CVG 2141 Lecture Notes - Lecture 8: Lignin, Elastic Modulus, Astm International

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Mechanical Properties of Wood:
Cutting Techniques: Quartersawn or flatsawn
Seasoning:
Controlled Drying of lumber by Air Drying or Kiln Drying
Prevents warping
Effect of SG on Strength:
Overall, mechanical properties increase (linear) as density increases.
Moisture Effects on Strength:
Mechanical decrease as MC increases until FSP is reached
When FSP is reached, the mechanical properties become constant (mechanical
properties become independent of MC)
Variation of strength on each axis:
Strongest in the longitudinal direction and weakest n the radial direction
Tension parallel to the grain is brittle with higher strength (2-4x of strength in compression ||)
Compression parallel is ductile with low strength
oBoth have linear elastic behaviour
Modulus of Elasticity:
Highest in longitudinal Approx. 7-14 GPa in air dry conditions. Hardwoods have a larger elastic modulus (stiffer)
Radial: is 10% of longitudinal
Tangential is ½ of radial
Decreases as MC increases
Tensile Strength
Parallel to grain: Has the highest strength. Failure is caused by transverse rupture of cell wall. Strength can be reduced
by discontinuities in the grain (knots)
Perpendicular to grain: Very small strength, caused by separation of cells (failure of lignin). Reduced by imperfections
in wood (knots, shakes, checks)
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