Micromechanical Behavior Of DKDP Crystal Defect Area And Its Effect On Micro-milling Repair Quality

Laser-based nuclear fusion is an important way to solve the energy problem.KDP / DKDP crystal has excellent nonlinear optical properties,and it is the only large-scale frequency multiplier that can be used in ICF optical system.However,the surface / subsurface defects of KDP / DKDP crystal cause laser damage of KDP / DKDP optical elements under the strong laser irradiation,which greatly reduces the laser damage threshold and seriously hinders the development of Laser-based nuclear fusion.Surface damage and surface defect repair of KDP/DKDP crystals can help prolong the engineering service life of KDP/DKDP crystal optical components in laser nuclear fusion that have great engineering value.At present,micro-milling is the most ideal repairing method.Therefore,This article takes the surface/subsurface defects of DKDP crystal as the research object to explore the effect of defects on mechanical properties and repair quality of micro-milling.On the one hand,it will help to understand the damage characteristics of micro-milling sub-surfaces and the degree of surface defects on the mechanical properties of materials.On the other hand,it has reference significance for micro-milling repair processing.By studying the mechanical properties of the fly-cutting surface and milling surface of DKDP crystals,it was found that the elastic modulus and hardness of the DKDP crystal milling surface changed by 16% and 13%,respectively,and the elastic modulus and hardness of the fly-cutting surface changed by 21% and 17%,indicating the anisotropy of the mechanical properties of the DKDP crystal milling surface is lower than the anisotropy of the mechanical properties of the fly-cutting surface.At the same time,the hardness and elastic modulus of the milling surface are lower than those of the fly-cutting surface except for the 45° crystal orientation.All these indicate that the milling surface of DKDP crystal has a lower resistance to elastoplastic deformation than the fly-cutting surface of DKDP crystal.This is because during micro-milling,the stress state at the cutter head is complicated,resulting in serious changes in the subsurface structure.At the same time,this paper studies the mechanical properties of the area near the surface micro-crack defects.The study found that the elastic modulus and hardness of the material in the range of 0.75?m near the crack defect have changed significantly,and the change range is 39% and 50%,respectively.At same time,the plastic flow direction of the material has also changed greatly.This paper used the method of finite element simulation to study the effect of defects on the micro-milling repair quality.In this paper,the load-depth curve of DKDP crystal was obtained by nanoindentation technology and fitted.The fitting curve was converted by dimensional analysis method to obtain the stress-strain relationship of DKDP crystal material,and the constitutive model of DKDP crystal material was established.Then,a three-dimensional simulation model of DKDP crystal micromilling repair was established,and the method of machining micro-grooves was used for repairing defects.It is found that the existence of defects during the milling process causes stress concentration and cutting force fluctuations,which increases the residual stress and surface roughness of the milling surface,thereby reducing the surface quality.A finite element simulation study of DKDP crystal micro-milling repair was carried out systematically.The effect of defects under different cutting parameters on the quality of micro-milling repair was studied.At the same time,the effect of defect size and position factors on the quality of micro-milling repair was studied.The influence of defects on the repair quality of micro-milling was obtained.