Multi-scale foam : 3D structure/compressive behaviour relationship of agglomerated cork

Abstract

This study focuses on the microstructural aspects of a cork-based by-product known as agglomerated cork and its influence on the compressive mechanical behaviour. The material consists in granulates of a natural polymeric foam - cork - mixed together with a small quantity of a bio-sourced resin.Optical and scanning electron microscopy (SEM) are first used to investigate on the bead geometry and placement and interfaces arrangement. Then X-ray computed tomography allows to study the spatial arrangement of agglomerated cork microstructure and hence to complete and confirm 2D observations. 2D and 3D observations show a transverse anisotropic material which is confirmed by the mechanical tests. SEM pictures demonstrate an intricate and heterogeneous material. Microtomography confirms the presence of macroporosities between cork granulates having a mean volume around 0.1 mm3. Cork cell specific geometry is also confirmed. The volume of those cells lies around 10−5 mm3. Finally quasi-static compression tests are run to establish a link between microstructure and mechanical behaviour thanks to digital image correlation (DIC). Cork agglomerate demonstrates strong strain localisation at its surface caused by its multi-scale structure.