ka, shingles, shingles, etc.) and as negative when driving nails, crutches, staples, screwing in screws.
Specific characteristics of mechanical properties. For a comparative assessment of the quality of wood, indicators of its mechanical properties (ultimate strength, modulus of elasticity, impact strength, hardness), referred to the unit of density, are used.The specific strength in compression and static bending in conifers is higher than in deciduous ones.
Specific hardness is also significantly higher in conifers (especially in spruce and fir wood). For other properties, the specific characteristics of deciduous wood are higher than that of conifers.
Specific characteristics of wood are of particular importance when a product or structure requires high strength and rigidity (depending on the modulus of elasticity) with low weight. This is important for transport engineering, aircraft construction, shipbuilding, construction, etc., in the selection of wood for the production of musical instruments and in other cases.
In terms of specific strength, wood is quite competitive with other modern materials, and in terms of specific rigidity (along the fibers) it is many times superior to polymers. So,] for example, the specific tensile strength of pine wood is 206 kPa-m 3 / kg, duralumin 150 ... 175 kPa-m 3 / kg, fiberglass 263 kPa-m 3 / kg. Specific stiffness of pine wood (along the grain) 24.6 MPa-m 3 / kg, polyacrylates 3.3 MPa-m 3 / kg, nylon 1.3 MPa-m 3 / kg.
Control questions
What are the features of mechanical testing of wood; from testing other materials?
What is the relationship between the tensile strength, compressive strength and static bending of wood?
What indicator is determined when testing wood for compression across the fibers?
What kind of fracture is typical for solid wood?
What stresses cause the destruction of wood during chipping?
What are the reasons for the formation of "frozen" residual deformations.
How does the duration of loading affect the ultimate strength of wood?
What is the difference between impact strength tests and wood strength tests?
What groups are the species divided into according to the hardness of the wood?
10. What are the reasons that keep nails and other fasteners in the wood?
Chapter 5 variability and relationships of wood properties
5.1. Variability of properties
The properties of wood, as already noted, significantly depend on the species. However, within the same species variability of properties is observed due to age-related changes in the tree, the influence of the environment and hereditary factors. The structural features of wood are reflected in its density. The thicker the cell walls, the longer the fibers and the higher the latewood content in the annual layers, the higher the density of the wood as a whole.
Density, in turn, is closely related to most of the physical and mechanical properties of wood. Therefore, considering the patterns of density change, one can get an idea of the variability and other properties.
The variability of the properties of wood in an individual tree. Along the radius of the trunk, the density changes periodically, which is especially noticeable in coniferous and annular deciduous species. For example, in pine, the density of the late zones is 2 ... 3 times higher than the early ones. With the distance from the core along the radius of the trunk, the density of the early zones first slightly decreases, then remains constant, and increases only near the bark itself. The density of the later zones gradually increases in the direction from the core to the cortex.
When combining the test results of samples taken at different levels of the trunk, it was found that in conifers at the age of maturity (pine, cedar, larch), the density of wood first increases in the direction from the core to the bark, reaches a maximum by about 2/3 of the radius, after which starts to decline again. In trunks of annular vascular deciduous species (oak, ash), the density of wood decreases, and in trunks of diffuse vascular species, it increases in the indicated direction. In the Far Eastern conifers and deciduous species, according to VIAM, the density change is as follows: from the core to the bark, it first increases, reaches a maximum, and then decreases again.
ILD studies of Siberian rocks have shown that the density of pine continuously increases from the core to the bark; in larch, the maximum density is observed at half the radius, while in spruce there is a minimum density. In birch, the density increases in the direction from the core to the bark, while in pine it decreases. For pine, spruce, birch and aspen growing in the north-west of the European part of the country, general patterns were obtained that indicate
Rice. 5.1. Changing the density of wood along the radius of the pine trunk
and birch:
a - the apex of the trunk; b - medium; v - butt
an increase in density with distance from the core (Fig. 5.1). The only exception was aspen wood, in which an inverse relationship was found in the top of the trunk.
In conifers, especially in pine, there is a zone of the so-called juvenile (immature) wood adjacent to the core. The formation of juvenile wood occurs in the first 5 ... 20 years of the tree's life. In juvenile wood, the cell walls are thinner, the fibers are shorter, and there are fewer cells in the later zones of the annual layers. This wood differs from mature wood in its lower cellulose content, lower compression density along the fibers, large longitudinal shrinkage, and other features.
A change in density is also observed along the height of the trunk. According to the ILD data for Siberian species, in pine, larch, birch, and aspen, the density decreases along the height of the trunk, while in spruce it increases. There is a greater variability of density along the trunk height than along the radius.
The dependencies shown in Fig. 5.2, give an idea of the change in the base density (pb) of tree species growing in the northwestern regions of the European part of the country.
The common nature of the density change in spruce and aspen is explained by the fact that the trees of these species (in contrast to pine and birch) have a low-set crown.
Rice. 5.2. Changing the density of wood along the height of the trunk:
/ - spruce; 2 - Pine; 3 - Birch; 4 - aspen
It should be borne in mind that the distribution of the density p ^ / in a growing tree is different.
Variability of wood properties within the breed. The influence of age is reflected in the increase in wood density in the oldest trees. In stands of different ages, the variability of density is greater than in those of the same age. In conifers for trees of the same age, there is an inverse relationship between trunk diameter and wood density. The latter depends on the shape of the trunk. In pine, spruce, birch, with an increase in the tapering of the trunk, the average density decreases.
There is no consensus on the influence of the position of the tree in the stand. In a number of works it is noted that the most dense wood is observed in small, oppressed trees, but in other works it was found that wood of this quality is observed in medium-sized coniferous trees. Among deciduous species, the density of wood in the largest, dominant trees is higher than that of the stunted ones. With an increase in the density of the plantation, the average density of coniferous wood increases.
A wide range of factors characterizing the influence of the external environment is included in the concept of growing conditions. These conditions include the quality and condition of the soil, climatic characteristics, type of forest, height above sea level, the geographical position of the stand, etc. Conifers under the worst growing conditions form a denser wood. For hardwoods (birch, aspen) in the north-west of the European part of the country, there is a tendency to an increase in density with an improvement in soil conditions.
