Scratch formation in brittle solids and its application to polishing
Abstract
The contact between a hard particle and the surface of a brittle solid is of fundamental interest for understanding material removal in ceramics and glasses by abrasion, erosion and machining. An experimental study has been made of the deformation and fracture taking place about scratches in brittle solids. In the experiments, a pyramidal diamond indenter is loaded against the surface of an optically transparent specimen and slid across it at speeds of a few millimeters per second. In situ observations of the indenter-specimen contact region during scratching have been made at high magnification using an optical microscope. Details of the scratch zone and wear debris have also been studied using optical microscopy and stylus profilometry. Scratch formation in a variety of optically transparent ceramics and soda lime glass has been analyzed using these techniques. The study has provided unique observations of the formation and evolution of median and lateral cracks around scratches, the formation of plastic scratch grooves and ductile, ribbon-like chips. Some new and interesting aspects of fracture and wear particle formation in brittle solids are presented and discussed. Implications of these observations to abrasive machining and wear are considered. By combining the theory of indentation hardness and fracture with an analysis of the size distribution of abrasive particles in polishing media, a model has been developed to describe the mechanics of lapping and polishing processes. The model has been used to predict the forces on abrasive particles and the number of these involved in material removal, to estimate polishing and scratch temperatures, and to calculate surface finish parameters for polished surfaces. It is shown that these predictions of the model are consistent with experimental results derived from the polishing of brittle solids. The model also suggests a few methods for significantly improving the efficiency of abrasive polishing.
Degree
Ph.D.
Advisors
Chandrasekar, Purdue University.
Subject Area
Industrial engineering|Mechanical engineering
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