AN EMPIRICAL-STUDY OF THE EFFECT OF STRESSED AREA ON THE STRENGTH OF FLOAT GLASS SURFACES

Strength tests have been carried out on 280 mm diameter discs of float glass loaded by hydraulic pressure against a 254 mm diameter anvil. T his arrangement gives nearly equibiaxial loading over a large part of the plate. Failure stress and position of failure have been determined for a large number of bottom (tin) surface samples subjected to a sta ndard handling procedure. Stresses have been calculated at the points of failure using the large deflection theory. By considering different concentric areas of the discs, and treating failures outside these re gions as statistical suspensions, strength distributions have been det ermined for different stressed areas of the discs. This procedure over comes the problem experienced by many workers in obtaining consistent samples for tests with different loading geometries. The distributions for the different stressed areas have an essentially constant Weibull modulus and a median stress that increases with decrease in stressed area. Calculations of the stress-area integral for the loading arrange ment show good agreement with weakest link predictions.