The degradation of longitudinal elasticity modulus occurs with the increase of the number of cycles, so after 20 alternating symmetrical cycles of traction-compression of the pine wood samples, there is a decrease of its values by 35%. The https:// ensures that you are connecting to the From the preliminary results, the cyclic loading will range between 1 kN and 2 kN, with loading speeds of 1 mm/min and 10 mm/min. 2227 February 2005. Wood is Swedens most traditional building material. info@swedishwood.com. ; validation, M.D.S. IOP Conf.
The sapwoods cells are also dead, except for about 510 percent, which are the nutrient-carrying parenchyma cells. In the case of the variation of the compression strains, a rapid increase of them is observed with the increase of the stress cycles, regardless of the intensity of the force, as can be seen in Figure 5b,d,f. Since wood is widely used in construction for structural frames, exterior and interior wall cladding, fittings, floor coverings, formwork and scaffolding, the list goes on it is important to understand how wood behaves under different conditions. During the growth season, new cells are formed in the vascular cambium. In the inner part of the stem, in the juvenile wood near the pith, the growth rings are often broad with thin summerwood bands. Learn more Bethesda, MD 20894, Web Policies The reason for this is that the summerwood band, the dark part of the growth ring, is wider in southern Sweden. This layer transports nutrients (carbohydrates) down through the stem and distributes them to the living cells in the trees branches, stem and roots. sharing sensitive information, make sure youre on a federal The effective thermal value of pine and spruce as a fuel is 19.3MJ per kg dry substance. The structure of pine samples in different degradation stages: (a) initial macros-structure of wood samples, before test; (b) optical view of wood fracture after test; (c) microscopic view of tracheid cells failure, magnification 100; (d) failure trend line, magnification 100; (e) schematic representation of traction deformation; (f) schematic representation of wood failure due to anisotropy.
Numerous factors affect woods burning properties: primarily moisture content, dimensions, density and fibre direction. Because the failure plane is not perpendicular to the applied load direction, the tensile strength consists of the total or effective stress, which has normal and shear stresses as components, as claimed by Christoforo et al. 29 The woods cells and composition, Fig. At compression parallel to the fibers, the structural changes begin with the increase of the stress level, and the instability of the fibers is observed by the appearance of some macroscopic kinks [6,21,25].
[14] and Andrianopoulos et al. So, the objective of the current study is to analyze the degradation of mechanical properties and structural failure produces by symmetric axial cyclic loading of Scots pine samples (Pinus sylvestris). Ion F., Taranu N., Secu A., Entuc I.S., Scutaru M.C., Ungureanu D. Evaluation of the wood strength class using the experimental approach. Note When calculating load-bearing capacity and stiffness, use the characteristic values stated in Eurocode 5, plus the associated national annex Boverkets frfattningssamling, BFS 2019:1 EKS 11. The density is therefore higher in a butt log than in a middle log or top log. The annual ring width of specimens ranges between 1.5 mm to 3 mm, so the Scots pine wood samples shows larger spreading of its annual values as Silvestru Grigore et al. 8600 Rockville Pike The time until ignition can vary greatly and depends on thermal radiation, ventilation and the presence of a naked flame. ; formal analysis, H.D.T. ; resources, H.D.T. [15] developed a three-dimensional orthotropic mechanical and mathematical model of wood, taking into account both the components of total deformation and rheological expressions, principles of moisture-stress analysis. Compression strength is high in the fibre direction, with the grain, but much lower, around 1/6, across the grain. During the compression stress, a part of the deformations produced at traction is recovered, adding to these the shortening of the wood, after which the resumption cycle. The true elastic strain range e (the strains from A to D points) represents the recovery strain after a complete cycle and total true plastic strain range p (the strains from D to 0 points) is the permanent strain after a complete loading cycle. This study reveals that, in the strength calculations and in the design norms, it is necessary to introduce some coefficients that take into account the speed of wood degradation at cyclical stresses. The strains values collected for first cycle, where is the total strain range; ethe true total elastic strain range; pthe true total plastic strain range; telongation strain; ccompression strain. Based on ASTM 04.10 Wood D143-09 [19] and EN 408 (2010) + A1 (2012) [20], the procedures and samples for axial cyclic tests were developed. Hassani M.M., Wittel F.K., Hering S., Herrmann H.J. government site. Dendrochronology is a method of determining the age of a tree.Sweden has continuous tree ring chronologies of oaks and pines dating back around 1,500 years. Fakoor M., Sabour M.H., Khansari N.M. A new approach for investigation of damage zone properties in orthotropic materials. The fura is the mature tree, where the diameter of the heartwood is more than half the diameter of the stem.. Wood has good thermal properties and solid wood has been used historically as a thermal insulation material. We are grateful to Transilvania University of Brasov, rector Ioan Vasile Abrudan for financial publication support. 2630 July 2015. The paper aims to analyze the viscoelastic behavior of pine wood subjected to cyclically loading to traction-compression with different loads (1 kN; 1.5 kN; 2 kN), applied at different speeds (1 mm/min; 10 mm/min). A three-dimensional plasticity-damage constitutive model for timber under cyclic loads. Silvestru Grigore C.V., Dinulic F., Sprchez G., Hllian A.F., Dinc L.C., Enescu R.E., Crian V.E. Wood, generally considered to be a viscous-elastic material, has creep deformations over time under the effect of a constant load. The novelty of the paper consists of better understanding of the mechanical behavior of softwood and determination of the hysteresis loops to tensile and compression. SE-102 04 Stockholm Pine is commonly used for joinery, mouldings and internal cladding, although spruce may be used. 40 Vertical grain Edge-glued panels and glulam panels are usually made from wood with a vertical grain for good dimensional stability.
