Fracture and subcritical growth characteristics of indented cracks in soda-lime glass

Abstract

Fracture and subcritical crack growth are investigated using indented cracks in soda-lime glass. The effect of residual stress is quantitatively calculated by obtaining the fracture toughnesses for cracks of various lengths. In this case, the as-indented short cracks were grown by bending the specimens during indentation and then extended cracks of various lengths were produced at each indentation load. The apparent fracture toughnesses thus obtained from the radial surface crack length and the crack depth initially increase with increasing crack length and indicate an upper-bound saturation fracture toughness at larger crack lengths. From the results, dimensionless indenter-material constants x r were determined for the surface crack and depth crack. Subcritical crack growth data in the surface and the depth directions 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, while the extended long cracks show normal growth behavior. This decrease in the crack velocity for the as-indented short crack can be explained by taking account of the residual stress.