Understanding and characterizing rough contact and wavy surfaces are essential for developing effective strategies to mitigate wear,optimize lubrication,and enhance the overall performance and durability of mechanical...Understanding and characterizing rough contact and wavy surfaces are essential for developing effective strategies to mitigate wear,optimize lubrication,and enhance the overall performance and durability of mechanical systems.The sliding friction contact problem between a thermoelectric(TE)half-plane and a rigid solid with a periodic wavy surface is the focus of this investigation.To simplify the problem,we utilize mixed boundary conditions,leading to a set of singular integral equations(SIEs)with the Hilbert kernels.The analytical solutions for the energy flux and electric current density are obtained by the variable transform method in the context of the electric and temperature field.The contact problem for the elastic field is transformed into the second-kind SIE and solved by the Jacobi polynomials.Notably,the smoothness of the wavy contact surface ensures that there are no singularities in the surface contact stress,and ensures that it remains free at the contact edge.Based on the plane strain theory of elasticity,the analysis primarily examines the correlation between the applied load and the effective contact area.The distribution of the normal stress on the surface with or without TE loads is discussed in detail for various friction coefficients.Furthermore,the obtained results indicate that the in-plane stress decreases behind the trailing edge,while it increases ahead of the trailing edge when subjected to TE loads.展开更多
Surface tension plays a central role in the mechanical behavior of soft materials such as gels.Elastocapillary deformation of elastic graded substrates is ubiquitous in soft materials.In this work,the effect of a part...Surface tension plays a central role in the mechanical behavior of soft materials such as gels.Elastocapillary deformation of elastic graded substrates is ubiquitous in soft materials.In this work,the effect of a partially wetting sessile liquid droplet on the elastocapillary deformation of a soft elastic graded substrate is studied.The modulus is assumed to have an exponential form along the thickness direction.By applying the Fourier transformation,a mixed boundary-value problem is reduced into a dual integral equation.The numerical results show that the surface displacement is strongly affected by the inhomogeneity of the material.The study of the wetting properties of gel substrates is essential for both understanding the wetting phenomena of gels and developing gels for applications as soft actuators and sensors that can be used in wearable electronics and soft robotics.展开更多
The contact problem for thermoelectric materials with functionally graded properties is considered.The material properties,such as the electric conductivity,the thermal conductivity,the shear modulus,and the thermal e...The contact problem for thermoelectric materials with functionally graded properties is considered.The material properties,such as the electric conductivity,the thermal conductivity,the shear modulus,and the thermal expansion coefficient,vary in an exponential function.Using the Fourier transform technique,the electro-thermoelastic problems are transformed into three sets of singular integral equations which are solved numerically in terms of the unknown normal electric current density,the normal energy flux,and the contact pressure.Meanwhile,the complex homogeneous solutions of the displacement fields caused by the gradient parameters are simplified with the help of Euler’s formula.After addressing the non-linearity excited by thermoelectric effects,the particular solutions of the displacement fields can be assessed.The effects of various combinations of material gradient parameters and thermoelectric loads on the contact behaviors of thermoelectric materials are presented.The results give a deep insight into the contact damage mechanism of functionally graded thermoelectric materials(FGTEMs).展开更多
The adhesion failure has become one dominant factor in determining the reliability and service life of miniaturized devices subject to loadings with arbitrary orientations.This article establishes an adhesive full sti...The adhesion failure has become one dominant factor in determining the reliability and service life of miniaturized devices subject to loadings with arbitrary orientations.This article establishes an adhesive full stick contact model between an elastic half-space and a rigid cylinder loaded in any direction.Using the Papkovich-Neuber functions,the Fourier integral transform,and the asymmetric bipolar coordinates,the exact solution is obtained.Unlike the Johnson-Kendall-Roberts(JKR)model,the present adhesive contact model takes into account the effects of the load direction as well as the coupling of the normal and tangential contact stresses.Besides,it considers the full stick contact which has large values of the friction coefficient between contacting surfaces,contrary to the frictionless contact supposed in the JKR model.The result shows that suitable angles can be found,which makes the contact surfaces difficult to be peeled off or easy to be pressed into.展开更多
