Elastic and viscoelastic behaviour of sandwich panels with glass-fibre reinforced polymer faces and polyethylene terephthalate foam core

This paper presents experimental and analytical investigations about the elastic and viscoelastic (creep) behaviour of sandwich panels made of glass-fibre reinforced polymer faces and a polyethylene terephthalate foam core, produced by vacuum infusion for civil engineering structural applications. First, the elastic response of the panels' constituent materials (glass-fibre reinforced polymer and polyethylene terephthalate) in tension, compression and shear was experimentally assessed; shear tests on the foam were carried out using a novel test method, the diagonal tension shear test. The creep behaviour in shear of the polyethylene terephthalate foam was evaluated for different load levels. The effective flexural properties of the full-scale sandwich panels as well as their flexural behaviour up to failure were experimentally assessed. Flexural creep and subsequent recovery experiments were also conducted for different load levels, to characterise the viscoelastic behaviour of the full-scale sandwich panels. Creep deformations of the polyethylene terephthalate foam and of the sandwich panels were found to be significantly lower than those corresponding to polyurethane foam and balsa wood reported in the literature; unrecoverable viscoelastic deformations were observed in the full-scale panels. In the analytical study, the creep response of the panels was modelled using Findley's power law and the composite creep modelling approach. The composite creep modelling predictions were reasonably accurate and allowed assessing the relative contributions of bending and shear deformations to the total sandwich panel creep deflections.