  The widespread use of sodium aluminosilicate glass in many engineering
applications due to its mechanical and optical properties (transparency,
dielectric, etc.), has become common in recent years. However, glass, a brittle
material, has its vulnerability to fracture. Processes such as heat treatment
(heat tempering) or chemical strengthening through ion-exchange have been used
to create residual stress profiles on the glass, in a bid to improve its
fracture strength. 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 important to designing new glasses that would be tougher while retaining
their transparency. The relationship between the glass residual stress
parameters such as the compressive stress (CS), depth of compression layer
(DOL), and central tension (CT) versus apparent (effective) fracture toughness
for different crack depth was investigated in this study using a Silicon
Carbide particle blast plus ring-on-ring (RoR) test method. The results also
showed that improving the fracture resistance of glass via chemical
strengthening requires a proper combination of CS, DOL, and CT, which is
particularly dependent on the initial/existing crack (flaw) depth. It was
determined that for a damage event involving the introduction of a shallow
crack depth, the criterion for optimal resistance to fracture, in terms of
apparent fracture toughness, is weighted more towards a high CS, than deep DOL
while for a deep flaw damage event, it is more weighted towards deep DOL, than
a high CS. These results provide a valuable piece of information in the design
of a more robust glass in engineering applications.

Materials Science