Molecular Dynamics Simulation Of Deformation Mechanism Of Gradient Nano-grain Polycrystalline Copper

Gradient nanomaterials have gained wide attention in recent years.This is the concept derived from the nano-treatment of metal surface,which is the grain size increases from small to large in space.This nanostructure can effectively enhance the material properties..In this paper,the deformation mechanism of gradient nanostructure polycrystalline copper was studied by molecular dynamics simulation method.The simulation includes uniaxial stretching and fatigue stretching cycle simulation.The simulation of uniaxial tension found that the gradient nanostructured polycrystalline copper has a unique stress distribution,and the high stress region is a triangular-like "pyramid" shape,which can coordinate large and small grains and avoid stress localization,and suppressing the generation of cracks,the whole model is stressed,and the material is effectively strengthened.By comparing the gradient models of different grain size distributions,it is found that the material strength is the highest when the grain size is linearly distributed;it is found by changing the maximum grain size,the maximum grain size(20 nm)is the highest strength and has the best elongation when it is four times to the minimum grain size(5nm),and the ability of the gradient structure to resist tensile deformation drops sharply when the maximum grain size(16 nm)is reduced to three times to the minimum grain size;In the fatigue cycle simulation,the gradient nanostructure polycrystalline copper can effectively alleviate the stress concentration,inhibit the crack initiation and prolong the fatigue life of the material.At the same time,when the ordinary structure polycrystalline copper fails,the crack rapidly expands and is accompanied by dislocation structure.In summary,this simulation proves that the gradient nanostructured polycrystalline copper is superior to the ordinary copper in terms o f strength,elongation and fatigue life.By observing and analyzing the deformation mechanism,it is found that the influencing factors are mainly the stress of the gradient structure model.The characteristic to effectively avoid stress localization and achieve overall stress,is consistent with the actual experimental results.