Wood is the second most popular material used in construction, furniture, flooring, and other items. Although stone still reigns supreme in building construction, wood has recently experienced a tremendous rise. Here are some further fascinating facts about wood and its various mechanical, chemical, and physical characteristics.
Color, luster, texture, macro-structure, odor, moisture, shrinkage, internal tensions, swelling, cracking, warping, density, and sound-electro-thermal conductivity are some of the fundamental physical characteristics of wood. The appearance of wood is influenced by its color, luster, texture, and macrostructure.
Different breeds of wood come in various colors, ranging from white (aspen, spruce) to black (ebony). Wood gains color from tannins, resin, and pigments in cell cavities. Well, in this article, I will be discussing all the properties of wood which include the physical, chemical, mechanical properties, etc.
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Properties of wood
The followings listed below are the major properties of wood:
- Mechanical properties
- Thermal properties
- Electric properties
- Acoustic properties
- Sensory characteristics
- Density and specific gravity
- Shrinkage and swelling
Color, luster, smell, flavor, texture, grain, figure, weight, and hardness of wood are examples of sensory properties. For purposes of identification or other uses, these additional macroscopic features are useful in describing a piece of wood. There are woods in a wide range of colors, although the majority of woods are tones of white and brown. Other colors include yellow, green, red, and practically pure white. Depending on the color differences between the heartwood, sapwood, earlywood, latewood, rays, and resin canals, variations may be visible on a single piece of wood. Bleaching or dyeing, as well as prolonged exposure to the environment, can alter the natural color. Black locusts, honey locusts, and a few tropical species are only a few examples of brilliant woods.
Some species, such as spruce, ash, basswood, and poplar, have a natural shine that is particularly noticeable on radial surfaces. Due to the volatile compounds found in wood, odor and taste are produced. They are sometimes useful distinguishing traits, although being challenging to articulate. The term “texture” refers to how uniformly a wood surface, typically transverse, appears. As in coarse, fine, or even texture or grain, grain is frequently used interchangeably with texture. It can also be used to describe the direction of wood parts, such as straight, spiral, or wavy. Sometimes the grain is used instead of a figure, as in the case of the silver grain in the oak. The figure refers to organic patterns or designs on wood surfaces (normally radial or tangential).
Weight and hardness are considered sensory properties in a diagnostic rather than a technical sense; weight is determined by simply lifting the hand, and hardness is determined by pressing with the thumbnail. There are lighter and heavier woods that can be found in the tropics, with weights ranging from 80 to 1,300 kg per cubic meter (5 to 80 pounds per cubic foot) for balsa and lignum vitae, respectively. Common temperate-climate woods typically range in weight from about 300 to 900 kg per cubic meter (roughly 20 to 55 pounds per cubic foot) in air-dry conditions.
Density and specific gravity
Specific gravity is the ratio of the weight or mass of wood to that of water, while density is the weight or mass of a unit volume of wood. Because 1 cc of water weighs 1 gram, the average density and specific gravity of Douglas fir wood are both 0.45 gram per cubic centimeter (g/cc), respectively, in the metric system of measurement. (One gram per cubic centimeter, or roughly 62.4 pounds per cubic foot, is expressed as weight per unit volume.) Since wood is hygroscopic, the amount of moisture considerably affects both its weight and volume, making determining its density more challenging than for other materials. Weight and volume are calculated at predetermined moisture values to produce similar results.
Weight and volume are calculated at predetermined moisture values in order to produce similar results. Oven-dry weight (almost little moisture content) and either oven-dry or green volume are the standards (green refers to moisture content above the fiber saturation point, which averages about 30 percent). Other representations of density, such as those based on air-dry weight and volume or weight and volume of green wood, are less precise but do have certain practical applications, like in the shipping of wood.
If in touch with water, wood can absorb it as a liquid or as a vapor from the air. Water is the most significant liquid or gas that wood can absorb, despite this. Wood always includes moisture due to its hygroscopic nature, whether it is a component of the living tree or a material. (The terms water and moisture are used interchangeably here.) Moisture has an impact on all aspects of wood, although it should be highlighted that only moisture found in cell walls is significant; moisture found in cell cavities does little more than add weight.
