Time and Temperature Dependent Mechanical Behaviour and Durability of Laminated Safety Glass

Abstract

Laminated safety glass (LSG) consists of two or more glass panes connected with interlayers of polyvinyl butyral (PVB). LSG is primarily used when a load-carrying capacity is needed after the breakage of a glass pane, e.g., for over-head glazing, glass to prevent people from falling or for glass fins.The mechanical properties of the PVB interlayer depend mainly on temperature and load duration. At low temperatures and short load duration the rigidity of the shear bond between the glass panes is higher than at high temperatures and long load duration. To determine the influences that govern the structural behaviour of LSG the mechanical behaviour of the structural elements has to be first analysed. GlassGlass, in almost all chemical compositions, behaves below the glass transition temperature (about 560°C for soda-lime-silicia glass) as an elastic solid until brittle fracture occurs when the failure strength is exceeded. For use in structural engineering glass can be regarded as a homogenous and isotropic material. Polyvinyl ButyralPVB is a member of the group of amorphous thermoplastic polymers and shows viscoelastic behaviour in all states of matter below disintegration at a temperature of about 140°C to 200°C. The viscoelastic behaviour depends highly on the thermodynamic state of the material as shown in a schematic graph in Fig. 1, which displays the change in shear or elastic modulus over temperature. A sufficient supply of heat can transform the chainlike molecule structure of the polymer from a rigid state to a deformable or even liquid state. This range is marked by the so-called glass-transition temperature T G of PVB and the melting temperature T M . CompositeA combination of an ideal elastic material like glass and a polymer material like PVB, which can display either elastic, viscoelastic or viscous behaviour depending on various parameters, raises the question of the structural behaviour of the composite. The structural behaviour of the laminate is determined by the ability of the interlayer to transfer shear between the glass panes. Therefore all parameters that influence the shear transfer, which is represented by the shear modulus, act on the composite behaviour and thus on the structural behaviour of the laminate. This depends on the temperature, the load duration, the amount of load, the load rate and the durability of the interlayer and the adhesion between interlayer and glass. A reduction of the number of these parameters (e.g., load rate, amount of load) is only possible if the structural application is limited in such a way (e.g., small deformations) that a linear viscoelastic behaviour can be assumed. Testing of Laminated Safety GlassTo analyse the influence of temperature and load duration on the structural behaviour of the laminate, a test program, sponsored by the German Research Foundation (DFG), was carried out. Laminated glass panes of different spans (1,0 m and 2,0 m), different thickness (2 × 10 mm and 2 × 4 mm) and a constant width of 0,36 m were tested in a four-point bending tes...

An approach to capture the residual strength of laminated safety glass according to the FMVSS 226 load caseEjection Mitigationwith the finite-element software LS-DYNA

“…The FMVSS 226 test procedures require a temperature between 18 • C and 29 • C and a humidity between 10% and 70% to achieve reproducible test results. Since the loading capacity of the PVB foil which strongly influences the remaining residual strength of the laminated safety glass is temperatureand humidity-dependent [17], the centre-punch procedure is performed right after removing the safety glass panes from the climate chamber. The drop test has to be performed afterwards to avoid a change of the PVB foil's material properties and a divergence in the experimental results.…”

Steigerung der Resttragfähigkeit von Verbundsicherheitsglas mittels Bewehrung in der Zwischenschicht

“…Dieser Zustand wurde schon umfassend in zahlreichen Forschungsarbeiten untersucht und wird in dieser Arbeit nur der Vollständigkeit halber kurz erläutert. Im Einzelnen wird auf [7], [10], [11], [17], [37], [62], [59], [60], [76] …”

Evaluate equivalent-sectional shear modulus for laminated glass beams using in torsion tests and photogrammetry method

“…The assessment of the structural response of laminated glass is complicated by the fact that the polymer behaviour is viscoelastic and temperature dependent [12]. In the design practice, the quasi-elastic approximation [13] is usually adopted.…”