Study On Mechanism And Damage Behavior Of Ultra-Precision Cutting Of Crystalline Germanium

With the continuous development of science and technology,crystalline germanium is increasingly used in aerospace,military equipment,new energy and other high-tech fields,which has a higher requirement on the processing accuracy and surface quality of materials.However,the high brittleness and high hardness of crystalline germanium make it difficult to obtain a good surface quality.The ultra-precision cutting technology could realize the nano-scale removal of materials,and the processing precision and surface quality of the materials have reached the nanometer level,which could meet the processing needs of crystalline germanium materials in the high-tech field.However,material removal at the nanometer level would produce a size effect,and the macrocutting theory based on continuous medium mechanics is no longer applicable to ultraprecision cutting.Therefore,the investigation of the ultra-precision cutting mechanism of crystalline germanium has become an important research topic.To date,molecular dynamics methods are generally used by domestic and foreign scholars to carry out related research on ultra-precision cutting mechanism,but most of the research objects are single crystal materials without defects rather than polycrystalline materials,and the researches on material factors and surface/subsurface damage behavior of materials are relatively rare.Therefore,in view of the above problems,molecular dynamics methods and nano-scratch experiments were used in this paper to study the ultra-precision machining mechanism and damage behavior of crystalline germanium(single crystal germanium,polycrystalline germanium)with various organizational structures.The research contents are as follows:Firstly,the molecular dynamics simulation theory and analysis methods were briefly described,and the construction method of the crystal germanium material model was introduced.The internal structural characteristics of the crystalline germanium material were analyzed from the perspective of internal stress and potential energy,and the mechanical properties of the crystalline germanium were studied by the nanoindentation method.The results show that: compared with single crystal germanium,the stress and potential energy distribution of polycrystalline germanium is more complex,and the mechanical properties are affected by the internal microstructure of the material.Secondly,the molecular dynamics method was used to carry out ultra-precision cutting simulation of single crystal germanium and polycrystalline germanium,the material removal and surface formation process,defect distribution and evolution,cutting force and stress and temperature were analyzed.Also,the effects of grain size,grain boundary structure and surface amorphous layer thickness on the cutting of crystalline germanium were investigated.The results show that: the machining mechanism of single crystal germanium and polycrystalline germanium are quite different.The crystal microstructure and surface material defects have a significant effect on the cutting force and defect evolution mechanism.Furthermore,the polycrystalline germanium cutting simulations under different cutting depths,cutting speeds and tool's radius were carried out,the subsurface defect distribution and evolution,surface roughness and stress distribution of the material under different processing conditions were analyzed in detail.The results show that: the increase of cutting depth and tool's radius can increase the number and extension depth of subsurface defects,which will lead to increased surface stress and surface roughness of the material;The change of cutting speed has little effect on the number of subsurface defects,so that properly increase the cutting speed could reduce the depth of subsurface damage,but will also increase the surface roughness.Finally,single scratch experiment of polycrystalline germanium and double scratch experiment of single crystal germanium were conducted,the scratch morphology,scratch depth,scratch force and elastic recovery rate under different conditions were studied,and a double scratch stress field model was established;The corresponding molecular dynamics simulations were carried out,and the correctness of the simulation results was qualitatively verified according to the experimental results.