Float glass fracture toughness determination by Hertzian contact: experiments and analysis

In this work, we use a Hertzian indentation test to estimate the fracture toughness of float glass. Reference is made to two models for fracture toughness determination, that are based on two different physical approaches, the first one on the crack appearing at the surface of the sample and the second one on the cone crack developed under the surface. Our experimental fracture toughness values were higher than the one expected from the literature. By analysing the reasons for errors and limitations of the models, it has been possible, by adapting the latter to our special case of indentation, to derive a toughness value close to the one generally assumed for glass and obtained by other techniques. When using indenters with mechanical properties different from those of glass, we show that the friction between indenter and sample has an important influence on the fracture toughness determination. But other aspects, such as residual stresses or mechanical properties changes under loading, can also to some extent yield faulty estimations of the fracture toughness of glass in the Hertzian indentation test.