Wood Flashcards
What is an exogenous tree?
Grows outward by adding new cells in a layer between existing wood and bark
EX. Softwoods (pine, spruce, fir, hemlock, cedar, cypress, redwood)
Hardwoods (oak, maple, ash, walnut, hickory, poplar, gum, birch)
What is an endogenous tree?
Grows inward y adding new cells to the old
EX. Bamboo, palm
What are the difference between softwoods and hardwoods with respect to growth of tree, mechanical and hygroscopic properties, and usages?
Softwoods are conifers or cone bearing
hardwoods are broad leafed and mostly deciduous
What are two main components of wood and their contributions to the strengths of wood
Cellulose- Provides tensile axial strength & elastic proper of wood.
Ligin- cements the cellulose together to provide compressive strength.
What is the growth region in an exogenous tree called?
Cambium Layer- Layer of new cells beneath the bark
What are heartwood and sapwood? What are their differences in terms of mechanical properties and decay resistance
Heartwood- inactive inner portion relatively darker in color. More resistant to decay.
Sapwood- active outer portion, light in color.
What are early and late woods in the growth region of a tree
Early wood (springwood)- inner light colored layer, grows in spring and relatively faster. Late wood- (Summerwood)- outer darker layer which grows in the summer and relatively slower.
How can the rate of growth of a tree be measured
Measured by the number of annual growth rings er distance (rings/inch) along a line perpendicular to the rings across a right section of the tree. Wood is stronger if rate of growth is slower
What is the typical specific gravity of cellulose in wood?
1.5
What factors effect the density of wood
Wood composition (air cavities) vs solid wood composition
Explain how wood contains moisture in its structure. What is the fiber saturation point?
Wood contains moisture in 2 forms, absorbed water in the capillaries of cell walls and free water in cell cavities.
Fiber saturation point is the moisture content at which the cell walls are saturated and no free water exists.
Explain how wood expands or shrinks with the changes in moisture content.
see paper
Describe the thermal expansion, heat conductivity, and electric conductivity of wood.
Thermal expansion is small compared with that due to moisture effects.
Thermal conductivity is low compared to that of concrete or steel
Electrical conductivity increases with moisture content. Moisture content can be estimated by measuring the electrical resistance of the wood.
Describe the effects of density and growth rate on the strength of wood.
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