Siebe Spronk

Experimental Characterization and Finite Element Modelling of Strain-rate Dependent Hyperelastic Properties of PVB Interlayers

Laminated glass provides safety in an impact or explosion event by way of a polymer interlayer to which glass fragments adhere upon fracture. The mechanical deformation of the interlayer defines how the impact energy can be absorbed to prevent calamities by flying glass debris, penetration of a blast wave, lacerations, etc. The PVB interlayer used in safety glass shows highly nonlinear viscoelastic material behaviour, with a great sensitivity to temperature and deformation rate. Although various material models for PVB can be found in literature, few publications discuss the full range of its mechanical behaviour and none are found to describe a material model that is valid in a wide range of deformation rates and up to high elongations. Such material model is necessary for the numerical study of the post-fracture response in a dynamic event. The article describes the mechanical behaviour of PVB interlayer and the constitutive models by which the polymer can be represented under different load cases. Tensile experiments of Saflex® PVB are presented for a wide range of deformation rates and up to tearing of the specimens. Subsequently, a method to calibrate a hyper-viscoelastic material model for the interlayer by numerically simulating the tensile tests is developed. The resulting material models are valid up to the tearing strain of the interlayer and are accurate within a specified range of deformation rates and temperatures.