The geographical position of the plantation determines the differences in soil conditions, the amount of precipitation, the duration of the growing season, which, in turn, affects the density of the wood. Numerous data on wood density from different growing areas are concentrated in the tables GSSSD 69-84 and GSSSD-R-237-87.
L mismanagement activities (thinning, drainage, fertilization, etc.) also affect the density
The influence of the felling time on the density and other physical and mechanical properties of wood was not experimentally found. It should be borne in mind that wood felled during the growing season tends to be less resistant to decay.
Debarking and tapping have no significant effect on density.
The annual layers in all sections of pine wood are clearly visible, the core rays are not visible, and the vessels are absent. The kernel is pink or brownish-red, the sapwood is wide, yellowish-brown. Pine wood is straight grained, resinous, lightweight, strong enough and amenable to processing. The early zone of the annual layer is light in color, the late zone is dark in color.
The core rays are clearly visible in the cross section of the wood. They appear as light specks on the dark-colored late part of the tree growth rings. On the longitudinal sections, you can see many large dark lines (the color is darker than wood) - these are longitudinal resinous passages.
The wide sapwood is yellowish or pale pink in color. The sapwood of only sawn pine can be yellow, and after drying it acquires a brownish tint. Pine has a uniform texture, which is mainly determined by the width of the growth rings, the difference in color of the late and early wood, as well as sapwood and kernel. The curving lines of the annual layers sometimes create a unique pattern.
Early and late woods are very different in their structure, therefore pines low uniformity... The early zone of the annual layer has a density two to three times lower than the density of the late zone of the annual layer. The annual layer contains an average of 27% late wood... One centimeter contains 4 to 14 annual layers. This is typical for the pine growing on the territory of Russia. In the northern regions of Russia, pines have more annual layers.
Physical properties of pine
The moisture content in the sapwood of growing pine averages 111%, and in the core - 32%. In the upper part of the tree, the moisture content is higher, while the moisture content of the kernel practically does not change. However, there are daily and seasonal fluctuations in humidity. The highest percentage of humidity is observed in the morning (on average, about 20-30% higher), by the evening it can drop to a minimum, and by morning it will rise again.In winter, the moisture content of pine wood has a maximum value (from November to February), and in summer it is minimum (from July to August). As mentioned above, this applies only to sapwood, the core of the pine has an almost constant moisture. The average moisture content in freshly cut wood is 85%.
Pine drying process
In Russia, logs and log cabins are used to build houses. Drying wood is one of the most important steps in preparing wood for use. Shrinkage percentage are very important parameters. The average percentage of shrinkage for pine wood in the tangential direction is 6.7% - the early part of the annual layers and 7.5% - the late part. But since wood is a hygroscopic material, when the air humidity rises, wood begins to absorb moisture. We can say that the drying process itself and the absorption of moisture are practically mutually reversible. Therefore, the change in the parameters of pine wood with a change in its moisture content is characterized by the swelling coefficient (percentage of parameter change per percentage of wood moisture). The average swelling factor for Scotch pine is:- Radial direction - 0.18;
- Tangential direction - 0.31;
- Volumetric - 0.50.
The density is exceeded in the direction from the core to the crust, reaching a maximum percentage of 2/3 of the radius, after which there is a decrease. The percentage of density also decreases with the height of the tree. Various fertilizers used to accelerate pine growth and other agrochemical measures reduce the density of wood by 5-15%.
Pine wood has high values of air permeability and moisture permeability, mainly in sapwood. At a high pressure of 0.1 MPa (one side of the sample), air permeability in the radial direction is 56.2 cubic meters. mm / sq. cm / s (sapwood), 2.6 cu. mm / sq. cm / s (core). Due to the sufficiently high moisture permeability, it is possible to use various protective substances. The sapwood of pine wood is perfectly impregnated with protective substances, therefore this tree species is called highly absorbent and the kernel is medium impregnated... A refractory spruce and larch are considered.
Thermal properties of pine
Wood of different species consists of practically the same substances, therefore the percentage of heat capacity of wood does not depend on the type of wood. The increase in thermal conductivity increases with increasing density. It is almost impossible to reveal the thermal expansion of wood, because it is masked by shrinkage and moisture absorption. The thermal insulation properties of wood are significantly higher compared to aluminum, which is used for the manufacture of windows, and slightly higher than that of PVC.About the electrical properties of wood
Wood is a dielectric. Completely dry pine wood has a specific volume resistivity of longitudinal fibers - 1.861015 Ohm / cm, and transverse - 2.361015 Ohm / cm. When the moisture content of the wood increases, then its resistivity decreases.About sound properties
Pine wood has a fairly low sound insulation. For example, a 30 mm partition is able to reduce the noise level by 12 dB, while, at the request of SNiP, it should be 40 dB.Electromagnetic and penetrating radiation
Light transmission: With the help of sensitive instruments, it was found that light radiation can penetrate 35 mm pine wood samples. In addition, it has been proven that the structure and strength of wood is practically unchanged by X-ray radiation. For this reason, X-ray is used for the inspection of assortments. Now wood is successfully used for shielding neutron radiation. The pine covering, the thickness of which is 100 mm, may well replace the polyethylene protection, since it has greater heat resistance and durability.Mechanical properties
The best strength properties have the wood of pine trees, which grow in the northern regions of Russia. Pine, among conifers, is second only to the Caucasian fir in terms of strength.Strength grade: Pine is a soft breed, therefore, it has a rather low wear resistance. Such wood does not hold the fasteners well (nails, screws). It should be said that in comparison - the hornbeam has this figure four 4 times higher.
Tensile strength
- with static bending - 70-92 MPa;
- when stretched along the fibers - 100-116 MPa;
- when compressed along the fibers - 40-49 MPa;
- when chipping along the radial plane - 6.1-7.6 MPa;
- when chipping along the tangential plane - 6.6-8.1 MPa; The modulus of elasticity in static bending is -8.0-13.1 GPa.
Technological and operational properties
- impact strength - 28-51 kJ / sq. m;
Hardness
- end - 28-33 N / sq. mm;
- radial - 21-25 N / sq. mm;
- end - 16-23 N / sq. mm.
