Direct observation of crack propagation in a liquid crystal display glass substrate during wheel scribing

Abstract

AbstractIn‐situ observation of crack propagation in an LCD glass substrate was performed during wheel scribing. It was found that a median crack initiated just beneath the wheel and stopped once, and that the crack re‐propagated after passing through the wheel. In this study, the first pop‐in median crack is defined as the first crack, and the re‐grown median crack is defined as the second crack. From in‐situ photoelastic measurements during a static indentation of the wheel, the maximum tensile stress was observed just beneath the wheel. The tensile stress beneath the wheel was also confirmed from FE analysis. It is considered that this tensile stress is the origin of the first crack nucleation. On the other hand, from post‐observation of the cross‐section of a scribing groove after scribing, it was found that the median crack was closed in the plastic zone. It is considered that this closure results from compressive stress in the plastic zone beneath the scribing groove, and that this compressive stress causes the first crack to be arrested.