Crack branching in float glass subjected to biaxial loading

Abstract

Failure of float glass plates in biaxial loading, occurs by well defined crack branching. As part of a study of the effect of handling damage on the strength of annealed glass, extensive observations have been made of crack branching in 4 mm thickness plates with strengths between 40 and 270 MPa, and more limited observations in plates of other thicknesses. Testing was carried out on discs loaded by hydraulic pressure against a circular anvil. For the 4 mm thick 280 mm diameter glass samples a 254 mm diameter anvil was used. Crack length at branching 2c b is related to the applied fracture stress σ b: σ b − σ 0 = A b/✓c b, where the branching constant, A b, is close to published mirror constants for uniaxial loading. The intercept σ 0 is larger than the residual surface stress in the sample, of which it is often considered to be a measure. The results have been analysed using the stress intensity factors for circular and elliptical cracks in a finite thickness plate and found to give good agreement with experiment for the variation of branch length with failure stress.