Abstract
The crack propagation behavior and the internal stress field during mechanical cleavage of non-alkali glass sheets (thickness : 0.7mm) were visualized by high-speed imaging techniques. At first, the effect of scribing conditions on the fractured surface quality was investigated when the scribing wheel with surface asperities was used. It was found that the surface quality was strongly influenced by an applied load. In the case of low load conditions (∼11N), the fractured surface exhibited rugged patterns known as ‘hackle’, and it gradually changed to regular striped pattern known as ‘ribmark’ with the increase of applied load (12N∼). In order to understand the reason why the surface quality changed with the applied load, the crack propagation behavior was observed using a high-speed camera. The results showed that the generated crack hardly propagated to thickness direction when the applied load was low, in contrast to the rapid propagation under the high load conditions. Because the crack propagation behavior was likely determined by the stress field around the generated crack, the phase difference measurement, which was proportional to the principal stress difference, was conducted using a high-speed polarization camera. The results showed that the phase difference gradually vanished, i.e. the stress relaxation occurred, with the crack propagation especially in the high load conditions. By the image analysis for obtained phase difference from the polarization camera, an in-process estimation method of fractured surface quality was proposed.
