Presentations

Impact on glass panes and the fracture energy equilibrium

The Griffith theory describes the behavior of brittle materials. For the description of a crack creation, an energy equilibrium is used. At annealed glasses this equilibrium is reduced to a simple formula containing the mechanical energy in the glass and the surface energy needed for crack creation. The paper deals with the question, whether ball drop test allows the demonstration of the crack creation principles. Furthermore the specific surface energy is the coefficient that describes the energy needed to create cracks. Therefore it will be discussed whether ball drop tests produce similar specific surface energy values like static tests, e.g. double cantilever of three-point-bending tests. The testing results show a constant surface energy coefficient at different drop height. Nevertheless the measured coefficient showed a significant difference to statically determined surface energy coefficients. This was explained by the only partly use of the potential energy of the ball drop for the crack creation. The damping of the glass pane, that is supported in a gasket play a significant role in energy absorption. Further, the influence of the hardness of the gasket used for testing is evaluated in terms of energy distribution. At a ball drop test the energy amount is defined and the energy input cannot be stopped during the experiment. Despite its easy build-up and processing the ball drop test seems not to be an appropriate investigation for the fracture mechanism of brittle glass.