Superlubricity phenomena, which were previously achieved merely under point contact conditions, have been observed under the linear contact condition between the silicon nitride (Si3N4) cylinder and the silica (SiO2) ...Superlubricity phenomena, which were previously achieved merely under point contact conditions, have been observed under the linear contact condition between the silicon nitride (Si3N4) cylinder and the silica (SiO2) ring in phosphoric acid solutions.After a total 800 s running-in period and low friction stage, the friction coefficient finally declined to about 0.003. The ultralow friction coefficient could last for more than 5 h. In these experiments, a torque sensor of high accuracy was used to make sure that the measuring result was credible. The differences between superlubricity experiments in our group and others were dis-cussed. Unlike the situations in other superlubricity experiments about silicon nitride, where the specimens were immersed in water totally, the phosphoric acid solution with volume of only 150 μL was used in these tests. It was proved that free water in the solution had a great relationship to the necessary time of acquiring superlubricity and phosphoric acid played a unique role in the superlubricity, which could not be explained properly by the hydrodynamic lubrication model proposed by others. Fi-nally, based on the results of the friction tests and the analysis with scanning electron microscope (SEM), a modified hydro-gen-bonded network and hydrated shearing layer model was proposed to explain the mechanism of superlubricity.展开更多
A contact model for describing the contact mechanics between the stator and slider of the standing wave linear ultrasonic motor was presented. The proposed model starts from the assumption that the vibration character...A contact model for describing the contact mechanics between the stator and slider of the standing wave linear ultrasonic motor was presented. The proposed model starts from the assumption that the vibration characteristics of the stator is not affected by the contact process. A modified friction models was used to analyze the contact problems. Firstly, the dynamic normal contact force, interface friction force, and steady-state characteristics were analyzed. Secondly, the influences of the contact layer material, the dynamic characteristics of the stator, and the pre-load on motor performance were simulated. Finally, to validate the contact model, a linear ultrasonic motor based on in-plane modes was used as an example. The corresponding results show that a set of simulation of motor performances based on the proposed contact mechanism is in good agreement with experimental results. This model is helpful to understanding the operation principle of the standing wave linear motor and thus contributes to the design of these types of motor.展开更多
We investigate the beam focusing technology of shear-vertical(SV) waves for a contact-type linear phased array to overcome the shortcomings of conventional wedge transducer arrays. The numerical simulation reveals the...We investigate the beam focusing technology of shear-vertical(SV) waves for a contact-type linear phased array to overcome the shortcomings of conventional wedge transducer arrays. The numerical simulation reveals the transient excitation and propagation characteristics of SV waves. It is found that the element size plays an important role in determining the transient radiation directivity of SV waves. The transient beam focusing characteristics of SV waves for various array parameters are deeply studied. It is particularly interesting to see that smaller element width will provide the focused beam of SV waves with higher quality, while larger element width may result in erratic fluctuation of focusing energy around the focal point. There exists a specific range of inter-element spacing for optimum focusing performance. Moreover, good beam focusing performance of SV waves can be achieved only at high steering angles.展开更多
The contact stiffness and the error analysis have an important effect on the manufacture and the optimization of Ball Linear Guide Feed Unit( BLGFU). In order to analyze the contact stiffness and linear errors or angl...The contact stiffness and the error analysis have an important effect on the manufacture and the optimization of Ball Linear Guide Feed Unit( BLGFU). In order to analyze the contact stiffness and linear errors or angle errors of BLGFU,in this paper,the contact stress and deformation mechanics between the ball and rail is analyzed. Based on Hertz theory of contact and theory of the multi-body system,a model of the contact stiffness considering the changes in contact angle is established. With the increasing of the external load,the varying trend of the contact deformation can be obtained. Therefore, the motion accuracy degradation of the BLGFU can be analyzed. By using a special experimental device and test system of the rolling linear guide worktable,the horizontal contact stiffness and the vertical linear stiffness are obtained,respectively. By comparing the contact stiffness of the experiment dates and the simulation results,the variation tendency of two curves is consisted and the difference between the measured values and the theoretical values is less than 18%. It is obvious that the model of the contact stiffness considering changes of contact angle has accuracy and feasibility. Thus,while external force point locating at different positions; the contact stiffness and the accuracy analysis of the BLGFU are proved validity by simulations.展开更多
