Environmental Engineering Reference
In-Depth Information
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Figure 6.5
Projection of a wood cell, showing its different layers.
Axial
Tangential
Radial
Ray
«Sponge»behaviour
Figure 6.6
Representation of the three different compression solicitations in wood, according
to the position of the cells and the ray.
At a mesoscopic level, the hollow cylindrical-shaped cells are orientated in the
same direction of the trunk. Radial sheets of horizontal cells rich in lignin run
from the centre of the trunk to the bark. They can be easily observed in a transver-
sal cut of the trunk because of their darker colour. The orientation of both the cells
and the rays causes anisotropy in wood. The mechanical properties of wood
depend on the direction of the mechanical solicitation (Figure 6.6).
Let us consider a wooden pencil: it is quite easy to crush it with our teeth in a
horizontal position, whereas it is very difficult to do the same if we place the
