Study On Mechanical Properties Of Carbon Nano Materials Based On Molecular Structural Mechanics Approach

Owing to their unique microstructures and superior mechanical properties,electronic properties,magnetic properties and optical properties,carbon nanomaterial hold a great promise of extensive applications in various fields.In the process of studying the mechanical properties of carbon nanomaterials,due to the limitations of micro-nano mechanical testing methods,the limitation of existing simulation methods such as nano-atom simulation and the incompleteness of carbon nanomaterials' own structure,researchers have adopted many numerical simulation methods.In order to realize the prediction of the mechanical properties of nano-carbon materials at the atomic scale,molecular mechanics theory was used to establish a mathematical model of the mechanical behavior of nano-carbon materials.Then the elastic properties of single-walled carbon nanotubes,double-walled carbon nanotubes,bamboo-shaped carbon nanotubes,and graphene nanoribbon were simulated using finite element analysis.The fracture problem of single-walled carbon nanotubes with vacancy defects was simulated.The influence of the microstructure and defects of nano-carbon materials on their mechanical properties was analyzed.The main contents are as follows:(1)A mathematical model for the study of mechanical behavior of carbon nanomaterials was established using the theory of molecular structure mechanics.Based on the energy equivalent of the atomic potential,the properties of the C-C covalent bond are assigned to the equivalent beam element.The Lennard-Jones potential is used to describe the interaction between the van der Waals forces of multi-walled carbon nanotubes,and the properties of the van der Waals force between layers are given to equivalent nonlinear spring elements.The modified Morse potential function was used to quantitatively describe the fracture of C-C bonds.(2)Elastic properties of single-walled and double-walled carbon nanotubes were estimated based on the theory of molecular structure mechanics.Tensile,bending and torsional loads were applied to the finite element models of single and double-walled carbon nanotubes to calculate the mechanical properties of carbon nanotubes.The effects of the structural parameters(diameter and chirality)of the carbon nanotubes on their performance were analyzed.(3)The fracture behaviors of different types of SWCNTs(SWCNTs without defect and with one-atomic vacancy defect and two-atomic vacancy defect)were simulated.The fracture of single-walled carbon nanotubes under axial tensile loading and the effect of defects on the fracture properties of single-walled carbcrease of defects,the performance decreases rapidly.Under the same conditions,the double atom vacancy defects have more influence on the performance than the single atom vacancy defects.(4)The microstructure of bamboo-shaped carbon nanotubes was observed experimentally.The tensile and bending behaviors of bamboo-shaped carbon nanotubes were simulated using molecular structural mechanics combined with finite element analysis.The mechanical properties of bamboo-shaped carbon nanotubes with different structural parameters were calculated and compared with the performance of ideal single-walled carbon nanotubes.(5)Simulation of tensile mechanical properties of monolayer and multilayer graphene nanoribbons.The influence of the structural parameters(length,width,and number of layers)of graphene nanoribbons with different edge shapes on their ten ones.In this paper,the effectiveness of molecular mechanic theory in the field of nano-carbon material mechanical properties was verified.This study predicts the mechanical properties of carbon nanomaterials at the atomic scale and provides methodological guidance and data accumulation to the mechanical properties of carbon nanomaterials.