Experimental investigations into SGP laminated glass under low velocity impact

The structural use of laminated glass (LG) is growing rapidly. To meet safety and post-breakage strength requirements, a SentryGlas®Plus (SGP) interlayer has been widely used in LG. Limited data has been available to date concerning the impact resistance of SGP LG. This paper describes an experimental investigation into the damage behaviour of SGP LG panels under hard-body impact. A mean minimum breakage velocity (MMBV) test approach has been employed to determine the breakage energy. By tracing the crack initiation through the use of high speed filming, six categories of breakage sequence have been classified. The characteristics of crack propagation, including the lagging time between the initiation of different cracks and the typical crack propagation speed, were also obtained. This is followed by the identification of the representative cracking morphology and the motion behaviour of the impactor. The impact resistance of SGP LG has been calculated by examining the effects of the design variables such as the LG panel size, interlayer thickness, the support conditions and the glass make-up. It was found that the influence of LG panel size on the MMBV and both pre- and post-breakage stiffness is limited, and increasing the interlayer thickness cannot improve the resistance to glass breakage under impact. The LG panel with clamped edges requires more MMBV to trigger glass breakage and has an increase of 44% in pre-breakage stiffness compared to the panel with bolted connections at four corners. The evident improvement in post-breakage stiffness due to the beneficial fragmentation pattern of heat strengthened (HS) glass, compared to its counterpart of fully tempered (FT) glass, has also been revealed. However, the differences in MMBV between them are modest. Results also indicate that a significant degradation of dynamic stiffness in the post-breakage stage can be found in both the double layered LG with thicker interlayer, and in the triple layered LG. The energy dissipation behaviours were also examined, and results suggest that the energy dissipation ratio can be greater than 40% in most instances, and the thicker interlayer will produce negative effects on dissipating impact energy. Two types of delamination are identified, and the dependency of their delamination growth on the impact velocity is analysed.