Evaluation of surface cracking in micron and sub-micron scale scratch tests for optical glass BK7

In order to obtain the fundamental information on the deformation and fracture behavior of brittle materials during precision and ultra-precision grinding, micron and sub-micron scale scratch tests were conducted on optical glass BK7 using Vickers indenters. Three types of surface cracking were observed around the scratch grooves. They are lateral cracking, radial cracking and cracking in front of the moving indenter. It is found that lateral cracking is the main damage type due to its large damage size and low crack initiation load. The effect of surface cracking on the relationship between the normal load and the square of scratch depth was studied. The plastic zone size as well as the sliding blister field strength was expressed as a function of the contact zone size of the indenter. A prediction model for the size of damage zone induced by lateral cracking was established and was compared with experimental results.