Abstract
Machining damage was examined using industrial alumina ceramics with several grain sizes. Alumina ceramics were formed by dry-pressing method with spray-dried granules, and sintered at 1570 degree C for 2-27 hours. Grain size of the sintered body was 3-9μm. Flexural specimens with 3×4×40mm were prepared by the cutting and grinding process. Grinding direction was perpendicular to longitudinal direction of the specimen. Specimens were impregnated in fluorescent dye, then, fracture strength was measured by 4-point bending test. The fracture surface was observed with a confocal scanning laser fluorescence microscope (CSLFM). Depth of machining damage and fracture origin were easily characterized by the fluorescent dye. The result showed that machining damages were spread deeply and widely in the specimen with small grain size. The fracture started from the region of the machining damage. The fracture strength depended remarkably on the depth of the machining damage.