The tensile and compression displacements were measured simultaneously with applied loading (Figure 2b,c). Fig. The mechanical properties of wood, respectively the elastic, plastic, and strength properties, depend on a large number of factors, due both to its structural and physical characteristics, as well as to the size, direction, nature, and speed of application of forces. Gong et al. There are also 26 percent extractive substances in the wood. endobj
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i!y a=/W,f<0cc dI9Oc?K}TUC8l%x&>Yc&F?3`ZsQ. Three types of variables they analyzed in experiments: the thermal treatment temperature (160, 190, and 220 C), the number of bending oscillations (103, 505 103 and 106), and the equilibrium moisture content at target climates of 20 C and 35%, 65%, and 95% relative humidity (RH). We advise that you only use the original value or one of its raw conversions in your calculations to minimize rounding Wood consists of a very complex system of fibers, cells, cementing substances, etc., whose physical and chemical cohesion poses particular problems in the calculations of strength and rigidity, compared to homogeneous and isotropic materials such as, for example, metals [4,5,6]. In addition, Swedish Wood represents the Swedish glulam and packaging industries, and collaborates closely with Swedish builders merchants and wholesalers of wood products..
Basic densityis defined as the mass of the dry wood sample divided by the volume of the fully hydrated wood sample. Knots and other fibre distortions (peculiarities) also affect the woods technical properties. The summerwood cells, which form during the summer months, are 2025 percent longer and have much thicker cell walls than the springwood. FOIA We are grateful to Timar Cristina Maria for permission to use the microscopic views (Figure 9) from Catalog of micro-structural characteristics of materials for restoration and ecodesign (December 2009), CNCSIS Project IDEI 856/2008: Creation and implementation of a scientific research methodology on restorationwood preservation and eco-design in the perspective of sustainable development.
Due to their own specific properties, each type of wood has typical areas of use. [23] which studied the pine wood samples subjected to tensile stresses. This is the case whether the load is caused by compression, tension or flexural stresses in the wood. Spruce is the wood of choice for construction timber. ; investigation, M.D.S. 1 0 obj Series: Materials Science and Engineering.
(Figure 6). [16,17] investigated the rheological characteristics of the black locust wood samples chemical treated with ammonia [16] and natural fibers composites [17] in terms of complex modulus, with its two components (the conservation modulus E and the loss modulus E) and the damping factor were determined dynamic mechanical analysis (DMA). Pine is easier to plane without getting this tear-out. and M.D.S. Varenik K.A., Varenik A.S., Sanzharovskij R.C. ; funding acquisition, M.D.S. official website and that any information you provide is encrypted These have the same values both in traction and compression. Generally speaking, gradual fractures, which account for most fractures in wood, are preferable. In Figure 1b, the characteristic curves of pine wood samples to different speed loading are presented. Stanciu M.D., ova D., Savin A., Ilia N., Gorbacheva G. Physical and Mechanical Properties of Ammonia- Treated Black Locust Wood. The strength is also affected by the moisture in the wood, its temperature and the period under which it is stressed. Degradation of mechanical properties of wood samples subjected to symmetrical cyclic stresses accompanied by microstructure degradation of wood. The values for strength and modulus of elasticity are average values, and refer to small test samples, with no imperfections, at an average temperature of 20C. and H.D.T. Thus, the late wood and early wood can be considered composite layers [1,2]. The lower parts of the stem need to be stronger to resist the stresses of wind and snow. Bending strength is usually measured with the grain. Thus, the first kinks develop between the late wood tracheids, at the boundary between two growth rings, the phenomenon spreading to the early wood tracheids. In terms of strength, pine and spruce are treated the same, and they are normally judged to have the same strength values: Stiffness and hardness may also be included in the strength properties. Burning wood only generates moderate amounts of smoke. Here you can easily find descriptions of many termes related to wood and wood industry. Storgatan 19 Yildirim M.N., Uysal B., Ozcifci A., Ertas A.H. Konstantinov et al.
