Effects of local strain rate and temperature on the workpiece subsurface damage in grinding of optical glass

Subsurface damage (SSD) generated during the grinding process directly affects the optical quality and the service life of optical components. It is of great significance to accurately predict and effectively control the depth of the SSD layer of the ground workpiece. However, most of the existing SSD depth prediction models are based on quasi-static and room temperature conditions. This paper presented a prediction model of SSD depth, which considered the combined effect of local strain rate and temperature on the SSD generation during grinding process. The variation of strain and strain rate in the local shear zone of an average abrasive grit on the grinding wheel was analyzed, considering the dynamic density of abrasive grits; Strain rate effect of the material was described by introducing a dynamic fracture toughness K-ID, which would increase with the strain rate; Grinding zone temperature and especially the temperature on the abrasive grits were analyzed. Combining the strain rate effect and temperature effect, a thermodynamic fracture toughness K-IDT model was further developed. On the basis of classic brittle material crack system and the kinematics of grinding, the SSD prediction model considering the dynamic variation of mechanical properties in grinding process was derived. The effects of local strain rate and temperature in grinding of BK7 optical glass were systematically studied under different grinding wheel speeds. The predicted SSD values using a conventional static model and current models considering the strain rate or grinding temperature effect or both, were compared with the measured values. The predicted SSD values using the theoretical model including both the strain rate and grinding temperature effects, agree well with the measured values. The proposed model therefore is anticipated to be meaningful to understand of the SSD of hard and brittle materials involved in a precision grinding process.