Low Cycle Fatigue Properties Of Nanoporous Copper:The Atomistic Simulations

Nanoporous metals have a wide range of applications in catalysis,sensing,aerospace,and automotive due to their unique surface and pore structures.Structural stability and performance are the prerequisites to ensure its application.Therefore,researchers have carried out a lot of research on the mechanical properties and deformation mechanisms of nanoporous metals by means of experiments and simulations.However,fatigue,especially low-cycle fatigue,as one of the common ways of structural failure of porous metal materials,has been rarely studied.Here,we perform the molecular dynamics simulation method to study the low-cycle fatigue properties of nanoporous copper,consider the influence of specific surface area,and analyze and study its microscopic deformation mechanism:The low-cycle fatigue properties of nanoporous copper have a strong specific surface area dependence.As the specific surface area increases,the fatigue life of the material decreases gradually.When the specific surface area increases from 0.42 nm^-1to 3.22 nm^-1,the nanoporous copper undergoes a transition from fatigue-resistant to fatigue-prone,corresponding to a transition point of 1.24 nm^-1.For fatigue-resistant nanoporous copper,it has larger ligaments and pores,thus providing space for dislocations to slip.The stress is effectively released through dislocation slip,avoiding behaviors such as ligament rupture and pore collapse inside the material,thereby delaying structural fatigue.For fatigue-prone nanoporous copper,smaller ligaments and pores hinder dislocation propagation within the material,thereby accelerating local stress concentration.During the loading process,the local fracture and collapse of the ligaments/pores leads to the filling of the pores and the propagation of cracks,which accelerates the fatigue process of the structure.Surface reconstruction and dislocation activity interactions in nanoporous copper:on the one hand,the surface undergoes reconstruction under cyclic shearing,and the roughened surface promotes dislocation nucleation,hinders dislocation propagation,and strengthens dislocation interaction;conversely,dislocation activity also drives surface reconstruction.On the other hand,surface reconstruction and dislocation activity can accelerate the stress release inside the material.When the surface reconstruction is dominant,the dislocation activity is suppressed,and when the dislocation activity is dominant,the surface tends to be stable.For nanoporous copper with smaller specific surface area(≤0.42 nm^-1),the surface reconstruction is more obvious and the incubation period of dislocations is longer,which greatly enhances the fatigue resistance of the structure.