Material removal of optical glass BK7 during single and double scratch tests

In order to get insight into the characteristics of chipping behaviors and material removal mechanism during grinding, both single and double scratch tests for optical glass BK7 were performed on a nanoindenter. Utilizing optical microscope, optical profiling system and displacement transducers, the scratch morphology, material removal volume and scratch depth were analyzed with applied normal load and scratch separation distance. In ductile mode of single scratching, obvious plastic ridges were formed on both sides of the groove and the volume of material removed is negligible. Under loading conditions discussed here, no obvious chipping occurs around the single scratch even when lateral and radial cracks were generated. During double scratching, three types of cracking interaction were observed and resulted in different chipping features. In brittle scratch mode, the material removal volume during double scratching is strongly dependent on separation distance. There exists a critical separation distance where the material removal volume reached its maximum. The difference in depths of the two sequential scratches was also found to be sensitive to both normal load and separation distance.