recent developments focus on the integration of transparent MXene films into the conventional lens materials,allowing multifunctional performance including photothermal therapy,antimicrobial and anti-inflammation protection,and dehydration resistance.These innovations offer promising strategies for ocular disease management and eye protection.In addition to their multifunctionality,improvements in MXene synthesis and device engineering have enhanced the stability,transparency,and wearability of these lenses.Despite these advances,challenges remain in long-term biostability,scalable production,and integration with wireless communication systems.This review summarizes the current progress,key challenges,and future directions of MXene-based smart contact lenses,highlighting their transformative potential in next-generation digital healthcare and ophthalmic care.展开更多
BACKGROUND Systematic reviews(SRs)synthesize and evaluate data,mainly from randomized trials,which then guides the development of clinical recommendations in evidence-based medicine.However,the data and methodological...BACKGROUND Systematic reviews(SRs)synthesize and evaluate data,mainly from randomized trials,which then guides the development of clinical recommendations in evidence-based medicine.However,the data and methodological information in the included papers can often be lacking or unclear,and reviewers usually need to contact the authors of included studies for clarifications.Contacting authors is recommended,but it is unclear how often SR teams do it,or what the level of response is.AIM To investigate how often reviewers undertake contact with the authors of included randomized controlled trials(RCTs)for clarification on data and risk of bias concerns,to explore the factors that influence whether SR authors contact or do not contact the authors,and the content and level of responses.METHODS We conducted a systematic electronic database search in MEDLINE using the search string“(systematic review)”AND“(RCT OR randomized OR trial)”for articles published between 1 January 2024 and 19 February 2024,without language restrictions.Screening and data extraction was done independently by two reviewers,and conflicts resolved by a senior author.Contact authors of included SRs were contacted for clarifications.RESULTS Of the 329 included SRs,38%(n=125)explicitly mentioned contact with the authors of included studies.The remaining 62%(n=204)did not.We attempted contact with all SR teams for clarifications and received 90 responses(19.4%).Of the 50 respondents who did not explicitly mention contact in their SRs,25(50%)replied that they did make contact.We received a total of 64 responses on the level and content of information sought.The mean±SD contacts SR teams made were 10(10),replies received 5(6.7),and response waiting time 10.1(28.3)weeks.Resources,time,poor previous experience,perceived likelihood of poor response and bias concerns were reported as barriers to attempting contact.CONCLUSION The majority of SRs published in 2024 did not confirm seeking clarifying or missing information from primary study authors.However,SR teams reported that 50%of contacted primary authors respond.Additional research can clarify this rate of response and establish methods to increase the integration of this core methodological element in SRs.展开更多
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 Natural Science Foundation of Heilongjiang Province(No.ZD2021E006)the National Natural Science Foundation of China(Nos.52174075 and 52074110).
文摘The models constructed by particle flow simulation method can effectively simulate the heterogeneous substance characteristics and failure behaviors of rocks.However,existing contact models overlook the rock cracks,and the various simulation methods that do consider cracks still exhibit certain limitations.In this paper,based on Flat-Joint model and Linear Parallel Bond model,a crack contact model considering linked substance in the crack is proposed by splitting the crack contact into two portions:linked portion and unlinked portion for calculation.The new contact model considers the influence of crack closure on the contact force-displacement law.And a better compressive tensile strength ratio(UCS/T)was obtained by limiting the failure of the contact bond to be solely controlled by the contact force and moment of the linked portion.Then,by employing the FISH Model tool within the Particle Flow Code,the contact model was constructed and verified through contact force–displacement experiments and loading-unloading tests with cracked model.Finally,the contact model was tested through simulations of rock mechanics experiments.The results indicate that the contact model can effectively simulate the axial and lateral strain laws of rocks simultaneously and has a relatively good reproduction of the bi-modularity of rocks.
