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
The Prandtl-Tomlinson(PT)model has been widely applied to interpret the atomic friction mechanism of a single asperity.In this study,we present an approximate explicit expression for the friction force in the one-dime...The Prandtl-Tomlinson(PT)model has been widely applied to interpret the atomic friction mechanism of a single asperity.In this study,we present an approximate explicit expression for the friction force in the one-dimensional PT model under quasi-static conditions.The‘stick-slip’friction curves are first approximated properly by sawtooth-like lines,where the critical points before and after the‘slip’motion are described analytically in terms of a dimensionless parameterη.Following this,the average friction force is expressed in a closed form that remains continuous and valid forη>1.Finally,an analytical expression for the load dependence of atomic friction of a single asperity is derived by connecting the parameterηwith the normal load.With the parameters reported in experiments,our prediction shows good agreement with relevant experimental results.展开更多
The elastic adhesive contact of self-affine fractal rough surfaces against a rigid flat is simulated using the finite element method. An array of nonlinear springs, of which the force-separation law obeys the Lennard...The elastic adhesive contact of self-affine fractal rough surfaces against a rigid flat is simulated using the finite element method. An array of nonlinear springs, of which the force-separation law obeys the Lennard–Jones potential, is introduced to account for the interfacial adhesion. For fractal rough surfaces, the interfacial interaction is generally attractive for large mean gaps, but turns repulsive as the gap continuously shrinks. The interfacial interactions at the turning point corresponding to the spontaneous contact are shown for various surfaces. For relatively smooth surfaces, the probability density distributions of repulsion and attraction are nearly symmetric. However, for rougher surfaces, the simulation results suggest a uniform distribution for attraction but a monotonously decreasing distribution with a long tail for repulsion. The pull-off force rises with increasing ratio of the work of adhesion to the equilibrium distance, whereas decreases for solids with a higher elastic modulus and a larger surface roughness. The current study will be helpful for understanding the adhesion of various types of rough solids.展开更多
The human body displays various symptoms of altitude sickness due to hypoxia in environments with low pressure and oxygen levels.While existing studies are primarily focused on the adverse effects of hypoxia and oxyge...The human body displays various symptoms of altitude sickness due to hypoxia in environments with low pressure and oxygen levels.While existing studies are primarily focused on the adverse effects of hypoxia and oxygen supplementation strategies at high altitudes,there is a notable gap in understanding the fundamental mechanisms driving altitude hypoxia.In this context,we propose a sophisticated two-way fluid–structure interaction model that simulates respiratory processes with precisely structured and deformable upper airways.This model reveals that,under identical pressure differentials at the airway’s inlet and outlet,the inspiratory air volume remains largely consistent and is minimally affected by specific pressure changes.However,an increase in the pressure differential enhances gas inhalation efficiency.Furthermore,airway morphology emerges as a pivotal factor influencing oxygen intake.Distorted airway shapes create areas of high flow velocity,where low wall pressure hampers effective airway opening,thus diminishing gas inhalation.These results may shed light on the effects of low-pressure conditions and upper airway structure on respiratory dynamics at high altitudes and inform the development of effective oxygen supply strategies.展开更多
Surface plays an important role in the physical and mechanical behavior of nanos- tructured materials and elements, however surface energy of curved solid surfaces has not been fully understood. In the present letter,...Surface plays an important role in the physical and mechanical behavior of nanos- tructured materials and elements, however surface energy of curved solid surfaces has not been fully understood. In the present letter, surface energy of spherical particles and cavities in FCC copper is calculated by embedded atom method. The numerical simulations reveal that the dis- tribution of atom energy is non-uniform on the curved surfaces. However, when the radius of spherical cavity or particle is larger than 4 nm, the average surface energy density keeps almost constant irrespective of its location and radius.展开更多
Surface energy plays an important role in the mechanical performance of nanomaterials; however, determining the surface energy density of curved surfaces remains a challenge. In this paper, we conduct atomic simulatio...Surface energy plays an important role in the mechanical performance of nanomaterials; however, determining the surface energy density of curved surfaces remains a challenge. In this paper, we conduct atomic simulations to calculate the surface energy density of spherical surfaces in various crystalline metals. It is found that the average surface energy density of spherical surfaces remains almost constant once its radius exceeds 5 nm. Then, using a geometrical analysis and the scaling law, we develop an analytical approach to estimate the surface energy density of spherical surfaces through that of planar surfaces. The theoretical prediction agrees well with the direct atomic simulations, and thus provides a simple and general method to calculate the surface energy density in crystals.展开更多
