Mechanical Properties Of Periodic Graphene Nanometamaterials

Most of the materials seen in daily life are positive Poisson's ratio materials.Positive Poisson's ratio materials will shrink laterally when subjected to tensile load and expand laterally when subjected to compressive load.On the contrary,the material with negative Poisson's ratio has the specific performance of transverse expansion when subjected to tensile load and transverse contraction when subjected to compressive load.This characteristic makes negative Poisson's ratio materials better than traditional materials in many fields.For this reason,negative Poisson's ratio materials have attracted more and more scientists' attention and gradually become a hot research field.The research shows that the tensile expansion behavior is usually due to the cooperative effect between the internal structure(geometric setting)of the material and the deformation mechanism it experiences when bearing stress.Graphene,as a novel nanomaterial with characteristics,has many excellent properties and wide application prospects.In this paper,inspired by the rotating rectangular rigid body structure,we design a new periodic rotating rectangular graphene model.Using molecular dynamics method and continuum theory under small strain,we explore the reasons for the negative Poisson's ratio effect of periodic rotating rectangular graphene structure and other mechanical properties of periodic rotating rectangular graphene structure.Specifically,we studied the Poisson's ratio,stress-strain curve,ultimate strength,ultimate strain,Young's modulus,and shear modulus of periodic rotating graphene structure,and tried to reveal the mechanism of negative Poisson's ratio effect of periodic rotating graphene structure.Finally,we also studied the effects of temperature and strain rate on the mechanical properties of tensile periodic rotating graphene structure.The specific research results of this paper are as follows:Firstly,the results show that the periodic rotating graphene structure can exhibit a negative Poisson's ratio effect,which is related to the aspect ratio a/b and connection angle of small rectangular graphene sheet ?.It is independent of temperature and axial tensile rate.Periodically rotating graphene structure even at large strain(??0.10),so it can be widely used,and the structure can withstand large deformation.In our simulation range,the young's modulus decreases with the increase of the aspect ratio a/b,but it's young's modulus is much smaller than that of perfect graphene.Secondly,when the periodically rotating rectangular graphene structure is uniaxially stretched,the deformation of the small rectangular graphene sheet and the mutual rotation movement between the small rectangular graphene sheets occur at the same time.The deformation and mutual rotation of the small rectangular graphene sheets increase the axial size of the overall structure,increasing of axial strain,while the mutual rotation between the small rectangular graphene sheets leads to the increase of the transverse size of the overall structure,that is,the mutual rotation between small rectangular graphene sheets that leads to the negative Poisson's ratio effect of the structure.Moreover,the young's modulus and shear modulus of the periodically rotating rectangular graphene structure is related to the aspect ratio a/b of the small rectangular graphene sheet.The young's modulus decreases with the increase of the aspect ratio,and the shear modulus first increases and then decreases with the increase of the aspect ratio.Generally speaking,whether it is axial tension or shear failure,the first failure position of the structure is located at the node connected between the small rectangular graphene sheets.The special structure of the structure is easy to concentrate the stress at the node,so the node is the first to be damaged.Finally,we also found that the ultimate strain,ultimate strength,and Young's modulus of periodic graphene showed a gradual decrease trend with the increase of temperature,and its ultimate strain,ultimate strength,and Young's modulus were much lower than that of singlelayer perfect graphene;the ultimate strain and ultimate strength of the periodic rotating graphene structure increased with the increase of the strain rate of the tensile material,but Young's modulus decreased with the increase of strain rate,but the amplitude was not large.