As suggested by the title, this extensive book is concerned with crack and contact prob- lems in linear elasticity. However, in general, it is intended for a wide audience ranging from engineers to mathematical physic...As suggested by the title, this extensive book is concerned with crack and contact prob- lems in linear elasticity. However, in general, it is intended for a wide audience ranging from engineers to mathematical physicists. Indeed, numerous problems of both academic and tech- nological interest in electro-magnetics, acoustics, solid and fluid dynamics, etc. are actually related to each other and governed by the same mixed boundary value problems from a unified mathematical standpoint展开更多
Boundary element-linear complementary equations are formulated to solve elastic contact problems with Coulomb frictions. It is also a new attempt to solve free boundary problems in solid mechanics by means of boundary...Boundary element-linear complementary equations are formulated to solve elastic contact problems with Coulomb frictions. It is also a new attempt to solve free boundary problems in solid mechanics by means of boundary element-mathematical programming techniques.展开更多
Compared with the traditional rigid plastic/rigid viscoplastic(RP/RVP) FEM(based on iteration solution),RP/RVP FEM based on linear programming (LP) has some remarkable advantages,such as it's free of convergence...Compared with the traditional rigid plastic/rigid viscoplastic(RP/RVP) FEM(based on iteration solution),RP/RVP FEM based on linear programming (LP) has some remarkable advantages,such as it's free of convergence problem and its convenience in contact,rigid zone,and friction force treatment.The numerical model of RP/RVP FEM based on LP for axisymmetrical metal forming simulation is studied,and some related key factors and its treatment methods in formulation of constraint condition are proposed.Some solution examples are provided to validate its accuracy and efficiency.展开更多
Three dimensional frictional contact problems are formulated as linear complementarity problems based on the parametric variational principle. Two aggregate-functionbased algorithms for solving complementarity problem...Three dimensional frictional contact problems are formulated as linear complementarity problems based on the parametric variational principle. Two aggregate-functionbased algorithms for solving complementarity problems are proposed. One is called the self-adjusting interior point algorithm, the other is called the aggregate function smoothing algorithm. Numerical experiment shows the efficiency of the proposed two algorithms.展开更多
The characteristics of linear transformer are studied analytically. The transformer is composed in one of modes of linear motor-transformer apparatus proposed for future wireless light rail vehicle (LRV). The secondar...The characteristics of linear transformer are studied analytically. The transformer is composed in one of modes of linear motor-transformer apparatus proposed for future wireless light rail vehicle (LRV). The secondary (onboard) power factor can be adjusted at any value by an onboard converter. The equivalent circuit is used to study the transferred power control. The parameters are determined by three-dimensional finite element method (FEM) analysis for one pole-pair model. Under the rated primary (input) and secondary voltage and current, which are specified for linear motor operation, the characteristics of the secondary power factor are cleared. It is also shown that the input capacitor can improve the primary power factor and decrease the input power capacity, but does not change the efficiency. This linear transformer has the efficiency of 91% and the input power factor of 0.87 when the apparatus without input capacitor is controlled at the secondary power factor of 0.4.展开更多