基金The financial supports by the Chinese Academy of Sciences(Nos.XDC04030300 and XDB0510303)CAS-HK Joint Laboratory of Nanomaterials and MechanicsShenyang National Laboratory for Materials Science are acknowledged.
文摘Rolling contact fatigue performance is among the most important issues for applications of bearing steels.In this work,a recently developed surface modification technique,surface mechanical rolling treatment,was applied on a rare-earth addition bearing steel.And rolling contact fatigue behavior of treated samples was compared with that of as-received counterparts at different contacting stresses.The results demonstrated that a 700μm-thick gradient nanostructured surface layer is produced on samples by surface mechanical rolling treatment.The grain size decreases while the microhardness increases gradually with decreasing depth,reaching~23 nm and~10.2 GPa,respectively,at the top surface.Consequently,the rolling contact fatigue property is significantly enhanced.The characteristic life of treated samples is~3.2 times that of untreated counterparts according to Weibull curves at 5.6 GPa.Analyses of fatigue mechanisms demonstrated that the gradient nanostructured surface layer might not only retard material degradation and microcrack formation,but also prolong the steady-state elastic response stage under rolling contact fatigue.
基金supported by the Beijing Natural Science Foundation(Z200011,L233004)the National Key Research and Development Program(2021YFB2500300)+3 种基金the National Natural Science Foundation of China(52394170,52394171,22109011,22393900,and 22108151)the Tsinghua-Jiangyin Innovation Special Fund(TJISF)(2022JYTH0101)the S&T Program of Hebei(22344402D)the Tsinghua University Initiative Scientific Research Program.
文摘All-solid-state lithium batteries(ASSLBs)are strongly considered as the next-generation energy storage devices for their high energy density and intrinsic safety.The solid-solid contact between lithium metal and solid electrolyte plays a vital role in the performance of working ASSLBs,which is challenging to investigate quantitatively by experimental approach.This work proposed a quantitative model based on the finite element method for electrochemical impedance spectroscopy simulation of different solid-solid contact states in ASSLBs.With the assistance of an equivalent circuit model and distribution of relaxation times,it is discovered that as the number of voids and the sharpness of cracks increase,the contact resistance Rcgrows and ultimately dominates the battery impedance.Through accurate fitting,inverse proportional relations between contact resistance Rcand(1-porosity)as well as crack angle was disclosed.This contribution affords a fresh insight into clarifying solid-solid contact states in ASSLBs.
基金supported by the National Natural Science Foundation of China(Grant Nos.12372100,12302126,and 12302141)the China Postdoctoral Science Foundation(Grant No.2023M732799)+1 种基金the Fundamental Research Funds for the Central Universities(Grant No.xzy012024020)Sihe Wang also thanks the support from the China Scholarship Council(CSC).
文摘In this paper,an incremental contact model is developed for the elastic self-affine fractal rough surfaces under plane strain condition.The contact between a rough surface and a rigid plane is simplified by the accumulation of identical line contacts with half-width given by the truncated area divided by the contact patch number at varying heights.Based on the contact stiffness of two-dimensional flat punch,the total stiffness of rough surface is estimated,and then the normal load is calculated by an incremental method.For various rough surfaces,the approximately linear load-area relationships predicted by the proposed model agree well with the results of finite element simulations.It is found that the real average contact pressure depends significantly on profile properties.
