Indentation crack initiation behavior of vitreous silica glasses containing different hydroxyl concentration

The indentation crack initiation behavior of eight vitreous silica specimens containing bulk OH concentrations ranging from 0.2 to 754 wt ppm was investigated. A recording microindentation instrument equipped with optical observation and acoustic emission detection was used to study, in situ, the cracking behavior from indentation with a Vickers diamond. No significant differences in the threshold loads for various types of cracking behavior of the specimens were found. In addition, the polishing medium was found to have little influence on the cracking behavior. The lengths of median-radial cracks around indentations varied little between specimens. The Vickers hardness of the specimens measured at 0.98 N ranged from 6.6 ± 0.3 GPa to 7.5 ± 0.7 GPa, and no trend with the OH concentration was apparent. In addition, the Vickers hardness of the specimens measured while under a 9.81 N maximum load (LVHmax), showed little variation, and no apparent trend with the OH concentration.