Small Hard Body Impact on Annealed, Heat Strengthened and Fully Tempered Laminated Glass

Neglecting the accidental soccer or golf ball hitting the window of the neighbors in a movie, actual impact on glass is rare. In architecture, the only significant case in the literature is where a fully tempered laminated panel of the New York Apple cube was hit by a small stone launched by a snow blower. Nowadays a lot of glass is used in sound screens next to high ways. These are however subjected to regular impact of small, fast-moving hard bodies. Mostly small stones which are removed from the asphalt road surface due to wear and are launched by car tires. This is a regular occurrence leading to safety questions and also to considerable cost as replacing the sound screen panels not only costs money but also requires closing down at least the outer lane of the highway, thus reducing the traffic flow. Thus a study was made of the impact resistance of annealed, heat-strengthened, and fully tempered laminated glass using test panels. This was followed by the testing of a full-size sound screen panel. The results show that the impact resistance of tempered glass is determined by the amount of compressive surface pre-stress. However, it is also noted that although fully tempered glass better resists impact, it has no residual strength after an impact with the critical energy.