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Functionally graded cellular materials, which combine cellular materials with a gradient of properties, have been recently investigated as cores of sandwich panels. The present work aims to evaluate the flexural properties of functionally graded cellular structures with a gradient of cell thickness on configurations recently proposed. The structures hexagonal honeycomb (Hr), lotus (Lt), and hexagonal honeycomb with Plateau borders (Pt) were designed with three different gradients of cell thickness. The parts were manufactured by material extrusion using FFF (Fused Filament Fabrication). To evaluate the mechanical properties, three-point bending tests were conducted, both experimentally and by numerical modelling, by means of the finite element method. The materials used were polylactic acid (PLA) and aluminum. Although experimental and numerical results exhibited some deviations, they revealed the same trends. The results showed that the stiffness and the absorbed energy of the graded Hr, Lt and Pt structures, made of PLA, are higher than such values for the regular hexagonal honeycombs. For the same gradient of cell thickness, the lotus structure tends to exhibit the highest stiffness and absorbed energy, while the hexagonal honeycomb arrangement achieves the largest value of strength. Graded aluminum specimens also attain higher values of stiffness, strength and absorbed energy in comparison with non-graded hexagonal honeycomb configurations. Thus, the use of gradients of cell thickness can promote structures with higher stiffness and absorbed energy, which may compete with the conventional structures of sandwich panel cores. [ABSTRACT FROM AUTHOR]

Sandwich structures are frequently used in automotive, aerospace and marine industries, as they provide adequate functional properties. The two-dimensional regular hexagonal cell shape, i.e. honeycomb is the most used core structure in sandwich panels. Recently, a new type of cellular structures composed of lattice struts has been proposed, as they combine high stiffness, strength and energy absorption with low weight. The main purpose of this research is to investigate the effect of the lattice topology on the flexural behaviour of sandwich panels. Five lattice geometries inspired in crystalline structures were designed, namely, body-centred parallelepiped, body-centred parallelepiped with struts in z -axis, body- and face-centred parallelepiped with struts in z -axis, face-centred parallelepiped with struts in z -axis and parallelepiped simple. The relative density of all the lattices was kept constant as 0.3. Both numerical and experimental approaches were used to evaluate the flexural properties and failure behaviour of the sandwich structures under three-point bending tests. The numerical analysis was undertaken with the finite element software NX Nastran. Taking advantage of additive manufacturing technologies, material extrusion was used to produce polylactic acid samples with the configurations aforementioned. The sandwich panels are composed by a single layer formed by the lattice core and two thin plates, at the bottom and top. The three parts of the panel were manufactured all together. The simulation results indicate that, among the lattices studied, topologies body-centred parallelepiped with struts in z -axis and body- and face-centred parallelepiped with struts in z -axis exhibit higher strength, while body- and face-centred parallelepiped with struts in z -axis shows higher stiffness and higher energy absorption, attaining values that do not differ much from the ones obtained with a two-dimensional hexagonal cellular structure, with the same relative density. As a consequence, some of the geometries studied may have the potential to be considered as alternatives to conventional structures in the design of sandwich structures. [ABSTRACT FROM AUTHOR]