Wood

Wood - a naturally occuring fiber-reinforced composite material

Wood is an example of a naturally occurring fiber-reinforced composite material.
Is an important structural material (used for houses, buildings, bridges, etc.) that, by tonnage, is used more than steel or concrete in the U.S.  It is also used to make composite materials such as plywood, particleboard, and paper.
                                     
There are hardwoods such as maple and oak and softwoods such as cedar and pine. Both types consist mainly of a complex array of cellulose cells reinforced by a polymeric substance called lignin and other organic compounds.
                                   
Structure of Wood
Here is a schematic of the microstructure of a soft wood.

Schematic of the microstructure of a soft wood.the directions of wood identified: tangential, radial and longitudnial
The structural features are:
                                                                             
Wood is Anisotropic

Wood is highly anisotropic. The properties will be different in the radial, longitudinal and tangential directions.
                                     
For example:
                                           
Wood and Moisture

The moisture content will affect the properties of wood.
wood moisture content (wt %)  =  (weight of water in sample / weight of dry wood sample)  x 100 %
                                                             
The green condition of wood is the moisture content in it while it is living. Greenwood shrinks as moisture is eliminated and causes distortion depending on which kind of cut the wood comes from. Kiln-dried wood is denser and stronger than wood in the green condition because without the water hydrogen bonding is stronger.



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