A recording microindentation instrument for in situ study of crack initiation in glass

A recording microindentation instrument equipped with optical observation and acoustic emission detection was built and used to examine, in situ, the crack initiation behavior of a commercial soda-lime-silica based float glass from contact with a Vickers diamond indenter. Indenter motion was provided by a piezoelectric actuator, while a strain gage load cell and capacitance displacement gages simultaneously monitored the indenter load and displacement, respectively, on the glass. It was found that both the maximum load and total indenter contact time influence the initiation behavior. Crack initiation occurred more readily when the total contact time and maximum load were increased. Increasing the maximum load from 0.2 kgf to 4 kgf resulted in the initiation of median-radial cracks on unloading at 6% Fmax up to 50% Fmax, respectively. In contrast, the initiation of lateral cracks was not significantly affected by the total contact time or the maximum load. Examination of the indentation crosssections beneath 1 and 4 kgf indentation sites revealed well-developed median-radial and lateral crack systems