Wood cladding with a thickness of 18 mm ( 12 mm without air gap behind the wood cladding) meets fire resistance classification D according to the European surface classes in standard SS-EN 13501-1. Bull. The cells in the heartwood are dead and some have been clogged up with resin, which means that they cant carry water and thus have a relatively low moisture content, 3050%. This is the case along the whole length of the tree. Technical data for pine and spruce is presented in table 6. The load-bearing capacity of wooden structures in a fire can be worked out mathematically. As the force increases, the law of variation of the wood flow changes. Accessibility Material properties vary between the different wood species.
The thermal capacity of wood is relatively high at around 1,300 J per kg C for absolutely dry wood. With planed timber, spruce often has slight tear-out both around and in the knot. Compare table 6. This is despite the fact that southern Swedish wood generally has broader growth rings than wood from northern Sweden. The main three zone in case of compression can be difficult distinguished, but the viscous-elastic behavior of wood is more pronounced in these cases (Figure 5cf). For data acquisition, the Nexygen Plus software was used. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (, pine wood, symmetric axial cyclic loading, viscous-elastic behavior, degradation of mechanical properties, creep. The moisture content of the sapwood varies from 120160%. Degradation rate of Youngs Modulus with cyclic loading. 36 Different fibre distortions in the wood, Fig. Sign up and get information about publications and other newsfrom Swedish Wood by email. The microscopic structure of pine wood before loading can be seen in Figure 9, in the three main sections of wood. Gong and Smith [1], Pinho et al. Taking into account the structural changes produced by cyclic stresses as well as the modification of the tensile breaking section of wooden samples, Christoforo et al.
In spite of the differences between pine and spruce, they should be considered equal in terms of building statics. 1416 July 1999; pp.
Mechanical and Rheological Behaviour of Composites Reinforced with Natural Fibres. [3] noticed.
This allows us to see which pages are visited most and which ones we need to improve or develop, while also giving us insights into how visitors move around the site. The input data of tested samples are presented in Table 1. They noticed that the fatigue failures began to occur as the stress level was or above 40% of Scots pine specimens average of modulus of rupture (MOR) and for beech specimens, fatigue failures began to occur when the stress level was above 50% of beech specimens average MOR. Since the sapwoods cells are not clogged with resin, they are able to carry water and dissolved nutrients from the roots to the needles of the tree. Shear strength is higher across the grain than with the grain, and so in most cases the shear strength with the grain is the critical factor, for example at the supported ends of a beam. Fig. Due to the alternating symmetrical cycles, it is found that the total true plastic deformation represents approximately 20% of the total value of the deformations. A high modulus of elasticity means high stiffness. Property values marked by an asterisk (*) have been taken from an unusually old reference source. Sharapov E., Mahnert K.C., Militz H. Residual strength of thermally modified Scots pine after fatigue testing in flexure. 12 kW/m2. The behavior of the tested specimens differs in the two types of axial stresses. ; writingreview and editing, H.D.T. Inst. The proportion of summerwood is thus higher, which gives the mature wood a higher density and strength. Table 6 Physical data for pine and spruce. display the information in a consistent format. In wood flooring, the springwood therefore wears more quickly than the summerwood.
Stanciu M.D., Teodorescu D.H., Tma F., Terciu O.M. and V.S. Maria Cristina TIMAR, Transilvania University of Brasov, Faculty of Wood Engineering). The wood species analyzed in this research was Scots pine samples (Pinus sylvestris) with 12% moisture contents (provided by the norm EN 384: 2004) [18]. When a length of wood with high stiffness is bent, it doesnt give very much, remaining quite straight. In Figure 8, the percentage variations of tensile and compression strains are presented for each studied case. The Swedish Forest Industries Federation, 2022. Softwood. The values obtained give us an image of the quality class of the Scots pine samples studied, namely that they are part of quality class C45 according to wood standard. Some of the values displayed above may have been converted from their original units and/or rounded in order to Strictly necessary cookies make a website usable by supporting basic functions such as page navigation and access to secure parts of the website. Master curves: (a) tensile strains of sample P3 subjected to 1 mm/min and F = 1kN; (b) compression strains of sample P3 subjected to 1 mm/min and F = 1kN; (c) tensile strains of sample P6 subjected to 1 mm/min and F = 1.5 kN; (d) compression strains of sample P6 subjected to 1 mm/min and F = 1.5 kN; (e) tensile strains of sample P9 subjected to 1 mm/min and F = 2kN; (f) compression strains of sample P9 subjected to 1 mm/min and F = 2 kN. The new PMC design is here! [11] performed studies applying asymmetric sinusoidal cyclic oscillations at 20 Hz frequency and load ratio p = 0.3. Phone: Tensile strength is high with the grain, but much lower, around 1/30, across the grain.
