The strength of any timber is highest in direction of ___________.
Anisotropy: Why Direction Matters in Wood
Wood is an anisotropic material, which means its properties are direction-dependent. This is because wood is composed of long, fibrous cells (like a bundle of straws) that are oriented along the length of the trunk. The strength of the timber depends on how the load is applied relative to the direction of these fibres, also known as the grain.
📝 Detailed Analysis of the Options
(c) an angle of 90 degree to grains
This direction is perpendicular to the grain. Applying a load here is like trying to pull the bundle of straws apart from the side. The bonds between the fibres are much weaker than the fibres themselves, so the wood is weakest in this direction and prone to splitting.
(a) an angle of 60 degree to grains & (d) an angle of 120 degree to grains
Any angle other than 0 or 90 degrees will result in a strength that is intermediate between the maximum and minimum values. The strength decreases as the angle of loading moves from parallel (0°) to perpendicular (90°).
(b) an angle of 0 degree to grains
This is the correct answer. This direction is parallel to the grain. When a load is applied along the length of the fibres, it is resisted by the full strength of the cellulose fibres themselves. This is like pulling on the bundle of straws from its ends—it is very strong. The annual rings and fibres remain intact and are not easily cut or separated, providing maximum tensile and compressive strength.
📊 Timber Strength vs. Grain Direction
| Direction of Load | Angle to Grain | Relative Strength |
|---|---|---|
| Parallel to Grain | 0° | Highest |
| Perpendicular to Grain | 90° | Lowest |
| At an Angle | e.g., 45°, 60° | Intermediate |
💡 Study Tips
- Think of a Rope: A rope is very strong when you pull on its ends (parallel) but can be easily frayed and pulled apart from the side (perpendicular). Wood fibres behave similarly.
- 0° = Parallel = Strongest: This is the key relationship to remember.
- 90° = Perpendicular = Weakest: This is the opposite and equally important relationship.