Study On The Regulation Of Mechanical Properties Of Graphene Sheet By Defect

Graphene,a two-dimensional carbon nanomaterial with single-atom thickness composed of carbon atoms with hexagonal honeycomb lattice structure,has become the emphase of researchers for many years due to its excellent performances and wide application prospects.The present chemical vapor deposition and graphite oxidation reduction are believed to the best methods for the industrialization of large size graphene films.Varying degrees of crystal structure defects,such as the absence of carbon atoms or grain boundaries,are inevitably generated in the graphene sheets prepared by above two methods,and its own properties will be affected.However,few studies have been conducted on the clever use of defects to regulate the mechanical properties of graphene sheets.In this paper,the effects of flaws on the mechanical properties of graphene sheets are firstly studied by means of molecular dynamics simulations,combined with the continuum mechanics theories and related experiments,and then the utilization of defects to enhance the mechanical properties of graphene sheets is further elaborated.The main research contents are as follows:(1)Molecular dynamics simulation is used to study the relationship between the crack growth angle and the chirality of single-layer open-hole graphene sheets under uniaxial tension.Subsequently,the stress concentration around the hole edge of graphene sheet is futher analyzed with the armchair open-hole graphene sheet as a precedent,which is compared with the elastic theory.With the increase of the chiral angle,the variation trend of the corresponding crack growth angle of graphene sheets presents an“N”shape.Moreover,in armchair open-hole graphene sheet,the farther away from the hole,the smaller ultimate tensile stress of the atom at break is and finally it tends to be stable(42 GPa).Above simulation results are not only confirmed to agree with the theoretical results,but also accuracy of the conclusions and the rigorousness of the simulation process are verified.(2)The method of modulating the mechanical anisotropy of two dimensional materials,graphene and black phosphorus,by regulating defects is raised.The results of molecular dynamics simulation are shown that the central crack and inclined elliptic hole are seen as the optimal defects for achieving the the mechanical isotropy of graphene and black phosphorus,respectively.Furthermore,the reliability of the simulation results is not only verified through the continuum theory,but also the nonlinear mechanical properties of the open-hole composite film materials are measured by means of macroscopic tension experiments,which corroborates the controllability of the mechanical anisotropy of two-dimensional materials.(3)The scheme of thermal activation for forming interlyer sp~2-sp~3 hybrid bonds is designed for effectively improving the interlayer load transfer capacity of multilayer open-hole graphene.The research results are shown that in comparision with unbonded multilayer graphene sheets,the structure of three-dimensional multilayer graphene papers is not damaged by the interlayer crosslinks,but the tensile strength and interlayer shear strength of thermally activated multilayer graphene papers are increased by around 20%and 3 times,respectively,which can be attributed to the higher bond strength of the interlayer bonds than that the interlayer Van Der Waals interactions.The achievements of this article not only provide new ideas for regulating the mechanical anisotropy of monolayer two-demensional materials,but also render an effective means for boosting the mechanical properties of multilayer open-hole graphene sheets.