Chemically strengthened glass by ion exchange: Strength evaluation

A linear fracture mechanics model is considered for strength evaluation of glass submitted to ion exchange below glass transition temperature. Former models of the ion exchange process were based on rough zero-order (constant) and first-order (linear) approximations of the residual stress field generated by the larger ions invading the glass matrix. In this study, the effective stress field generated by the invading ions is taken into account for strength evaluation. Both stress non-relaxation approximation and stress relaxation are analyzed and discussed. A comparison of results predicted by the introduced models with experimental data of glass strength before and after ion exchange is presented. The hypothesis of conservation of surface flaws geometry (shape and depth) after ion exchange is critically discussed.