伊東 翔

Abstract Wheel scribing on glass generates a vertical crack with a periodic stripe pattern beneath the wheel (hereafter referred to as the first crack). After the passage of the scribing wheel, sometimes seconds later, the first crack is repropagated with a smooth surface (the second crack). The second crack propagates to 90% or more of the glass thickness under suitable scribing conditions, facilitating the breaking process. The mechanism of secondary crack propagation has not been sufficiently explained in previous studies. Therefore, this study used analytical and experimental methods to examine stress distribution and crack propagation behavior during wheel scribing. Finite element analysis suggests that the increase in the stress intensity factor contributing to the propagation of the second crack was due to not only the crack opening force but also the bottom deformation of the glass specimen. An analytical model accounting for the bottom deformation can simulate the characteristic behavior, such as rapid deepening when the scribing load exceeds a specific threshold value, of the second crack. This study indicates that the elastoplastic deformation caused by wheel contact induces the deformation of the entire specimen, and the state of the bottom constraints is important for controlling the second crack.

This work reports a selective median crack propagation phenomenon in glass, leading to a novel glass cutting process. We found that by scribing a glass sample to the extent of plastic deformation with a deformation depth of 100–400 nm, followed by inducing an initial crack, a subsurface crack with a depth of ~ 10 μm was propagated backward along the centerline of the scribed region with a speed of 1 μm/s order. The crack depth and propagation speed were increased by increasing the scribing load. We conclude that the propagation direction was determined by the effect of the shear stress caused by a scribing tip sliding motion.