The mechanical properties of wood, are linked to its strength, i.e., the ability to withstand the action of external forces or stresses such as pressures, impacts, and tensions.
The use of this material, whether in its raw or semi-finished state, is widely prevalent in civil and naval constructions, carpentry works, the paper production industry, and artistic activities such as sculpture and cabinetmaking. This utilization primarily depends on its main characteristics, such as combustibility, lightness, availability, durability, and workability.
To better understand the advantages and disadvantages of the various types of wood, it is useful to know the physical properties, which are related to appearance, and the mechanical properties, which are related to the material's reactions to external forces. Understanding these properties can thus influence the applications and uses for which they are intended.
Physical properties
When wood is observed with the naked eye, it is already possible to identify its external characteristics, such as color, which can vary from white to yellow, red to brown, and even shades of dark brown and black. In addition to color, by looking at this material, one can discern the grain, which can be pronounced or almost imperceptible, enhancing its beauty. The physical properties of wood also include odor, hygroscopicity, elasticity, rigidity, density, strength, and hardness. Some of these characteristics give rise to what are defined as mechanical properties.
The cross-section of a wooden
By observing a cross-section of a wooden stem, a clear distinction of tissues can be made, grouped into two main zones: the first is called the cortical zone and includes the bark, which is the outer part that has no resistance; the phloem, which consists of a thin layer through which the plant's sap flows; and the cambium, a thin layer that develops the tissues of the more internal layers. The second zone is called the internal zone or wood, which includes the sapwood (the young, not yet fully formed wood), the heartwood, also known as the core (the innermost part), and the pith (a cylinder of soft, spongy tissue).
Compression strength
Wood is characterized by high compressive strength: particularly when used in construction, it needs to be very resistant to compression. This can be distinguished into two types based on the direction of the grain: perpendicular or parallel to the grain.
Perpendicular to grain
In the direction perpendicular to grain, the compressive strength is relatively low. For example, in softwoods, the strength is about nine times lower compared to that in the parallel direction.
Parallel to grain
When compression occurs along the grain, the strength is considerable and higher than in the perpendicular direction.
Shear strength
The ability to resist shear varies depending on whether the cut is made along the fibers or perpendicular to them: in the first case, the resistance is lower compared to the second case.
Tensile strength
The tensile strength of wood refers to its ability to withstand tension or stretching forces. This property varies significantly depending on the direction of the grain (wood exhibits its highest tensile strength when the force is applied parallel to the grain, while when the force is applied perpendicular to the grain, the tensile strength is significantly lower.
Traverse or bending strength
The traverse or bending strength of wood, also known as flexural strength, refers to its ability to resist deformation under load. This property is critical in applications where the wood will be subjected to bending forces, such as beams, joists, and other structural elements. The bending strength of wood can vary widely depending on species, moisture content, and grain orientation.
Torsional strength
Torsional strength is the ability to withstand torsional loads and refers to how well wood can resist stress before breaking.
Breathability of wood
Breathability, or the ability of wood to be permeated by vapor molecules, is generally very high in wooden materials, especially when used in structures and buildings. The higher the breathability, the less condensation will form on the surface of the material, providing two important advantages: greater durability of the material and a higher degree of thermal insulation. Compared to other construction materials, wood is much more breathable than concrete or brick masonry.
Thermal conductivity
Understood as the amount of heat a material can transmit, wood has a low thermal conductivity, thereby ensuring excellent insulation properties.
Hardness
Hardness in wood refers to its resistance to indentation or scratching. It's typically measured using standardized tests like the Janka hardness test, which involves measuring the force required to embed a steel ball into the wood surface to a certain depth.
Mechanical properties of wood related to processing and use
The mechanical characteristics of wood depend on various factors such as the dry specific gravity, moisture content, fiber direction relative to the stress, and the presence of knots and other physical characteristics of the material. These factors determine the wood's suitability for processing.
Predisposition to cut
The predisposition to cut, a critical characteristic influencing the primary woodworking techniques (both manual and mechanical), can be achieved with tools that produce chips or sawdust. It is highest parallel to the grain and minimal perpendicular to it. Predisposition to cut can vary based on wood type and even within different parts of the same wood type.
Predisposition to folding
The predisposition to folding indicates how easily wood maintains its shape after pressure is applied and released. This characteristic depends on the wood's composition and type. For instance, woods like ash, beech, and larch are more prone to bending, while oak, maple, and walnut are less flexible.
Fendibility
Closely related to flexibility is the fendibility, which is the ability to split along the grain. Wood with long, regular fibers and no knots is more splitable, allowing for cutting without tearing. Species like spruce, alder, and chestnut are more prone to splitting.
Workability
This characteristic indicates how well a material can be processed or undergo a specific production process. For example, spruce, known for its softness, is easy to work with and cut, as are maple and chestnut. However, larch, despite having highly elastic fibers, is difficult to work with due to its high resin content.
Choosing the type of wood: the latest trends
There are multiple types that differ not only in aesthetics but also in various characteristics and intended uses. Understanding the physical and mechanical properties of wood allows you to choose the right type based on your processing needs.
Soft or hard, durable, and high-quality wood has always been a trendy material in furniture and design. Thanks to its versatility and eco-sustainability—qualities that enhance its beauty—wood is now a key element in living spaces. Currently, the focus on eco-design and sustainability is gaining more and more attention: a new trend is recycled wood or wood with FSC certification, which guarantees that the material comes from responsibly managed forests.
Among the latest trends, there is a preference for minimalism, the choice of neutral and natural colors, and the search for unexpected combinations of different but refined styles.
Important factors to consider when selecting a CNC machine
After discovering the physical and mechanical characteristics of wood, you have all the elements to choose the CNC machine that best suits your needs and processes. Depending on your industry sector, requirements, and the intended use of wood, we can offer you various CNC technologies. Visit our product range page to discover which technology is most suitable for you.