Glasses: New approach to fracture behavior analysis

The rectangular specimen edges of optical and technical glasses were fractured in the tests with conical indenters and pyramids. It was demonstrated that in the Rockwell indentation, away from those edges a ring crack and a Hertzian cone were formed. But when the indentation point approaches the specimen edge, only fragments of ring cracks develop and chip scars look like a Hertzian quasi-cone. The behavior of glasses was investigated with the edge fracture (EF) test method. It is shown that the fracture resistance of float glass is higher than that of fused silica and other optical glasses, the lowest fracture resistance is displayed by heavy flint. When glass surfaces are indented by a Berkovich indenter, lead glasses exhibit a better fracture resistance. It was revealed that glasses possessed the barrier to the onset of fracture, not typical of conventional brittle materials. The results confirm that the time- and cost-saving EF test method can be quite promising for comparative estimates of the ability of glasses to resist fracture.