Relationship between subsurface damage depth and breaking strength for brittle materials

Subsurface damages (SSD) induced by lapping strongly influence performances of optical components. However, to date, a wide variety of destructive and non-destructive techniques for measuring the SSD depth have been explored. In the present study, a novel destructive technique was proposed based on breaking strength of the lapped materials. The proposed technique relates the length of median cracks, formed through the Vickers indentation test, and the breaking strength of the indented samples. With this technique, subsurface damage depth can be practically evaluated via measuring breaking strength of lapped samples. The subsurface damage depth and surface roughness of ground and lapped BK7 glass were measured by the bonded interface sectioning technique and contacting profilometer, respectively. In order to validate the feasibility of the proposed technique, the values of SSD depth obtained by the calibration curve were compared with the values of SSD depth measured by the bonded interface sectioning technique. The obtained results are in concordance in the both used methods, which prove the efficiency of our technique to estimate the SSD depth of brittle materials.