基金Projects(52108347, 52179112, 52178371) supported by the National Natural Science Foundation of ChinaProjects(2020C01147, 2023C01165) supported by the Primary Research and Development Plan of Zhejiang Province,ChinaProject(LQ22E080010) supported by the Outstanding Youth Project of Natural Science Foundation of Zhejiang Province,China。
文摘When the interface of a multilayered saturated soil is rough with noticeable gaps, heat flow lines converge towards the actual contact points, causing thermal flow contraction. Conversely, in the interface between two layers of soil with different properties, pore water flows slowly along the pore channels, demonstrating laminar flow phenomenon. To predict the thermal contact resistance and flow contact resistance at the interface, this paper constructs general imperfect thermal contact model and general imperfect flow contact model, respectively. Utilizing a thermo-hydro- mechanical coupling model, the thermal consolidation behavior of multilayered saturated soil under two-dimensional conditions is investigated. Fourier and Laplace transformations are applied to decouple the governing equations, yielding expressions for the temperature increment, pore water pressure, and displacement in multilayered saturated soil. The inverse Fourier-Laplace transformation is then used to obtain numerical solutions, which are compared with degeneration solutions to validate the computational accuracy. The differences in the thermal consolidation process under various thermal contact and flow contact resistance models are discussed. Furthermore, the impact of parameters such as the thermal resistance coefficient, partition thermal contact coefficient, flow contact resistance coefficient, and partition flow contact coefficient on thermal consolidation are investigated. Results indicate that thermal contact resistance creates a relative thermal gradient at the interface, leading to increased pore water pressure and reduced displacement nearby. In contrast, flow contact resistance generates a relative pore pressure gradient at the interface, resulting in increased displacement within the saturated soil with minimal effect on temperature increment distribution.
基金Sponsored by Natural Science Foundation of Hebei Province(Grant No.E2019209153)Tangshan Science and Technology Program(Grant No.22130219G).
文摘The contact characteristics between cycloidal gear teeth and pinwheel teeth significantly impact the operational performance of cycloidal pinwheel mechanisms.Current research methods tend to rely primarily on theoretical calculations,with limited use of experimental methods for detecting dynamic contact properties.We propose a novel method for testing the dynamic contact characteristics of cycloidal pinwheel mechanisms.By combining Hertzian contact theory and contact strength theory,we establish a force and meshing stiffness model for the cycloidal and pinwheel gears,and determine the maximum contact stress and variations in pinwheel gear force and meshing stiffness.Based on the principle of photoelasticity,we built a testing platform for the cycloidal pinwheel mechanism to assess its contact characteristics.This platform provides the stress distribution of the cycloidal pinwheel mechanism and allows us to deduce key parameters such as the number of meshing teeth and the meshing interval.This study provides an experimental method for investigating the contact characteristics of cycloidal pinwheel mechanisms.
基金by the Natural Science Foundation of Shandong Province,China(No.ZR2023QE159).
文摘This paper investigates interfacial heat transfer characteristics in amulti-layer structure under ultra-high heat flux conditions,focusing on thermal contact resistance(TCR)between adjacent layers.Athree-layer computational model with dual rough interfaces was developed to systematically analyze the synergistic effects of interfacial pressure,surface emissivity,and thermal interface materials(TIMs).Surface reconstruction using experimental measurement data generated two representative roughness models to quantify the impact of surface roughness on heat dissipation.Numerical simulations demonstrate that the absence of TIMs leads to insufficient thermal dissipation capacity under ultra-high heat flux conditions.Compared to TIMapplication,merely increasing the convective heat transfer coefficient shows limited effectiveness in enhancing heat dissipation efficiency.
基金Projects(42477162,52108347,52178371,52168046,52178321,52308383)supported by the National Natural Science Foundation of ChinaProjects(2023C03143,2022C01099,2024C01219,2022C03151)supported by the Zhejiang Key Research and Development Plan,China+6 种基金Project(LQ22E080010)supported by the Exploring Youth Project of Zhejiang Natural Science Foundation,ChinaProject(LR21E080005)supported by the Outstanding Youth Project of Natural Science Foundation of Zhejiang Province,ChinaProject(2022M712964)supported by the Postdoctoral Science Foundation of ChinaProject(2023AFB008)supported by the Natural Science Foundation of Hubei Province for Youth,ChinaProject(202203)supported by Engineering Research Centre of Rock-Soil Drilling&Excavation and Protection,Ministry of Education,ChinaProject(202305-2)supported by the Science and Technology Project of Zhejiang Provincial Communication Department,ChinaProject(2021K256)supported by the Construction Research Founds of Department of Housing and Urban-Rural Development of Zhejiang Province,China。
文摘This study proposes a general imperfect thermal contact model to predict the thermal contact resistance at the interface among multi-layered composite structures.Based on the Green-Lindsay(GL)thermoelastic theory,semi analytical solutions of temperature increment and displacement of multi-layered composite structures are obtained by using the Laplace transform method,upon which the effects of thermal resistance coefficient,partition coefficient,thermal conductivity ratio and heat capacity ratio on the responses are studied.The results show that the generalized imperfect thermal contact model can realistically describe the imperfect thermal contact problem.Accordingly,it may degenerate into other thermal contact models by adjusting the thermal resistance coefficient and partition coefficient.