Like all conifers, pine bends poorly. However, due to its softness, it can be easily processed with a cutting tool. For pine, the level of specific cutting force in comparison with birch is approximately 1.7-1.8 times lower, and if compared with oak, then it is 2-2.5 times lower. Approximately the same ratio in the periods of service life of cutting tools (bluntness).
Depending on the moisture content and hardness of the wood, the widening to the side may be different. For example, for wet wood, the maximum side widening is 0.7-0.85 mm, and the minimum for dried and hard wood is 0.4-0.5 mm. The sharpening angles of the teeth for band and circular saws, as well as the indicator of the value of their broadening, are the same for both coniferous and deciduous trees.
Pine lends itself well to polishing. Microroughnesses can have a height of 8-60 microns, while oak, ash and maple - up to 200 microns. As mentioned above, pine wood is well impregnated with various protective substances, however, in its high degree of moisture permeability, there is also a negative side - it is a large consumption of materials for finishing work. In addition, before applying the paint and varnish coating, resin removal is required, since pine wood contains quite a lot of resin. For demineralization, substances that dissolve or soap the resin are used, that is, the wood is treated with gasoline, acetone, alcohol and special alkaline solutions.
Pine wood is resistant to biological influences, in other words, it is not susceptible to fungal attack. As a comparison, it should be said that spruce, for example, belongs to the medium-hardy group, and birch wood belongs to the weak-hardy group. The degree of biostability increases with the age of the tree. The lower part of the barrel offers maximum durability. The wood of a tree felled during the growing season is more susceptible to rotting.
In principle, the mechanical and operational-technological properties of pine wood are not influenced by the time of tree felling. The percentage of these indicators after drying at high temperatures is significantly reduced. When drying, microwave currents are used, which do not cause any harm to the properties of wood.
Within fifteen days, the strength of completely dry wood at high temperatures (80-100 ° C) decreases by 5-15 percent, and in half an hour - by 10-30 percent. The maximum strength of frozen wood during compression and static bending increases by 35%, while chipping - by 75%. But the impact strength is reduced by almost half. The strength of pine sapwood decreases by 10-15% after staying in sea water for 30 days, while the core does not change its strength properties under the same conditions. Pine wood has the following characteristic defects:
- Smooth growths are formed, which have a large percentage (in relation to the main wood) of density, shrinkage, as well as a low percentage of strength.
- Pieces of wood impregnated with resin - pitching, appear due to damage to the trunk. Grinding can be noticed on round assortments due to damage to the trunk or a large amount of resin. They are of a darker color than the base wood and are visible on low-thickness assortments. Sometimes you can see the so-called resin pockets, although they are less common than in spruce.
Use of pine wood
Pine wood can be used in a wide variety of industries. In construction, wood is used as materials for structures and finishes. In addition, machine building, furniture production, railroad transport, etc. are indispensable without pine wood. Gum is extracted from pine. Pine needles are used for the production of biologically active substances.Pine is not very popular in furniture production. Usually, its resinous and softwood is used for the manufacture of cabinet furniture. At the same time, thick veneer of more noble species (for example, mahogany) is used for facing the pine frame.
Most often, pine is used in the construction of saunas and stairs. But first, the wood is processed to remove excess resin and seal from it. Light pine panels are not only very beautiful, but also smell good. In addition, pine wood is inexpensive, which is why the manufacturers of saunas in the economy class use this particular wood. For simpler saunas, as a rule, ordinary pine is used, and for elite-class saunas - Canadian pine (hemlock).
Scotch pine
Pine is a tree that, in the best growing conditions, reaches a height of 30-40 meters (sometimes up to 45) and more than a meter in diameter. The crown is transparent with a rounded or flat top, raised high. Branching is whorled, but on trunks and thick branches such whorliness is obscured by the development of individual branches and overgrowing of traces from dead and fallen branches. Nevertheless, up to 30-40 years old, the age of a tree can be determined quite accurately by clearly visible whorls, considering that one whorl is formed annually.
Burned with a bright flame
The pines are old, mighty,
Dressed up coniferous nets
And the bedspreads are gold-woven.
S. Yesenin.
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The mechanical properties of wood include: strength, hardness, stiffness, impact strength and others.
Strength - the ability of wood to resist destruction from mechanical forces, characterized by ultimate strength. The strength of wood depends on the direction of the load, wood species, density, moisture, presence of defects.
Only the bound moisture contained in the cell membranes has a significant effect on the strength of wood. With an increase in the amount of bound moisture, the strength of the wood decreases (especially with a moisture content of 20-25%). A further increase in humidity beyond the hygroscopic limit (30%) does not affect the strength of the wood. The tensile strength indicators can only be compared with the same moisture content of the wood. In addition to moisture, the mechanical properties of wood are also influenced by the duration of the load.
Vertical static loads are constant or slowly increasing. Dynamic loads, on the other hand, act for a short time. The load that destroys the structure of the wood is called destructive. The strength, bordering on destruction, is called the tensile strength of wood, it is determined and measured with wood samples. The strength of wood is measured in Pa / cm2 (kgf per 1 cm2) of the cross-section of the sample in the place of destruction, (Pa / cm2 (kgf / cm2).
The resistance of the wood is determined both along the grain and in the radial and tangential directions. There are the main types of action of forces: stretching, compression, bending, shearing. Strength depends on the direction of action of the forces, the type of wood, the density of the wood, moisture content and the presence of defects. The mechanical properties of wood are given in the tables.
Most often, wood works in compression, for example, uprights and supports. Compression along the fibers acts in the radial and tangential directions (Fig. 1).
Ultimate tensile strength. The average tensile strength along the fibers for all rocks is 1300 kgf / cm2. The tensile strength along the grain is greatly influenced by the structure of the wood. Even a slight deviation from the correct fiber placement causes a decrease in strength.
The tensile strength of wood across the fibers is very low and averages 1/20 of the tensile strength along the fibers, that is, 65 kgf / cm2. Therefore, wood is almost never used in parts that work in tension across the fibers. The tensile strength of wood across the fibers is important when developing cutting modes and drying modes for wood.
Compressive strength. Distinguish between compression along and across the fibers. When compressed along the fibers, the deformation is expressed in a slight shortening of the sample. Compression failure begins with buckling of individual fibers, which in wet specimens from soft and viscous rocks manifests itself as crushing of the ends and buckling of the sides, and in dry specimens and in hardwood it causes one part of the specimen to shift relative to the other.
