Non-Linearity of the Mirror Constant for Glasses Fractured in Flexure

Fractography relies on topographic features on the fracture surfaces to deduce the stress state of the failed component. Traditionally, fractographers assumed that the fracture strength of brittle materials was related to the reciprocal of the square root of the mirror radius linearly, in accordance with the empirical equation formally postulated by Orr in 1972. In this manuscript a novel analytical model to describe the dynamic behavior of elliptical cracks was derived on the basis of thermodynamic principles. Unlike Orr’s equation, the proposed model considered the effects of the plate thickness and it could be used to improve the strength prediction based on the plate’s geometry and material properties. To verify the validity of the model, 39 annealed, 2mm thick, soda-lime silicate glass plates were fractured by four-points bending test and the fracture surfaces were imaged by confocal laser microscope and carefully studied. Excellent agreement was observed between the experimental data and the proposed theoretical framework. © 2018, Shanghai Jiaotong University and Springer-Verlag GmbH Germany, part of Springer Nature.