Mechanical Properties Of Wood: What Does It Have? What Is Strength, What Does It Depend On And How Does It Differ From Elasticity? What Other Properties Are Mechanical?

2024 Author: Beatrice Philips | [email protected]. Last modified: 2024-01-15 04:10

Wood is a fairly popular material that finds its application in various areas of human life. At the same time, not every person knows that raw materials have a number of unique characteristics. Today in our article we will take a closer look at the mechanical properties of wood.

Peculiarities

The mechanical properties of wood characterize the overall quality of the material and are in direct proportion to it. The most important indicators of mechanical strength include the ability of a tree to withstand loads of both static and dynamic types.

For that to determine the mechanical properties that a material possesses, it is stretched, compressed, bent and sheared . It should be borne in mind that wood is called an anisotropic material, respectively, the raw material can have different properties depending on the direction in which it is affected. There are 2 directions in total: radial and tangential.

What is strength and what does it depend on?

The most important mechanical feature of wood is its strength. Strength characteristics have a direct impact on how and at what level a material can resist and resist unwanted fractures.

It is worth noting the fact that there is a direct relationship between strength and direction of impact on wood. So, the strength of the raw material is 20 times increased when the impact is along the fibers than if the pressure is applied across.

The middle (so-called "intermediate") class is occupied by conifers . Higher rates are characteristic, for example, for birch - that is why various supporting and supporting structures are very often made from it, as well as elements for which increased wear resistance is important.

It is interesting. Indicators of permissible strength and its limits (both minimum and maximum) cannot be determined independently at home. Such procedures are performed exclusively in laboratory conditions. At the same time, experiments and experiments are carried out exclusively on the basis of current state regulations.

It should be noted that the level of strength and elasticity is influenced by the level of moisture . So, when moistened, specific reactions occur inside the wood, which reduce its strength. Moreover, this provision is relevant only if the moisture level rises to 25%. Further moistening does not differ in any significant reactions and does not affect the strength indicators. Experts understand this.

For that to compare the strength indicators of different rocks, you need to make sure that their moisture indicators are identical - only in this case it is possible to speak about an objective and impartial result.

In addition to moisture, when measuring strength, it is also important to pay attention to the nature and duration of the loads . For example, static loads are constant. In addition, they are characterized by a slow and gradual increase. On the other hand, the dynamic loads are relatively short. One way or another, both loads can destroy wood.

It should also be borne in mind that strength indicators, its limits and limits differ depending on the specific type of deformation

Stretching . If we talk about the tensile strength of wood, then this indicator is 1,300 kgf / cm2 (and this parameter is relevant for all varieties). In such a situation, the internal structure of the wood is of decisive importance. If the fibers are arranged correctly and structured, then the strength increases (and vice versa). Strength differs depending on whether the wood is stretched along or across. In the first case, the indicator is quite large, and in the second, it is 20 times less and amounts to 65 kgf / cm2. It is because of these mechanical features that wood is rarely used to create products that work in transverse tension.

Compression . Like any other impact on wood, it can be carried out both in the longitudinal and transverse directions. If we talk about compression along the fibers, then it is worth noting that in this case the rock will shorten (this is how the deformation process will manifest itself outside). It should also be borne in mind that the strength of wood, which is compressed not along, but across, is significantly reduced, specifically by 8 times. In laboratory conditions, the tree is compressed in the radial and tangential directions. In the course of conducting such experiments, scientists have established for certain that the compressive strength of different rocks is not the same. So, rocks with core rays are distinguished by higher indicators under radial compression. On the other hand, conifers show fairly high strength values even under tangential compression.

Static bending . A distinctive feature of this type of impact, such as static bending, is that different layers of wood receive different effects, namely, the upper layers of wood receive compressive stress, and the lower ones - tension along the fibers. Between the upper and lower layers there is a special layer that does not experience any pressure. Traditionally, this layer is called neutral. Initially, the destruction of the material begins in the lower stretched zone, in connection with which the outermost fibers of the wood are torn. There is an average strength indicator, which is typical for a large number of wood species, it is 1,000 kgf / cm2 (while there may be deviations from this indicator, depending on the unique indicators of each specific species, as well as on the level of moisture).

