Fracture behavior of engineered stress profile soda lime silicate glass

Multi-step ion-exchange processing can produce complex stress profiles in glass surfaces, which can result in increased fracture strength, reduced strength dispersion, flaw tolerance and multiple cracking behavior. Glass displaying this set of properties is termed engineered stress profile (ESP) glass. Treatments at 400–450 °C in molten KNO 3 and NaNO 3 salt baths were used to create residual stresses in the surface of soda lime silicate float glass. Stress profiles were measured using optical stress birefringence, allowing derivation of apparent fracture toughness curves and prediction of crack stability over a range of flaw sizes. Specimens were tested in the four-point bend configuration to determine fracture strength and to study the multiple cracking which results from crack growth stabilization. The results were compared to predictions from the fracture toughness curves, in terms of the strength dispersion and crack stability criteria. Indented specimens were tested to determine the response of the glass to contact damage.