here is some info on basic structure structure of woods. for more in detail check for references in the slides

1. STRUCTURE OF WOODS
MATERIAL TECHNOLOGY
7740 Ravi Bhivra
7741 Aniket Devadiga

2. Outline
» What it is like at…?
» Types of woods…
» Structure of wood in detail.
» Stiffness of wood.
» Strength of wood.
» Research paper’s.

3. What it is like at “CELLULAR LEVEL” ?
• The basic unit of wood structure is the plant cell, which is the smallest unit of living matter capable
of functioning independently.
• The cell has many functions, such as the manufacture of proteins, polysaccharides and mineral
deposits. A plant cell varies in diameter from 10–100 μm.
• The main difference between the plant and animal cell is that plant cells have a cell wall outside the
plasma membrane, which is 0.1 to 100 μm thick.
• This makes the cells rigid, among other effects prohibiting the locomotion typical of animals.

4. What it is like at “CELLULAR LEVEL” ?
http://www.doitpoms.ac.uk/tlplib/wood/structure_wood_pt1.php

5. What it is like at “MACROSCOPIC LEVEL” ?
• Wood has extreme anisotropy because 90 to 95% of all the cells are elongated and vertical (i.e.
aligned parallel to the tree trunk).
• The remaining 5 to 10% of cells are arranged in radial directions, with no cells at all aligned
tangentially. http://www.doitpoms.ac.uk/tlplib/wood/structure_wood_pt2.php
• The diagram shows a cut through of a tree trunk:

6. It’s Complete Structure
• The structure of the tree trunk has now been discussed at both the cellular and
macroscopic scale.
• At the level of the complete structure, there is a further point of interest: the tree is
prestressed due to wind which makes it necessary for the trunk to have two different
type of material properties.
• The center of tree trunk is in compression, and the outer layers are in tension.
• The stressing is achieved as the inner sapwood shrinks as it dries and becomes
heartwood.
• As the heartwood has lower moisture content it is better able to resist compression.

7. It’s Complete Structure
http://www.doitpoms.ac.uk/tlplib/wood/structure_wood_pt3.php

8. Types of wood
• There are basically two types of woods:-
1. “SOFTWOOD”
2. “HARDWOOD”

9. SOFTWOOD
• PINE
» ASH
• HICKORY
» BEECH
• BIRCH
» CEDAR
• REDWOOD
» HEMLOCK
• FIR
» SPRUCE

10. HARDWOOD
• OAK
» MAPLE
• MAHOGANY
» CHERRY
• WALNUT
» ROSEWOOD
• TEAK http://www.hoovedesigns.com/woods.html

11. The structure of wood “SOFTWOOD"
• A scanning electron micrograph of a softwood specimen is shown next.
• Softwoods consist mainly of long (3 to 5 mm) cells called trachoids which
are about 20 to 80 x 10-6m.
• This structure mainly eliminates the need for vessels as the transport of
the fluids are conducted by the rays.
• This in term increases the chances of softwood to undergo warping
• This is mainly due to the ability of the whole soft to transport water thus
allowing it to get moisturised

13. The structure of wood “HARDWOOD”.
• Hardwoods consist mainly of two kinds of cells: Wood
Fibers and Vessel Elements
• Wood fibers are elongated cells which are similar to
trachoids except they are smaller, only 0.7 to 3 mm long
and less than 20 x 10-6m in diameter, and they do not
serve for fluid transport in the living tree.
• The vessel elements do serve for fluid transport in the
living tree, and they can have a wide range of sizes.
• Due to this arrangement of fluid transport hardwood can
easily resist warping and making it brittle as the trachoids
are small reducing its shock absorbing capacity.

14. RAY
FIBERS
VESSELS

15. Structure of wood in a “Broader sense”
Earlywood or spring wood
• Formed during spring season.
• Formed early in a year.
• Consists of xylem tissues with
wider vessels.
• Produced more in amount.
• Less dense.
• A broad zone of wood.
• Not as strong as late wood.
Latewood or autumn wood
• Formed during winter season.
• Formed after the early wood.
• Consists of xylem elements with
narrow vessels.
• Produced less in amount.
• More dense.
• A narrow zone of wood.
• Stronger than early wood due to
larger volume of wall materials.

16. Structure of wood in “DETAIL”
Earlywood & Latewood.

17. Structure of wood along its “FIBERS”
Why isn’t wood not used on a large scale though being easy to machine?
• Longitudinal direction: parallel to the long axis of the stem.
• Radial direction: perpendicular to both the growth rings and the long axis of the stem
• Tangential direction: tangent to the growth rings.
http://www.ce.berkeley.edu/~paulmont/CE60New/wood.pdf

18. Stiffness of wood
The stiffness of wood can be measured using a simple threepoint bend
test as shown below:
http://www.doitpoms.ac.uk/tlplib/wood/wood_stiffness.php

19. Stiffness of wood
• The width (w) and height (h) of wood samples are measured, and the
specimens are placed in a three-point bend testing apparatus with the height of
the wood oriented vertically in the apparatus. The distance (L) between the two
supports is also measured.
• The deflection of the middle of the beam, as a function of load on the pan of
the apparatus, is measured to calculate the stiffness.

20. Stiffness of wood
• The resulting load (m) – displacement ( ) curves on loading and unloading for
(a) balsa, (b) Scots pine and (c) greenheart are shown below

21. Stiffness of wood
http://www.doitpoms.ac.uk/tlplib/wood/wood_stiffness.php

22. Stiffness of wood

23. Stiffness of wood
CALCULATION
Using the equation for the deflection of a material under symmetric threepoint bending:
The Young’s modulus for each sample is calculated from:

24. Strength of wood
• The strength of wood can also be determined by the very same
method of “three point bend test”.
http://www.doitpoms.ac.uk/tlplib/wood/wood_strength.php

25. Strength of wood
• The width (w) and height (h) of wood samples are measured, and the specimens
are placed in the three-point bend testing apparatus with the height of the wood
orientated vertically in the apparatus.
• The distance (L) between the two supports is also measured.
• The wood samples are again loaded in 100 g increments.
• If the micrometer needle continues to move after a 100 g load has been added to
the pan, the reading is allowed to stabilise before further mass is added.
• The mass on the pan is increased in this way until the sample fails.
• At this point the load and deflection of the sample before failure are noted.

26. Strength of wood
• By following this method and repeating for three samples of balsa, Scots pine
and greenheart the following results were obtained:

27. Strength of wood
• To calculate the strength the following equation is used:

28. Any Questions.. ?

29. Thank You