Micromechanics of Material-Removal Mechanisms from Brittle Surfaces: Subsurface Damage and Surface Microroughness

LLE Review, Volume 74 131 The cold processing of optical glasses usually involves rough grinding, microgrinding, and polishing. In microgrinding,1,2 the resulting brittle-material-removal rate produces a cracked layer near the glass surface, referred to as subsurface damage (SSD). [Editor’s note: The acronym for subsurface damage (SSD) used in this article should not be confused with its more common use as an acronym for smoothing by spectral dispersion.] Of course, the optical quality as well as the strength of the resulting surface is affected by such subsurface damage, so there is the need to understand the generation of subsurface damage as well as its measurement. Preston3 was the first to observe that the damaged layer usually increases in proportion to the surface microroughness (SR). Preston measured a proportionality factor of 3 to 4, which seemed to be independent of the grinding conditions. We emphasize that subsurface damage is a statistical measure of the ground surface rather than a reflection of the deepest flaw that might control, say, the mechanical strength of the surface.