Since Griffith published his classic paper in 1920, glass scientists and engineers have understood the importance of cracks on strength. Cracks on the surface or in the bulk cause strengths to be orders of magnitude lower than the theoretical strength because cracks are enourmously effective at concentrating stresses. However, surface cracks are more likely to be fracture origins, since contact damage and localized thermal shock occur at the surface, while the interior is usually free of such stress concentrators. Recording microindentation technique is an important tool for understanding crack initiation behaviour of glasses, as examples in this paper demonstrate. In turn, this understanding is essential in helping glass manufacturers with issues such as scratchability, strength, and less-brittle glasses. Further research is ongoing.
