Ultimate limit state analysis of FRP composite sandwich plates – development of a semi-analytical method

Paper in proceeding, 2016

The development of Sandwich PULS, a semi-analytical calculation tool for predicting the ultimate limit state (ULS) of FRP composite sandwich plates is presented. This was done by extending DNV GL’s semi-analytical calculation tool Composite PULS, which is used for quick estimation of the ULS for unstiffened composite plates. ULS was evaluated in terms of the first buckling load and the first ply failure (FPF). The Sandwich PULS code was developed by implementing formulations for sandwich plate theory. First-order shear deformation theory (FSDT) was implemented to include the transverse shear deformations that are highly important for sandwich plates with poor shear stiffness of the core. The Sandwich PULS code was evaluated against nonlinear finite element analyses (FEA). It was concluded that Sandwich PULS shows good agreement with FEA-predicted critical buckling loads. For all inspected plates, Sandwich PULS shows improved results compared to Composite PULS. Differences between Sandwich PULS and FEA are caused by the difference in evaluating shear stiffness. It has been shown that neglecting shear stiffness of faces results in good agreement between Sandwich PULS and FEA, while use of conventional shear correction factors proved to be unfavourable for sandwich plates. It was found that Sandwich PULS is limited in terms of slenderness. Sandwich plates with soft core should not have slenderness below 20 to assure an accurate solution.