Timber 1 Flashcards
What are the three sub-systems of a tree?
Crown
Trunk
Root
What is bark?
The outer layer of a tree
corklike and provides protection to the tree
What is bast?
The inner bark which carries enriched sap from leave to cells
What is cambium
Layer of living cells between the bast and the sapwood
What is sapwood?
New growth carries raw sap up to the leaves- usually lighter in colour
What is heartwood?
Mature timber that no longer carries sap- the heart of the tree providing the strength
usually darker in colour
What are annual/growth rings?
Layers inside the tree which show age
What trees do softwoods come from?
Evergreen coniferous trees
What are the 6 types of grains?
Diagonal
Straight
Irregular
Spiral
Wavy
Interlocked
What level of anisotropy does wood have?
90-95% of cells are elongated and vertical
What are the vertical elements of softwoods called?
Trachieds
What’s the function of trachieds?
In softwoods they’re arranged geometrically to allow liquid sap to pass through the
What do the vertical elements in hardwoods do?
Vary in size and are made up of fibres with very thick walls to support the trees
What is the main constituent of timber?
Cellulose
What is lignin?
Chain molecules that are intermeshed with cellulose
What 4 properties make timber a good choice for light structures?
Tensile strength is one direction
Lightweight
good in bending
strength/weight ratio is good
What is the coefficient of thermal expansion of wood?
3.8 x 10^-6 mm/celcius
What are the three different orientations of wood fibres?
Longitudinal
radial
Tangenital
What greatly affects woods properties?
Water
How does increasing water content affect wood?
Lowers its strength
What kind of tension does wood work well under and why?
Uni-axial due to the high strength of cellulose micro-fibris
What are the four types of failure in tension parallel to the grain?
Splintering tension
Combined tension and shear
Shear
Brittle tension
What are the 3 types of failure in tension perpendicular to the grain
Tension failure of earlywood
Shearing along a growth ring
Tension failure of wood rays
What are the 6 types of failure of nonbuckling wood
crushing
wedge splitting
shearing
splitting
crushing and splitting
brooming or end rolling
Failure types in bending with span parallel to the grain
simple tension
cross-grain tension
splintering tension
brash tension
compression
horizontal shear
Which type of wood loses moisture content faster once felled?
Softwood
How much water in wet wood is chemically bound?
20-30%
What is free water?
Water held in the cell cavities
What is bound water?
Water contained within the cell wall