Measuring the surface tension and elastic mod- ulus of soft materials and biological tissues under different physiological and pathological conditions is of significance for understanding various phenomena associated ...Measuring the surface tension and elastic mod- ulus of soft materials and biological tissues under different physiological and pathological conditions is of significance for understanding various phenomena associated with defor- mation. In this paper, the nanoindentation of a circular fiat punch on a soft solid is analyzed with the influence of surface tension. By solving the corresponding singular integral equa- tion, the relation between load and indent depth is obtained. When the radius of the flat punch shrinks to the same order as the ratio of surface tension to elastic modulus, surface ten- sion significantly affects the indentation load-depth relation, which provides a facile method to measure surface tension in soft solids and biological tissues.展开更多
Atomistic simulations are performed to study the statistical mechanical properties of gold nanoparticles.It is demonstrated that the yielding behavior of gold nanoparticles is governed by the dislocation nucleation ar...Atomistic simulations are performed to study the statistical mechanical properties of gold nanoparticles.It is demonstrated that the yielding behavior of gold nanoparticles is governed by the dislocation nucleation around surface steps.Since the nucleation of dislocation is an activated process with the aid of thermal fluctuation,the yield stress at a specific temperature should vary statistically rather than being a definite constant value.Molecular dynamics simulations reveal that the yield stress follows a Gaussian distribution at a specific temperature.As the temperature increases,the mean value of yield stress decreases while the width of distribution becomes larger.Based on the numerical analysis,the dependence of mean yield stress on temperature can be well described by a parabolic function.This study illuminates the statistical features of the yielding behavior of nanostructured elements.展开更多
Micro-/nano-indentation has become prevalent in evaluating the mechanical characteristics of biological samples,such as cells and tissues.However,the existing contact models describing conical indentation ignore the j...Micro-/nano-indentation has become prevalent in evaluating the mechanical characteristics of biological samples,such as cells and tissues.However,the existing contact models describing conical indentation ignore the joint effects of surface energy and substrate,and consequently cannot accurately extract the Young's modulus of biological samples deposited on substrate.Through finite element methods,we examine the conical indentation of biological films on substrates while taking surface energy into account.Based on the dimensional analysis,the explicit relationship between load and indentation depth is achieved for films with their moduli varying from 0.001 to 100 times that of the substrate.If the classical Sneddon's model was employed to analyze the load-depth data,the measured modulus could reach 18 times the real modulus for films on harder substrates,but only 4%of the real modulus for films on softer substrates.Meanwhile,in micro-/nano-indentations,neglecting the contribution of surface energy would result in an overestimation of the Young's modulus of films depending on the contact size.The analytical expression provided here can be utilized to precisely deduce the mechanical characteristics of biological films deposited on substrate from the load and indentation depth data of a conical indentation.展开更多
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the National Natural Science Foundation of China(Grant Nos.12302141,12372100,and 12102322)the China Postdoctoral Science Foundation(Grant No.2023M732799)the General Research Fund(Project No.CityU 11302920)from the Research Grants Council of the Hong Kong Special Administrative Region is acknowledged.
文摘The Prandtl-Tomlinson(PT)model has been widely applied to interpret the atomic friction mechanism of a single asperity.In this study,we present an approximate explicit expression for the friction force in the one-dimensional PT model under quasi-static conditions.The‘stick-slip’friction curves are first approximated properly by sawtooth-like lines,where the critical points before and after the‘slip’motion are described analytically in terms of a dimensionless parameterη.Following this,the average friction force is expressed in a closed form that remains continuous and valid forη>1.Finally,an analytical expression for the load dependence of atomic friction of a single asperity is derived by connecting the parameterηwith the normal load.With the parameters reported in experiments,our prediction shows good agreement with relevant experimental results.
基金supported by the OPPO Research Fund.The support from the National Natural Science Foundation of China(Grant Nos.12372100 and 12302126)is acknowledged.
文摘The elastic adhesive contact of self-affine fractal rough surfaces against a rigid flat is simulated using the finite element method. An array of nonlinear springs, of which the force-separation law obeys the Lennard–Jones potential, is introduced to account for the interfacial adhesion. For fractal rough surfaces, the interfacial interaction is generally attractive for large mean gaps, but turns repulsive as the gap continuously shrinks. The interfacial interactions at the turning point corresponding to the spontaneous contact are shown for various surfaces. For relatively smooth surfaces, the probability density distributions of repulsion and attraction are nearly symmetric. However, for rougher surfaces, the simulation results suggest a uniform distribution for attraction but a monotonously decreasing distribution with a long tail for repulsion. The pull-off force rises with increasing ratio of the work of adhesion to the equilibrium distance, whereas decreases for solids with a higher elastic modulus and a larger surface roughness. The current study will be helpful for understanding the adhesion of various types of rough solids.
基金National Natural Science Foundation of China(Grant Nos.12072252)the Natural Science Basic Research Plan in Shaanxi Province of China(No.2019JC-02)Guang-kui Xu+1 种基金National Natural Science Foundation of China(Grant No.12302221)Jiu-Tao HangFundamental Research Funds for the Central Universities of China Guang-kui Xu and Jiu-Tao Hang National Natural Science Foundation of China(Grant No.11972361)Dong Wei.
