Fracture mechanics of impacted laminated glass subjected to various fatigue stressing conditions

This paper investigates the fracture mechanics of micro-cracks in the laminated glass plates of car windshields. Foreign objects such small pieces of gravel impacting a car windshield can induce micro-cracks, which may propagate and lead to dangerous glass fracture events. A major issue is to identify the parameters controlling fracture propagation from the initial micro-crack to catastrophic macroscopic failure. The main conclusion of this study is that cyclic fatigue is not a controlling factor in crack propagation in impacted glass. A subcritical propagation effect, related to chemical reaction between SiO2 glass and humidity, appears to be the main mechanism of crack propagation. An equivalent “stress intensity factor – time” power formalism is introduced to rationalize crack propagation endurance, for constant and variable cyclic stress conditions.