Numerical Simulation And Analysis Of Deformation And Failure Of Metallic Materials With Defects Based On Molecular Dynamics

The deformation failure of metal materials is mainly caused by the formation and expansion of internal defects.Under the micro scale,the generation and expansion of defects are carried out in the nanometer scale,the failure mechanism of deformation and failure can not be analyzed by means of macroscopical experiment and finite element method and molecular dynamics is the mainstream method to study the deformation and failure of metal materials.In this paper,molecular dynamics software LAMMPS is used to study the deformation and failure process of single crystal Ni,?-Ti and NiTi alloy under tensile loading,the content includes :First,the deformation and failure process of single crystal Ni with hole and the influence of various factors on its mechanical properties.The results show that:During the whole uniaxial tension process,it can be divided into two stages: elastic deformation and plastic deformation,which is similar to macroscopic tension.The stress-strain relationship in elastic stage accords with Hooke's law.Single crystal Ni in the [100] direction under uniaxial tension,the main reason of failure is: dislocation nucleation surface atoms in the cavity,resulting in the slip surface along the slip direction of <110> {111} formation of dislocation shear loop,and constantly staggered growth,the slip surface atoms appear fcc structure into HCP structure.Temperature,strain rate and hole radius have influence on the yield strength and modulus of elasticity of single crystal Ni: the yield strength and modulus of elasticity decrease with the increase of temperature.The tensile strain rate increases,the yield strength increases,and the modulus of elasticity is not affected.The increase of the radius of hole leads to the decrease of yield strength and modulus of elasticity.Second,The effect of temperature and strain rate on the crack propagation is analyzed in the [0001] direction uniaxial tensile process of a crack single crystal containing a-Ti.The results show that during the whole uniaxial tension process,it can be divided into two stages: elastic deformation and plastic deformation,similar to macroscopic tension,and the stress-strain relationship in elastic stage accords with Hooke's law.The failure mechanism is as follows: first,crack passivation phenomenon,then tip dislocation nucleation-dislocation emission-atomic slip-twinning phenomenon-few phase transition,final fracture,in this process,dislocation emission and the twin phenomenon played major role,temperature and strain rate rise will lead to lower yield strength.Finally,The superelastic behavior of single crystal NiTi shape memory alloy under cyclic loading is studied and the influence of different Ni and Ti atoms on the superelastic behavior is analyzed.It is concluded that the superelastic behavior of the single crystal NiTi alloy is due to the occurrence of the austenite B2 to martensitic B19 'phase transition during the loading process.There are three stages of austenitic elastic deformation,martensitic transformation and martensite elastic deformation.During unloading,martensitic elastic deformation,martensitic reverse transformation and austenite elastic deformation occur in three stages.Within a certain range,different single crystal Ni,Ti ratio and single crystal NiTi alloy all have super elasticity.With the increase of Ti,the critical stress of phase transition increases and the critical stress of reverse phase transformation decreases.