Abstract

Composite sandwich structures with core cellular materials are widely used in diverse industries such as the aerospace, marine, car, and wind industries due to their good mechanical properties on bending. The growing environmental awareness has increased the interest in the use of materials from biodegradable and renewable sources. During recent years, there has been an increasingly growing interest in the use of agglomerated cork as a core material in sandwich structures, replacing synthetic polymeric foams in specific applications.

Among its remarkable combination of properties, we can find a hyperelastic behaviour, low thermal conductivity, low permeability, and good energy absorption and vibration damping properties. Additionally agglomerated cork is produced from the waste of the cork industry, being a renewable and biodegradable material that is environmentally sustainable.

The aim of this work is to address the quasi-static and dynamic compression testing of two types of agglomerated cork of different densities, using a servo-hydraulic testing machine and drop weight tower. The mechanical behaviour and energy absorption properties at different strain rates are evaluated from the contact force measurements and estimations of impact kinetic energy. Additionally, Digital Image Correlation (DIC) is used to estimate the variability in the local strain through the test specimen.

Abstract

E-glass/vinylester composite crash structures manufactured by ultraviolet (UV) pultrusion process have shown high values of especific energy absorption (SEA). However, comparing the radial compression behaviour of the tubular structures with the axial crushing behaviour, it has been noticed that the stiffness and the strength of the structures to radial compression is too low. In order to improve the radial compression behaviour of the structures manufactured by UV pultrusion, different cores have been designed and manufactured by 3D printing using FDM (Fused Deposition Modeling) technology. On the one hand, an hexagonal core consit on a thin external skin made with ABS and filled with 3D printing support material has been analyzed. Otherwise, an hexagonal core designed following the honeycomb concept has been printed and tested. The composite structures with the cores have been tested in radial compression in quasi-static conditions and they have shown higher stiffness and strengh due to the 3D printed internal cores. The composite structure with the hexagonal ABS skin core and support material has improved the stiffness of the composite tubular structure 9 times while the strength has increased 5 times. In the case of the honecomb ABS core, the stiffness of the structure has increased from 1.15 kN/mm to 22 kN/mm (19 times more). Meanwhile, the strenght values using the ABS honeycomb core has been 17 times higher than the empty composite structure.