Mechanical Properties of Interlayers in Laminated Glass - Experimental and Numerical Evaluation
Abstract: The architectural and engineering trend leads towards greater use of glass in buildings. Growing safety awareness often requires laminated glass. Laminated glass is formed as a sandwich of two or more sheets of glass and a plastic interlayer. Laminated glass can for example be used in stairs, floors, roofs, facades and balcony railings. This thesis deals with the most common interlayer polyvinyl butyral (PVB). There are many varieties of PVB and this thesis investigates the mechanical properties of a variety of PVB. Experimental tensile tests have been conducted on six PVB with various properties. The tests have been conducted with different loading rates to take the time dependency into account. PVB shows time and temperature dependency and in numerical simulations it is often simplified as a linear elastic material. By using the generalized Maxwell model, which is a mechanical model that describes a linear viscoelastic material behaviour, a Prony series have been determined from the experimental tests. A tensile test has been modelled in the commercial finite element software Abaqus. The Prony series have been implemented in the Abaqus-model to create a viscoelastic material model. The model has been created for of one of the experimentally tested interlayers, a standard PVB with a thickness of 0.76 mm. Thereafter the viscoelastic model has been used in a laminated glass model to show how the time of loading affects the structural behaviour. The results from the experimental tests show that there are differences in all the tested PVB. Some are stiffer, and some are softer. The numerical tensile test model was in good agreement with the laboratory results for standard PVB 0.76 mm. The numerical application where a laminated glass unit was subjected to long-term and short-term loads showed a loss in structural resistance due to the time dependent behaviour. One could see that with longer loading time, an increase in the stresses occur and the plate behaves more like a layered unit than a monolithic plate. This leads to the conclusion that it is important to take into account the time dependent behaviour when using laminated glass as a structural element.
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