Study On The Axial Pressure Instability Process And Mechanical Mechanism Of Film-Substrate System Based On Nanotube

The fold instability process like rolling up sleeves can be defined as a model system for axial compression of a film on a rigid substrate.Such a model system is more complex than a axial compression of a two-dimensional material on a rigid substrate due to its curvature effect.At the macro scale,this model system has been maturely studied.Through experiments,computations and theoretical analyses,the sliding problem of the soft shell film of a rigid cylinder is explored,and a new post-buckling phenomenon is found in the process.Today’s nanotechnology has made a great progress.Low-dimensional nanomaterials such as graphene and carbon nanotubes have gradually been known by others.Nanomaterials have also attracted great attention from researchers due to their excellent physical properties.In this thesis,the film-substrate system composed of nanomaterials is used as the research object.The molecular dynamics method is used to study the axial compression characteristics of nanotubes under the action of the substrate.The deformation and mechanical mechanisms of the nanotubes are analyzed,and a film-substrate system model at the nanoscale was proposed.The wrinkle instability process of the soft shell film under axial compression on the substrate and the deformation behavior of a non-idealized rigid substrate under the radial stress of the axial compression film were obtained.The following research results were obtained:(1)Analyze the transition process of smooth-wrinkle-ridge-sagging occurrence of the ideal model of soft membrane-basal system at the nanometer scale and the law of the critical values between state transitions.During the compression process,the nanotubes first bend into wrinkles.After further compression,the transition from wrinkles to ridge is completed.When the compression strain rate increases to a third critical value,the ridge height reaches its limit and the symmetry is broken with the ridge sagging into a recumbent fold.Both carbon nanotubes and boron nitride nanotubes are formed of two-dimensional materials with a sixmembered ring structure.This results in armchair nanotubes and zigzag nanotubes have different Young’s moduli due to different chirality,and cause the wrinkle instability process to have an effect.In addition,the increase in temperature will exacerbate the thermal motion of the atoms in the nanotubes and change the fold instability process of the nanotubes.The results show that the change of temperature has no effect on the transformation of carbon nanotube morphology,but the increase of the transformation temperature has a slight distortion of carbon nanotubes,and this phenomenon is exacerbated with the increase of temperature.(2)The influence of the chirality of carbon nanotubes on the instability of axial compression folds of film-substrate system was analyzed.The effects of different chirality on the instability of carbon nanotube folds at the same temperature were investigated.Under the same temperature condition,the carbon nanotubes of the zigzag type in the non-deformed area are more smooth,and there have secondary ridge formation during the growth process of the drooping ridges after the ridges sag.Under the same basic model size,the Young’s modulus of the zigzag nanotube is higher than the benchmark armchair nanotube.(3)Analyze the actual deformation of the substrate atoms when it can move freely.The differences in substrate deformation under the same temperature environment model and the same calculation settings were examined.The results show that under the influence of the dual size effect of nanotubes and nanopillars of the thin film-substrate model system,the smaller the diameter is deformation of the internal copper nanopillars is.(4)The differences between the boron nitride nanotubes and carbon nanotubes of the same size in the simulation calculation process are analyzed.On the ideal model of a rigid substrate,the wrinkle state of the armchair boron nitride nanotube is irregular,the ridges sag in the opposite direction to the carbon nanotubes,and the smooth areas outside the deformation zone are extremely smooth and the stress distribution is more regular.It can complete the transition process of smooth-wrinkle-ridge-sagging on the free substrate,and the wrinkles are periodically strengthened and the sagging direction is consistent with that of carbon nanotubes,accompanied by the phenomenon of secondary ridge formation.The young’s modulus of boron nitride nanotubes is larger than that of carbon nanotubes of the same size.