The fracture of samples was analyzed with optical devices. However, due to the anisotropic characteristics of wood and the different strength of late wood and early wood layers, the fracturing mechanism does not occur in one direction [4]. PMC legacy view
Wood, due to its polymeric and layered structure, is considered a natural composite material. The cells that are formed in spring and early summer are short and relatively wide, with thin walls. Please, End. Sharapov et al. ; supervision, V.S. The preliminary test: (a) tensile test; (b) characteristic curves of pine wood subjected to tensile with different loading speeds. Postal address: Load-bearing wooden structures should be designed, built and checked in line with Swedish building regulations BBR-BFS 2011:6. 28. Swedish Woods aim is to increase the size and value of the market for Swedish wood and wood products in construction, interior design and packaging. The difference between extensions and shortenings depends on the intensity of the force applied and the loading speed. In the tangential-longitudinal section, the parenchyma rays with nuclei are very visible (Figure 9b). Rheological Model for Wood. Cookies for analysis allow us to count the number of visits and to see the sources of traffic to the website. Their widths, proportion and density vary, depending on the specific environment and soil conditions from year to year [3]. the wood fibres misalignments lead to shearing stresses between the fibres and longitudinal cracks or parenchyma rays disposals act as stress concentrators. Wood retains a significant load-bearing capacity even during a fire, not least due to the protective charred layer that forms on the burnt surface. Thermal conductivity is greatest in the direction of the fibres, and increases with the moisture level and density. See also fig. The longer wood is placed under stress, the more its strength reduces. Federal government websites often end in .gov or .mil. Variation of symmetric cyclic loading to tensile-compression: (a) 1000 N; (b) 1500 N; (c) 2000 N. Figure 4 shows the hysteresis loop for the first stress cycle, being highlighted the values of lengthening and shortening the sample. Moreover, the resin canal can be observed in the transversal section. [13] examined the fatigue and static strength of Scots pine and beech wood subjected to bending test. HHS Vulnerability Disclosure, Help Growth improves after thinning due to better access to light and nutrients, and conversely growth can fall if a tree has grown too close to other larger neighbouring trees. You can also find links to relevant pages in Choosing Wood. The site is secure. Even within the same wood species, there are major variations between trees grown in different locations, but also between different trees grown in the same location. Before
Pine tends to have oval knots. Also, the structural modifications of wood cells are presented by means of optical microscope. In the first stage, a set of samples with different loading speeds were tested for tensile to rupture, in order to establish the maximum value of the load to alternating symmetrical cyclic stresses (Figure 1a). Archit. All authors have read and agreed to the published version of the manuscript. Short-term mechanical behaviour of softwood in high-stress-level compression parallel to grain; Proceedings of the Fourth International Conference on the Development of Wood Science, Wood Technology and Forestry; Missenden Abbey, UK. Konstantinov A.Y., Lomunov A.K., Iuzhina T.N., Gray G.T., III Investigation of wood anisotropy under dynamic loading. The degree of bending depends on the grain of the wood and on its modulus of elasticity. The charring rate is around 0.51.0 mm per minute. Users requiring more precise data for scientific or engineering
In this study, axially symmetrical cyclic loads (traction-compression) samples of pine wood in the direction parallel to the grain were tested. Higher levels of thermal radiation are required for ignition without a naked flame. 1) Does not fall into class E and must not be used in buildings under Boverkets Building Regulations (BBR). Figure 2 shows the experimental equipment and some details from tests.
Forest products reduce our climate footprint, Climate-positive products that build the future, Working environment and living environment, Wood construction systems in the building process, Factory-painted and quality-assured external cladding, Moroccan designers explore the potential of Swedish pine. The second category of pine specimens denoted with A10; B10; C10 was subjected at a speed of 10 mm/min, having similarly to the first category, three sets of samples tested at different intensities of the applied load. All the values relate to wood with 12% moisture content. Based on the Boltzmann superposition principle, which describes the response of a material to different loading histories and fitting the deformations peaks for each cycle [21,22], in Figure 5af are graphically represented the master curves covering the accumulated peak deformations in tensile (Figure 5a,c,e) and compression tests (Figure 5b,d,f). and M.D.S. Brownian dynamics investigation of the Boltzmann superposition principle for orthogonal superposition rheology. error. If you dont want to accept all cookies, you can change your settings by clicking Manage settings. ASTM D143-14 Standard Test Method for Small Clear Specimen of Timber. Fig. Fractures may be gradual or brittle. Regarding the behaviour of Scots pine (Pinus sylvestris) as control samples and thermally modified subjected to cyclic bending, Sharapov et al. Comparison of strains in cases of different load speeds and intensity: (a) tensile and compression strains; (b) total true elastic and plastic strain range after a complete cycle. Visiting address: No vendors are listed for this material. and V.S. Ferreira D., Fonseca E., Pinto C., Borges P. Tensile strength of pine and ash woodsexperimental and numerical study; Proceedings of the 6th International Conference on Mechanics and Materials in Design; Ponta Delgada, Azores. The total strain range (the strains from A to C points) is calculated as total of tensile strain and compression strain containing both elastic and plastic strains. In the centre of the stems cross-section sits the pith, which runs through the whole tree and terminates at the top with a bud.
