Study On The Mechanical Characteristics Of Copper Crystal Based On The Discrete Dislocation Dynamics

With the rapid development of aerospace,precision mechanism and other industries,the demand for MEMS has been greatly increased in recent years.Higher performance requirements have been put forward for MEMS.Copper crystal materials have been widely used in MEMS as a basic component,whose size is on the micron and submicron scales.At this scale,copper crystals exhibit scale dependent mechanical properties,which cannot be explained by traditional macro mechanics.Therefore,in order to improve the performance and reliability of ME MS,the studies on the mechanical properties of small scale copper crystal materials is urgent.By studying the scale dependent mechanical characteristics,theoretical and experimental foundation can be laid for the design of MEMS.For the simulation of small scale materials,the discrete dislocation dynamics method can be used to analyze the motion behavior of dislocations with high computational efficiency,which is an effective mesoscopic scale method.However the study of discrete dislocation dynamics on the micro tensile and nano indentation are not complete,which are commonly used in small scale material testing.In this paper,self-developed discrete dislocation dynamics software has been used to study the two typical experimental conditions,which is of positive significance for further understanding the internal mechanism of small scale copper crystal materials.Firstly,based on the 2.5D discrete dislocation dynamics framework and the contact algorithm of ABAQUS software,the discrete dislocation d ynamics finite element coupling calculation program for small-scale single crystal copper has been developed by using MATLAB and PYTHON language.On the basis of this program,corresponding dislocation initialization module,cloud chart and curve post-processing module have been developed.Secondly,A uniaxial tensile finite element model of single crystal copper is established on the basis of the discrete dislocation dynamic finite element coupling calculation program for the single crystal tensile(111)surface of the single crystal copper.The stress distribution and internal dislocation motion mechanism in uniaxial tension of single crystal copper have been analyzed by coupling calculation.The internal mechanism of the thickness and orientation affectin g the uniaxial tensile properties of single crystal copper was investigated.Thirdly,a simulation model for nanoindentation on Cu(111)surface has been established,and the behavior of dislocation and the force displacement curve of nanoindentation have been obtained.The connection between nanoindentation stress-displacement curve and dislocation multiplication speed together with avera ge dislocation distance has been studied from two aspects including dislocation source density and initial dislocation density.Finally,the nanoindentation test of Cu(111)has been carried out,and the stressdisplacement data of Cu(111)were obtained.The surface topography around the indentation has been researched by SEM.The distribution of dislocation lines around the indentation was researched by TEM.The specific states of dislocations have been observed at the atomic stacking level by HRTEM.The correctness of the simulation model have been preliminary verified through the experiment.