The lift force was reported not to be high enough to support the dragonfly’s weight during flight in some conventional investigations,and higher lift force is required for its takeoff.In this study,by employing a thi...The lift force was reported not to be high enough to support the dragonfly’s weight during flight in some conventional investigations,and higher lift force is required for its takeoff.In this study,by employing a thin plate model,impact effect is investigated for the wing deformation in dragonfly flapping during takeoff.The static displacement is formulated to compare with the dynamical displacement caused by impact.The governing equation of motion for the impact dynamics of a dragonfly wing is derived based on Newton’s second law.Separation of variables technique and assumed modes method are introduced to solve the resulting equations.Further,lift force is presented for the cases of considering and without considering the impact on the wing flapping which indicates that the impact has prominent effects for the dragonfly’s aerodynamic performance.Numerical simulations demonstrate that considering the impact effect on the wing flapping can increase the wing deformation,which results in the rise of the lift force.The enhanced lift force is of critical importance for the dragonfly’s takeoff.展开更多
The laser frequency could be linked to an radio frequency through an external cavity by the combination of Pound-Drever-Hall and Devoe-Brewer locking techniques.A stable and tunable optical frequency at wavelength of ...The laser frequency could be linked to an radio frequency through an external cavity by the combination of Pound-Drever-Hall and Devoe-Brewer locking techniques.A stable and tunable optical frequency at wavelength of 1.5μm obtained by a cavity with high finesse of 96000 and a fiber laser has been demonstrated,calibrated by a commercial optical frequency comb.The locking performances have been analyzed by in-loop and out-loop noises,indicating that the absolute frequency instability could be down to 50 kHz over 1 s and keep to less than 110 kHz over 2.5 h.Then,the application of this stabilized laser to the direct absorption spectroscopy has been performed.With the help of balanced detection,the detection sensitivity,in terms of optical density,can reach to 9.4×10^(-6).展开更多
Multilayer thin-film thermoelectric materials are of technological importance. This paper describes a method to analyze the heat conduction in a multilayered thermoelectric plate containing some non-collinear cracks. ...Multilayer thin-film thermoelectric materials are of technological importance. This paper describes a method to analyze the heat conduction in a multilayered thermoelectric plate containing some non-collinear cracks. The material properties in one layer may be different from those in another even though each layer may still be homogeneous. Using the Fourier integral transforms, the boundary value problem is reduced to a system of general singular integral equations. The model is sufficiently general to account for any number of layers and any number of cracks. As a numerical illustration, the electric flux intensity factor, energy flux intensity factor and thermal flux intensity factor for a three-layer plate specimen with two cracks are presented. The effects of strip width on the electric flux intensity factor and thermal flux intensity factor are studied.展开更多
基金Project supported by the National Natural Science Foundation of China(Nos.12262033,12272269,12062021,and 12062022)Ningxia Hui Autonomous Region Science and Technology Innovation Leading Talent Training Project of China(No.2020GKLRLX01)the Natural Science Foundation of Ningxia of China(Nos.2023AAC02003 and 2022AAC03001)。
文摘Understanding and characterizing rough contact and wavy surfaces are essential for developing effective strategies to mitigate wear,optimize lubrication,and enhance the overall performance and durability of mechanical systems.The sliding friction contact problem between a thermoelectric(TE)half-plane and a rigid solid with a periodic wavy surface is the focus of this investigation.To simplify the problem,we utilize mixed boundary conditions,leading to a set of singular integral equations(SIEs)with the Hilbert kernels.The analytical solutions for the energy flux and electric current density are obtained by the variable transform method in the context of the electric and temperature field.The contact problem for the elastic field is transformed into the second-kind SIE and solved by the Jacobi polynomials.Notably,the smoothness of the wavy contact surface ensures that there are no singularities in the surface contact stress,and ensures that it remains free at the contact edge.Based on the plane strain theory of elasticity,the analysis primarily examines the correlation between the applied load and the effective contact area.The distribution of the normal stress on the surface with or without TE loads is discussed in detail for various friction coefficients.Furthermore,the obtained results indicate that the in-plane stress decreases behind the trailing edge,while it increases ahead of the trailing edge when subjected to TE loads.
基金supported by the National Natural Science Foundation of China(Nos.12272195,12272269 and 12262033)。
文摘Surface tension plays a central role in the mechanical behavior of soft materials such as gels.Elastocapillary deformation of elastic graded substrates is ubiquitous in soft materials.In this work,the effect of a partially wetting sessile liquid droplet on the elastocapillary deformation of a soft elastic graded substrate is studied.The modulus is assumed to have an exponential form along the thickness direction.By applying the Fourier transformation,a mixed boundary-value problem is reduced into a dual integral equation.The numerical results show that the surface displacement is strongly affected by the inhomogeneity of the material.The study of the wetting properties of gel substrates is essential for both understanding the wetting phenomena of gels and developing gels for applications as soft actuators and sensors that can be used in wearable electronics and soft robotics.
