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

•An original test system is developed to investigate the crack propagation in laminated glass.•The crack propagation rate of micro-cracks is investigated for various fatigue stress ratio.•The crack propagation is controlled by KImax and loading time, not by the fatigue stress ratio.•A “KImax-time” power law is introduced to predict the endurance of impacted laminated glass.•The fatigue failure of laminated glass is controlled by a “subcritical” stress corrosion process.

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.