Sub-critical crack growth in sodium borosilicate glasses

Abstract

Sub-critical crack growth in sodium borosilicate glasses was investigated in inert environment by using the DCDC technique. The intrinsic fatigue behaviors of these glasses drastically changed with their compositions. It is found that the intrinsic fatigue parameter can be affected by the ratio of 3-fold coordinated borons to the total borons and by the microscopic phase separation. As for fracture toughness, the maximum value of 1.03 MPam^1/2 was obtained at the composition of Na₂O-B₂O₃-4SiO₂, which had the largest ratio of 4-fold coordinated borons. It is elucidated that the glass structure in a microscopic scale, such as the coordination number of network forming cations and the phase separation in a nm-scale, determines its fracture and fatigue behaviors.