The tribal structure

A coniferous tree trunk consists of cross section of marrow, heartwood, sapwood and bark. In some tree species has a darker tint than the heartwood splints, such as larch and oak. Of other tree species do not differ from splint and core wood shade, such as fir and silver fir. But despite that, there is the heartwood of most tree species. Heartwood of tree species with dark core usually has better resistance to microbial degradation than heartwood of tree species with bright core.

In addition, the heartwood is always more durable than sapwood. In ground contact, the difference is marginal, but above ground is in most cases considerable. In the heartwood moisture content is between 30% and 50%. In sapwood moisture content increases from about 50% in nuclear brink of 160% out of the bark.

At the micro level have a wooden structure similar to small layers bonded tubes (cells). Pipes diameter and wall thickness can vary, but the wall material characteristics are similar in most types of wood. This concerns in particular the density, which is approximately 1 500 kg/m³, which means that timber properties such as elastic modulus, tensile strength and density are strongly linked to pipes wall thickness.

Symmetrical structure

The structure means that the tree trunk is (almost) cylindrically symmetric with respect to an axis along the stem by the bone. If you cut a small wooden cube from the marrow, there are three planes discerned, which are perpendicular to one another. Wood is often regarded as an orthogonal anisotropic material. The various symmetry planes are often designated with L (= along the grain), R (= radially to the growth rings) and T (= tangentially to the growth rings).

Nutrient transport

The sapwood is the transport of water and dissolved nutrients up to the tree's needles and leaves, where photosynthesis takes place. In Photosynthesis converts nutrients, carbon dioxide and solar energy into nutrients that are transported to the tree all living cells. The transport takes place in the inner bark, outside of the sapwood and the growth layer, right down to the tree's finest roots. Most of the tribe's cross-section is the bark, which protects the trunk from infection and dehydration.

Strength

Strength varies due to anisotropy.The following approximate values have been measured for flawless spruce and pine wood with a density of around 420 kg/m³ and with a moisture content of around 12%:

In the fiber direction
(MPa)

Across fiber direction
(MPa)
Tensile Strength
100
3
Compressive Strength
50
7
Shear Strength
10
5

Hardness

The hardness of wood is an important trait in some contexts, such as in the floor. The hardness is also linked to the density and the higher the density, the greater hardness. Hardness is usually measured by a small steel ball pressed into the wood surface with a certain force, which is called Brinell hardness test.

Types Of Wood Hardness (Brinelltal)
End
Main surface
Alder
3.7
1.4
Elm
6.4
2.1-3.8
Ash
6.5
3.0-4.1
Balsa
0.7
0.2-0.3
Birch
-
2.2-2.7
Red beech
7.2
2.7-4.0
Oak (European)
6.4-6.6
3.4-4.1
Pine
4
1.9
Spruce
3.2
1.2
Larch (European)
5.2
1.9-2.5
Basic structure of tree trunk
Basic structure of tree trunk
Comparison of wood grain
Comparison of wood grain
Transport of water and nutrients in a tree trunk
Transport of water and nutrients in a tree trunk

 
European Wood (in China)
C412, Beijing Lufthansa Center
50 Liangmaqiao Road, Chaoyang District
Beijing, P.R. China 100125
T +86 10 6462 2066, F +86 10 6462 2067
info@europeanwood.org.cn
Sino-European Wood Center
Room 202, Engineering Department,
Taoliyuan Hou, Xuhui Campus of Jiaotong University,
No.655 Panyu Road, Xu Hui District, Shanghai
Tel/Fax:021-53098550
info@europeanwood.org.cn