International audienc

Cork is a complex natural cellular material with quite unknown or not well understood properties. It is available in the natural and in the agglomerate form and it is an ecological and very durable material. That is why it is used today as thermal and acoustic insulator, as a seal and as an energy-absorbing medium in flooring, shoes and packaging, among others. However, the application of agglomerate cork as filler inside structural thin-walled sections, in order to increase the energy absorption, has not been much explored. Dynamic experimental tests were carried out on empty and micro-agglomerate cork-filled tubes with 22 and 50 mm in internal diameter ðDÞ and length ðLÞ, respectively, and numerical simulations were performed with the finite element method software LS-DYNA TM , showing good agreement in terms of load-displacement curves and deformation patterns. Having validated the numerical model with experiments, the finite element model was used to undertake a systematic study of circular tubular structures impacted at 10 m/s. The load-deformation characteristics, energy-absorption response and collapse mode transitions of empty and cork-filled aluminium tubes with varying diameters and thicknesses (t), lengths of 25, 300 and 350 mm, but with constant slenderness ratios D=t and D=L were thus studied. Relevant comparisons were raised, showing that the slenderness ratios are very important parameters that globally govern the percentage increase in energy absorbed by tubular structures after cork-filling during an impact loading. r

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-For reasons of energy saving and pollution reduction, there is a growing interest in the development of lightweight structures manufactured with materials of natural origin and recyclable. Agglomerated cork is a mixture of natural cork and an organic binder, and can be considered an alternative to polymeric foams used in structural applications with a high capacity of energy absorption. One of these applications involves impact-absorbing elements in vehicles, which are subjected mainly to dynamic compressive loads. In this work, the dynamic crushing behaviour of agglomerated cork was experimentally studied, analysing the influence of the specimen thickness on the energy-absorption capacity, contact force, displacement, and strain. Dynamic crushing tests with specimens of four different thicknesses were performed in a drop-weight tower. An increase in the maximum contact force, displacement, and strain was observed when the impact-energy/thickness ratio increased. For each specimen thickness a linear variation of the maximum displacement and energy absorbed with the impact-energy/thickness ratio was found. It was observed that the energy absorbed by agglomerated cork did not depend on the specimen thickness, but only on the impact energy.

Samples having nominal compositions of AlSi12 and Al6082-T4 were prepared using a lost wax casting process, with nominal relative densities of 20%, 40%, and 60%, as well as arrangements of a uniform cell structure (US) or a dual-size cell (DS). For comparison, samples of aluminium foam-filled tubes having the same nominal composition were also prepared with the same technique, with nominal relative densities of 20% and similar arrangements (US and DS). Impact tests at different velocities were performed using a split Hopkinson pressure bar (SHPB). It is possible to conclude that Al6082-T4 foams have better performance, in both configurations, than the AlSi12 ones. Considering a uniform cell structure and a density of 20%, the absorbed energy by the Al6082-T4 foams was around 25% higher than the value observed for the AlSi12 ones. In terms of arrangement, the US structure presents absorbed energy around 57% lower than the DS ones, while the AlSi12 foams with a relative density of 20% were compared. Finally, the absorbed energy growths from 2.8 × 105 to 5.2 × 105 J/m3, when the density increased from 20% to 60%. However, when these foams were involved with a tube, the performances increased substantially.