Research Of Mechanics Property And Deformation Mechanism Of Cu-Pb Alloy And Polycrystalline Copper Based On Molecular Dynamics Simulation

Currently, research on MEMS manufacturing has been developed, but the study on NEMS mechanism remains blank. Size effect and surface effect under nanoscale allow NEMS having features that MEMS does not have, enabling nanoscale mechanical movement and special functions. However, current NEMS research is still at the theoretical level which mainly due to the extremely harsh experimental conditions and practical basis. These factors limit the mechanical properties and machining mechanism of NEMS. On the basis of molecular dynamics theory, this thesis studied the mechanical properties and deformation mechanism at atomic scale, by building nanoscale metal model and simulating material deformation in machining.This thesis conducted multi-core parallel computation on the molecular dynamics model based on LAMMPS software. Alloy model at different time and parameters of microstructure mechanical were obtained by the simulation of Cu-Pb alloy. Derivation process graph of polycrystalline copper internal defect structure was obtained by the indentation and scratch simulation of polycrystalline block conducted by scanning probe. It revealed the change of materials mechanism and internal microstructure in the process of stretch and scratch of metal materials. The result showed that: grain boundary structure with high activation energy, transition state atomic arrangement and high stress gradient was more likely to have defections; low dimensional trigeminal grain boundary and vertex group carried a higher internal stress in the machining process; the second phase alloy elements could suppress the generation of internal defects in material and improve the toughness of the material; the defects of polycrystalline copper in the machining process was caused by the scratch of probe and generated in the local area of probe, which differed from metal drawing process.Cu-Pb alloy models with different garin size were established using Voronoi methods and Hall-Petch relationship and Cu-Pb alloy material properties were studied. The grain size of Cu-Pb alloy is in micron dimension, with a higher proportion of grain boundary atoms and barrier was produced because grain atoms’ energy was less than those of grain boundary atoms’. Significant compressive stress and shear stress were in the alloy grains. Tensile deformation process of Cu-Pb alloy was simulated, and the result showed that the grain boundary structure played an important role in the mechanical properties of the alloy. Grain boundary structure with high activation energy and stress gradients were more likely to drive dislocation into nucleation; dislocation moved along slip system within the grains but it was unable to pass through the grain boundary expanding internally to adjacent grains; microstructure with lower dimension beard high internal stresses in the process. Additionally, the second phase element enabled strength and toughness properties of the metal material to improve significantly.Creasing and scoring model of polycrystalline copper was established by using Voronoi method. Through the indentation and scratch of polycrystalline copper surface conducted by simulation probe, combined with internal stress analysis of polycrystalline materials, the machining mechanism of metal materials at the nanoscale was studied. The results showed that polycrystalline copper moved significantly under the force in the direction of probe movement and the rest directions were under a lower force and was accompanied by volatility, the machining process of polycrystalline copper was accompanied with accumulation and release of energy and nucleation and slip of dislocation, similar to alloy stretch, microstructure with lower dimension born larger stress in the machining process. In both stretching and machining process, metal deformation was mainly influenced by dislocation slip mechanism, consistent with the Hall-Petch relationship.