Average tensile strength when compressed along the fibers for all rocks is 500 kgf / cm2.
The compressive strength of wood across the fibers is approximately 8 times lower than along the fibers. When compressing across the fibers, it is not always possible to accurately determine the moment of destruction of wood and determine the magnitude of the breaking load.
The wood is tested for compression across the fibers in radial and tangential directions... In hardwoods with wide core beams (oak, beech, hornbeam), the strength under radial compression is one and a half times higher than under tangential compression; in conifers, on the contrary, the strength is higher under tangential compression.
 |
| Rice. 2. Testing the mechanical properties of wood for bending. |
Static bending strength. When bending, especially at concentrated loads, the upper layers of the wood experience compressive stress, and the lower ones - tension along the fibers. Approximately in the middle of the height of the element is a plane in which there is neither compressive stress nor tensile stress. This plane is called neutral; maximum shear stresses arise in it. Compressive strength is less than tensile strength, so fracture begins in the compressed zone. The visible destruction begins in the stretched zone and is expressed in the rupture of the outermost fibers. The tensile strength of wood depends on the species and moisture content. On average, for all rocks, the flexural strength is 1000 kgf / cm2, that is, 2 times the ultimate strength in compression along the fibers.
Shear strength of wood. External forces that cause movement of one part of the part in relation to another are called shear. There are three cases of shear: shearing along the fibers, across the fibers and cutting.
Shear strength along grain makes up 1/5 of the compressive strength along the grain. In hardwoods with wide pith rays (beech, oak, hornbeam), the shear strength along the tangential plane is 10-30% higher than along the radial one.
Shear strength across fibers approximately half the ultimate shear strength along the grain. The strength of the wood when cut across the grain is four times higher than the shear strength.
Hardness is the property of wood to resist the penetration of a body of a certain shape. The hardness of the end surface is 30% higher than the hardness of the lateral surface (tangential and radial) for deciduous species and 40% for conifers. According to the degree of hardness, all tree species can be divided into three groups: 1) soft - end hardness of 40 MPa or less (pine, spruce, cedar, fir, juniper, poplar, linden, aspen, alder, chestnut); 2) solid - end hardness 40.1-80 MPa (larch, Siberian birch, beech, oak, elm, elm, elm, sycamore, mountain ash, maple, hazel, walnut, persimmon, apple, ash); 3) very hard - end hardness more than 80 MPa (white acacia, iron birch, hornbeam, dogwood, boxwood, pistachios, yew).
The hardness of wood is of significant importance when processing it with cutting tools: milling, sawing, peeling, as well as in those cases when it is subjected to abrasion during the construction of floors, stairs, railings.
Hardness of wood
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Ebony |
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White acacia |
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Olive |
Paduc |
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Yarra |
Afromosia |
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Kumaru |
Hornbeam |
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Lapacho |
Elm smooth |
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Amaranth |
Birch |
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Walnut |
Teak |
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Kempas |
Irokko (flounder) |
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Bamboo |
Cherry |
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Panga panga |
Alder |
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Wenge |
Larch |
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Guatambu |
Field maple |
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Norway maple |
Pine |
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Ash |
Korean pine |
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Merbau |
Aspen |
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Sucupira |
Kumier |
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Jatoba (Meryl) |
Pear |
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Swinging (mahogany) |
Sapelli |
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Dussie |
Linden |
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Turbulence |
Chestnut |
| Wood species | Hardness, MPa (kgf / cm 2) | ||
| for the surface of the cross section | for radial cut surface | for tangential cut surface | |
| Linden | 19,0(190) | 16,4(164) | 16,4(164) |
| Spruce | 22,4(224) | 18,2(182) | 18,4(184) |
| Aspen | 24,7(247) | 17,8(178) | 18,4(184) |
| Pine | 27,0(270) | 24,4(244) | 26,2(262) |
| Larch | 37,7(377) | 28,0(280) | 27,8(278) |
| Birch | 39,2(392) | 29,8(298) | 29,8(298) |
| Beech | 57,1 (571) | 37,9(379) | 40,2(402) |
| Oak | 62,2(622) | 52,1(521) | 46,3(463) |
| Hornbeam | 83,5(835) | 61,5(615) | 63,5(635) |
Impact strength characterizes the ability of wood to absorb work on impact without destruction and is determined by bending tests. The impact strength of deciduous wood is on average 2 times higher than that of coniferous wood. The impact hardness is determined by dropping a steel ball with a diameter of 25 mm from a height of 0.5 m onto the surface of the sample, the value of which is the greater, the lower the hardness of the wood.
Wear resistance - the ability of wood to resist wear, i.e. gradual destruction of its surface zones during friction. Tests for wear resistance of wood have shown that wear from the side surfaces is much greater than from the surface of the butt cut. With an increase in the density and hardness of the wood, wear has decreased. Wet wood has more wear than dry wood.
The ability of wood to hold metal fasteners: nails, screws, staples, crutches, etc. are its important property. When a nail is driven into wood, elastic deformations occur, which provide sufficient frictional force to prevent the nail from being pulled out. The force required to pull out a nail driven into the end of the specimen is less than the force applied to a nail driven across the grain. With increasing density, the resistance of wood to pulling out a nail or screw increases. The efforts required for pulling out screws (all other things being equal) are greater than for pulling out nails, since in this case the resistance of the fibers to cutting and tearing is added to the friction.
