Crack growth threshold in soda lime silicate glass: role of hold-time

Abstract

Atomic force microscopy was used to examine the shapes of cracks and residual features left behind on the fracture surface after holding cracks at a stress–intensity factor below the fatigue threshold for soda lime silicate glass. After propagating a crack at a stress–intensity factor of K I=0.37 MPa m 1/2, the crack was held either at K I=0.24 MPa m 1/2, or K I=0.1 MPa m 1/2 for periods ranging from 1 h to approximately 200 h. Cracks held at the higher K I left featureless lines on the fracture surface. Becoming more pronounced as the hold-time increased, these lines marked the position of a corrosive notch that formed during the hold period. At about 30 nm from the crack tip, the crack surface displacement decreased reaching zero at the crack tip. The crack tip shape was that of an ogee arch. At the lower hold valued of K I, crack bifurcation occurred during which the crack became wavy, part of the crack propagating into the crack plane, part out of the crack plane when the crack was repropagated. A smaller crack tip displacement was observed for these cracks. Results of this study are believed to be a consequence of corrosion of the fracture surface caused by a basic solution formed when alkali ions (Na + and K +) at the crack tip exchange with hydrogen ions in solution.