Investigations on the thermorheologically complex material behaviour of the laminated safety glass interlayer ethylene-vinyl-acetate

Abstract

Laminated safety glass has become an indispensable component in building construction, automotive and solar industry. It consists of at least two glass panes, that are laminated together with a polymeric interlayer. Mechanically speaking, the polymeric interlayer enables a shear transfer between the two glass panes. Here, the difficulty lies in the understanding of the real shear transmission. On the one hand, polymeric interlayers show a time dependent material behaviour, which can be described with a ‘Prony-series’ in the linear viscoelastic area. On the other hand, polymeric interlayers show a temperature dependent material behaviour. Hence, a Prony-series is only valid for one specific temperature. However, since relaxation is based on molecular movements and rearrangement processes, which can be thermally activated, an increase in temperature leads to an acceleration of the relaxation process. The time-temperature correlation can be taken into account by means of a ‘Time-Temperature-Superposition-Principle’ (TTSP). The relaxation curve of a thermorheologically simple material shifts solely horizontal along the time axis due to temperature changes, while its shape remains constant. Mathematically, this means, that all relaxation times of the Prony-series are multiplied by the same shift factor aT. Recent research of the authors shows, that some polymeric interlayers don’t follow a simple TTSP. The experimental identification through ‘Dynamical-Mechanical-Thermal-Analysis’ as well as ‘Differential Scanning Caliometry’ and numerical incorporation of this thermorheologically complex material behaviour into state-of-the-art Finite-Element-Software will be investigated on the example of ‘Ethylene-vinyl acetate’ in the following paper.