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The characterisation of the mechanical behaviour of folded core structures for advanced sandwich composites under flatwise compression load using a virtual testing approach is presented. In this context dynamic compression test simulations with the explicit solvers PAM-CRASH and LS-DYNA are compared to experimental data of two different folded core structures made of aramid paper and carbon fibre-reinforced plastic (CFRP). The focus of the investigations is the constitutive modelling of the cell wall material, the consideration of imperfections and the representation of cell wall buckling, folding or crushing phenomena. The consistency of the numerical results shows that this can be a promising and efficient approach for the determination of the effective mechanical properties and a cell geometry optimisation of folded core structures.

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A low-velocity impact characterisation of a sustainable sandwich panel based on upcycled bottle caps as circular honeycomb is conducted. The recycled core aims to develop an alternative route of reusing waste bottle caps disposed in landfills. Ecological alternatives to skin (recycled PET foil) and adhesive (bio-polyurethane) are also compared with classic components (aluminium skin and epoxy polymer). A low-cost reinforcement (cement particles) is also proposed to enhance the mechanical strength of the panel. The samples are tested at several levels of impact energy, according to the type of skin, to observe their effect on mechanical behaviour. Metal skins achieve higher impact loads and energy absorption compared to PET foil. The bio-adhesive leads to a similar or enhanced maximum impact load and energy absorption compared to the epoxy adhesive. Specific properties highlight the promising performance of the bio-based adhesive with aluminium skins, reaching increments of up to 378%. The cement increases the maximum load and reduces the duration of the impact event, leading to lower energy absorption. The unreinforced epoxy polymer shows a visible adhesive peeling off from aluminium skin, while particle inclusions lead to reduced overall delamination. Biopolymer exhibits marginal adhesive debonding and stable deformation, revealing a progressive failure. In general, PET samples show core shear failure due to rupture of the skin. Crack propagation in PET samples made with biopolymer adhesive is reduced at lower energy levels. The results evidence the promising application of bottle caps in a more sustainable honeycomb core to build eco-friendly structures.