Multi-scale Simulation Of Deformation And Failure Of The Metal Materials Based On Finite Element Method And Molecular Dynamics

The deformation and failure process of materials involves the coupling effect in multiple scales.It is difficult to accurately describe the deformation and failure mechanism of materials based on the macro-scale method,therefore,it is necessary to carry out the research of material deformation and failure at various scales.Firstly,The effects of the model size,crack length,temperature and strain rate on monocrystalline aluminum strength and crack propagation were invesesgated using molecular dynamics(MD)simulation method.Then multiscale model of the two-dimensional metal silver was established to observe the process and micromechanism of crack propagation from nano-scale to macro-scale by multiscale analysis(MD and FEM).Futher,the fitting values of zirconium cobalt alloy potential function was calculated by first principles,including crystal structures,formation enthalpy,cohesive energy and elastic constants.The effects of doping on the hydrogen storage properties and mechanical properties of zirconium cobalt alloy in macro-scale were discussed in detail from electronic in nano-scale based on band theory.The thesis was arranged as follows: the research significance,current situation and main methods of material deformation and failure at different scales,and multi-scale numerical simulation was detailly introduced in chapter 1.The basic theory of the molecular dynamics method and the first principle method,as well as the common multiscale connection method were discussed in chapter 2.In the third chapter,the influence of the size,temperature,strain rate and crack length on the strength and microcosmic mechanism of the single crystal aluminum containing central crack was analyzed in detail by molecular dynamics method.In the fourth chapter,a two-dimensional model of silver crystal fracture was estabilished based on the method which coupled the molecular dynamics and finite element method,and the scientificity and feasibility of the model were verified by the literature.In the fifth chapter,We explored the fitting values of potential function for molecular dynamics simulation,calculated the parameters needed for molecular dynamics potential function simulation,and discussed the microscopic mechanism.The sixth chapter made a summary of the whole text,and looked forward to the prospect of the research content and methods in the future.The crack propagation of single crystal aluminum plate with central crack under tensile loading was investigated using MD.The effects of model size,crack length,temperature and strain rate on the strength and crack propagation of single crystal aluminum plate were analyzed in detail.With the increase of the model size,crack length and strain rate,the plastic yield point of the single crystal aluminum plate is increased,the plastic yield stress is reduced,and the plastic deformation ability of the material is enhanced.However,the temperature has little effect on the strength of the single crystal aluminum plate,which is in good agreement with the literature results.With the increase of the size of the model,the yield stress of the material decreases,the yield point is advanced,and the fracture toughness is improved.In elastic stage,material deformation is related to point defects and surface defects of atoms in the system.In plastic deformation stage,material deformation is related to dislocation growth and slip.The stress concentration at the tip of the crack is the cause of the phase transition near the crack tip,and the release of the energy after the phase transition leads to the stress relaxation.A multiscale model of the two-dimensional metal silver was established to observe the process and micromechanism of crack propagation from nano-scale to macro-scale by multiscale analysis(MD and FEM).The stress boundary information was proposed based on the stress intensity factor,the continuum region and discrete atomic region were combined based on displacement parameters.The model parameters and materials were consistent with the parameters in the literature.The simulation results have excellently agreed with the theoretical and experimental conclusions,which proved the rationality of the method.The fitting values of zirconium cobalt alloy potential function was calculated by first principles,including crystal structures,formation enthalpy,cohesive energy and elastic constants.The influence of Ti/Hf doping on the hydrogen storage properties and mechanical properties in ZrCo alloy at macro-scale were analyzed using electronic structure at nano-scale based on the band theory.