Assessment of Surface Integrity of Machined Ceramics Using Image Processing

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Recent manufacturing advancements have allowed designers to create ceramic materials with tightly controlled microstructures and compositions. Some advantageous properties of these materials are their light weight, high strength, and resistance to heat and corrosion. However, advanced ceramics pose additional reliability problems. Specifically, the brittle nature of advanced ceramics often leads ceramic components to sudden catastrophic fracture during service.

To address the problem of inadequate reliability caused by microcracks formed on the surface, direct contact techniques such as stylus profilometry, scanning tunneling microscopy, and atomic force microscopy have been traditionally used to assess the surface integrity. Some problems associated with these assessment techniques are the lack of achievable resolution and the introduction of additional damage during the measurement process. In this thesis, DICOR/MGC, a dental restorative ceramic, is selected for this study. Specimens are prepared by a milling process using a designed set of machining parameters to examine their roles on surface integrity. A surface assessment system incorporating environmental scanning electron microscopy and image processing techniques is used to quantify the surface integrity in terms of roughness average and cavity density. By utilizing the image data, the developed technique allows assessment of surface integrity in a unique nondestructive manner. The unique contribution of the thesis is the establishment of penetration depth and parameters of the developed image system to explore the potential of assessing surface cracking. Analysis of the internal stress distribution using finite element method provides deep insights of the micro- scale mechanism of material removal during machining. Significant findings are directing the development of a crack controlled machining technology.