Fracture of ion-exchange-strengthened thin cover glass investigated using a phase-field model

Ion-exchange-(IOX)-strengthened cover glass has been used ubiquitously in portable electronics to keep them from impact damage. However, a quantitative relation between residual-stress profile and fracture strength remains elusive because the experimental data are significantly scattered caused by the uncertainty in the severity of surface flaws. Therefore, we propose a phase-field fracture model (PFFM) to study the detailed fracture processes and the shielding effect of surface compressive stress (CS) on a pre-existing surface flaw. In particular, we discussed the strengthening efficiency due to different combinations of surface CS and the depth of layer (DOL) under compression based on the ring-on-ring (ROR) and ball-drop (BD) tests. The simulated contour maps of fracture strength and BD height indicate that in ROR experiments, a higher surface CS is more decisive in crack inhibition and that in BD experiments, DOL is more important.