Post-fracture performance of laminated glass panels under consecutive hard body impacts

Abstract

Many problems may arise due to the accidental breakage of glass layers in laminated glass (LG) under extreme loads such as hard body impacts. This paper experimentally investigates the progressive post-fracture performance of double or triple layered polyvinyl butyral (PVB) LG panels under consecutive hard body impacts. Six cracking cases were initially defined. The impact energy and peak impact force at the breakage point were then obtained. Through investigating the impactor motion and strain variation at different breakage stages, the influence due to the tension-stiffening (TS) effect by adhesion and the interlocking effect between fragments on both local and global impact responses of cracked LG were subsequently examined. Thereafter, the dynamic stiffness variations in various cracking cases were identified. Finally, the effective thickness and effective modulus of post-fracture LG were determined via analysing the spectrum characteristics from the recorded vibration data. The results show that, in post-fracture cases with only one outer glass layer cracked, adequate interlocking efficiency of glass fragments in contact allows the local fractured glass to have a similar performance to intact glass. Due to the partial resistance against tensile action introduced by the TS effect and pre-compression by the volume expansion of the fragments, LG with the inner glass layer cracked presents an identical initial out-of-plane stiffness to that of LG with the outer glass layer cracked. However, as the impact energy increases, the stiffness contribution via TS is found to be less than that by the interlocking effect.