Basic technical properties of various tree species
| Wood species | Shrinkage ratio,% | Mechanical strength for wood with 15% moisture content, MPa (kgf / cm 2) | ||||
| radially | in tangential direction | for compression along the grain | bending | chipping | ||
| in the radial plane | in the tangential plane | |||||
| Conifers | ||||||
| Pine | 0,18 | 0,33 | 43,9 | 79,3 | 6,9(68) | 7,3(73) |
| Spruce | 0,14 | 0,24 | 42,3 | 74,4 | 5,3(53) | 5,2(52) |
| Larch | 0,22 | 0,40 | 51,1 | 97,3 | 8,3(83) | 7,2(72) |
| Fir | 0,9 | 0,33 | 33,7 | 51,9 | 4,7(47) | 5,3(53) |
| Hardwood trees | ||||||
| Oak | 0,18 | 0,28 | 52,0 | 93,5 | 8,5(85) | 10,4(104) |
| Ash | 0,19 | 0,30 | 51,0 | 115 | 13,8(138) | 13,3(133) |
| Birch | 0,26 | 0,31 | 44,7 | 99,7 | 8,5(85) | 11(110) |
| Maple | 0,21 | 0,34 | 54,0 | 109,7 | 8,7(87) | 12,4(124) |
| Elm | 0,22 | 0,44 | 48,6 | 105,7 | - | 13,8(138) |
| Elm | 0,15 | 0,32 | 38,9 | 85,2 | 7(70) | 7,7(77) |
| Deciduous trees | ||||||
| Aspen | 0,2 | 0,32 | 37,4 | 76,6 | 5,7(57) | 7,7(77) |
| Linden | 0,26 | 0,39 | 39 | 68 | 7,3(73) | 8(80) |
| Black alder | 0,16 | 0,23 | 36,8 | 69,2 | - | - |
| Black aspen | 0,16 | 0,31 | 35,1 | 60 | 5,8(58) | 7,4(74) |
Standard resistance of pure pine and spruce wood
| Resistance type and characteristics of elements under load | MPa (kgf / cm 2) |
| Resistance to static bending R t : | |
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16(160) |
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15(150) |
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13(130) |
| Compression resistance R squeeze and surface compression R p.szh : | |
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13(130) |
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1,8(18) |
| Compression resistance of local surface R p.szh : | |
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2,4 (24) |
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3(30) |
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4(40) |
| Resistance to stretching along the fibers R plant in : | |
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10(100) |
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8(80) |
| Resistance to splitting along the grain R reckoning in | 2,4(24) |
| Splitting resistance across R reckoning in fibers | 1,2(12) |
Average indicators of resistance of wood to pulling out nails
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Wood species |
Density, kg / m 3 |
Sizes of nails, mm |
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galvanized |
not galvanized |
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1.2 x 25 |
1.6 x 25 |
2 x 4 |
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Average resistance indicators in directions |
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radial |
tangential |
radial |
tangential |
radial |
tangential |
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Larch |
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The force required to pull out a nail driven into the end is 10-15% less than the force applied to a nail driven across the fibers.
The ability of wood to bend allows you to bend it. The ability to bend is higher in ring-vascular species - oak, ash, etc., and in scattered-vascular - beech; conifers have less bending ability. Wood is subjected to bending, which is in a heated and damp state. This increases the pliability of the wood and allows, due to the formation of frozen deformations during subsequent cooling and drying under load, to fix the new shape of the part.
Splitting wood is of practical importance, since some assortments are prepared by splitting (riveting, rim, knitting needles, shredding). The radial splitting resistance of hardwood is less than the tangential splitting. This is due to the influence of core rays (in oak, beech, hornbeam). In conifers, on the contrary, splitting is less along the tangential plane than along the radial one.
Deformability. Under short-term loads, mainly elastic deformations occur in wood, which disappear after loading. Up to a certain limit, the relationship between stresses and strains is close to linear (Hooke's law). The main indicator of deformability is the proportionality coefficient - the modulus of elasticity.
Elastic modulus along the grain E = 12-16 GPa, which is 20 times more than across the fibers. The higher the modulus of elasticity, the harder the wood is.
With an increase in the content of bound water and the temperature of the wood, its hardness decreases. In loaded wood, during drying or cooling, a part of elastic deformations is converted into “frozen” residual deformations. They disappear when heated or humidified.
Since wood consists mainly of polymers with long flexible chain molecules, its deformability depends on the duration of the load. The mechanical properties of wood, like other polymers, are studied on the basis of the general science of rheology. This science examines the general laws of deformation of materials under the influence of a load, taking into account the time factor.
And lumber and other assortments obtained from wood contaminated with spores of wood-destroying fungi bear signs of rot. Further, the development of rotten processes takes place in buildings. The damage caused by fungi to wood in warehouses is sometimes significant.
After a tree has been cut, the wood retains for some time the condition and properties inherent in the wood of a growing tree, and this> protects it from fungal damage. The main protective properties of felled wood at this time are high humidity, reaching 130% in conifers in sapwood and up to 70% of the absolutely dry weight of wood in heartwood, and bark, which is still intact and impervious to fungi. As the wood dries up, changes occur that contribute to its deterioration by fungi - this is a decrease in the moisture content of the wood, the formation of cracks in the ends and along the trunk, lagging of the bark, damage by insects. Most fungi develop on wood, the moisture content of which ranges from 20-150%. Wood with a moisture content below 20% is usually not affected.
Wood-coloring pioneers in the settlement of mushrooms on wood. Coloring of wood can be associated with the release of certain pigments by the fungi, but sometimes it is a purely optical phenomenon based on the diffraction of light between the colorless walls of wood cells and the darker hyphae of the fungus.
Studies of wood-coloring fungi on pine were carried out by V.V. Miller et al., E.I. Meyer, Yu.V. Ado, I.G. Krapivina, S.N. Gorshin, T.P. Sizova et al., I. A. Petrenko. The influence of these fungi on the strength, water absorption and moisture absorption of wood was determined, and the ability of blue-colored wood to decay more quickly in the ground was revealed. Thus, the fungus Ceratocystis (Ophiostoma) pini, which causes severe destruction of the secondary walls and numerous perforations of the tracheid walls, can reduce the resistance to impact bending by 34%.
V. Ya. Chastukhin and MA Nikolaevskaya identified several phases of decomposition of dead wood. The first phase is associated with the development of various wood-coloring fungi on wood. The next phase is determined by the activity of the main wood destroyers - Fomitopsis pinicola, Trametes squaveolens (Fr.) Fr., Lentinus squamosiis. The final stage is due to the development of fungi from the Agaricaceae family.
