Imperfections or irregularities may present in the structure of a wood. They are also known as defects.
The presence of
defects reduces the strength and durability of wood. Thus, they should be
considered during the design and construction.
A knot is a cross
section or longitudinal section of branches that were cut off. The wood grains
deviate around the knot, and the mechanical properties of wood are
significantly different than any other part. Stress concentration is expected
to occur at knot.
A check is defined
as a lengthwise separation of wood across the annual rings.
A shake is a crack
occurring between or parallel to the annual rings.
A split usually
occurs at the ends of the lumber. It is the complete separation of wood fibres.
Check, shake and
split are cracks take place in different parts of a wood, while showing distinctive
patterns.
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