| Due to high uniformity of its structure,consistency and stability of its optical properties,and optical functional diversity,optical glass has wide application in related engineering fields.However,its high hardness,low fracture toughness,and low impact resistance make it difficult to ensure the accuracy and quality of the workpiece during the traditional grinding and forming process.Ultrasonic vibration grinding has advantages of reducing cutting force,reducing cutting temperature,and improving processing efficiency.However,the crack nucleation and propagation mechanism and material damage form of optical glass workpieces under high-speed impact are not yet clear.The research of the subsurface damage prediction of the optical glass under the ultrasonic vibration is still imperfect.Therefore,the research on the subsurface damage of optical glass in ultrasonic vibration grinding has important reference significance and theoretical value for realizing precision low-damage processing of optical glass.The research on the dynamic mechanical properties of BK7 optical glass under high frequency ultrasonic vibration is the basis for the resrarch on subsurface microcrack propagation mechanism in the ultrasonic vibration grinding of optical glass.In this paper,the stress-strain curves and the destructive form of BK7 optical glass under high frequency ultrasonic vibration are obtained through Hopkinson pressure bar experiment,and dynamic mechanical properties such as stress,strain and strain rate of BK7 optical glass under the corresponding pressure value is calculated by the formula of three-wave method.Combined with the BK7 optical glass Hopkinson pressure bar experimental simulation analysis,the impact experiment waveforms of BK7 optical glass at high strain rate were compared with the simulation waveforms,and the reliability of the simulation model was verified.The experimental and simulation results were used to analyze the destructive form of BK7 optical glass under high-speed impact.The relevant parameters of the Johnson-Holmquis-Ceramics constitutive model were adjusted,which provided a theoretical basis for the numerical simulation of the microcrack propagation process of BK7 optical glass.The subsurface microcracks generated during the ultrasonic vibration grinding of optical glass are the main reasons for material removal and subsurface damage.Based on the Johnson-Holmquis-Ceramics constitutive model of BK7 optical glass materials under high strain rate conditions,smooth particle hydrodynamics and finite element coupling method are used to simulate the ultrasonic vibration assisted scratching of BK7 optical glass.The ultrasonic vibration assisted scratching of BK7 optical glass was carried out.The experimental results and simulation results were compared and analyzed to verify the reliability of the simulation model,and the nucleation and propagation of subsurface cracks under constant depth of cut and varying depth of cut were analyzed.The nucleation and propagation of subsurface cracks under constant depth of cut and variable depth of cut were analyzed.Combined with the analysis of the abrasive grain kinematics under ultrasonic vibration,the influence of the scratching process parameters on the scratching force and scratched surface cracks was researched.Based on this research,ultrasonic vibration grinding experiment of BK7 optical glass was conducted to further analyze the effect of grinding parameters and ultrasonic vibration parameters on the subsurface crack propagation depth of BK7 optical glass,and it can provide theoretical and experimental basis for the establishment of the subsurface crack propagation depth model of BK7 optical glass in ultrasonic vibration grinding.The effective prediction of the subsurface crack depth of BK7 optical glass in the ultrasonic vibration grinding is of great significance for the optimization of processing parameters,the improvement of processing quality,and the reduction of subsequent polishing allowance.Based on the related theories of fracture mechanics,impact dynamics of brittle materials,and the analysis of subsurface crack nucleation and propagation under high-speed impact,the relationship between the depth of subsurface cracks and the surface roughness is deduced.The subsurface damage prediction model of BK7 optical glass in ultrasonic vibration grinding was established,and the ultrasonic vibration grinding verification experiment was carried out under different grinding parameters,which verified the effectiveness of the subsurface crack depth prediction model. |
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