Molecular Dynamics Simulations And Experimental Study On Nano-indentation Of Fused Silica

With the rapid development of nanofabrication technology, fused silica withhigh surface quality has been widely applied in atomic energy, aerospace, radar,missile and some other industrial fields, especially in the field of optics, fused silicawith much higher surface and sub-surface quality is increasingly required, however,owing to the huge differences in the processing scale between nano-machining andtraditional processing, the direct observation of microscopic processes is almostimpossible, so that the domestic theory of the microscopic mechanism onnanofabrication is relatively scarce, which has severely confined the processingaccuracy of important optical materials like fused silica. Therefore, by the use ofmolecular dynamics simulation, researching the nano-processing and defectgeneration mechanism of fused silica from the atomic level, on the base of whichdeeply analyzing the effects of multiple parameters on machining process from theperspective of the plastic deformation may raise an extremely importantsignificance.Firstly, the research status of the molecular dynamics simulation in the field ofnanofabrication has been comprehensively overviewed, the basic principles andmethods of molecular dynamics simulation have been researched, and on the base ofwhich the molecular dynamics model of fused quartz has been established byMaterials Studio; the feasibility of Rentsch’s method has been discussed and finallyconfirmed; the potential function and some other parameters have been determined,thus accomplished the compilation and debugging of the simulation program.Secondly, by the nano-indentation and scratching simulations using LAMMPSsoftware, we have researched the load and temperature of the tool, as well as theinteratomic potential energy in relaxation and nano-cutting process, thus revealingthe micro-nano-machining mechanism and the transfer mechanism of sub-surfacedefects in fused quartz; by the calculation of the simulation data, the validity of themodel has been assessed.Thirdly, in order to characterize the plastic deformation of the fused silica innano-cutting process, we have put forward three analytical methods which includeaccumulation-measuring, density analysis and configure backtracking; On the basisof those methods, a lot of indentation and scratching simulations on differentparameters have been carried out, and we’ve got the effects of multiple parameters,such as cutting thickness, corner radius and cutting speed, on the plastic deformationand processing quality of the fused silica materials; by the observation of the cuttingprocess in VMD visualization windows, the formation mechanism of the surface material uplift and the machined surface has been analyzed in the perspective ofdefect atoms’ or atomic clusters’ movement.Finally, lots of nano-indentation experiments on fused silica specimen havebeen carried out with the nano-indenter, and two parameters--the residual depth andthe surface material uplift—have been put up to characterize the material’s plasticdeformation in indentation process; as an authentication of the conclusions achievedfrom the simulation, experiments on multiple parameters have been performed;moreover, the impact of the tip geometry and the cyclic loading on materials’ plasticdeformation has been briefly analyzed.