Note:  The Japanese version of this paper has been published in the Journal of the Japanese Society for Strength and Fracture of Materials, 55 (2022), 39–46.
Abstract: In order to investigate new crack generation in thermally tempered glass, crack propagation and crack divergence were observed using Cranz-Schardin high speed camera. Tempered glass of 3.5 mm thick was used as a specimen. Generation of cracks due to two crack-collision was also observed in 3.5 mm tempered glass, as well as those observed by Caustics method in 10 mm thick tempered glass. Regarding the presence/absence of new cracks the dependence of two cracks on the collision angle was confirmed. Considering that it is based on the synthesis of stress 𝜎CR generated at the crack tip, tensile stress necessary for the new crack generation could be created.
Keywords: New crack generation, crack collision, high-speed photography, stress 𝜎CR and collision angle, 3.5 mm thick tempered glass