Based on Hertz contact theory, contact area parameters between ball and raceway are calculated. Using the Creep theory of Cater and V-J theory, adhesive area and micro-slip area in the contact area are analyzed. It is...Based on Hertz contact theory, contact area parameters between ball and raceway are calculated. Using the Creep theory of Cater and V-J theory, adhesive area and micro-slip area in the contact area are analyzed. It is considered that micro-adhesion wear of micro convex body in the slip area is the main reason for accuracy degradation of a linear ball guide pair. And, the characteristics of the contact area between ball and raceway of slider are characterized using the fractal function. Fractal parameters are obtained using the least squares fitting double logarithmic graph structure function. Considering the lubrication condition between the ball and rail of slider, stress analysis is carried out on the adhesive area. A fractal-creep model of contact surfaces is established in the micro-slip region. The fractal parameters of a certain guide rail are measured, and the wear degradation process of linear rolling guide is simulated. Finally, the relationship between wear and relative tangential velocity, normal load and running mileage of linear ball guide is obtained.展开更多
A new algorithm for solving the three-dimensional elastic contact problem with friction is presented. The algorithm is a non-interior smoothing algorithm based on an NCP-function. The parametric variational principle ...A new algorithm for solving the three-dimensional elastic contact problem with friction is presented. The algorithm is a non-interior smoothing algorithm based on an NCP-function. The parametric variational principle and parametric quadratic programming method were applied to the analysis of three-dimensional frictional contact problem. The solution of the contact problem was finally reduced to a linear complementarity problem, which was reformulated as a system of nonsmooth equations via an NCP-function. A smoothing approximation to the nonsmooth equations was given by the aggregate function. A Newton method was used to solve the resulting smoothing nonlinear equations. The algorithm presented is easy to understand and implement. The reliability and efficiency of this algorithm are demonstrated both by the numerical experiments of LCP in mathematical way and the examples of contact problems in mechanics.展开更多
This paper investigates the distribution of contact resistance of the aluminum alloy in the squeeze stage. A new method of measuring path＇ s resistance is proposed firstly. Contact resistances are calculated accurate...This paper investigates the distribution of contact resistance of the aluminum alloy in the squeeze stage. A new method of measuring path＇ s resistance is proposed firstly. Contact resistances are calculated accurately by the systems of 5 linear equations and solutions show that three contact resistances are different. The probability density functions of contact resistance in workpiece/workpiece（ W/W） and upper electrode/workpiece（ E/W） show that the curve shape has steeper peak and heavier tail than that of the normal distribution. Non-parameter hypothesis test is performed and the result shows that R2 , R4 reject the normal distribution using chi-square and kolmogoroo statistic D method. Therefore, the Asymmetric Laplace distribution is fitted to empirical distributions and is applied to quantify the influence of random contact resistance. The result illustrates that AL distribution is very close to contact resistance of W/W and upper E/W and normal distribution has some deviation. The paper is helpful to research the initial nugget conditions, weldability and the transient multi-coupling field.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 51075227, 51222507)the Program for New Century Excellent Talents in University of Ministry of Education of Chinathe Basic Research Program of Shenzhen (Grant No. 0021539012100521066)
文摘Superlubricity phenomena, which were previously achieved merely under point contact conditions, have been observed under the linear contact condition between the silicon nitride (Si3N4) cylinder and the silica (SiO2) ring in phosphoric acid solutions.After a total 800 s running-in period and low friction stage, the friction coefficient finally declined to about 0.003. The ultralow friction coefficient could last for more than 5 h. In these experiments, a torque sensor of high accuracy was used to make sure that the measuring result was credible. The differences between superlubricity experiments in our group and others were dis-cussed. Unlike the situations in other superlubricity experiments about silicon nitride, where the specimens were immersed in water totally, the phosphoric acid solution with volume of only 150 μL was used in these tests. It was proved that free water in the solution had a great relationship to the necessary time of acquiring superlubricity and phosphoric acid played a unique role in the superlubricity, which could not be explained properly by the hydrodynamic lubrication model proposed by others. Fi-nally, based on the results of the friction tests and the analysis with scanning electron microscope (SEM), a modified hydro-gen-bonded network and hydrated shearing layer model was proposed to explain the mechanism of superlubricity.
