Virtual testing of sandwich core structures using dynamic finite element simulations

Virtual testing using dynamic finite element simulations is an efficient way to investigate the mechanical behaviour of small- and large-scale structures reducing time- and cost-expensive prototype tests. Furthermore, numerical models allow for efficient parameter studies or optimisations. One example, which is the focus of this paper, is the configurational design of cellular sandwich core structures. From classical honeycomb cores to innovative folded core structures, a relatively large design space is provided allowing for tailoring of the cellular core geometry with respect to the desired properties. The method of determining the effective mechanical properties of such cellular sandwich core structures of different geometries using dynamic compression, tensile and shear test simulations is discussed covering a number of important modelling aspects: the cell wall material modelling, the influence of mesh size and number of unit cells, the inclusion of imperfections, etc. A comparison of numerical and experimental results is given for Nomex® honeycomb cores and Kevlar® or carbon fibre-reinforced plastic (CFRP) foldcore structures. A good correlation with respect to cell wall deformation mechanisms and stress–strain data was obtained. Therefore, these models not only allow for a complete mechanical characterisation of cellular core structures but also for a detailed investigation of cell wall deformation patterns and failure modes to get a better understanding of the structural behaviour, which can be difficult using solely experimental observations. To show that this efficient virtual testing method is suitable for the development of cellular core geometries for specific requirements, an optimisation study of a CFRP foldcore geometry with respect to its compressive behaviour was performed.