Examination of internal stress by photoelasticity in laser cleaving of glass

Abstract

Laser cleaving is a glass-cutting technique in which thermal stress induced by laser heating and cooling produces cracks in the glass. Stress measurement during the laser cleaving process is critical in elucidating the crack-propagation mechanism and solving the problems of the laser cleaving method. In this study, we measured the birefringence retardation using a high-speed polarization camera and evaluated the relevance and accuracy of the measured values by comparing them with the results of a numerical calculation. The birefringence retardation at the crack tip was also observed in the experimental process. For the experiment, a soda lime glass was cleaved using CO2 laser irradiation. Then, the birefringence retardation and azimuthal angle obtained using the polarization camera were compared with the numerical calculation results. The birefringence retardation around the crack tip corresponded with that of the deformation caused by mode I. The crack propagation was arrested when the crack tip approached the edge of the glass. The birefringence retardation observed using the polarization camera confirmed that the mode I deformation decreased as the crack approached the edge.