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DOI 10.1007/s00107-008-0248-2
DOI 10.1007/s00107-010-0516-9
The behaviour of cork under tensile stress in the tangential direction was evaluated in relation
with its structural characteristics
Cork is known as the material used for the production of wine stoppers. The specific properties of
cork, e.g. low density, very low permeability to water, elastic properties and inertness have made it the
best sealant for quality wine. Here we studied the relation between compression, tensile and bending
stress in cork and the influence of structural characteristics of cork on its mechanical behaviour. The
material was sampled from raw cork planks of good quality (class 1) and poor quality (class 4) collected at
one industrial mill after post-harvest six-month air stabilization, water boiling and air drying as usually
applied in cork industrial processing. The samples had densities ranging 0.123 - 0.203 g.cm-3 and
porosities between 0.5 and 22.0%.
There are differences between the type of stress and the corresponding direction of stress. For
the same direction of stress, the Young modulus in tension is higher then in bending and it is lowest in
compression. The bending Young modulii were well correlated with the tensile Young modulii, because
while in bending the sample is submitted to both tensile and compression stresses, the fracture occurs in
the tensile zone. There were no significant differences in the mechanical properties of cork samples
obtained from cork planks of different quality classes but the density is an important factor and samples
with higher density showed overall larger resistance. Mechanical properties were influenced by the
structural features related to the lenticular channels, namely the presence of thick walled and lignified cells
that may border the lenticular channels.
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