Glass-water interaction of a potassium phospho-aluminosilicate glass: Influence on mechanical behavior

The mechanical behavior of a potassium phospho-aluminosilicate (KPAS) glass which is known to develop near-surface compressive stress profiles resulting from low-temperature water diffusion was explored. Region I of the macro-crack growth curve for the KPAS glass exhibited a steeper slope corresponding to a higher fatigue parameter, n, than soda-lime glass despite a lower n at crosshead speeds of 10⁻¹–10² mm/min and no decrease in strength at lower rates in dynamic fatigue testing. The fatigue limit was easily observed in 50% RH air for the KPAS glass at velocities ~10⁻⁶–10⁻⁷ m/s giving rise to the delayed restart of cracks aged below the fatigue limit. Additionally, a 75% strength increase of the KPAS glass was measured after abraded specimens were aged for 100 days in humid air relative to specimens which were tested immediately following abrasion. The effects of swelling stress, surface stress relaxation, crack healing, and crack tip blunting are discussed.