They noticed that at a low strain rate, the damage to the specimen was seen to be insignificant, while at a high strain rate the integrity of the specimen was exceeded leading to sample failure. The width of growth rings and the proportion of summerwood varies within the stem. As such, it is possible to see indicators of good and poor growth years, and how the conditions for growth have been affected by different silviculture measures. The fibre direction deviates from the direction of the forces at knots and when the fibres are not parallel with the edge of the wood. The specimens were loading with a constant speed of 1 mm/min and then 10 mm/min, being subjected successive to 1 cycle, 10 cycles and 20 cycles. Feio A., Machado J., Lourenco P. Parellel to the grain behavior and NDT correlations for chestnut wood (Castanea sativa Mill); Proceedings of the International Conference Conservation of Historic Wooden Structures; Florence, Italy. Thus, after 20 alternately symmetrical cycles, the longitudinal modulus of elasticity decreases by approximately 28%, and with the increase of the loading speed, for some cases, there was even destruction of the samples. Summerwood, which weighs 900 kilos per cubic metre dry wood, is three times denser than springwood, which weighs 300 kilos per cubic metre dry wood. Some studies analyze the fatigue behavior of chemically or thermally modified wood compared to control samples, finding that both the modulus of bending elasticity (MOE) increased by about 21% in the case of pine wood modified by impregnation with phenol formaldehyde resin [10]. With pine there is a clear difference between the darker heartwood and the sapwood. An application to Bridgman experiments. A brittle fracture is sudden and occurs without warning. ; software, H.D.T. Force required to imbed a 0.444 inch steel ball to one-half its diameter, Side. In the radial section, can be noticed the axially aligned tracheid cells with different sizes in late wood and early wood (Figure 9c). Similar to the composite materials and kinking fibres of them studied by Pinho et al.
The density is therefore low in the wood near the pith, compared with the mature wood further out along the radius of the stem. The 18th cases as combination between loading intensity, number of cycles and speed of loading were analyzed on samples of solid wood of Scots pine cut radially, having the nominal dimensions of length L = 150 mm, width b = 15 mm, thickness h = 5 mm (Figure 2a).
The sapwoods cells are also dead, except for about 510 percent, which are the nutrient-carrying parenchyma cells. In the case of the variation of the compression strains, a rapid increase of them is observed with the increase of the stress cycles, regardless of the intensity of the force, as can be seen in Figure 5b,d,f. Since wood is widely used in construction for structural frames, exterior and interior wall cladding, fittings, floor coverings, formwork and scaffolding, the list goes on it is important to understand how wood behaves under different conditions. During the growth season, new cells are formed in the vascular cambium. In the inner part of the stem, in the juvenile wood near the pith, the growth rings are often broad with thin summerwood bands. Learn more Bethesda, MD 20894, Web Policies The reason for this is that the summerwood band, the dark part of the growth ring, is wider in southern Sweden. This layer transports nutrients (carbohydrates) down through the stem and distributes them to the living cells in the trees branches, stem and roots. sharing sensitive information, make sure youre on a federal The effective thermal value of pine and spruce as a fuel is 19.3MJ per kg dry substance. The structure of pine samples in different degradation stages: (a) initial macros-structure of wood samples, before test; (b) optical view of wood fracture after test; (c) microscopic view of tracheid cells failure, magnification 100; (d) failure trend line, magnification 100; (e) schematic representation of traction deformation; (f) schematic representation of wood failure due to anisotropy.
Numerous factors affect woods burning properties: primarily moisture content, dimensions, density and fibre direction. Because the failure plane is not perpendicular to the applied load direction, the tensile strength consists of the total or effective stress, which has normal and shear stresses as components, as claimed by Christoforo et al. 29 The woods cells and composition, Fig. At compression parallel to the fibers, the structural changes begin with the increase of the stress level, and the instability of the fibers is observed by the appearance of some macroscopic kinks [6,21,25].