基金Funded by the National Basic Research Program (973 program) (No. 2011CB707602)the Digital Manufacturing Equipment and Technology National Key Laboratory,Huazhong University of Science and Technology (No. DMETKF2009002)National Sciences Foundation-Guangdong Natural Science Foundation,China (No.U0934004)
文摘A contact model for describing the contact mechanics between the stator and slider of the standing wave linear ultrasonic motor was presented. The proposed model starts from the assumption that the vibration characteristics of the stator is not affected by the contact process. A modified friction models was used to analyze the contact problems. Firstly, the dynamic normal contact force, interface friction force, and steady-state characteristics were analyzed. Secondly, the influences of the contact layer material, the dynamic characteristics of the stator, and the pre-load on motor performance were simulated. Finally, to validate the contact model, a linear ultrasonic motor based on in-plane modes was used as an example. The corresponding results show that a set of simulation of motor performances based on the proposed contact mechanism is in good agreement with experimental results. This model is helpful to understanding the operation principle of the standing wave linear motor and thus contributes to the design of these types of motor.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11774377 and 11574343)。
文摘We investigate the beam focusing technology of shear-vertical(SV) waves for a contact-type linear phased array to overcome the shortcomings of conventional wedge transducer arrays. The numerical simulation reveals the transient excitation and propagation characteristics of SV waves. It is found that the element size plays an important role in determining the transient radiation directivity of SV waves. The transient beam focusing characteristics of SV waves for various array parameters are deeply studied. It is particularly interesting to see that smaller element width will provide the focused beam of SV waves with higher quality, while larger element width may result in erratic fluctuation of focusing energy around the focal point. There exists a specific range of inter-element spacing for optimum focusing performance. Moreover, good beam focusing performance of SV waves can be achieved only at high steering angles.
基金Sponsored by the National Natural Science Foundation of China(Grant Nos.51505012 and 51575014)the Natural Science Foundation of Beijing(Grant No.KZ201410005010)+2 种基金the Important National Science&Technology Specific Projects of China(Grant No.2012ZX04010021-001-004)the China Postdoctoral Science Foundation Funded Project(Grant No.2016M591033)the Beijing Postdoctoral Research Foundation(Grant No.2015ZZ-13)
文摘The contact stiffness and the error analysis have an important effect on the manufacture and the optimization of Ball Linear Guide Feed Unit( BLGFU). In order to analyze the contact stiffness and linear errors or angle errors of BLGFU,in this paper,the contact stress and deformation mechanics between the ball and rail is analyzed. Based on Hertz theory of contact and theory of the multi-body system,a model of the contact stiffness considering the changes in contact angle is established. With the increasing of the external load,the varying trend of the contact deformation can be obtained. Therefore, the motion accuracy degradation of the BLGFU can be analyzed. By using a special experimental device and test system of the rolling linear guide worktable,the horizontal contact stiffness and the vertical linear stiffness are obtained,respectively. By comparing the contact stiffness of the experiment dates and the simulation results,the variation tendency of two curves is consisted and the difference between the measured values and the theoretical values is less than 18%. It is obvious that the model of the contact stiffness considering changes of contact angle has accuracy and feasibility. Thus,while external force point locating at different positions; the contact stiffness and the accuracy analysis of the BLGFU are proved validity by simulations.
文摘As suggested by the title, this extensive book is concerned with crack and contact prob- lems in linear elasticity. However, in general, it is intended for a wide audience ranging from engineers to mathematical physicists. Indeed, numerous problems of both academic and tech- nological interest in electro-magnetics, acoustics, solid and fluid dynamics, etc. are actually related to each other and governed by the same mixed boundary value problems from a unified mathematical standpoint
文摘Boundary element-linear complementary equations are formulated to solve elastic contact problems with Coulomb frictions. It is also a new attempt to solve free boundary problems in solid mechanics by means of boundary element-mathematical programming techniques.
文摘Compared with the traditional rigid plastic/rigid viscoplastic(RP/RVP) FEM(based on iteration solution),RP/RVP FEM based on linear programming (LP) has some remarkable advantages,such as it's free of convergence problem and its convenience in contact,rigid zone,and friction force treatment.The numerical model of RP/RVP FEM based on LP for axisymmetrical metal forming simulation is studied,and some related key factors and its treatment methods in formulation of constraint condition are proposed.Some solution examples are provided to validate its accuracy and efficiency.