基金supported by the National Key Research and Development Program of China(No.2023YFC3010400)。
文摘The complex geometrical features of mechanical components significantly influence contact interactions and system dynamics.However,directly modeling contact forces on surfaces with intricate geometries presents considerable challenges.This study focuses on the helically twisted wire rope-sheave contact and proposes a contact force model that incorporates complex geometric features through a parameter identification approach.The model's impact on contact forces and system dynamics is thoroughly investigated.Leveraging a point contact model and an elliptic integral approximation,a loss function is formulated using the finite element(FE)contact model results as the reference data.Geometric parameters are subsequently determined by optimizing this loss function via a genetic algorithm(GA).The findings reveal that the contact stiffness increases with the wire rope pitch length,the radius of principal curvature,and the elliptic eccentricity of the contact zone.The proposed contact force model is integrated into a rigid-flexible coupled dynamics model,developed by the absolute node coordinate formulation,to examine the effects of contact geometry on system dynamics.The results demonstrate that the variations in wire rope geometry alter the contact stiffness,which in turn affects dynamic rope tension through frictional energy dissipation.The enhanced model's predictions exhibit superior alignment with the experimental data,thereby validating the methodology.This approach provides new insights for deducing the contact geometry from kinetic parameters and monitoring the performance degradation of mechanical components.
基金supported by National Natural Science Foundation of China(Grant No.92266201).
文摘As the performance of the box-type multiple launch rocket system(BMLRS)improves,its mechanical structures,particularly the plane clearance design between the slider on the rocket and the guide inside the launch canister,have grown increasingly complex.However,deficiencies still exist in the current launch modeling theory for BMLRS.In this study,a multi-rigid-flexible-body launch dynamics model coupling the launch platform and rocket was established using the multibody system transfer matrix method and the Newton-Euler formulation.Furthermore,considering the bending of the launch canister,a detection algorithm for slider-guide plane clearance contact was proposed.To quantify the contact force and friction effect between the slider and guide,the contact force model and modified Coulomb model were introduced.Both the modal and launch tests were conducted.Additionally,the modal convergence was verified.By comparing the modal experiments and simulation results,the maximum relative error of the eigenfrequency is 3.29%.thereby verifying the accuracy of the developed BMLRS dynamics model.Furthermore,the launch test validated the proposed plane clearance contact model.Moreover,the study investigated the influence of various model parameters on the dynamic characteristics of BMLRS,including launch canister bending stiffness,slider and guide material,slider-guide clearance,slider length and layout.This analysis of influencing factors provides a foundation for future optimization in BMLRS design.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.62374088 and 12074193)。
文摘Ohmic contacts are fundamental components in semiconductor technology,facilitating efficient electrical connection and excellent device performance.We employ first-principles calculations to show that semimetallic graphene is a natural Ohmic contact partner of monolayer semiconducting black arsenic(BAs),for which the top of the valence band is below the Fermi energy of the order of 10~2 meV.The Ohmic contact arises from the giant Stark effect induced by van der Waals electron transfer from BAs to graphene,which does not destroy their respective band features.Remarkably,we show that this intrinsic Ohmic contact remains robust across a wide range of interlayer distances(adjustable by strain)or vertical electric fields,whereas the weak spin splitting of the order of 1 meV induced by symmetry breaking plays little part in Ohmic contact.These findings reveal the potential applications of graphene–BAs in ultralow dissipation transistors.