According to I.A.Petrenko, most of the imperfect mushrooms are not capable of decomposing wood. Imperfect mushrooms primarily use readily available organic compounds (starch, dextrins, fats and simple sugars), as well as the protoplasm of cells. And only a long-term (for 2-3 years) effect of these fungi on wood in optimal conditions for their existence causes destruction in the walls of the tracheids of late wood. But wood affected by blue fungi is destroyed by the main soil destroyers - higher fungi much more intensively than healthy wood. This is evidently due to the ability of blue fungi to destroy resins, which are natural bio-preservatives.
Under the influence of higher fungi, the destruction of pine wood samples reaches 55%, and the destruction by some imperfect fungi does not exceed 3%.
The most common wood color is blue caused by the marsupial fungi Ceratocystis (Ophiostoma) pini, C. coeruleu, Ceratocystis sp., C. pilifera and imperfect Cladosporium herbarum, Discula pinicola (Naum.) Petr. var. mammora Lagerh and others. For example, the marsupial fungus Ceratocystis (Ophiostoma) pilifera causes blue stains that penetrate deep into lumber. The perithecia of the fungus are formed on the black felt plexus of the mycelium, which causes the surface color (black spots and streaks). Its imperfect stage is Sphaeronaema piliferum Sacc.
Pink coloring wood is caused by the fungus Fusarium sambucinum Discula rubra H. Meyer. Discula brunneo-tingens H. Meyer causes brown coloration of pine sapwood.
Hulme points out that if some species of pines (P. strobus, P. lambertiana) after felling are in warm (125 °) and humid conditions for one or more days, then a brown color develops on the lumber with further artificial drying. Coloring proceeds quickly, often within the first 24 hours of artificial drying. Temperature, storage time, initial temperature during artificial drying have a strong influence on the intensity of the color. However, even in the most unfavorable conditions, no coloration develops on a part of the log. Often the coloration is located around the knots.
Hulme on the Pinus strobus sawlog to the most dangerous wood-coloring mushrooms includes Ceratocystis sp., Graphium sp., Altemaria sp., Phialophora sp., Cladosporium sp., Aurcobasidium sp.
Infection of wood occurs from the surface; the fungus quickly penetrates deep into the wood along the core rays. The optimum temperature for the growth of mushrooms is in the range of 20-25 °, at a temperature of 7-8 °, the growth of the fungus begins to slow down. When the moisture content of the wood is below 23% and more than 70%, the wood is not affected by the blue. The development of these fungi is very fast (5-6 days). The color of wood depends on the color of the hyphae penetrating into the wood cells and on the pigment secreted by the hyphae. Fungi feed on the contents of the sapwood parenchymal cells without destroying the cell walls. The chemical composition of wood under the influence of blue does not change noticeably, with the exception of a slight decrease in the amount of petosans.
According to the place of appearance and the degree of distribution, they distinguish lateral and end blue in round assortments, and in lumber - log and plaque. Lateral is typical for conifers, species, end - for non-nuclear deciduous. Plaid blue is observed as a spotted or solid blue-gray color of sapwood. The log blue has the appearance of spots and stripes at the edges.
Due to the fact that the fungus does not destroy cell membranes, it does not have a noticeable effect on the physical and mechanical properties of wood, but it is a defect that reduces its grade. Therefore, in some assortments of responsible or special purposes, wood with blue is not allowed. Most of the most common species of blue fungi do not significantly affect the mechanical properties of wood, even after prolonged exposure, but certain species, for example Cyratocvstis piceae (Munch.) Bakshi (Ophiostoma piceae), etc., can cause a significant decrease in some of its mechanical properties. Pine wood was mainly subjected to physical and mechanical tests. Blue does not significantly affect the strength of wood under static loads. Sometimes there is a decrease in static bending strength (up to 5%) and a reduced resistance to impact bending (by 10%). The latter is associated with a decrease in the amount of pentosans in the wood with blue color.
According to EI Meyer, the causative agents of the blue of the genera Harmonema, Leptographium accelerate the growth of house fungi (real, white and filmy). She believes the blue color may have an impact on the rate of infection by mushroom houses.
V.V. Miller et al. Note that dull wood is more easily wetted with water and absorbs it faster than healthy wood. Some species of blue fungus (Pullularia pullulans (de Vagu) Berhout, Leptographium lundbergii), by their presence in wood, stimulate the development of house fungi.
To mushrooms that cause the so-called stock rot and quite often found in forest stock exchanges, include Corticium laeve, Stereum sanguinalentum Alb. et Schw., Peniophora gigantea (Fr.) Mass. and other mushrooms. All of them are found on a round forest rolled out of the water. There are also pine and root sponges, bordered tinder fungus, honey fungus, etc.
Pine timber in warehouses is often populated with so-called warehouse mushrooms. Among them, there are groups that cause weak, medium and strong destruction of wood. Among the weak, it should be noted common cracker- Schizophyllum commune Fr. This fungus causes slight surface rotting of pine wood and other coniferous and deciduous species. It is found on stumps, valezha and dry forest trees. It is known as the crevice mushroom. Fruit bodies are usually located in crevices and look like small, 1-4 cm in diameter, thin, rounded caps attached at one point. Sometimes there is an anlage of a lateral pedicle. The surface of the caps is light gray, felt, with slightly curved edges. The hymenophore plates are fan-shaped. They are grayish or purple-brown, sometimes split, leathery.
Coniophora putcana (Schum. Ex Fr.) Karst. - filmy mushroom... Refers to medium-destructive mushrooms. Causes superficial brown or yellow destructive rot. Affected wood completely loses its mechanical strength and disintegrates into prisms. Fruiting bodies have the appearance of open brown films with a light fringed edge. A sterile white mycelium develops under the bark of the logs. Fruit bodies develop on the bark and under the bark of harvested round timber. Harvested wood is infected with round spores. The mycelium in wood grows mainly in the tracheids. In them, in addition to weakly branching hyphae up to 1 micron in size, there are also thick colorless hyphae up to 4 microns, collected in 2-3. Thin hyphae have medallion-like buckles. With the affected timber, the fungus is introduced into buildings. It is classified as one of the dangerous house mushrooms.
Among the strong destroyers in warehouses are the fence, or pole, sleeper, red-bordered mushrooms and the giant peniophora.
Gloeophyllum sepiarium (Fr.) Karst. - pole, or fence, mushroom... Often settles in various open structures (sheds, bridges, sleepers, poles, fences, sheds). It is found in forest warehouses, where it settles on long-term storage timber, as well as in the forest on stumps, valezha. It affects mainly coniferous wood saturated with moisture.
