Effect of Ion-Exchange Chemistry on the Fracture of Chemically Strengthened Sodium Aluminosilicate Glass

The widespread use of sodium aluminosilicate glass in many critical applications due to its hardness, weight, density and optical properties (transparency, dielectric etc.), instead of metals or plastics has become common in recent years. However, glass which is known to be a brittle material has its own vulnerability to fracture. Processes such as heat treatment (heat tempering) or chemical strengthening, through ion-exchange have been deployed to create residual stress profile on the glass, in a bid to improve its strength for applications such as in the automobile windshield design, consumer electronics mobile communication devices e.g. smartphones and tablet etc. However, failure still occurs which is mostly catastrophic and expensive to repair. Therefore, understanding, predicting and eventually improving the resistance to damage or fracture of chemically strengthened glass is significant to designing new glasses that would be tougher, while retaining their transparency. The relationship between the glass residual stress parameters, compressive stress (CS), depth of layer (DOL), center tension (CT) and fracture strength was investigated in this study using a grit particle blast plus ring on ring test method, based on IEC standard for retained biaxial flexural strength measurements. This technique can be used to measure both the surface and edge fracture strength of the glass. Preliminary results showed that for a reasonable level of CS, and CT, high DOL are beneficial to resisting fracture due to severe surface damage, while a high CS and low CT are beneficial to resisting fractures due to shallower flaws. The correlation of critical stress intensity factor versus DOL and CT for various level of CS were also determined and discussed. These results provide a valuable piece of information in the design of a more robust glass in engineering applications.