Strength of glass panels estimated by fracture mechanics

This paper is concerned with the strength of annealed glass panels when subject to static point loading and is a pre-cursor to further investigations on the resistance to impact by tools or flying objects. The current probabilistic models that are implicit in contemporary codes of practices for the determination of the strength of plain annealed glass is first reviewed. The alternative approach based on fracture mechanics is then introduced. With the fracture mechanics approach, factors controlling the strength of glass are resolved into the fracture toughness, which characterizes the resilience of glass as a material, and the depth of the Griffith flaws which control the strength of the panel. In essence, the strength of a glazing panel can be related to the depth of the critical Griffith flaw assuming a constant fracture toughness. The probabilistic distribution of the critical Griffith flaw depth is modelled by the extreme value theory based on Gumbel. This study is distinguished from earlier studies in that what is being modelled is the probabilistic distribution of the depth of the critical flaw in a glass panel. Results of static tests undertaken by the authors have been demonstrated to match better with the proposed model than with the popularly used Weibull model. Importantly, the characteristic strength of the panel has been shown to be very sensitive to its dimension.