Abstract
The demand for bio-sourced materials is currently increasing. Cork material because of its unique properties (fire resistant, energy absorbing, …) is then an excellent candidate for a large set of applications. In order to widen its possible uses, cork agglomerates with reinforcements at a 0.48 density were studied to compare their mechanical performances with classical cork agglomerates. This paper investigates the effect of these foreign reinforcements on the properties of agglomerated cork under a compressive loading. The material behavior has been determined as a function of the average strain rate and the direction of solicitation. The microstructure was first observed through optical and scanning electronic microscopy, spotting charges between each cork bead. The characterisation of cork at different strain rates was then carried out. An electromechanical testing machine was used to apply an uniaxial compression at quasi-static strain rates. Reinforced agglomerated cork was found to be anisotropic and strain-rate dependant. Its micro-structure reveals at complex composite material influencing strongly mechanical properties. Both Young's modulus and absorbed energy density at 0.6 strain increase with the cross-head speed displacement. From 12.7 MPa and 0.77 J.mm-3 when compressed at 0.05 mm·min-1 to 19.9 MPa and 1.44 J·mm-3 at 500mm·min-1 in the Off-plane direction.
Highlights
Cork is a natural material coming from the bark of the oak tree Quercus Suberus L. growing in sub-desertic areas
Its most popular application - stoppers for glass bottles - was perfected in the 18th century in a Benedictine Abbey at Hautvillers, France [3]
As cork is a cellular material, its absorbing properties for dynamic loadings are being considered for impact-absorbing applications as core material in sandwich structures [5]
Summary
Cork is a natural material coming from the bark of the oak tree Quercus Suberus L. growing in sub-desertic areas. Europe produces 80 % of the world’s cork and almost three quarter of them come from Portugal [1]. It is formed by prismatic cells disposed in successive layers (Fig. 1) exhibiting a relatively homogeneous honeycomb structure. The others are lignin, cellulose and hemicelluloses [2] It is a very unique material due to its low density - around 0.17 -, great elasticity, chemical stability, its no permeability to liquid and gases and its resistance to fire [3]. As cork is a cellular material, its absorbing properties for dynamic loadings are being considered for impact-absorbing applications as core material in sandwich structures [5]. Ranging from the container for the transport of sensible pieces to sports items and including lightweight aeronautic components, a wide range of applications is foreseen [1, 6]
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