Effects of residual stress on fracture toughness and subcritical growth of indented cracks in glasses

Fracture and subcritical crack growth were investigated using indented cracks in soda-lime glass, aluminosilicate glass and; borosilicate glass. The effect of residual stress was experimentally determined by obtaining the fracture toughnesses for cracks of various lengths. Extended cracks of various lengths-were produced at the same indentation load. From the results, dimensionless indenter-material constants chi(r) were determined for the surface crack and depth crack of semi-elliptical shape. Subcritical crack growth data for the as-indented short cracks show anomalous behavior, i.e. negative dependence of crack velocity on the stress intensity factor during small crack growth. This decrease in the crack velocity for the as-indented short crack can be explained by taking account of the residual stress.