The defect in timber that causes longitudinal separation of woods between the annular ring is known as __________.
Understanding Defects in Timber Growth
Defects in timber can arise from various sources, including natural forces that affect the tree as it grows. These defects can take the form of irregular growth, grain distortions, or internal cracks and separations that compromise the wood's structural integrity.
📝 Detailed Analysis of the Options
(a) Knots
Knots are the remnants of branches that have been enveloped by the growing tree trunk. They appear as hard, dark circles and disrupt the grain pattern, but they are not separations or cracks.
(b) Rind gall
This is a surface defect, appearing as a swollen lump where the tree has healed over a wound. It is an abnormal growth, not a longitudinal separation.
(d) Twisted fibers
This defect, also known as spiral grain, occurs when the wood fibres grow in a spiral or twisted manner around the tree's axis instead of straight up. While it affects strength, it is a distortion of the grain, not a separation between rings.
(c) Shakes
This is the correct answer. Shakes are longitudinal cracks that occur between the annular rings, meaning they run parallel to the direction of the rings. They are caused by stresses in the growing tree, such as high winds or extreme temperatures. There are several types of shakes:
- Heart Shake: A crack that starts at the pith (heart) and widens towards the sapwood.
- Star Shake: A series of cracks radiating from the pith, wider on the outside and narrower towards the center. Often caused by severe frost or rapid seasoning.
- Cup Shake: A curved crack that follows the line of an annual ring, separating it from the adjacent ring.
📊 Comparison of Growth-Related Defects
| Defect | Description | Nature of Defect |
|---|---|---|
| Shakes | Longitudinal separation between annual rings | Internal Crack |
| Knots | Embedded base of a branch | Grain Disruption |
| Rind Gall | Swollen growth over a wound | Surface Deformity |
| Twisted Fibers | Spiral growth of wood fibers | Grain Distortion |
💡 Study Tips
- Shakes Separate Rings: The key feature of a shake is that it separates the layers of wood along the growth rings. Think of a layer cake coming apart.
- Checks Cross Rings: Don't confuse shakes with checks. Checks are also cracks, but they are caused by seasoning and run *across* (perpendicular to) the annual rings.
- Knots are Branches: Remember that knots are simply overgrown branches, not cracks.