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Shrinkage and swelling
When the moisture level in wood varies below the fiber saturation point, dimensional changes occur. Shrinkage and swelling are caused by moisture gain and loss, respectively. These dimensional changes are anisotropic, meaning they differ in the axial, radial, and tangential directions. Roughly 0.4 percent, 4 percent, and 8 percent, respectively, are the average shrinkage values. Volume loss is around 12%, but there are significant differences between species. These numbers are provided as a percentage of green dimensions and correspond to transformations from the green to oven-dry condition. The cell wall structure is primarily responsible for differential shrinking and swelling in various development orientations.
The orientation of the microfibrils in the layers of the secondary cell wall can be used to explain the variations between axial and the two lateral (radial and tangential) directions, however, it is unclear why these discrepancies exist in radial and tangential directions.
Bacteria, fungi, insects, marine borers, as well as environmental, mechanical, chemical, and thermal variables, all contribute to the destruction of wood. The look, structure, or chemical makeup of wood can change due to degradation, which can impact living trees, logs, or products. These changes can range from minor discoloration to irreversible transformations that render wood utterly worthless. As evidenced, for instance, by furniture and other wooden artifacts discovered in perfect condition in the tombs of ancient Egyptian pharaohs, wood can last for hundreds or thousands of years (see Egyptian art). Only under the influence of outside elements does wood deteriorate or get destroyed.
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The mechanical, or strength, properties of wood are signs of its capacity to withstand external forces that could potentially tend to alter its size and shape. The amount and method of application of these forces, as well as the density and moisture content of the wood, affect the resistance to those forces. In the axial direction, or parallel to the grain, wood’s strength characteristics are noticeably different from those across the grain (in the transverse direction).
The strength of wood in tension and compression (measured in axial and transverse directions), shear, cleavage, hardness, static bending, and shock are some of its mechanical characteristics (impact bending and toughness). Respective tests determine stresses per unit of loaded area (at the elastic limit and maximum load) as well as other strength criteria, including toughness, rupture modulus, and modulus of elasticity (a measure of stiffness). Small, transparent specimens having a cross-section of 2 x 2 cm or 2 x 2 inches are typically used for testing.
Even though wood expands and contracts with variations in temperature, shrinkage, and swelling brought on by changes in moisture content are much more significant dimensional alterations. Such temperature-related expansion and contraction are typically insignificant and of no practical consequence. Surface checks can only occur at temperatures below 0 °C (32 °F); frost cracks can occur in living trees due to uneven contraction of the outer and inner layers.
Compared to materials like metals, marble, glass, and concrete, wood has a low thermal conductivity (high heat-insulating ability). Light and dry woods are superior insulators because thermal conductivity is highest in the axial direction and increases with density and moisture content.
Electrical insulation can be found in oven-dried wood. However, when moisture content rises, electric conductivity rises as well, causing saturated wood (wood with the highest moisture content) to behave more like water. It is noteworthy how dramatically electric resistance falls as moisture content rises from 0 to the point at which fibers are saturated. Electric resistance drops by more than a billion times in this range, but only by around 50 times from the fiber saturation point to the highest moisture content. The electric resistance of wood is mostly unaffected by other parameters, such as species and density; variations across species are related to the chemistry of the extractives. The axial resistance is roughly half of the transverse resistance.
The dielectric or poor conductor, properties of wood are also important. Dielectric constant and power factor play a practical role in making electric meters (capacity and radio-frequency power-loss type) for measuring wood’s moisture content, drying wood with electric current (a theoretical possibility, though not currently a reality), and gluing wood with high-frequency electric current. The electric polarization (the appearance of opposite electric charges on opposite sides of a piece) that occurs when mechanical stress is applied causes wood to show the piezoelectric effect. Contrarily, wood experiences mechanical deformation when exposed to an electric field (changes in size).
Wood can both create sound (by direct striking) and magnify or deflect sound waves coming from other objects. It is a special material for musical instruments and other acoustic applications because of these factors. The size, density, moisture content, and elastic modulus of the wood all have an impact on the frequency of vibration, which in turn affects the pitch of the sound generated. Higher density and elasticity reduced moisture content, and smaller dimensions all contribute to higher-pitched sounds.
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That is all for this article, where the properties of wood are listed and explained. I hope you get a lot from the reading, if so, kindly share with others. Thanks for reading, see you around!