Mechanical properties of wood
The mechanical properties of wood are its fitness
and ability to resist applied external force. By external forces are meant
any force outside of a given piece of material which tends to deform it in any manner.
There
are other properties such as orthotropic, elasticity, strength properties,
vibration properties.
Elastic properties of wood
Elastic properties relate the resistance of a
material to deformation under an applied stress to the ability of the material
to regain its original dimensions when the stress is removed Wood is not ideally
elastic in that some deformation from loading is not immediately recovered when
the load is removed; however, residual deformations are generally recoverable
over a period of time. although
technically considered a viscoelastic material, wood is usually assumed to
behave as an elastic material for most engineering applications.
Compression
When a
compression loads are applied parallel to grain of it, it produces stress that deforms
(shortens) wood cells along their longitudinal axis. When wood is stressed in
compression parallel to grain, failure initially begins as the microfibrils
begin to fold within the cell wall, thereby creating planes of weakness or instability
within the wall of cell. As stress in compression parallel to grain continues to
increase, the wood-cells themselves fold into shape of S. forming visible wrinkles
on the surface. Large deformations occur from the internal crushing of the
complex cellular structure.
Service deficiencies of wood
There are some service deficiencies of wood. Wood is
not better water resistance material.it is decayed.
Substitutes for wood
Nowadays wood is very expensive material.so people
going to substitute other cheap materials for wood. plastic, aluminum ,cheep
board are some of that.
Wood Preservation
Wood products can be protected from the attack of
decay fungi, harmful insects by applying chemical preservatives.The degree of
protection achieved depends on the preservative used and the proper penetration
of the chemicals.
Preservative treatments greatly increase the life of wood structures, so it is reducing replacement costs and allowing more efficient use of forest resources.
Methods of Wood
Preservation
·
chemical Wood
Preservation
Chromated
copper arsenate (CCA), Alkaline copper
quaternary, Copper azole ,.etc.
·
natural Wood
Preservation
tun oil,heat
treatments,mud treatments
The methods of applying preservatives
(a)
brushing and spreading
(b)
spraying, deluging and fogging
(c)
immersion
(d) hot
and cold steeping in open tanks http://www.applog.com/preservation/
(e) diffusion
(f)
pressure impregnation
(g) double
vacuum