Shift . Basically, shear is a deformation, which is the displacement of one part in relation to another. There are several different types of shear: shearing (it can occur in any direction) and shearing. In this case, it is especially important to monitor how strong the tree remains. So, chipping along negatively affects the strength indicators, the rock remains stronger during transverse chipping.

As we have seen, strength is the most important mechanical characteristic of wood. At the same time, a variety of influences can affect its level. All these factors should be taken into account during the operation of the material so as not to violate its integrity.

Other basic mechanical properties

In addition to strength, wood is also characterized by other mechanical and physical-mechanical properties. Let's take a closer look at the main ones.

Hardness

First of all, it is necessary to say about such a characteristic of a natural material as hardness. Hardness is one of the most important features of the material and is the ability of the raw material to resist in relation to the penetration of a solid body of a certain shape . Distinguish between end and side hardness (depending on the side of the material that is affected). The end hardness is higher in terms of its performance.

Important. It should be noted this fact: despite the fact that some wood species are distinguished by an increased level of hardness, this material is still inferior in these characteristics to such raw materials as, for example, metal.

Depending on the hardness indicators, such a building material as wood is divided into 3 main groups:

• soft (for example, pine, spruce, cedar, fir, linden, aspen, alder, chestnut, etc.);
• solid;
• extra hard.

Accordingly, in the manufacture of certain products, it is very important to take into account such a parameter as hardness. For example, it is desirable to make decorative elements from soft varieties, and only especially hard varieties are suitable for creating support structures.

The hardness of the wood is critical during the application and processing of the material . Depending on your specific needs and scope of application of wood, one or another option may be the most relevant and suitable.

Impact strength

Another important characteristic that differs between certain types of wood (for example, maple and spruce) is impact strength. This property designates and determines the ability of a material to absorb dynamic loads . At the same time, the higher the impact strength, the less damage and integrity violations you will observe on the tree in the process of applying these very dynamic loads. In general, we can say that for most breeds this indicator is at a fairly high level.

Wear resistance

Particular attention should be paid to wear resistance, since it is this parameter that determines whether the wood is capable of resisting in relation to prolonged frictional loads. Depending on how high the wear resistance is, the possible life of the material will vary significantly . The cutting direction and the unique characteristics of each particular wood species have a decisive influence on the level of wear resistance. It should be borne in mind that high wear resistance is characteristic of end surfaces. In terms of wear resistance, dry and wet wood differ - the first has a higher level.

The ability to hold metal mounts

As mentioned above, wood is one of the most popular, widespread and demanded materials that is used to create furniture, decorative elements and a large number of other products. Accordingly, when processing it, a large number of fasteners are driven into it, most often - metal . Therefore, such an indicator as the ability to hold metal fasteners is of paramount importance. So, for example, nails can cut or move apart the fibers of a tree, and screws can catch the fibers.

The ability to bend

In order to create functional and aesthetically pleasing products, wood must be folded. In this regard, the ability to bend is another important mechanical property of wood. Please note that different breeds have different levels of bending ability . So, for example, with regard to conifers, the rule is that when bending the needles must be moistened, but a dry tree practically does not bend (and when high pressure is applied, it can break at all).

Deformability

Deformation characteristics are also essential. They affect how quickly (if at all) tree species recover from a short-term dynamic impact on them. In combination with deformability, such a characteristic as the elasticity model also plays an important role.

Due to the fact that wood is used in various spheres of human life and is one of the most demanded materials, it is very important to know all its properties in detail. Accordingly, before using the material to create certain products (for example, furniture, decorative elements, etc.) all chemical, physical and mechanical properties should be carefully examined. Only then will your product be durable and reliable. Remember that different types of wood are suitable for different purposes. In addition, some rocks cannot be exposed at all, otherwise they will simply collapse. This knowledge is especially relevant for professional cabinetmakers and other representatives of the construction industry.