Simulating dynamic glass fracture in an air blast event

Abstract

In modern-day architecture, large glass facades often define the skin of prestigious buildings. When these buildings are considered a target for terroristic attack, great care is required in the structural design as to saveguard human life. Above all, the window components need to be considered, since glass shard debris is the main cause of injury in any urban impact event. Typically, laminated glass panes are used in blast resistant glazing systems. These consist of 2 glass plies, bonded together by one or more polymer interlayers to retain glass fragments upon fracture. The efficiency of a laminated glass against impact loading depends on a number of factors: ply thicknesses, viscoelastic properties of the interlayer material and bonding strength between layers. The frame connection also plays an important role. Ideally, the window should remain in its frame without glass fragments being propulsed and without tearing of the interlayer. Then the questions are: - How and when does the glass fracture? - How are the fragments kept together by the interlayer? - How much of the impact energy can be dissipated by the window without causing danger to humans? Or practically, up to which load is a glazing panel able to withstand the attack? It may be clear that destructive testing is a complex and expensive manner to assess the applicability of a structural wall configuration. Computer simulation offers a tool that can save time and costs, and the possibility to gain a deeper insight in the quantification of the main failure mechanisms: brittle cracking, delamination, interlayer tearing and frame connection failure.Our aim is to develop a numerical modelling technique for laminated glass under impact and blast loads, validated by laboratory experiments. The finite element model takes into account non-linear material behaviour and allows for localised fracture, using upcoming techniques such as the cohesive zone method