Vibration Characteristic And Buckling Behavior Of Piezoelectric Nanowires By Considering Surface Effect

A variety of materials with nanostructures,such as nanowires,nanotubes,nanofilms,nanoplates and so on,have been continuously fabricated due to the rapid development of nanotechnology.These extensively used nano-structural materials are the important components of nano-electromechanical systems(NEMS)including nano-sensors,nano-actuators,nano-resonators and nano-generators.In order to better promote their practical application,it becomes very important to investigate the physical properties of nanomaterials.It needs to consider the influence on the properties of nanomaterials from the surface effect.This is because that nanomaterials have nano magnitude on some certain dimensions and thus have large surface/volume ratio,i.e.,the ratio of the number of surface atoms to the number of total atoms.Under the surface effect,most of physical quantities,e.g.,elastic parameters,Young's modulus,piezoelectric coefficients,resonant frequency,critical buckling loads are prominently dependent on the size of nanomaterials.In this thesis,we studied the vibration characteristic and buckling behavior of piezoelectric nanomaterials by taking into account the surface elasticity,surface piezoelectricity and residual surface stress.Firstly,the surface elastic theory of piezoelectric nano wires were built by considering the surface elasticity,surface piezoelectricity and residual surface stress.On this basis,the size dependence of the constitutive relation and Young's modulus of piezoelectric nanowires were derived.The law of surface elasticity and surface piezoelectricity acting on the effective reduced Young's modulus were discussed.The results indicate that the surface elasticity and surface piezoelectricity make the effective reduced Young's modulus obviously harder as the thickness of piezoelectric nanowires decreases.For the piezoelectric nanowires with hexagonal lattice structure(PZT-5H),as the size of nanowires decreases,surface elasticity firstly plays zhe important role,however,the size continues to decrease to a certain value,surface piezoelectricity takes a dominant effect.Next,the influence on the bending vibration and axial buckling behaviors of piezoelectric nanowires from surface elasticity,surface piezoelectricity and residual surface stress were investigated by using the above surface elastic theory of piezoelectric nanowires.The size dependence of the natural vibration frequency and critical axial compressive loads of piezoelectric nanowires with hexagonal lattice structure were calculated.It is found that the reduced natural frequency and critical compressive load of piezoelectric nanowires are increased by the positive residual surface stress and negative polarized voltage but decreased by the negative residual surface stress and positive polarized voltage.Besides,the reduced natural frequency and critical compressive load are increased by surface elasticity.With decreasing the thickness of nanowires,the size dependence of surface piezoelectricity on the natural frequency of piezoelectric nanowires enhances obviously.NEMS has extensive potential on application.It is believed that our results will lead to theoretical guidance on the research of NEMS.