基金Supported by National Science and Technology Major Project of China(Grant No.J2019-VII-0001-0141).
文摘The contact stiffness of the tool-holder assembly interface affects the overall dynamic performance of the milling system.Currently,the contact parameters are primarily established by minimizing the frequency response in modal tests and through dynamic simulation results.However,alterations in the structure or material of the tool-holder system necessitate multiple modal tests,thereby increasing computational costs.This study aims to streamline the process of determining contact stiffness and enhance accuracy by developing an analytical model that considers tool-holder contact properties.Initially,the microstructure of the contact surface is characterized via fractal theory to determine its fractal parameters.Then the contact coefficient is introduced to precisely depict the area distribution function of the microcontact.Building upon this,a contact stiffness model is established which is verified by the modal tests.The test results indicate that utilizing this model can reduce the structural modal frequency calculation error to 0.56%.Finally,the Monte Carlo algorithm is employed to investigate the sensitivity of fractal parameters and radial interference on contact characteristics.The findings demonstrate that the fractal dimension has the greatest influence on the dynamic behavior of the tool-holder structure.This study proposes a milling tool-holder contact stiffness modeling method from a microscopic perspective,which offers sufficient computational accuracy to provide a theoretical basis for the selection of milling tool-holder structures in practical machining.
基金support from the National Natural Science Foundation of China(12102085)the Postdoctoral Science Foundation of China(2023M730504)+2 种基金the Sichuan Province Regional Innovation and Cooperation Project(2024YFHZ0210)supported by the European Union-NextGenerationEU through the Italian Ministry of University and Research under the following programs:(NM)PRIN2022(Projects of Relevant National Interest)grant no.2022SJ8HTC-Electroactive Gripper for Micro-Object Manipulation(ELFIN)(NM)PRIN2022 PNRR(Projects of Relevant National Interest)grant no.P2022MAZHX-Tribological Modeling for Sustainable Design of Industrial Frictional Interfaces(TRIBOSCORE).
文摘This paper investigates the frictional adhesive contact of a rigid,electrically/magnetically conductive spherical indenter sliding past a multiferroic coating deposed onto a rigid substrate,based on the hybrid element method.The adhesion behavior is described based on the Maugis-Dugdale model.The adhesion-driven conjugate gradient method is employed to calculate the distribution of unknown pressures,while the discrete convolution-fast Fourier transform is utilized to compute the deformations,surface electric and magnetic potentials as well as the subsurface stresses,electric displacements,and magnetic inductions.The goal of this study is to investigate the influences of adhesion parameter,friction coefficient,coating thickness,and surface electric and magnetic charge densities on contact behaviors,such as contact area and pressures,electric and magnetic potentials,and subsurface stresses.
文摘AIM:To gain insight into the future research directions in scleral contact lenses(SCLs)through a comprehensive bibliometrics study.METHODS:The publications related to SCLs were screened from the Web of Science Core Collection(WOSCC)database.All bibliographic information was extracted and used to conduct a performance analysis.CiteSpace and VOSviewer were employed to visualize annual publication counts,journals,authors,countries,institutions,collaboration networks,keywords,and references.RESULTS:A total of 498 articles were included in our analysis and the number of publications about SCLs showed a significant yearly increase.These publications predominantly emanated from 523 institutions across 38 countries,with the United States and Australia leading in frequency.Totally 1361 authors were identified,among whom Vincent J.Stephen exhibited the highest number of publications,while Jacobs S.Deborah received the most citations.Notably,the journal Contact Lens&Anterior Eye emerged as the primary publisher of studies,and it also boasted the highest citation rate.“Fluid-ventilated,gas-permeable scleral contact lens is an effective option for managing severe ocular surface disease and many corneal disorders that would otherwise require penetrating keratoplasty”was the most cited paper published in eye&contact lens in 2005.The most prevalent keywords encompassed“keratoconus”,“scleral contact lenses”,“management”,“contact lenses”,“scleral contact lens”,“ocular surface disease”,“dry eye”,and“contact lens”.CONCLUSION:Although SCLs have demonstrated significant potential in ophthalmological care,the results offer valuable insights pertinent to future research directions and clinical practice.Greater emphasis should be placed on developing enhancements in design,materials,and fitting technique,as well as on reducing the complications associated with SCLs.