[14] and Andrianopoulos et al. So, the objective of the current study is to analyze the degradation of mechanical properties and structural failure produces by symmetric axial cyclic loading of Scots pine samples (Pinus sylvestris). Ion F., Taranu N., Secu A., Entuc I.S., Scutaru M.C., Ungureanu D. Evaluation of the wood strength class using the experimental approach. Note When calculating load-bearing capacity and stiffness, use the characteristic values stated in Eurocode 5, plus the associated national annex Boverkets frfattningssamling, BFS 2019:1 EKS 11. The density is therefore higher in a butt log than in a middle log or top log. The annual ring width of specimens ranges between 1.5 mm to 3 mm, so the Scots pine wood samples shows larger spreading of its annual values as Silvestru Grigore et al. 8600 Rockville Pike The time until ignition can vary greatly and depends on thermal radiation, ventilation and the presence of a naked flame. ; formal analysis, H.D.T. ; resources, H.D.T. [15] developed a three-dimensional orthotropic mechanical and mathematical model of wood, taking into account both the components of total deformation and rheological expressions, principles of moisture-stress analysis. Compression strength is high in the fibre direction, with the grain, but much lower, around 1/6, across the grain. During the compression stress, a part of the deformations produced at traction is recovered, adding to these the shortening of the wood, after which the resumption cycle. The true elastic strain range e (the strains from A to D points) represents the recovery strain after a complete cycle and total true plastic strain range p (the strains from D to 0 points) is the permanent strain after a complete loading cycle. This study reveals that, in the strength calculations and in the design norms, it is necessary to introduce some coefficients that take into account the speed of wood degradation at cyclical stresses. The strains values collected for first cycle, where is the total strain range; ethe true total elastic strain range; pthe true total plastic strain range; telongation strain; ccompression strain. Based on ASTM 04.10 Wood D143-09 [19] and EN 408 (2010) + A1 (2012) [20], the procedures and samples for axial cyclic tests were developed. Hassani M.M., Wittel F.K., Hering S., Herrmann H.J. government site. Dendrochronology is a method of determining the age of a tree.Sweden has continuous tree ring chronologies of oaks and pines dating back around 1,500 years. Fakoor M., Sabour M.H., Khansari N.M. A new approach for investigation of damage zone properties in orthotropic materials. The fura is the mature tree, where the diameter of the heartwood is more than half the diameter of the stem.. Wood has good thermal properties and solid wood has been used historically as a thermal insulation material. We are grateful to Transilvania University of Brasov, rector Ioan Vasile Abrudan for financial publication support. 2630 July 2015. The paper aims to analyze the viscoelastic behavior of pine wood subjected to cyclically loading to traction-compression with different loads (1 kN; 1.5 kN; 2 kN), applied at different speeds (1 mm/min; 10 mm/min). A three-dimensional plasticity-damage constitutive model for timber under cyclic loads. Silvestru Grigore C.V., Dinulic F., Sprchez G., Hllian A.F., Dinc L.C., Enescu R.E., Crian V.E. Wood, generally considered to be a viscous-elastic material, has creep deformations over time under the effect of a constant load. The novelty of the paper consists of better understanding of the mechanical behavior of softwood and determination of the hysteresis loops to tensile and compression. SE-102 04 Stockholm Pine is commonly used for joinery, mouldings and internal cladding, although spruce may be used. 40 Vertical grain Edge-glued panels and glulam panels are usually made from wood with a vertical grain for good dimensional stability.
The tensile and compression displacements were measured simultaneously with applied loading (Figure 2b,c). Fig. The mechanical properties of wood, respectively the elastic, plastic, and strength properties, depend on a large number of factors, due both to its structural and physical characteristics, as well as to the size, direction, nature, and speed of application of forces. Gong et al. There are also 26 percent extractive substances in the wood. endobj
+46 8 762 72 60
x[ms7G]&dnLqbw$(]Z|c9{tV5?O81 ghEwEK\7^78d2dpII "K?BIm\/r|.n$_w%i}ag~XA*z2a6
i!y a=/W,f<0cc dI9Oc?K}TUC8l%x&>Yc&F?3`ZsQ. Three types of variables they analyzed in experiments: the thermal treatment temperature (160, 190, and 220 C), the number of bending oscillations (103, 505 103 and 106), and the equilibrium moisture content at target climates of 20 C and 35%, 65%, and 95% relative humidity (RH). We advise that you only use the original value or one of its raw conversions in your calculations to minimize rounding Wood consists of a very complex system of fibers, cells, cementing substances, etc., whose physical and chemical cohesion poses particular problems in the calculations of strength and rigidity, compared to homogeneous and isotropic materials such as, for example, metals [4,5,6]. In addition, Swedish Wood represents the Swedish glulam and packaging industries, and collaborates closely with Swedish builders merchants and wholesalers of wood products..
