Fracture strength prediction of float glass: The Coaxial Double Ring test method

Abstract

The fracture strength of float glass (FG) is generally difficult to predict, since it is governed by a number of different factors. To bypass the influence of the above-mentioned variables, ruling out any possible source of uncertainty, a reliable testing procedure should be able to produce an equibiaxial stress state in the central part of the specimen. The Coaxial Double Ring (CDR) test configuration is able to achieve such an ideal condition, but only if geometric nonlinearities are of lesser importance. A number of alternative test set-ups have been investigated in recent years, but none of these offers such advantages as to be preferred a priori. To this end, this study aims at finding out, through experimental investigations, an alternative CDR configuration to predict the failure strength of glass plates as a starting point for the development of a design-by testing procedure. A total of 393 FG square-shaped specimens, with different edge lengths (100 or 400 mm) and thicknesses (4, 5, 6, 8 or 10 mm), were tested using four different types of CDR test set-ups (obtained by varying the dimensions of the loading area). Laboratory outcomes, after being corrected via FEM simulations, were then interpolated using a Weibull-type statistical distribution to derive the best-fit parameters of probability density functions, which were finally used to provide the characteristic values of the glass failure strength.