Numerical modelling of the creep behaviour of GFRP sandwich panels using the Carrera Unified Formulation and Composite Creep Modelling

Sandwich panels often need to be designed to sustain significant permanent loads, raising the need to accurately account for long-term creep deformation. However, the accurate prediction of creep in sandwich panels is not trivial, particularly owing to their composite multi-layered nature, the multitude of possible face and core material combinations, and the possible existence of through-thickness shear reinforcement (ribs/webs). This paper presents numerical investigations on the creep behaviour of composite sandwich panels produced by vacuum infusion with glass-fibre reinforced polymer (GFRP) faces and ribs, and polyurethane (PUR) and polyethylene terephthalate (PET) foam cores. Carrera Unified Formulation (CUF) is implemented, for the first time using 1D elements with an equivalent single layer (ESL) methodology, to model the creep response of simple and ribbed panels by adopting a Composite Creep Modelling (CCM) approach. Previous experimental results from creep tests carried out on such sandwich panels and their constituent materials are used to obtain time-dependent constitutive relations for the materials in various layers and validate the numerical results. Additionally, results from analytical beam models using Timoshenko beam theory (TBT) with multi-layered sections are used to further validate the numerical outputs obtained with CUF. The developed numerical models were able to predict the experimental creep behaviour of the full-scale sandwich panels with reasonable accuracy. Differences observed between the CUF and TBT models mainly stem from the inherent approximations concerning the shear correction factors used with TBT, which contrast with the solutions provided by CUF, where such factors do not need to be considered when higher degrees of approximation are used. (C) 2017 Elsevier Ltd. All rights reserved.