Novel measurement technique of crack length for indentation fracture (IF) method using high contrast image of crack tips through thin film coating

In order to improve the reproducibility of the indentation fracture (IF) method, a novel visualizing technique of the crack tips was developed. Coating a visualizing solution on the indented surface of silicon carbide could enhance the contrast of the crack tips. In order to verify our new approach, a round-robin test on the indentation fracture resistance, KIFR, of silicon carbide was conducted with nine laboratories. The clear identification of the crack tips could reduce the errors in reading crack lengths markedly even when measured with the ordinal metallurgical microscope at a low total magnification of 100×. Thus, good matching of KIFR was obtained between laboratories. Two main mechanisms of the enhanced contrast of the crack tips were proposed as follows; (a) the reduction of diffuse scattering from the smooth surface of the coating, (b) the interference color due to the slight change in thickness of the coating around the cracks.