The wood affected by the fungus first turns yellow, then becomes reddish, and small cracks appear in it. At a later stage of decay, the wood turns light brown and cracks in annual layers. At the last stages of destruction, the rot becomes homogeneous, dark brown, and large radial cracks appear in it. In the cracks, clusters of yellowish-brown mycelium sometimes form. On the surface of the affected parts, a thin felt coating and thin cords of a dirty-white color are formed, which then take on a yellow, and later brownish color. Affected wood gives off a peculiar pleasant smell. Optimal conditions for the growth of mycelium are at 35, the minimum is about 5 °, the maximum is 44 °.
Fruit bodies usually develop in cracks in eroding materials. They look like thin, corky-leathery caps, attached sideways or half-spread. Their surface is dark brown, tuberous at the base, sometimes hairy with concentric zones. The edges are lighter, yellowish-brown. The hymenophore is light brown or rusty-brown, in the form of low branched plates, diverging f radially. The tissue of the fruiting body is 1-2 mm thick, cork, reddish brown.
Lentinus lepideus (Fr.) Fr. - sleepermushroom... It causes a very strong and rapid decay of wood and is the main destroyer of sleepers. It settles on coniferous wood (stumps, dead wood, sometimes on the trunks of living trees, stored timber, as well as in cellars, sheds, mines). The rot is brown, fissured, easily disintegrating into oblong pieces, crumbly. In the cracks of rotten wood, white deposits and thin films of mycelium are often formed. Over time, yellowish brown spots appear on the films.
Fruit bodies in the form of rather thick, dense, hardening caps up to 12 cm in diameter, with a dense central stem or somewhat displaced. The surface of the cap is creamy yellow or ocher red, covered with dark scales. The edges of the cap are thin, sinuous. The leg is scaly, yellowish, woody at the base. The plates of the hymenophore are incident, yellowish, serrated or dissected.
Peniophora gigantea - peniophora giant... It is considered an active destroyer of softwood. Usually found on unbarked wood. Rot has a fibrous, unclear corrosive structure. Affected wood at first almost does not change its color, then turns brown and softens, sometimes slight indistinct cracks appear. On the surface of the affected parts, whitish cotton-like, sometimes quite powerful mycelium films and very thin fan-shaped cords are formed. Fruit bodies are scarious, widely spread, dirty-white or yellowish, up to 50 cm long. In damp weather they swell, and when dry they become parchment-like and easily detach from the substrate. The hymenophore is completely smooth, pale, yellowish-gray. The fungus develops especially well on fresh timber, if their moisture content is more than 30%. Sometimes the fungus can develop in buildings, getting in with infected wood.
In addition to these fungi, pine wood (lumber and logs) in warehouses is destroyed by Hyphodontia arguta Erikss, H. subalutacea (Karst.) Erikss, Ceriporia giivescens, Sphaeronaema piliferum Sacc.
Warehouse mushrooms and mushrooms infecting pine timber with contaminated materials can get into various wooden structures, where they will cause destruction of wooden structures. Usually mushrooms that destroy wood in buildings are called brownies. A significant part of wood-destroying warehouse mushrooms ends up in buildings when using non-antiseptic or poorly impregnated wood.
Among house mushrooms there are species that are capable of destroying wood and growing trees (edged tinder fungus, honey fungus, etc.).
By causing the destruction of wooden structures, house mushrooms sometimes very quickly disable relatively new buildings. If 5% of wooden buildings die from fire, then 95% from mushrooms.
Most of the house mushrooms belong to the polyporaceae family and are represented by real, small brownies (S. minor), white house mushrooms, Fibuporia Vailantii (DC.ex Fr.) Bond, et Sing., Filmy brownies (Coniophora cerebella), and from this. Agaricnceae lamellar - mine (Paxilius acheruntius), etc.
According to A.M. Zhukov, in addition to these mushrooms in rural buildings, you can find mushrooms that are found in forest warehouses and in forest conditions. These are representatives of the genera Lentinus, Uloeophyllum, Fomitopsis, Coriolus, Funalia, Bjerkandera, Mycoleptodon, etc. Active destroyers. They usually attack hedges, temporary pens, sheds, etc., shortening the possible lifespan of the timber.
House mushrooms belong to the group of cellulose-destroying mushrooms. For their food, they use cellulose and similar substances. Therefore, the wood destroyed by them turns into a brown decaying mass, belonging to the type of destructive rot.
The defeat of wood and the growth of house mushrooms in it occurs as follows. The fungal hyphae initially penetrate into the core rays, and then pass into other elements of the wood. House fungi spread in wood by separate branching hyphae along the cell cavities and can easily penetrate the cell membranes anywhere, first causing their enzymatic dissolution.
House fungi hyphae usually grow in cell cavities. The walls collapse unevenly. Cellulose-destroying fungi primarily affect those areas of the cell membrane that are less stiff.
House mushrooms can infect wood with mycelium and spores. One fruiting body produces a million spores per day. Studies have shown that in the presence of several fruiting bodies of house mushrooms on the wood of the underground, 1 m 3 of air contained 79,000 spores of fungi, even in the rooms of the first floor in 1 m 3 of air there were 16,000 spores. Spores can be spread by air, water, insects (grinder beetle), rodents and the person himself (on clothes, shoes, with contaminated tools).
In relation to temperature, house mushrooms behave differently: optimum 20-27 °, minimum 5-9 °, maximum 35-37 °. Only a real house mushroom has a maximum of 26-27 °.
Most typical house mushrooms develop most vigorously in conditions of high humidity and immobility, stagnant air. If the wood contains no more than 18% moisture, then such wood is inaccessible to mushrooms. However, if the wood is already infected, then after it dries below 18% of the moisture content, the mycelium of house mushrooms can remain viable in it for up to 1-1.5 years, and when this wood is moistened, the decay process resumes.
The acidity of the substrate is also important for the development of the fungus. Most of them develop best at pH values of 3-6.
Direct sunlight slows down the growth of mycelium of house mushrooms. All other house mushrooms prefer to settle on coniferous wood (white house mushroom is never found on hardwood).
