Blast performance of silicone-bonded laminated glass

Abstract

Blast resistant glazing systems typically use laminated glass to reduce the risk of flying glass debris in an explosion. Laminated glass has a bonded polymer interlayer that retains glass fragments upon fracture. With proper design, the flexibility of the interlayer in laminated glass can offer protection from significantly higher blast loads when compared to an equivalent monolithic pane. This thesis investigates the post-fracture behaviour of laminated glass under blast loading and aims to build the knowledge required to improve design methods for blast resistant glazing. Full-scale open-air blast tests were performed on laminated glass containing a polyvinyl butyral (PVB) interlayer. Test windows ranged in size from 1.5m×1.2m to 3.5m×1.8m and were bonded to robust frames using structural silicone sealant. Blast loads were produced using charge masses of 15 kg to 500 kg (TNT equivalent) and distances of 10m to 30 m. Deflection and shape measurements were obtained using high-speed digital image correlation. Measurements of loading at the joint were also made with strain gauges. The main failure mechanisms observed were the cohesive failure of the bonded silicone joint and tearing of the interlayer. These failure mechanisms were investigated further using a highspeed tensile test machine to reproduce blast loading conditions. Cracked laminated glass samples were loaded in tension at varying rates. Their response was characterised by a rate dependant plateau force which can be used to estimate the maximum load on the glazing joint. Delamination between the PVB and glass was found to play a key role in the laminate response. Thinner PVB and higher strain rates reduced the delamination area, leading to premature tearing of the interlayer. The strength of structural silicone sealant in a blast situation was also investigated. A novel test method was used to determine the bond length required to retain the laminated glass window in a blast event. A nominal strength of not greater than 1.1MPa should be used for design of conventional single-sided silicone joints. A finite element model of the laminated glass response to blast loading was developed using the results of the experimental investigations. The failure predictions of the model were compared against a single-degree-of-freedom (SDOF) model and showed good agreement. Differences in the deflected shape at maximum deflection were seen between the model and those measured in blast testing.