Abstract

The Twyman effect was evaluated for loose abrasive grinding of ULE and Zerodur. It was shown that surface stress increases dramatically in the transition from brittle to ductile mode grinding. This is believed to be the result of an increase in subsurface deformation in the ductile process. It is well known that brittle mode grinding produces surface stress in glass. The stress is thought to be caused by localized flow, occurring when individual abrasives indent the ground surface. In brittle mode, most of the grinding energy contributes to the fracture process, with small stress fields produced by localized deformation near the crack tips. In ductile mode, however, glass deformation is more extreme, resulting in a significant increase in stress. The depth of this stress varies from tens of micrometers to tenths of a micrometer, decreasing the abrasive size. In ductile mode, the thickness of the stressed layer has been seen to be as small as 22 nm. Less stress was found in ULE than in Zerodur when ground under the same conditions, however, a factor of 2 to 4 increase in stress was observed for both materials in the transition from brittle to ductile mode.

© 1990 Optical Society of America