Effect of Hydrostatic Pressure on Fracture Strength of Glass Ceramics.

Abstract

In order to examine hydrostatic stress effects on the fracture strength of brittle material subjected to multiaxial stress states, glass ceramic specimens with an indentation-induced flaw were tested by four point bending under both atmospheric and hydrostatic pressures of up to about 100 MPa. The tests were conducted under both low and high stressing rates to provide data for different conditions of subcritical crack growth for the respective cases. The maximum tensile stress at fracture clearly increased with hydrostatic pressure in high stressing rate tests, though little significant difference was observed in strengths in low stressing rate tests. Such increase in fracture strength under high stressing rate conditions was attributed to the fact that the subcritical crack growth in region III which depend on the crack tip structure in the glass ceramics would be restricted by hydrostatic pressure ; because of this, a wide cohesive region at the crack tip favors abrupt fracture.