Characterization of laminated safety glass interlayers – Thermorheology, Crystallinity and Viscoelasticity

Laminated safety glass enables the safe construction of transparent structures. The mechanical behaviour depends on the polymeric interlayer both in the intact and in the post fracture state. In the present work, the mechanical behaviour of ethylene vinyl acetate-based (EVA) and ionoplastic interlayers is investigated for the intact laminated safety glass condition. The mechanical behaviour of the interlayer in the fractured laminated safety glass is carried out on polyvinyl butyral-based (PVB) interlayers. The interlayer creates a shear coupling between the glass plies in intact laminated safety glass, which varies, among other things, on the temperature- and load duration-dependent shear modulus of the interlayer and is considered by means of Prony series and time-temperature-superposition principles. Since Prony series and time-temperature shifts have so far predominantly been determined for PVB interlayers, the structure of EVA and ionoplastic interlayers is investigated in more detail in this work. Using X-Ray Diffraction, Differential Scanning Calorimetry and Dynamic-Mechanical-Thermal-Analysis, a semicrystalline structure is detected and characterized for different temperature rates and physical ages. The displacement factors required for mastercurve generation are divided into a purely temperature-dependent and a purely crystallinity-dependent part, so that the material behaviour can be predicted for any temperature and crystallinity combination. In the fractured state, large deformations occur in the interlayer, so that the loading level is also taken into account in the mechanical characterization of the interlayer. First, the temperature and frequency (time) dependent linearity limits of two different PVB interlayers are determined in Dynamic-Mechanical-Thermal-Analyses. The nonlinear viscoelastic material behaviour is investigated with tensile relaxation tests at different temperatures and strain levels. If the initial degree of nonlinearity, the linear viscoelastic material behaviour and the linearity limit function are known, it can be predicted after which time period the linear viscoelastic material behaviour is reached again. In addition, the Schapery model is investigated to represent the nonlinear viscoelastic material behaviour. This model combines the linear viscoelastic Prony series with several strain-dependent nonlinearity factors, which are determined by shifting the test data horizontally and vertically