Study Of Surface Buckling Caused By Contact And Friction

The buckling of thin film is widely discussed because the phenomenon is ubiquitous in daily life and engineering.We can construct some surface patterns with particular morphology by using the buckling of thin film.We can also get the mechanical parameters of materials by surface instabilities which are produced by indenter test.However,as the material with micro and nano scale exhibit size effect,therefore,how to characterize the size effect turns into the focus of research.On the other hand,it is also important to study how to measure the size effect of materials by experiment.Meanwhile,numerous researches currently concentrated in the buckling of thin film caused by capillary force of droplet while for buckling of thin film caused by indenter,now also are lack of relevant theoretical discuss.In this case,based on energy variation principle and took advantage of linear perturbation analysis,we discussed the relation between critical strain of the buckling of film-substrate system and mechanical parameters of material with consideration of interfacial slip and surface energy.It revealed that substrate's Poisson's ratio and interfacial slip has slightly effect on critical strain,therefore,we can assume that the film is perfect bond with substrate and the substrate is incompressible material for simplicity.However,when the film thickness is no more than ten nanometers,the surface/interface effect would have significant impact on critical strain.Furthermore,the present results may open up the opportunity of determining the surface/interface parameters by using the wrinkling of thin films on compliant substrates.After that,based on Von Karman plate theory and took advantage of perturbation method,moment discontinuity method and membrane theory,respectively,we obtained the internal stress and displacement before the thin film buckled.Afterwards,based on the moment discontinuity method,we studied the relation between wave number of the buckled film and pressure of indenter with WKB method.It revealed that when pressure is small,the results from WKB method and membrane theory are quite different.In reference to the reasons,on one hand it can be the neglect of the bending effect of the film in membrane theory,on the other hand,it's supposed to be the membrane theory having no consideration for the adhesion effect between indenter and film.