| Penta-graphene(PG)is a newly proposed quasi-two-dimensional metastable carbon structure composed only of carbon pentagons.Due to its unique geometric configuration,PG exhibits very different physical and chemical properties from graphene.PG has rare negative Poisson’s ratio properties and ultra-high mechanical properties.In recent years,the research on PG has become one of the research hotspots in the fields of materials science and condensed matter physics.In terms of mechanical properties,the mechanical behaviors and failure mechanism of PG under tensile and shear loads have been widely studied.However,how PG responds under indenter indentation loads still lacks of systematic investigation.In this work,based on molecular dynamics simulations of nanoindentation combined with continuum mechanics theory,the mechanical properties and failure mechanisms of PG under spherical indenter and cylindrical indenter were respectively studied,and various factors on the mechanical properties of PG were also analyzed.The main work is as follows:1.The mechanical properties and failure mechanism of PG under spherical indenter and cylindrical indenter were systematically studied.The results show that under the external loading of the two types of indenters PG exhibits similar plastic deformation characteristics which is consistent with that obtained by applying tensile and shear loads.The plastic deformation was caused by irreversible pentagon-to-polygon structural transformation.The nanoindentation results also show that the deformation and failure process of the pentagonal graphene film can be roughly divided into the following four stages:(1)elastic deformation stage,which is characterized by carbon-carbon bond elongation and there is no transformation of carbon rings;(2)plastic deformation stage,at which there is pentagon-to-polygon structural transformation;(3)strengthening stage,during which the indenter load and indentation depth show a linear relationship;(4)fracture stage,which is manifested as the breaking of carbon-carbon bonds and the formation of new defects.2.The influence of various factors on the mechanical properties of PG was systematically studied,and the nanoindentation parameters for obtaining the intrinsic mechanical properties of PG were obtained.The results indicate that under spherical indenter,when the ratio of PG radius to spherical indenter radius is not less than 15,and the film radius is not less than 22.5 nm,the Young’s modulus of PG can be accurately obtained,which is about 256.65-265.66 N/m.The elastic limit is insensitive to the radius of the PG film and the radius of the indenter.Different from the results under the spherical indenter,the Young’s modulus of PG obtained from nanoindentation under cylindrical indenter is not affected by the ratio of the film length to the radius of the cylindrical indenter and the size of the film.When the width of the PG film is the same as the width,the lateral boundary effect can be eliminated by applying periodic boundary conditions on the side of the PG film.During the nanoindentation process,the Young’s modulus of PG show a linear decreasing trend with the increase of temperature,while the indenter loading rate had little effect on the Young’s modulus. |
