Multiscale Simulation Of Micro/Nano-scale Contact Behavior

Surface forces (such as surface adhesion and friction) has become an importantfactor in determining system performance with the miniaturization of micro/nanoelectromechanical system (M/NEMS)．There are serious surface adhesion， friction andwear problems which are the key problems of impeding the MEMS products to enterthe market．Therefore studying the contact behavior in micro/nano-scale，being appliedto the design and manufacture of M/NEMS，which plays an important role to developnanoscience．As an empirical approach，multiscale simulation could give an explanationof the phenomenon which is beyond understanding by theoretical analysis andexperimental observation．Molecular dynamics simulation is an effective method tostudy the affection of the surface topography and the adhesion force between thesurfaces in contact behavior．The basic principles of atomic/continuum multiscale method and the coupling ofmolecular dynamics simulation and finite element analysis of a bridging domain methodare introduced．Being on the basis of the analysis of the existing multiscale simulationsoftware，the bridging domain method has been chosen．We have improved someshortcomings in the functionality and performance of the software and solved the lowcomputational efficiency and accuracy and the stress being not output on the frameworkof the open-source multiscale simulation software Libmultiscale，which Provides themultiscale simulation tools for the micro/nano contact behavior．The bridging domain method and improved Libmultiscale are performed to studythree-dimensional contact behaviors between a rigid spherical tip and a smooth flatsubstrate，which is compared with the results of full-atom molecular simulations．Wefocus on the relaxation behavior under a given load，the continuity of the displacementand stress at bridging domain，variation of normal force and contact radius withdisplacement and so on．The results show that the bridging domain method can quicklyreach equilibrium and have smaller oscillation under the given external load and smallthe relative error when the initial temperature of system at0K．The bridging domainmethod can continuously transmit the displacement and stress from molecular domainto continuum domain，and has the good coupling effect，the normal force-displacementand contact radius-displacement curve are nearly coincide with the molecularsimulation results，and have high computational accuracy． After obtaining the better accuracy，the behavior of contact between the rigid flatindenter and a fractal surface has been simulated by the bridging domain method．Therelationship between contact area and the load，contact stress distribution and theprobability distribution have also been studied．The results show that the relationshipbetween the area of rough surface contact and load is linear and the surface morphologychanges do not affect the linear relationship，which is consistent with the prediction theof Greenwood-Williamson model of the continuum mechanics．The stress distributionof contact surface depends on the fractal surface morphology，the probability of contactstress distribution is consistent with the continuum mechanics prediction．...