Evaluation of Crack Growth Characteristics in Float Glass and Thermally Tempered Glass Based on the Crack Length Measurement Using Au Ion Sputtered Film

Thermal tempered glass is made by rapidly cooling after heating float glass to near the softening point. Compressive residual stresses at the surface layer of thermally tempered glass strengthen the material, and tensile residual stresses are also generated at the same time in the interior of the material to balance with the surface compressive residual stresses. It is considered that the fatigue crack growth characteristics of thermally tempered glass are remarkably different from that of float glass, due to the existence of those residual stresses. In this study, Au film made by ion sputtering method and an optical microscope are used to measure the crack length of the thermally tempered glass and float glass, and these fatigue crack growth characteristics are investigated. As a result, it is confirmed that the crack length measurement with an Au film has high accuracy of measurement. Furthermore, it is found that the higher stress intensity factor is needed to cause the crack growth in thermally tempered glas than in flat glass.