Novel experimental approach for longitudinal-radial stiffness characterisation of clear wood by a single test

Abstract : Experimental results obtained from maritime pine (Pinus pinaster Ait.) wood are presented for the characterisation of all LR=(1,2) orthotropic stiffness parameters of clear wood specimens by a single test. The approach relies on application of the virtual field method (VFM) to a rectangular specimen loaded in the Iosipescu fixture. The displacement field over the gauge surface of the specimen is measured by the grid method. Two configurations are investigated: (1) with grain aligned along the specimen length (0° configuration) and (2) with grain at 45°. For the 0° configuration, only the parameters Q11 and Q66 are correctly identified, with coefficients of variation of the same order of magnitude as those obtained from reference tensile and shear tests. Better identification is obtained for the 45° configuration, for which only the parameter Q12 exhibits large scatter. This improvement results from a more balanced influence of all stiffness parameters on the response of the 45° specimen. However, all stiffness parameters identified were systematically underestimated by approximately 30% in comparison to reference values. This deviation is due to the vertical spatial variation of the mechanical properties of wood within the stem. Literature data confirm this interpretation.