Mechanical properties and spatial fiber angle in veneers and plywood materials

It is well known that wood has, compared with other materials, a very good density : strength ratio (specific strength). This property is given by the specific wood structure and the strength of the individual components, primarily by the strength of the individual fibers. For all fiberreinforced composite materials the strength of the interphase and the fiber orientation is important for the mechanical properties. The fiber orientation can be influenced only insofar as the interphase adhesion between the fibers and the binder substance, which is formed in wood by the lignin, enable this. Finally the fiber orientation is a not or only very limited modifiable structure property. If there are no specific growth characteristics, the fibers are unidirectional oriented in growth direction (longitudinal). However, almost all trees or stems have specific growing characteristics as reaction wood, spiral grain and intergrown knots. This has, additional to the directional dependency of properties (tangential, radial), effects on the mechanical properties. The strong dependency of the direction of the mechanical properties is one of the decisive reasons for the development of different wood-based materials or composites.