基金supported by the National Natural Science Foundation of China(Nos.11972257,11832014,11762016,11472193)the Fundamental Research Funds for the Central Universities(No.22120180223)。
文摘The contact problem for thermoelectric materials with functionally graded properties is considered.The material properties,such as the electric conductivity,the thermal conductivity,the shear modulus,and the thermal expansion coefficient,vary in an exponential function.Using the Fourier transform technique,the electro-thermoelastic problems are transformed into three sets of singular integral equations which are solved numerically in terms of the unknown normal electric current density,the normal energy flux,and the contact pressure.Meanwhile,the complex homogeneous solutions of the displacement fields caused by the gradient parameters are simplified with the help of Euler’s formula.After addressing the non-linearity excited by thermoelectric effects,the particular solutions of the displacement fields can be assessed.The effects of various combinations of material gradient parameters and thermoelectric loads on the contact behaviors of thermoelectric materials are presented.The results give a deep insight into the contact damage mechanism of functionally graded thermoelectric materials(FGTEMs).
基金supported by the National Natural Science Foundation of China(Nos.11972257,11832014,and 11472193)the China Scholarship Council(CSC)the Fundamental Research Funds for the Central Universities(No.22120180223)。
文摘The adhesion failure has become one dominant factor in determining the reliability and service life of miniaturized devices subject to loadings with arbitrary orientations.This article establishes an adhesive full stick contact model between an elastic half-space and a rigid cylinder loaded in any direction.Using the Papkovich-Neuber functions,the Fourier integral transform,and the asymmetric bipolar coordinates,the exact solution is obtained.Unlike the Johnson-Kendall-Roberts(JKR)model,the present adhesive contact model takes into account the effects of the load direction as well as the coupling of the normal and tangential contact stresses.Besides,it considers the full stick contact which has large values of the friction coefficient between contacting surfaces,contrary to the frictionless contact supposed in the JKR model.The result shows that suitable angles can be found,which makes the contact surfaces difficult to be peeled off or easy to be pressed into.
基金National Natural Science Foundation of China(Project No.11972261,11572229)Fundamental Research Funds for the Central Universities(Project No.22120180063).
文摘The lift force was reported not to be high enough to support the dragonfly’s weight during flight in some conventional investigations,and higher lift force is required for its takeoff.In this study,by employing a thin plate model,impact effect is investigated for the wing deformation in dragonfly flapping during takeoff.The static displacement is formulated to compare with the dynamical displacement caused by impact.The governing equation of motion for the impact dynamics of a dragonfly wing is derived based on Newton’s second law.Separation of variables technique and assumed modes method are introduced to solve the resulting equations.Further,lift force is presented for the cases of considering and without considering the impact on the wing flapping which indicates that the impact has prominent effects for the dragonfly’s aerodynamic performance.Numerical simulations demonstrate that considering the impact effect on the wing flapping can increase the wing deformation,which results in the rise of the lift force.The enhanced lift force is of critical importance for the dragonfly’s takeoff.
基金supported by the National Key R&D Program of China(Grant No.2017YFA0304203)the National Natural Science Foundation of China(Grant Nos.61875107,61905136,61905134,62175139)+1 种基金Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi,China(Grant No.2019L0062)Opening Foundation of Key Laboratory of Laser&Infrared System(Shandong University)。
文摘The laser frequency could be linked to an radio frequency through an external cavity by the combination of Pound-Drever-Hall and Devoe-Brewer locking techniques.A stable and tunable optical frequency at wavelength of 1.5μm obtained by a cavity with high finesse of 96000 and a fiber laser has been demonstrated,calibrated by a commercial optical frequency comb.The locking performances have been analyzed by in-loop and out-loop noises,indicating that the absolute frequency instability could be down to 50 kHz over 1 s and keep to less than 110 kHz over 2.5 h.Then,the application of this stabilized laser to the direct absorption spectroscopy has been performed.With the help of balanced detection,the detection sensitivity,in terms of optical density,can reach to 9.4×10^(-6).
基金Financial supports from the Outstanding Youth Cultivation Project of Ningxia Higher Education (NGY2017002), the National Natural Science Foundation of China (11762016, 11762017), the Natural Science Foundation of Ningxia (NZ17009) and Ningxia overseas study project are gratefully acknowledged.
文摘Multilayer thin-film thermoelectric materials are of technological importance. This paper describes a method to analyze the heat conduction in a multilayered thermoelectric plate containing some non-collinear cracks. The material properties in one layer may be different from those in another even though each layer may still be homogeneous. Using the Fourier integral transforms, the boundary value problem is reduced to a system of general singular integral equations. The model is sufficiently general to account for any number of layers and any number of cracks. As a numerical illustration, the electric flux intensity factor, energy flux intensity factor and thermal flux intensity factor for a three-layer plate specimen with two cracks are presented. The effects of strip width on the electric flux intensity factor and thermal flux intensity factor are studied.