Design and characterization of an isotropic reconstituted wood for energy absorbers

Wood has been used for years in the making of containers for transport of nuclear materials because of the good compromise offered by wood between resistance to impact and fire resistance. However wood is an anisotropic material especially when compressive strength is considered, parallel or perpendicular to the grain. The arrangement of wood inside the containers has to take into account different types of impact, especially oblique ones for which the choice of the orientation of wood elements is very difficult; for cylindrical containers with plane covers, corner zones are weak because the out of axis mechanical performances of wood is not good enough to insure a good behaviour during strong oblique shocks. In our Laboratory of Wood Rheology we decided, in co-operation with CEA/CESTA, to design an isotropic wood based material to be especially used in the corner zones of containers; on the other hand such an isotropic material is represented by very simpler constitute laws for computer modelling of crash-tests. This material was named IWOC for Isotropic Wood Composite. IWOC was studied, in connection with its elaboration process, for quasi-static simple or multiaxial compression in the elastic-plastic domain, even with high compression ratios, then for dynamic compression tests with impact speed up to 10 ms-1, with a falling mass system. These tests show that IWOC has good properties for energy absorption, especially when it is confined by metallic or fiber casings; its static or dynamic performances are not scattered at all; its sensitivity to deformation rate, in the range which was analyzed, can be correlated to the sensitivity of the different elements of this wooden composite material. (authors)