文摘AIM:To compare the Ishihara test errors scores of colour vision deficiency(CVD)subjects when wearing four different types of red-tinted contact lenses(RCL)that differ in their transmittance as determined using a spectrophotometer.METHODS:Six congenital CVD subjects volunteered to participate in this study.Ishihara plates were used to determine the colour vision errors made,whereas Farnsworth-Munsell 100 Hue test was conducted to determine the total error scores(TES)and type of CVD.Four types of RCL(Types A,B,C and D)were inserted in the non-dominant eye and tested in a randomised manner by a masked operator.Errors scores in Ishihara test were determined at baseline without any contact lens and after wearing the four different RCL.The subjects were then divided into two groups based on the mean TES.RESULTS:Repeated measures ANOVA with Greenhouse-Geisser corrections showed that there was a highly significant effect of RCL type on Ishihara error score[F(2.056,10.282)=30.214,P<0.001].Error scores with RCL Type B were significantly lower than errors made when no lens was worn,and with RCL Type C and Type D(all P<0.001).Error scores with RCL Type B were also lower than those made with RCL Type A,however,they were not significantly different.For subjects with TES values less than 180,RCL type B showed the largest improvement in Ishihara error score(50%)compared to the other three RCLs.RCL type A showed the best performance in TES value of more than 180,with an improvement of 80%in Ishihara score.RCL Type A has the lowest transmittance at the confusion wavelength(450-568 nm),followed by RCL Types B,D and C.CONCLUSION:This study shows that RCL can improve Ishihara error scores.RCL with lower transmission at 450-568 nm and 90%transmittance beyond 637 nm are the most effective.Lenses which could block more light between 550-580 nm are more effective for colour defectives with more severe colour defects.
基金supported by National Key R&D Program of China(2022YFB3605103)National Natural Science Foundation of China(62425408,62121005,U22A2084,12234018)+2 种基金Youth Innovation Promotion Association of the Chinese Academy of Sciences(2023223)Natural Science Foundation of Jilin Province(20230101345JC,20230101360JC,SKL202302026)Young Elite Scientist Sponsorship Program by CAST(YESS20200182).
文摘AlGaN-based LEDs with peak wavelength below 240 nm(far-UVC)pose no significant harm to human health,thus highlighting their broader application potential.While,there is a significant Schottky barrier between the n-electrode and Alrich n-AlGaN,adversely impeding electron injection and resulting in considerable heat generation.Here,we fabricate V-based electrodes of V/Al/Ti/Au on n-AlGaN with Al content over 80%and investigate the relationship between the metal diffusion and contact properties during the high-temperature annealing process.Experiments reveal that decreasing V thickness in the electrode promotes the diffusion of Al towards the surface of n-AlGaN,which facilitates the formation of VN and thus the increase of local electron concentration,resulting in lower specific contact resistivity.Then,increasing the Al thickness inhibits the diffusion of Au to the n-AlGaN surface,suppressing the rise of Schottky barrier.Experimentally,an optimized n-electrode of V(10 nm)/Al(240 nm)/Ti(40 nm)/Au(50 nm)on n-Al_(0.81)Ga_(0.19)N is obtained,realizing an optimal specific contact resistivity of 7.30×10^(−4)Ω·cm^(2).Based on the optimal n-electrode preparation scheme for Al-rich n-AlGaN,the work voltage of a far-UVC LED with peak wavelength of 233.5 nm is effectively reduced.
