The Contact And Friction Investigation Between Single Crystal Copper Substrate And Diamond Indenter Based On Molecular Dynamics Method

Surface contact characteristics determine the operating characteristics of many machines,especially reliability and security of which the roles are closely related to the reliability and security of micro machine products,and have became a research field by many domestic and foreign scholars.However,to weaken the contact and fiction force and improve the ability of material resistance deformation.It is not only can save resources and energies,but also plays an important role in contributing low carbon society.The contact surface is not smooth in actual working conditions,in addition,it includes many different sizes and shapes of rough peak in nanoscale,and the material often happens plastic deformation in micro/nanoscale,especially in two components contact,which result in the adhesive force have evident effect on causing contact surface failures.Furthermore,the models with traditional continuum theory have not been able to describe molecular dynamics phenomenon in material,so it is necessary to investigate the force behaviors about object from the perspective of atomic and molecular structures.Thus,a molecular dynamics method is adopted to research the nanoscale contact and friction problems in this paper.Considering the exist of adhesive force and substrate elastic-plastic deformation and crystal anisotropy in simulation.The processes between contact--separation and contact--friction are simulated through adopting EAM and Morse potentials and Verlet algorithms,and analyzed the differences of the contact force and the extent of void collapse and energy dissipation in single crystal copper material with different void sizes and indentation depth.Moreover,it is revealed that the reasons of different rough peak with hemispherical and conical shapes and sizes have significant influence on the contact force and friction force and material elastic-plastic deformation.In MD simulations,the results show that some atoms at the top level of substrate happened "snap back" phenomenon significantly and the hysteretic displacement phenomenon can be seen obviously in contact and separation processes.Moreover,the contact force tends to be increases with the curvature radius increases.Evidently,the lager adhesive force,the easier adhesive contact failures will happen.Furthermore,considering the single crystal copper material with a spherical void.The results show that the void defects would soften copper mechanical properties which result in the ratio of the contact force versus indentation depth and the extent of void collapse and energy dissipation are smaller than without a void defect.Furthermore,as void with the same location depth,the extent of void collapse became weaker,the ratio of the contact force versus indentation depth became lower with a void radius size increases,which result in energy dissipate smaller,as void with the same radius size,the extent of void collapse became severely,the energy dissipation became high,and the ratio between the contact force and indentation depth became larger with the indentation depth of a void increases as well.In contact and friction processes,two different shapes and size of rough peak have differences effect on substrate elastic-plastic deformation evidently.The dislocation loop indicated that the substrate happened plastic deformation.Furthermore,the lager dislocation loop grows up,the more fierce plastic deformation of substrate become.In addition,the rough peak of hemispherical shape has lager effect on the ratio of contact force versus displacement and substrate plastic deformation than the rough peak of conical shape.