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

An extensive test program was carried out to investigate the structural behaviour of laminated safety glass with a polyvinyl butyral (PVB) interlayer. The viscoelastic nature of the polymer interlayer is influenced by many parameters such as temperature, load duration, load rate, shear angle and durability against environmental influences like ultraviolet radiation and moisture. Knowledge of the dependency of the interlayer upon these parameters is necessary if the shear bond is taken into account for structural design of laminated safety glass. To evaluate the shear modulus of the interlayer for various temperatures and load durations, four-point bending tests with variable short-term loading and constant long-term loads were performed in a temperature range from 0°C to 60°C. From the measured strain at midspan the shear modulus of laminated glass elements was determined using a linear analytical solution for a composite beam with elastic bond. The results of the experiments have shown that the shear-modulus decreases with increasing temperature and load duration, displaying linear viscoelastic behaviour, independent of load rate and shear angle. From small-scale shear tests it was evident that ultraviolet radiation and moisture diminish the shear modulus of the PVB interlayer. Laminated glass elements subjected to dynamic long-term loading showed no decrease in the shear stiffness of the interlayer.