文摘The human body displays various symptoms of altitude sickness due to hypoxia in environments with low pressure and oxygen levels.While existing studies are primarily focused on the adverse effects of hypoxia and oxygen supplementation strategies at high altitudes,there is a notable gap in understanding the fundamental mechanisms driving altitude hypoxia.In this context,we propose a sophisticated two-way fluid–structure interaction model that simulates respiratory processes with precisely structured and deformable upper airways.This model reveals that,under identical pressure differentials at the airway’s inlet and outlet,the inspiratory air volume remains largely consistent and is minimally affected by specific pressure changes.However,an increase in the pressure differential enhances gas inhalation efficiency.Furthermore,airway morphology emerges as a pivotal factor influencing oxygen intake.Distorted airway shapes create areas of high flow velocity,where low wall pressure hampers effective airway opening,thus diminishing gas inhalation.These results may shed light on the effects of low-pressure conditions and upper airway structure on respiratory dynamics at high altitudes and inform the development of effective oxygen supply strategies.
基金supported by the the NCET Program and the SRF for ROCS of the Ministry of Educationthe National Natural Science Foundation of China (No.11072186)
文摘Surface plays an important role in the physical and mechanical behavior of nanos- tructured materials and elements, however surface energy of curved solid surfaces has not been fully understood. In the present letter, surface energy of spherical particles and cavities in FCC copper is calculated by embedded atom method. The numerical simulations reveal that the dis- tribution of atom energy is non-uniform on the curved surfaces. However, when the radius of spherical cavity or particle is larger than 4 nm, the average surface energy density keeps almost constant irrespective of its location and radius.
基金supported by the National Natural Science Foundation of China (Grants 11272249 and 11525209)
文摘Surface energy plays an important role in the mechanical performance of nanomaterials; however, determining the surface energy density of curved surfaces remains a challenge. In this paper, we conduct atomic simulations to calculate the surface energy density of spherical surfaces in various crystalline metals. It is found that the average surface energy density of spherical surfaces remains almost constant once its radius exceeds 5 nm. Then, using a geometrical analysis and the scaling law, we develop an analytical approach to estimate the surface energy density of spherical surfaces through that of planar surfaces. The theoretical prediction agrees well with the direct atomic simulations, and thus provides a simple and general method to calculate the surface energy density in crystals.
基金supported by the National Natural Science Foundation of China(Grant 11272249)
文摘Measuring the surface tension and elastic mod- ulus of soft materials and biological tissues under different physiological and pathological conditions is of significance for understanding various phenomena associated with defor- mation. In this paper, the nanoindentation of a circular fiat punch on a soft solid is analyzed with the influence of surface tension. By solving the corresponding singular integral equa- tion, the relation between load and indent depth is obtained. When the radius of the flat punch shrinks to the same order as the ratio of surface tension to elastic modulus, surface ten- sion significantly affects the indentation load-depth relation, which provides a facile method to measure surface tension in soft solids and biological tissues.
基金Support from the National Natural Science Foundation of China(Grant No.11525209)is acknowledged.
文摘Atomistic simulations are performed to study the statistical mechanical properties of gold nanoparticles.It is demonstrated that the yielding behavior of gold nanoparticles is governed by the dislocation nucleation around surface steps.Since the nucleation of dislocation is an activated process with the aid of thermal fluctuation,the yield stress at a specific temperature should vary statistically rather than being a definite constant value.Molecular dynamics simulations reveal that the yield stress follows a Gaussian distribution at a specific temperature.As the temperature increases,the mean value of yield stress decreases while the width of distribution becomes larger.Based on the numerical analysis,the dependence of mean yield stress on temperature can be well described by a parabolic function.This study illuminates the statistical features of the yielding behavior of nanostructured elements.
基金supported by the National Natural Science Foundation of China(Grant Nos.12102322 and 12372100)the China Postdoctoral Science Foundation(Grant No.2018M64097)the General Research Fund(Grant No.CityU 11302920)from the Research Grants Council of the Hong Kong Special Administrative Region。
文摘Micro-/nano-indentation has become prevalent in evaluating the mechanical characteristics of biological samples,such as cells and tissues.However,the existing contact models describing conical indentation ignore the joint effects of surface energy and substrate,and consequently cannot accurately extract the Young's modulus of biological samples deposited on substrate.Through finite element methods,we examine the conical indentation of biological films on substrates while taking surface energy into account.Based on the dimensional analysis,the explicit relationship between load and indentation depth is achieved for films with their moduli varying from 0.001 to 100 times that of the substrate.If the classical Sneddon's model was employed to analyze the load-depth data,the measured modulus could reach 18 times the real modulus for films on harder substrates,but only 4%of the real modulus for films on softer substrates.Meanwhile,in micro-/nano-indentations,neglecting the contribution of surface energy would result in an overestimation of the Young's modulus of films depending on the contact size.The analytical expression provided here can be utilized to precisely deduce the mechanical characteristics of biological films deposited on substrate from the load and indentation depth data of a conical indentation.
