Compressive behaviour of softwood under uniaxial loading at different orientations to the grain

The compressive behaviour of spruce wood under uniaxial loading is studied at different orientations with regard to the longitudinal and radial direction. The dependence of the Young modulus, Poisson ratio and crushing strength on the loading angle with respect to the longitudinal direction is shown and described by a simple theory of orthotropic elasticity and a Tsai–Hill like strength criterion. The deformation and failure behaviour was also strongly influenced by the loading orientation. The different deformation and failure mechanisms found ranged from buckling of the elongated cells at loading in the longitudinal direction followed by final failure due to longitudinal cracks to shear deformation and failure at annual ring borders at loading angles of 20° and 45° due to the abrupt density change at the ring border and to the plastic yielding and collapsing followed by densification for loading in the radial direction.