| Subsurface damage(SSD) on optical element caused in the porgrace of lapping can directly affect many important indictors such as the life cycle,stability,imaging quality,coating quality,anti-laser damage threshold and so on. The improvement of processing quality through accurate inspection and evaluation of SSD becomes one of the critical problems in optical fabrication. This project aims to investigate the SSD of the typical brittle optical material K9 glass polished with the fixed abrasive pad(FAP). Through the investigation and analysis of the SSD on K9 glass,this project explores the relationship between the SSD and the mechanism of subsurface crack generation and spread,and the processing parameters of the FAP.The main research content and the results of this study cover the following aspects:1. BOE step etching method to measure the depth of SSD.A new method to measure the depth of the SSD on optical materials is proposed,which consists of the elaboration of the inspection process, the analysis of the inspection mechanism,the experimental validation and the comparison with the other SSD inspection methods.2. The generation and spread mechanism of the subsurface cracks on optical materials by single grain.Designed reasonable experimental scheme and inspection methods so as to accurately observe the initial subsurface crack(micron)on optical materials by single grain. The author built a mechanical model for the SSD on optical materials by single grain and analyzed the generation and spread of the initial subsurface crack on optical materials. The author simulated the generation and spread of the subsurface crack on optical materials with different load using the 3 dimensional finite element analysis software,ANSYS/LS-DYNA.3. Establish a SSD model of K9 glass lapped by fixed abrasive.Analyze the average depth of cutting of the FAP surface grain and the impact of the range interval between grains on subsurface cracks(median cracks,transverse cracks),which is based on the model of subsurface plastic yielding region on optical materials by single grain.Build the relationship between SSD and the processing parameters of FAP lapping under two scenarios,i.e.,the consistent protrusion height of the FAP surface grains(average depth of cutting) and the inconsistent protrusion height(maximum depth of cutting).4. The numerical simulation and experimental validation of the SSD on FAP lapping glass.Acquired the depth of SSD on K9 glass and silica glass polished by FAP with different abrasive grains through the BOE step etching method and built the mathematical relationship between the depth of the SSD and the average size of the grains. Simulate the progress of SSD on optical materials polished by FAP and compared the results with the experiments. |
