Wood, a very previous raw material, has particular structural characteristics derive from its biological nature.
Bending of wood, unlike other materials, for example metals, is often an unknown factor due to the non homogenous distribution of the fibres along the section.

In semi-finished products which undergo bending two types of forces are present:

• tensile stress in the convex peripheral zone;
• compression in the internal concave zone of the arc.

If subjected to overstrain, wood breaks, beginning with the surface layers on the external part of the bending arc.
Remaining in the field of elastic deformation, bending under normal temperatures returns to its primary state on termination of strain. To make a deformation permanent it is necessary to increase the "plasticity" of the wood, that is its capacity to assume a certain shape.

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