Study Of The Mechanical Behaviors Of Carbon Honeycomb Via Molecular Dynamics Simulation

Carbon honeycomb(CHC)is a novel carbon allotrope with a stable threedimensional hexagonal structure.It consists of graphene nanoribbons that are connected at their edges to form an array of hexagonal pillars with porous networks exhibiting a honeycomb structure.Due to the porous structure feature,CHC holds great potential in the areas of gas and liquid storage,molecular filtration membrane,porous electrode materials,composites,and impact-resistant materials.Therefore,it is of great practical significance to investigate the mechanical behaviors of CHC,which could facilitate its applications in the corresponding areas.In this paper,molecular dynamics simulation is adopted to study the mechanical behaviors of CHC under static and dynamic loadings,respectively.Specifically,the mechanical behaviors of CHC under uniaxial tension,and the dynamic response of CHC under shock loading are investigated.The investigation of the mechanical behaviors of CHC under static loading demonstrates that under uniaxial tensile loading,CHC possesses anisotropic mechanical properties,zero-stiffness,and the negative Poisson’s ratio effect,and these phenomena are closely related to the deformation of its constitutive graphene nanoribbons.To illustrate the underlying deformation mechanisms of the nanoribbons and establish the relationship between these mechanisms and the macroscopic deformation behaviors of CHC,the evolution of its atomic structure during its tensile deformation process is characterized by calculating several characteristic bond lengths and angles,and the atomic stress distribution.The simulation results indicate that when tensile loading is applied in the armchair direction,the deformation process of CHC can be divided into three stages.In the first stage,the graphene nanoribbons undergo severe distortion;the distortion is flattened subsequently as the tensile strain increases in the second stage,leading to the zero-stiffness behavior;the local fracture initiates in CHC at the end of the third stage.For the tensile loading applied in the zigzag direction,the distortion of graphene nanoribbons is absent,giving rise to the anisotropic tensile response of CHC.In addition to the zero-stiffness and anisotropic behaviors,the negative Poisson’s ratio effect is also observed when a tensile loading is applied in the armchair direction and is explained by the evolution of the atomic structure.The increase of temperature does not significantly affect the tensile response of CHC in the first deformation stage,but it will shorten the second and the third deformation stages and reduce the ultimate strength and fracture strain of CHC.The study of the mechanical behaviors of CHC under dynamic loading indicates that the propagation of shock wave in CHC is also anisotropic.The simulation results indicate that the propagation speed of shock waves in CHC in the pillars direction is much higher than that in the armchair and zigzag directions,which follows the order of the Young’s moduli of CHC in different directions.The shock wave energy decays with the propagation distance exponentially regardless of the direction.In addition,the energy decay is accelerated at elevated temperatures.Moreover,when vacancies are introduced into CHC,the shock wave propagation in it is significantly impeded due to the large deformations of the vacancies in the form of shrinkage and expansion caused by the shock wave.Furthermore,the calculation of the critical shock wave intensity at which structure failure of CHC initiates shows that the pillars direction of CHC can sustain a high shock wave intensity which is over two times higher than those for the other two directions.The research results in this paper provide a theoretical understanding of the mechanical behaviors of CHC in the process of tensile and shock deformation,which is helpful to promote the practical applications of CHC.