Anisotropic nature of wood

1. Anisotropic Nature of Wood
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GROUP :01
MS-150501
MS-110513
MS-150516
MS-150521
Student ID:

2. Definition of wood
Wood is a three dimensional, anisotropic and
hygroscopic raw material which mainly composed of
cellulose hemicelluloses and lignin.
Anisotropy of wood
The dimensional changes in wood are unequal along
the three structural directions (longitudinal, tangential
and radial).
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3. Why to know about anisotropy
For determining properties of various direction
Wise utilization of wood
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4. Principle Directions
“With the Grain” =
Longitudinal
•“Cross Grain” or
“Perpendicular to
Grain” = Radial or
Tangential
Strength and
Shrinkage Properties
are different in each
direction
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5. Orientation of microfibrils: cell wall layers
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Anisotropic Characteristics of Wood
Shrinkage and Swelling Properties
• Tangential shrinkage is about twice as high as that
the radial direction.

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• The restricting effect of the ray on the radial plane
• The difference in degree of lignification between radial and
tangential walls
• Small difference in the microfibrillar angel between the two walls
• The increased thickness of the middle lamella in tangential wall
compared to the radial wall.
Reasons for higher tangential shrinkage:
Anisotropic Characteristics of Wood cont’d

8. Strength Properties
longitudinal axis are generally significantly higher than
those in the tangential or radial axes. Strength related
properties in the longitudinal axis are usually referred to
as parallel-to-grain properties.
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Anisotropic Characteristics of Wood cont’d

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Thermal conductivity
• Thermal conductivity is nearly the same in the radial and
tangential directions.
• Conductivity along the grain has been reported as greater
than conductivity across the grain.
Coefficient of Thermal Expansion
• The thermal expansion coefficient of ovendry wood parallel to
the grain appears to be independent of specific gravity and
species.
• Thermal expansion coefficients across the grain (radial and
tangential) are proportional to specific gravity.
• These coefficients range from about 5 to more than 10 times
greater than the parallel-to-grain coefficients.
Anisotropic Characteristics of Wood cont’d

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Electrical Properties
• Conductivity is greater along the grain than across the grain
and slightly greater in the radial direction than in the tangential
direction.
• Relative conductivity values in the longitudinal, radial, and
tangential directions are related by the approximate ratio of
1.0:0.55:0.50.
Elastic Properties
• MOE of douglas fir parallel to the grain is 20 times greater
than perpendicular to the grain.
Anisotropic Characteristics of Wood cont’d

11. Shear strength parallel to grain
• Ability to resist internal slipping of one part upon another
along the grain. Values presented are average strength in
radial and tangential shear planes.
Compressive strength parallel to grain
• Maximum stress sustained by a compression parallel-to-
grain.
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Anisotropic Characteristics of Wood cont’d

12. Thank You