基金The project supported by the National Natural Science foundation of china(10225212,50178016.10302007)the National Kev Basic Research Special Foundation and the Ministry of Education of China
文摘Three dimensional frictional contact problems are formulated as linear complementarity problems based on the parametric variational principle. Two aggregate-functionbased algorithms for solving complementarity problems are proposed. One is called the self-adjusting interior point algorithm, the other is called the aggregate function smoothing algorithm. Numerical experiment shows the efficiency of the proposed two algorithms.
文摘The characteristics of linear transformer are studied analytically. The transformer is composed in one of modes of linear motor-transformer apparatus proposed for future wireless light rail vehicle (LRV). The secondary (onboard) power factor can be adjusted at any value by an onboard converter. The equivalent circuit is used to study the transferred power control. The parameters are determined by three-dimensional finite element method (FEM) analysis for one pole-pair model. Under the rated primary (input) and secondary voltage and current, which are specified for linear motor operation, the characteristics of the secondary power factor are cleared. It is also shown that the input capacitor can improve the primary power factor and decrease the input power capacity, but does not change the efficiency. This linear transformer has the efficiency of 91% and the input power factor of 0.87 when the apparatus without input capacitor is controlled at the secondary power factor of 0.4.
基金Supported by the National Natural Science Foundation of China(No.51505012,51575014)the Natural Science Foundation of Beijing(No.3154029,KZ201410005010)+1 种基金the Important National Science&Technology Specific Projects of China(No.2012ZX04010021-001-004)Beijing Postdoctoral Research Foundation(No.2015XX-13)
文摘Based on Hertz contact theory, contact area parameters between ball and raceway are calculated. Using the Creep theory of Cater and V-J theory, adhesive area and micro-slip area in the contact area are analyzed. It is considered that micro-adhesion wear of micro convex body in the slip area is the main reason for accuracy degradation of a linear ball guide pair. And, the characteristics of the contact area between ball and raceway of slider are characterized using the fractal function. Fractal parameters are obtained using the least squares fitting double logarithmic graph structure function. Considering the lubrication condition between the ball and rail of slider, stress analysis is carried out on the adhesive area. A fractal-creep model of contact surfaces is established in the micro-slip region. The fractal parameters of a certain guide rail are measured, and the wear degradation process of linear rolling guide is simulated. Finally, the relationship between wear and relative tangential velocity, normal load and running mileage of linear ball guide is obtained.
文摘A new algorithm for solving the three-dimensional elastic contact problem with friction is presented. The algorithm is a non-interior smoothing algorithm based on an NCP-function. The parametric variational principle and parametric quadratic programming method were applied to the analysis of three-dimensional frictional contact problem. The solution of the contact problem was finally reduced to a linear complementarity problem, which was reformulated as a system of nonsmooth equations via an NCP-function. A smoothing approximation to the nonsmooth equations was given by the aggregate function. A Newton method was used to solve the resulting smoothing nonlinear equations. The algorithm presented is easy to understand and implement. The reliability and efficiency of this algorithm are demonstrated both by the numerical experiments of LCP in mathematical way and the examples of contact problems in mechanics.
基金This research was supported by National Natural Science Foundation of China(No50575159)Project of Chinese Ministry ofEducation(No106049, 20060056058)Natural Science Foundation of Tianjin (06YFJMJC03400)
文摘This paper investigates the distribution of contact resistance of the aluminum alloy in the squeeze stage. A new method of measuring path＇ s resistance is proposed firstly. Contact resistances are calculated accurately by the systems of 5 linear equations and solutions show that three contact resistances are different. The probability density functions of contact resistance in workpiece/workpiece（ W/W） and upper electrode/workpiece（ E/W） show that the curve shape has steeper peak and heavier tail than that of the normal distribution. Non-parameter hypothesis test is performed and the result shows that R2 , R4 reject the normal distribution using chi-square and kolmogoroo statistic D method. Therefore, the Asymmetric Laplace distribution is fitted to empirical distributions and is applied to quantify the influence of random contact resistance. The result illustrates that AL distribution is very close to contact resistance of W/W and upper E/W and normal distribution has some deviation. The paper is helpful to research the initial nugget conditions, weldability and the transient multi-coupling field.
