Nanomanipulation plays an important role in nanofabrication, it is also a technology necessary in exploring the secrets of nanoworld, and it thus becomes a start point to research future nanomachine. In this study, ma...Nanomanipulation plays an important role in nanofabrication, it is also a technology necessary in exploring the secrets of nanoworld, and it thus becomes a start point to research future nanomachine. In this study, manipulation and cutting of carbon nanotubes have been conducted in order to examine whether we can move a nano-component from one site to another by using the tip of atomic force microscope (AFM). The technique may also be valuable for providing the constructive materials of nanofabrication. While exploring the method for manipulating and cutting of nanotubes, some new phenomena have been observed during the process. Results show that carbon nanotubes present a feature of deformation combining bending and distortion when subjected to large mechanical forces exerted by the tip of AFM. In special cases, long carbon nanotubes can be cut into two parts, by which we can remove the part where crystal lattice is flawed, and therefore a perfect nanocomponent can be obtained.展开更多
This paper presented a numerical approach to solving the problem of a flat-ended punch in contact with a half-space matrix embedded with multiple three dimensional arbitrary-shaped inhomogeneities.Based on the semi-an...This paper presented a numerical approach to solving the problem of a flat-ended punch in contact with a half-space matrix embedded with multiple three dimensional arbitrary-shaped inhomogeneities.Based on the semi-analytical method(SAM)and the equivalent inclusion method,numerical procedures were developed and the effects of inclusion shape and distribution were analyzed.Fast Fourier transform technique was implemented to accelerate the calculation of surface deformation and subsurface stress.Interactions of inter-inclusions and inclusion-matrix were taken into account.Numerical results showed the presence of inhomogeneities(i.e.,microstructures in solids)indeed had a great effect on local contact pressure and a strong disturbance to the subsurface stress field in the vicinity of inclusions.The effects were dependent on the shape and distribution of inclusions and inter-inclusion interactions.The physical significance of this study is to provide an insight into the relation between the material microstructure and its response to the external load,and the solution approach and procedures may find useful applications,for example,the analysis of fatigue and crack propagation for composite materials,prediction of stress field in solids containing material defects,and study of the mechanism of chemical-mechanical polish(CMP)for inhomogeneous materials,etc.展开更多
Piston and piston ring lubrication is a factor that strongly affects the performance of thereciprocating internal combustion engine. When the oil film thickness becomes smaller than a cer-tain value, depending upon th...Piston and piston ring lubrication is a factor that strongly affects the performance of thereciprocating internal combustion engine. When the oil film thickness becomes smaller than a cer-tain value, depending upon the roughness of the surfaces in contact, mixed lubrication has to beconsidered. This paper analyzes the lubrication of piston ring and predicts pressure distribution,lubricant film thickness and surface deformation. The work is based on a unified numerical ap-proach assuming that the pressure distribution obeys Reynolds equation in hydrodynamic lubrica-tion regions while in asperities contact regions, the contact pressure can be obtained through theso-called reduced Reynolds equation. The computation experience shows the unified equationsystem is stable and can deal with severe operating conditions.展开更多
Scuffing, a major cause of failure in automobile engines, is considered as a dynamicprocess in this study. Local adhesions may occur randomly in lubricated contacts due to the exis-tence of asperity contact and breakd...Scuffing, a major cause of failure in automobile engines, is considered as a dynamicprocess in this study. Local adhesions may occur randomly in lubricated contacts due to the exis-tence of asperity contact and breakdown of lubricating films. Scuffing would take place if the localevents develop rapidly into a large-scale plastic deformation and catastrophic failure. A systemdynamic established in the present paper allows one to predict dynamic behavior of a tribologicalsystem through numerical solutions of a group of differential equations. A simplified analysis basedon this model confirms that the system will develop into a state of instability if the friction force atthe interface increases with temperature.展开更多
基金This work was supported by the National Natural Science Foundation of China (Grant Nos. 50075043, 50135040 and 50173001)the Doctorate Designation Fund of the Ministry of Education of China (Grant No. 2000000339).
文摘Nanomanipulation plays an important role in nanofabrication, it is also a technology necessary in exploring the secrets of nanoworld, and it thus becomes a start point to research future nanomachine. In this study, manipulation and cutting of carbon nanotubes have been conducted in order to examine whether we can move a nano-component from one site to another by using the tip of atomic force microscope (AFM). The technique may also be valuable for providing the constructive materials of nanofabrication. While exploring the method for manipulating and cutting of nanotubes, some new phenomena have been observed during the process. Results show that carbon nanotubes present a feature of deformation combining bending and distortion when subjected to large mechanical forces exerted by the tip of AFM. In special cases, long carbon nanotubes can be cut into two parts, by which we can remove the part where crystal lattice is flawed, and therefore a perfect nanocomponent can be obtained.
基金supported by the National Basic Research Program of China(Grant Nos.2009CB724200,2011CB013404 and 2011CB706602)
文摘This paper presented a numerical approach to solving the problem of a flat-ended punch in contact with a half-space matrix embedded with multiple three dimensional arbitrary-shaped inhomogeneities.Based on the semi-analytical method(SAM)and the equivalent inclusion method,numerical procedures were developed and the effects of inclusion shape and distribution were analyzed.Fast Fourier transform technique was implemented to accelerate the calculation of surface deformation and subsurface stress.Interactions of inter-inclusions and inclusion-matrix were taken into account.Numerical results showed the presence of inhomogeneities(i.e.,microstructures in solids)indeed had a great effect on local contact pressure and a strong disturbance to the subsurface stress field in the vicinity of inclusions.The effects were dependent on the shape and distribution of inclusions and inter-inclusion interactions.The physical significance of this study is to provide an insight into the relation between the material microstructure and its response to the external load,and the solution approach and procedures may find useful applications,for example,the analysis of fatigue and crack propagation for composite materials,prediction of stress field in solids containing material defects,and study of the mechanism of chemical-mechanical polish(CMP)for inhomogeneous materials,etc.
文摘Piston and piston ring lubrication is a factor that strongly affects the performance of thereciprocating internal combustion engine. When the oil film thickness becomes smaller than a cer-tain value, depending upon the roughness of the surfaces in contact, mixed lubrication has to beconsidered. This paper analyzes the lubrication of piston ring and predicts pressure distribution,lubricant film thickness and surface deformation. The work is based on a unified numerical ap-proach assuming that the pressure distribution obeys Reynolds equation in hydrodynamic lubrica-tion regions while in asperities contact regions, the contact pressure can be obtained through theso-called reduced Reynolds equation. The computation experience shows the unified equationsystem is stable and can deal with severe operating conditions.
文摘Scuffing, a major cause of failure in automobile engines, is considered as a dynamicprocess in this study. Local adhesions may occur randomly in lubricated contacts due to the exis-tence of asperity contact and breakdown of lubricating films. Scuffing would take place if the localevents develop rapidly into a large-scale plastic deformation and catastrophic failure. A systemdynamic established in the present paper allows one to predict dynamic behavior of a tribologicalsystem through numerical solutions of a group of differential equations. A simplified analysis basedon this model confirms that the system will develop into a state of instability if the friction force atthe interface increases with temperature.
