Deterministic failure prediction of toughened glass when impacted by ice

The study presented in this paper deals with failure prediction of a thermally toughened glass panel caused by impact of ice. Ultimate failure was found from the study to be triggered by fast growth of cracks on the backside of the glass pane implying flexural failure. The deterministic predictive model developed in the study comprises closed form expressions which are without any calibrated coefficient. The input parameters are the size of the ice impactor, impact velocity, temperature of ice, glass pane thickness and the pre-existing stresses. Digital microscopy and micro-CT scanning techniques were employed to survey the dimensions of a purposedly preformed crack. As much of the uncertainties related to the critical crack has been resolved in the survey, no calibration of any modelling coefficient is required. Developing this new form of deterministic procedure was accomplished by capitalizing upon a model developed recently by the authors for predicting the (ice impact generated) transient stresses that are formed at the critical crack. The dynamic stress intensity can therefore be predicted conveniently by use of closed form expressions as opposed to (time consuming) numerical simulations. Accuracy of the model has been validated by impact testing involving accelerating ice impactors on the glass specimen by a gas gun. Twenty-one test cases involving two glass thicknesses, two sizes of ice spheres and seven preformed crack depths were conducted. Failure velocity was found to correlate strongly with crack depth, and was insensitive to changes in the crack length.