Basic densityis defined as the mass of the dry wood sample divided by the volume of the fully hydrated wood sample. Knots and other fibre distortions (peculiarities) also affect the woods technical properties. The summerwood cells, which form during the summer months, are 2025 percent longer and have much thicker cell walls than the springwood. FOIA We are grateful to Timar Cristina Maria for permission to use the microscopic views (Figure 9) from Catalog of micro-structural characteristics of materials for restoration and ecodesign (December 2009), CNCSIS Project IDEI 856/2008: Creation and implementation of a scientific research methodology on restorationwood preservation and eco-design in the perspective of sustainable development. Due to their own specific properties, each type of wood has typical areas of use. [23] which studied the pine wood samples subjected to tensile stresses. This is the case whether the load is caused by compression, tension or flexural stresses in the wood. Spruce is the wood of choice for construction timber. ; investigation, M.D.S. 1 0 obj Series: Materials Science and Engineering.
(Figure 6). [16,17] investigated the rheological characteristics of the black locust wood samples chemical treated with ammonia [16] and natural fibers composites [17] in terms of complex modulus, with its two components (the conservation modulus E and the loss modulus E) and the damping factor were determined dynamic mechanical analysis (DMA). Pine is easier to plane without getting this tear-out. and M.D.S. Varenik K.A., Varenik A.S., Sanzharovskij R.C. ; funding acquisition, M.D.S. official website and that any information you provide is encrypted These have the same values both in traction and compression. Generally speaking, gradual fractures, which account for most fractures in wood, are preferable. In Figure 1b, the characteristic curves of pine wood samples to different speed loading are presented. Stanciu M.D., ova D., Savin A., Ilia N., Gorbacheva G. Physical and Mechanical Properties of Ammonia- Treated Black Locust Wood. The strength is also affected by the moisture in the wood, its temperature and the period under which it is stressed. Degradation of mechanical properties of wood samples subjected to symmetrical cyclic stresses accompanied by microstructure degradation of wood. The values for strength and modulus of elasticity are average values, and refer to small test samples, with no imperfections, at an average temperature of 20C. and H.D.T. Thus, the late wood and early wood can be considered composite layers [1,2]. The lower parts of the stem need to be stronger to resist the stresses of wind and snow. Bending strength is usually measured with the grain. Thus, the first kinks develop between the late wood tracheids, at the boundary between two growth rings, the phenomenon spreading to the early wood tracheids. In terms of strength, pine and spruce are treated the same, and they are normally judged to have the same strength values: Stiffness and hardness may also be included in the strength properties. Burning wood only generates moderate amounts of smoke. Here you can easily find descriptions of many termes related to wood and wood industry. Storgatan 19 Yildirim M.N., Uysal B., Ozcifci A., Ertas A.H. Konstantinov et al.
Wood cladding with a thickness of 18 mm ( 12 mm without air gap behind the wood cladding) meets fire resistance classification D according to the European surface classes in standard SS-EN 13501-1. Bull. The cells in the heartwood are dead and some have been clogged up with resin, which means that they cant carry water and thus have a relatively low moisture content, 3050%. This is the case along the whole length of the tree. Technical data for pine and spruce is presented in table 6. The load-bearing capacity of wooden structures in a fire can be worked out mathematically. As the force increases, the law of variation of the wood flow changes. Accessibility Material properties vary between the different wood species.
The thermal capacity of wood is relatively high at around 1,300 J per kg C for absolutely dry wood. With planed timber, spruce often has slight tear-out both around and in the knot. Compare table 6. This is despite the fact that southern Swedish wood generally has broader growth rings than wood from northern Sweden. The main three zone in case of compression can be difficult distinguished, but the viscous-elastic behavior of wood is more pronounced in these cases (Figure 5cf). For data acquisition, the Nexygen Plus software was used. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (, pine wood, symmetric axial cyclic loading, viscous-elastic behavior, degradation of mechanical properties, creep. The moisture content of the sapwood varies from 120160%. Degradation rate of Youngs Modulus with cyclic loading. 36 Different fibre distortions in the wood, Fig. Sign up and get information about publications and other newsfrom Swedish Wood by email. The microscopic structure of pine wood before loading can be seen in Figure 9, in the three main sections of wood. Gong and Smith [1], Pinho et al. Taking into account the structural changes produced by cyclic stresses as well as the modification of the tensile breaking section of wooden samples, Christoforo et al.
In spite of the differences between pine and spruce, they should be considered equal in terms of building statics. 1416 July 1999; pp.
Mechanical and Rheological Behaviour of Composites Reinforced with Natural Fibres. [3] noticed.
