Atomic Simulation Of Cylindrically Converging Shock Response In Single Crystal Cu

The research on the structural and mechanical response behavior and law of materials under high pressure impact loading has important guiding significance for weapon design,material synthesis and forming,energy development and other related fields,and is also an important research direction of compression science.Due to the influence of the ultra-fast response process and the system under extreme conditions such as high pressure and high temperature,the current research on the impact response of materials mainly focuses on the planar impact loading that are easy to be realized and diagnosed technically.The deformation mode in planar impact response is usually the simplest,but it can only reflect the very limited stress and strain states in practical applications and complex experiments.Compared with the planar impact,materials are subjected to different strain constraints under cylindrical or spherical impact loading.The relative motion among the internal cells of the material causes significant local deformation,so the impact response and micro response mechanisms of materials are obviously different from that under the planar impact loading..In order to understand the constitutive relation of materials under the entire stress and strain state and improve the confidence of dynamic material model,it is necessary to further study the response law of materials under more complex non-planar impact loading conditions.In this thesis,combined with the interaction between a potential wall and atoms,nonequilibrium molecular dynamics simulation is carried out under cylindrical converging impact loading technique in non-planar impact loading.The converging impact responses along the cylindrical axis [001],[110] and [111] directions are studied.The content of the impact study is as follows:(1)Under the cylindrical impact loading with the cylindrical axis [001] direction,due to the anisotropy of the elastic wave,the waveforms will change from the original cylindrical shape to quadrangular one.The elastic wave propagation along <100> direction falls behind that along <110>direction,while the plastic wave propagation is opposite.This also appears in the case of [110].(2)In all three cases,the temperature of wave front is relatively high,and it will drop as the shock wave propagates.The stress required for dislocation nucleation under cylindrical impact loading is smaller than under the planar impact loading.This is attributed to that the position of the dislocation occurrence is a hot spot area.Due to the converging effect,the temperature rise under cylindrical impact is higher than that under planar impact.Because the HEL generally decreases with temperature increasing,so the stress required for dislocation nucleation in our study is smaller than under the planar impact loading.(3)Due to the low velocity of the study in this paper,the main defect is the stacking fault,and no twins have been observed.Combining the c-axis analysis method and pole figures,we have obtained four slip planes for [001] case,six slip planes for [110] and four slip planes for [111].Under the [001] case,we have calculated the resolved shear stresses(RSS)and normal stress of possible slip systems.Because stress required for dislocation nucleation depends on the RSS and normal stress to the slip plane.The dislocation loop motion in the [110] and [111] is explained respectively,and found that the dislocation loop motion is similar to the uniaxial tension.Based on dislocation(DXA)analysis,the synthetic and decomposition reactions of dislocation are observed.