Numerical modelling of sandwich panels with soft core and different rib configurations

This paper presents numerical modeling of the flexural behaviour of sandwich panels composed of [0/90] woven glass fibre reinforced polymer skins and polyurethane foam core, including various patterns of glass fibre reinforced polymer ribs, as well as cores of different densities. A robust finite element model has been developed. It accounts for material nonlinearities; most pronounced in soft cores and [0/90] glass fibre reinforced polymer ribs in shear, as well as geometric nonlinearities arising in panels without ribs, in the form of a reduction in panel thickness and excessive shear deformation. The model captures both material failures and stability failure, essentially skin wrinkling in compression. The model is successfully validated using a large experimental database and predicts well full flexural responses. It is shown that ribs allow compression skin to reach its full material strength. Panels without ribs fail by skin wrinkling under concentrated loads, while those under distributed loads fail either by excessive shear deformation or diagonal fracture of the core, depending on core density. Failure of glass fibre reinforced polymer tension skin never occurred in this study. For panels without ribs, the three-dimensional finite element model agrees closely with a simplified two-dimensional model. A parametric study addressing longitudinal rib spacing showed that flexural strength increases as rib spacing reduces, until it stabilizes at a rib spacing-to-panel thickness ratio of 2.93.