High strain-rate effects from blast loads on laminated glass: An experimental investigation of the post-fracture bending moment capacity based on time–temperature mapping of interlayer yield stress

Abstract

To enhance the resilience of buildings, laminated glass panels are increasingly used in glazed façades. These ductile panels provide a superior blast resistance to that provided by monolithic glass panels, due to the improved residual capacity offered by the polymer interlayer following the fracture of the glass layers. The complex interaction between the attached glass fragments and the interlayer is still only partially understood. To help address this, this paper investigates experimentally the post-fracture bending moment capacity of laminated glass.Three-point bending tests are performed at low temperature on specimens pre-fractured before testing, to ensure controlled and repeatable fracture patterns. The low temperature simulates the effects of the high strain-rates that result from short-duration blast loads by taking advantage of the time-temperature dependency of the viscoelastic interlayer. In these experiments, polyvinyl butyral is considered as the interlayer, this being the most common interlayer for laminated glass used in building facades. A new time-temperature mapping equation is derived from experimental results available in the literature, to relate the temperatures and strain-rates that result in the same interlayer yield stress. The results of the low-temperature tests demonstrate an enhancement of the ultimate load capacity of the fractured glass by two orders of magnitude, compared to that at room temperature. This suggests an improved post-fracture bending moment capacity associated with the now stiffer interlayer working in tension and the glass fragments working in compression. Due to the time-temperature dependency of the interlayer, a similar enhancement is therefore anticipated at the high strain-rates associated with typical blast loading. Finally, the assumed composite bending action is further supported by the results from additional specimens with thicker PVB and glass layers, which result in enhanced capacity consistent with the bending theory of existing analytical models.

The influence of fracture pattern on the residual resistance of laminated glass at high strain-rates: an experimental investigation of the post-fracture bending moment capacity based on time-temperature mapping of interlayer yield stress

“…To ensure controlled and repeatable fracture patterns, the specimens were pre-fractured before testing, by first scoring both glass faces with a hand-held glass cutter (hardened steel) and then impacting them at the location of the score, from both sides, to produce fullthickness cracks in each glass layer. Similar methods of pre-fracturing have been described by Nhamoinesu and Overend (2010), Hooper (2011), Samieian et al (2018) and Angelides et al (2020).…”

“…The specimens were laminated in a commercial, glass laminating autoclave to BS EN ISO 12543-2, using the same glass and PVB products for all specimens. The specimens are identical to the CS1 specimens considered in the experimental investigation of Angelides et al (2020).…”

“…The results from all three patterns are also compared to the idealised fracture pattern considered by Angelides et al (2020), which, in comparison to the baseline pattern, has four additional cracks at 20 mm spacing from the mid-span location, as discussed in Sect. 1 and shown in Fig.…”

“…No crushing failure is observed in the former, whereas the evolution of the fracture pattern in laminated glass at different time stamps shows further cracking after the initial fracture pattern has formed. These analytical models were later experimentally validated by Angelides et al (2020), who performed three-point bending tests (3-PBT) on pre-fractured laminated glass specimens at −100 °C. The tests were initially performed on specimens (labelled as CS1 by Angelides et al) with two glass layers (with t G 3 mm) and a single interlayer (t PV B 0.38 mm).…”

Blast response of laminated glass panels: a critical review of analysis and design methods

“…Furthermore, previous research on the bending stiffness of a fractured panel under blast loads is not available to enable any comment on the implication of Morison's assumption, nor those of the other ESDOF methodologies. Recent experimental work has indicated a significant enhancement of the post-fracture bending capacity at high strain-rates (Angelides et al, 2020). It is possible that the bending contributions to the mid-panel displacement are accounted for by the empirical factors applied in the various ESDOF methods to fit the experimental results but further research is required to confirm this.…”