| Optical glass is widely used in aerospace,chemical production,national defense information and other fields with its excellent physical,chemical and optical properties.With the continuous development of modern technology,new requirements for the processing accuracy and efficiency of optical glass have been put forward.However,due to its high brittleness and low toughness,brittle fracture is prone to occur during ultra-precision processing.Therefore,it is difficult for optical glass to obtain ultrasmooth surface and non-damaged subsurface.Although the current research on the ultra-precision technology of optical glass has gradually improved the processing accuracy and efficiency.Due to the lack of the research on the mechanism of ultraprecision removal,it is impossible to explain the specific reasons for its improvement and fundamentally improve the precision and efficiency of ultra-precision processing of optical glass.Therefore,it is necessary to conduct a more in-depth study on the mechanism of ultra-precision removal of optical glass.The single particle removal mechanism has gradually become the basic method to study the material removal mechanism.Therefore,based on SPH simulation methods,a single-particle diamond scratching optical glass model was established.The simulation results found that the single-particle scratching removal mode of optical glass includes three modes:complete ductile,ductile-brittle transition and complete brittle mode.The critical condition of ductile-brittle transition for optical glass is obtained.The initiation and propagation mechanism of cracks during the removal process and the influence of the scratching depth and scratching speed on the surface and subsurface cracks,scratching force and stress are obtained.Secondly,based on the SPH method,a simulation model of single-particle alumina impact optical glass was established.First,the phenomenon of ductile removal occurs and then lateral cracks are generated from around the deformation zone and gradually expand to the surface of the material.The subsurface layer of the material produces radial cracks perpendicular to the surface of the material,and gradually expands to the deeper subsurface layer.The increase of the impact speed can increase the material removal rate,but it leads to the occurrence of brittle removal and reduces the surface and subsurface quality.When the impact angle is between 45°-75°,the material removal rate is the largest.The increase in particle diameter will cause the material removal mode to change from ductile removal to brittle removal.Finally,the influence of different impact parameters on energy loss is analyzed.Then,by designing the experiment of single-particle scratching optical glass,the SPH model of single-particle diamond scratching optical glass was verified in terms of the removal mode and the critical depth of ductile-brittle transition.And as the scratching speed increases,the critical depth of ductile-brittle transition will increase accordingly.As the scratching depth gradually increases,the depth and width of cracks increase.And at the same scratching depth,as the scratching speed increases,radial and median cracks become less and less.Finally,the experiment of single particle impact optical glass removal was carried out.The experimental results show that the single particle will cause three impact removal phenomena on the surface during the jet polishing process,namely carter,scratches and micro-dents.The increase in impact speed will cause a shift in the material removal mode.The increase in impact speed leads to an increase in the width and depth of the carter and an increase in material removal rate.In addition,the increase of impact speed will cause lateral cracks around the carter after impact.Finally,comparing the width and depth of crater after the experiment with the simulation result of single particle alumina impact optical glass based on the SPH method,it verifies the correctness of the SPH simulation model. |
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