基金supported by the National Natural Science Foundation ofChina(GrantNo.12402291)the Beijing Natural Science Foundation(No.3244043)the Research Start-up Funds of Hangzhou International Innovation Institute of Beihang University(Grant Nos.2024KQ008,2024KQ062).
文摘This study experimentally investigates the oscillatory dynamics of wind-driven droplets using high-speed imaging to capture droplet profiles within the symmetry plane and to characterize their natural oscillation frequencies.Results reveal that the eigenfrequencies vary spatially due to distinct oscillation modes occurring at different droplet locations.Notably,the fundamental eigenfrequency decreases with reducing droplet volume,while droplet viscosity exerts minimal influence on this frequency.Prior to the onset of motion,the dynamic contact angle consistently remains between the advancing and receding angles.The inertial forces generated by droplet oscillation are found to be significantly greater than the adhesion forces,indicating that classical static models are inadequate for capturing inertial contributions to droplet motion.These findings offer new insights into the role of oscillatory behavior in influencing the dynamics of droplet motion,and contribute to a more detailed understanding of wind-driven droplet transport phenomena.
文摘MXene-based smart contact lenses demonstrate a cutting-edge advancement in wearable ophthalmic technology,combining real-time biosensing,therapeutic capabilities,and user comfort in a single platform.These devices take the advantage of the exceptional electrical conductivity,mechanical flexibility,and biocompatibility of two-dimensional MXenes to enable noninvasive,tear-based monitoring of key physiological markers such as intraocular pressure and glucose levels.Recent developments focus on the integration of transparent MXene films into the conventional lens materials,allowing multifunctional performance including photothermal therapy,antimicrobial and anti-inflammation protection,and dehydration resistance.These innovations offer promising strategies for ocular disease management and eye protection.In addition to their multifunctionality,improvements in MXene synthesis and device engineering have enhanced the stability,transparency,and wearability of these lenses.Despite these advances,challenges remain in long-term biostability,scalable production,and integration with wireless communication systems.This review summarizes the current progress,key challenges,and future directions of MXene-based smart contact lenses,highlighting their transformative potential in next-generation digital healthcare and ophthalmic care.
文摘BACKGROUND Systematic reviews(SRs)synthesize and evaluate data,mainly from randomized trials,which then guides the development of clinical recommendations in evidence-based medicine.However,the data and methodological information in the included papers can often be lacking or unclear,and reviewers usually need to contact the authors of included studies for clarifications.Contacting authors is recommended,but it is unclear how often SR teams do it,or what the level of response is.AIM To investigate how often reviewers undertake contact with the authors of included randomized controlled trials(RCTs)for clarification on data and risk of bias concerns,to explore the factors that influence whether SR authors contact or do not contact the authors,and the content and level of responses.METHODS We conducted a systematic electronic database search in MEDLINE using the search string“(systematic review)”AND“(RCT OR randomized OR trial)”for articles published between 1 January 2024 and 19 February 2024,without language restrictions.Screening and data extraction was done independently by two reviewers,and conflicts resolved by a senior author.Contact authors of included SRs were contacted for clarifications.RESULTS Of the 329 included SRs,38%(n=125)explicitly mentioned contact with the authors of included studies.The remaining 62%(n=204)did not.We attempted contact with all SR teams for clarifications and received 90 responses(19.4%).Of the 50 respondents who did not explicitly mention contact in their SRs,25(50%)replied that they did make contact.We received a total of 64 responses on the level and content of information sought.The mean±SD contacts SR teams made were 10(10),replies received 5(6.7),and response waiting time 10.1(28.3)weeks.Resources,time,poor previous experience,perceived likelihood of poor response and bias concerns were reported as barriers to attempting contact.CONCLUSION The majority of SRs published in 2024 did not confirm seeking clarifying or missing information from primary study authors.However,SR teams reported that 50%of contacted primary authors respond.Additional research can clarify this rate of response and establish methods to increase the integration of this core methodological element in SRs.
