A new approach to formulate the general strength theories for anisotropic discontinuous materials. Part A: The experimental base for a new approach to formulate the general strength theories for anisotropic materials on the basis of wood

Experimental investigation carried out on wood indicates different overlapped failure mechanisms for compression and tension in the principal orthotropy plane. Different failure mechanisms result in different descriptions for compression and tensile failure stress. The consequence of these two different descriptions is the first order discontinuity (discontinuity of derivative) of failure hypersurface for normal stresses equal to zero. This discontinuity made it impossible to use failure stresses as components of the stress tensor in the whole of six-dimensional hyperspace and its sections of failure stresses in principal and structural system axes. Experimental investigation and observation of the damaged structure of wood lead to a conclusion that tensorial relationships are not satisfied in the macroscale of wood. Therefore, a new theoretical approach to describe the anisotropic materials with complicated structure on the basis of experimental data and observations of the damage processes of wood structure is proposed.