EXPERIMENTAL INVESTIGATIONS ON SUBSURFACE DAMAGE IN ROTARY ULTRASONIC MACHINING OF GLASS BK7

The present study aimed to establish an exact comprehension of the subsurface damage patterns generated during rotary ultrasonic machining (RUM) of glass BK7 process. First, the subsurface damage of the specimens produced with and without ultrasonic using three different diamond tools was compared and characterized by means of the bonded interface sectioning technique. Then, the RUM scratching tests were conducted on the polished specimen surfaces with two diamond tools to investigate the subsurface damage formation mechanisms involved in formal RUM process. The damage characteristics of the RUM scratches were investigated with respect to the kinematics principles of the abrasives and the dynamic fracture theory of the brittle material. As a result, three types of RUM-induced subsurface damage were identified: pulverization, chipping and cracking. The pulverization layer characterized by finer debris was just populated near the top surface of the RUM specimen without extending into the interior material. The finer debris should emerge simultaneously, resulting from the increased strain rate and the decreased dynamic fracture toughness of the material, both of which were aroused by the inertia loading of the abrasive when reaching the vertex of its sinusoidal trajectory.