Wedge-shaped folded sandwich cores for aircraft applications: from design and manufacturing process to experimental structure validation

Abstract

The problem of honeycomb sandwich structures with moisture ingression can be avoided by replacing the honeycombs through chevron-folded cores. The application to real aircraft components often requires wedgeshaped sandwich. With folded cores, this kind of geometric shape can be obtained only by special folding schemes which have a significant influence on the mechanical performance. A comprehensive experimental investigation of the relation between folding geometry and structural properties of wedge-shaped folded cores (WSFC) is very time consuming and expensive. Therefore, a procedure based on numerical methods has been developed to predict the structural response of this kind of cores under compressive and shear loading. The approach is based on a numerical tool that provides finite element models of arbitrary WSFC as well as the explicit finite element solver LS-DYNA for simulation. These tools were applied to investigate the influence of the inner core geometry and different materials on the mechanical properties of WSFC structures. To verify these results, a test programme was conducted. Test samples were manufactured using a newly developed folding process. Also special test devices to determine the compression and shear properties of the WSFC specimens were developed. The achieved test results show a good agreement with the behaviour predicted by simulation.

Transverse stiffness and strength of Kirigami zero-ν PEEK honeycombs

“…Material property values used in the normalisation, and the sources thereof, are shown in [37] show that resin content qualitatively affects the behaviour of Nomex paper; dry paper behaves in a ductile manner, and each subsequent resin impregnation increases its stiffness and makes it behave in a more brittle manner. Hähnel et al [38] provide also comprehensive mechanical properties for resin-impregnated Nomex paper, and the values from the latter paper have been used in this work's normalisation. Figure 11 to Figure 16 show the flatwise compression and shear properties of SILICOMB obtained in this work, compared to commercially available cores.…”

Engineering Origami: A Comprehensive Review of Recent Applications, Design Methods, and Tools

“…Fold-core structures have been extensively implemented in the design of sandwich panels. Mainly applied in aeronautic and aircraft engineering, [119][120][121][122] their potential applications range from civil [123] (Figure 12a) to space structures. [124] Although desirable structural properties can be already achieved by means of honeycomb cores, [125] origami-based designs promise to reach optimized performance [126] and tackle current limitations as gas and fluid flow within fold-core systems.…”

From Folds to Structures, a Review

“…Whereas folded cores are known since several decades, there was a recent regain of interest thanks to improved fabrication process and the possibility to ventilate the core 3 . A large amount of experimental work was done in order to investigate the mechanical behavior of these cores [122,123,124,125,126,127,128,129,130,131,132,133], as well as simulations [125,134,74,75,135,136,137,138]. The key issue remains the strength capacity of these cores.…”