Infestation of buildings with house mushrooms and their development is facilitated by dampness in buildings due to leaking roofs, faulty water supply, insufficient heating, poor ventilation, etc. The infection with house mushrooms becomes noticeable when the process of wood destruction goes far. This is manifested in wall settlements, beams deflections, skewed door frames, unsteadiness of floors. In some places, the plaster is flaked and collapsed, and even fruiting bodies and films of the fungus appear. Most often, they form in damp corners of rooms, bathrooms, unheated rooms. The strong development of house mushrooms can lead to skewed floors, collapse of ceilings and interfloor ceilings. Destruction can occur within a year.
Serpula lacrymans - real mushroom house... This is the most dangerous mushroom. It can destroy large wooden structural elements within 6-10 months. This mushroom is also dangerous in that it has the ability to moisten wood and transfer moisture over long distances using special formations - cords. It is known that rotting 1 m 3 of wood produces 140 liters of water. This moisture moisturizes areas close to rotten wood and promotes the spread of rot in them.
The fungus forms lush, cotton-like clusters of mycelium. It is white at first, then sometimes canary yellow or pinkish in color. At the end, the mycelium collapses, turning into dirty gray films or pillows.
The spread of the fungus along the surface of the walls, from floor to floor, often occurs with the help of cords, the length of which can reach several meters. The cords are rather thick (up to 6-7 mm), sometimes flat, whitish or ash-gray, woody, brittle when dry.
Fruit bodies are wide-spread, sometimes very large (up to 0.5 m or more in diameter), thick, spongy, up to 1-4 cm thick, often adherent to the substrate, less often half-bent or free. The edge of the fruiting body is thickened, white when young, clearly visible. The hymenophore is in the form of low, twisting intertwining folds, cellular and sometimes coarse-mesh or sinuous-toothed. Its color is ocher yellow, then bright rusty to rusty brown. Cells up to 2-3 mm in diameter and approximately the same depth. On the clusters of mycelium and along the edges of the fruit bodies, drops of aqueous liquid are released, due to which the mushroom got its name (lacrymans means crying).
This mushroom house is found mainly in various floors and in closed structures of residential, factory and office buildings, as well as in basements, vegetable stores, poorly ventilated warehouses and other buildings.
Serpula minor - small mushroom house... Very similar to a real house mushroom. It is distinguished by the small size of the mycelium, the fruiting body with a brown-yellow color. Rot is similar to a real house mushroom. It is found mainly in ceilings above basements and in cellars.
Coriolus vaporarius (Fr.) Bond, et Sing - Whitebrowniemushroom... One of the most common house mushrooms. It develops a lush, flocculent or cotton-like, always white mycelium. In damp confined spaces, especially powerful clusters of loose mycelium, fibrous strands and cords are formed. The cords are thick (up to 4-6 mm), soft, unbreakable, weakly branched, white. In narrow spaces, the mushroom forms white films of a radiant-fan-shaped structure, sometimes in the form of layers of pressed cotton wool.
Fruiting bodies are very rare. They are usually small, outstretched, adherent, at first soft, sometimes in the form of a crust, with a narrow, indistinctly pronounced edge. The color of the fruiting body is whitish, subsequently yellowish to reddish, reddish-yellow. The hymenophore is tubular. The tubules are white, later yellowish or light brown. The pores are large, unequal, on average 1–2X1 µm, rounded or angular, first with solid and then finely toothed margins. This fungus occurs most often in the sterile (mycelial) stage. It is found in the interfloor ceilings of residential buildings, less often in forest warehouses and in outbuildings.
The destruction of wood under the influence of this fungus occurs very quickly. It is considered to be very dangerous, especially in the presence of a certain humidity and lack of ventilation. Infected wood at first takes on a brown color, then it cracks with transverse and longitudinal cracks into large prismatic areas, and in the final stage of decay it easily crumbles into powder. Only pine, spruce, fir, larch wood is affected by the white house fungus.
Paxillus acherutius - lamellar brownie, or mine, mushroom... The mycelium is initially very scanty, colorless, cobweb, later yellowing, sometimes with a violet or lilac tint, fan-like growing. Old grayish mycelium. The fungus also forms thin, filamentous, branched, intertwining cords, at first light, then greenish-yellow, sometimes forming a loose film.
Fruit bodies in the form of caps without a stem or with a short lateral stem. Caps 2-6 cm in diameter, thin, fleshy, of various shapes: often fan-shaped or shell-shaped, bifurcated, narrowed to the base, sometimes prostrate. The surface of the cap is yellowish ocher or dirty yellow, sometimes with a violet tinge or brown, pubescent or slightly tomentose, naked and smooth in old age. The edge of the cap is thin, sharp, tucked or straight, wavy-lobed. The fabric of the cap is soft, spongy, odorless. The plates of the hymenophore are radially diverging, narrow, wavy, soft, dichotomously branching, whitish when young, then egg-yellow or brownish.
Under favorable conditions, that is, when the moisture content of wood is 50-70% and the ambient air is at least 100%, lamellar mushroom causes rapid and strong destruction of wood, mainly pine. In the early stages of rot development, the affected wood becomes greenish-yellow, then turns brown, acquires a fibrous state and, finally, cracks mainly in the longitudinal direction.
The fungus is often found in subfloors, in the frames of houses and peat-backed ceilings, in cellars and especially in mines, where it is one of the main destroyers of fastening timber. In this regard, he received the name "mine" mushroom.
T.P. Sizova, S.N. Gorshin, I.G. Krapivina et al. Published diagnostic signs of a poorly studied species Stachybotrys macrocarpa (Sterigrnatobotrus macrocarpa), widespread on pine wood in contact with sandy soil, and causing its moderate rot (Kizhi ).
Widespread in warehouses and buildings as well mold rot capturing the upper layers of wood. At the same time, the wood becomes soft, when it dries, transverse cracks form on it. Such rot is caused by some marsupials and imperfect fungi (Chaetomium, Rhizoctonia, etc.). Mold rot affects pine and other wood in structures with a constantly humid environment (dams, lower parts of poles, sleepers, etc.).
Mold fungi, with prolonged exposure to wood, are capable of destroying the secondary walls of the tracheids in a manner close to "moderate rot".
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