Impact is the largest single cause of the fracture of glass objects, although thermal stresses and simple overloading, including pressure loading, also contribute. Impact fractures of glass may be caused either by the glass object contacting a hard surface, such as when champagne glasses are thrown into a stone fireplace, or by a projectile striking the glass such as baseball encountering a window, or a stone striking an auto windshield. In every instance, the impact fracture of glass appears to occur instantaneously, accompanied by an acoustic outburst. For these reasons, many glass impact fractures, particularly those of beverage containers, are attributed erroneously to explosions. The study and analysis of glass-impact fractures and the resulting crack patterns provide understanding that can potentially lead to improved design for resistance.