This allows us to see which pages are visited most and which ones we need to improve or develop, while also giving us insights into how visitors move around the site. The input data of tested samples are presented in Table 1. They noticed that the fatigue failures began to occur as the stress level was or above 40% of Scots pine specimens average of modulus of rupture (MOR) and for beech specimens, fatigue failures began to occur when the stress level was above 50% of beech specimens average MOR. Since the sapwoods cells are not clogged with resin, they are able to carry water and dissolved nutrients from the roots to the needles of the tree. Shear strength is higher across the grain than with the grain, and so in most cases the shear strength with the grain is the critical factor, for example at the supported ends of a beam. Fig. Due to the alternating symmetrical cycles, it is found that the total true plastic deformation represents approximately 20% of the total value of the deformations. A high modulus of elasticity means high stiffness. Property values marked by an asterisk (*) have been taken from an unusually old reference source. Sharapov E., Mahnert K.C., Militz H. Residual strength of thermally modified Scots pine after fatigue testing in flexure. 12 kW/m2. The behavior of the tested specimens differs in the two types of axial stresses. ; writingreview and editing, H.D.T. Inst. The proportion of summerwood is thus higher, which gives the mature wood a higher density and strength. Table 6 Physical data for pine and spruce. display the information in a consistent format. In wood flooring, the springwood therefore wears more quickly than the summerwood.
Stanciu M.D., Teodorescu D.H., Tma F., Terciu O.M. and V.S. Maria Cristina TIMAR, Transilvania University of Brasov, Faculty of Wood Engineering). The wood species analyzed in this research was Scots pine samples (Pinus sylvestris) with 12% moisture contents (provided by the norm EN 384: 2004) [18]. When a length of wood with high stiffness is bent, it doesnt give very much, remaining quite straight. In Figure 8, the percentage variations of tensile and compression strains are presented for each studied case. The Swedish Forest Industries Federation, 2022. Softwood. The values obtained give us an image of the quality class of the Scots pine samples studied, namely that they are part of quality class C45 according to wood standard. Some of the values displayed above may have been converted from their original units and/or rounded in order to Strictly necessary cookies make a website usable by supporting basic functions such as page navigation and access to secure parts of the website. Master curves: (a) tensile strains of sample P3 subjected to 1 mm/min and F = 1kN; (b) compression strains of sample P3 subjected to 1 mm/min and F = 1kN; (c) tensile strains of sample P6 subjected to 1 mm/min and F = 1.5 kN; (d) compression strains of sample P6 subjected to 1 mm/min and F = 1.5 kN; (e) tensile strains of sample P9 subjected to 1 mm/min and F = 2kN; (f) compression strains of sample P9 subjected to 1 mm/min and F = 2 kN. The new PMC design is here! [11] performed studies applying asymmetric sinusoidal cyclic oscillations at 20 Hz frequency and load ratio p = 0.3. Phone: Tensile strength is high with the grain, but much lower, around 1/30, across the grain.
The fracture of samples was analyzed with optical devices. However, due to the anisotropic characteristics of wood and the different strength of late wood and early wood layers, the fracturing mechanism does not occur in one direction [4]. PMC legacy view
Wood, due to its polymeric and layered structure, is considered a natural composite material. The cells that are formed in spring and early summer are short and relatively wide, with thin walls. Please, End. Sharapov et al. ; supervision, V.S. The preliminary test: (a) tensile test; (b) characteristic curves of pine wood subjected to tensile with different loading speeds. Postal address: Load-bearing wooden structures should be designed, built and checked in line with Swedish building regulations BBR-BFS 2011:6. 28. Swedish Woods aim is to increase the size and value of the market for Swedish wood and wood products in construction, interior design and packaging. The difference between extensions and shortenings depends on the intensity of the force applied and the loading speed. In the tangential-longitudinal section, the parenchyma rays with nuclei are very visible (Figure 9b). Rheological Model for Wood. Cookies for analysis allow us to count the number of visits and to see the sources of traffic to the website. Their widths, proportion and density vary, depending on the specific environment and soil conditions from year to year [3]. the wood fibres misalignments lead to shearing stresses between the fibres and longitudinal cracks or parenchyma rays disposals act as stress concentrators. Wood retains a significant load-bearing capacity even during a fire, not least due to the protective charred layer that forms on the burnt surface. Thermal conductivity is greatest in the direction of the fibres, and increases with the moisture level and density. See also fig. The longer wood is placed under stress, the more its strength reduces. Federal government websites often end in .gov or .mil. Variation of symmetric cyclic loading to tensile-compression: (a) 1000 N; (b) 1500 N; (c) 2000 N. Figure 4 shows the hysteresis loop for the first stress cycle, being highlighted the values of lengthening and shortening the sample. Moreover, the resin canal can be observed in the transversal section. [13] examined the fatigue and static strength of Scots pine and beech wood subjected to bending test. HHS Vulnerability Disclosure, Help Growth improves after thinning due to better access to light and nutrients, and conversely growth can fall if a tree has grown too close to other larger neighbouring trees. You can also find links to relevant pages in Choosing Wood. The site is secure. Even within the same wood species, there are major variations between trees grown in different locations, but also between different trees grown in the same location. Before
Pine tends to have oval knots. Also, the structural modifications of wood cells are presented by means of optical microscope. In the first stage, a set of samples with different loading speeds were tested for tensile to rupture, in order to establish the maximum value of the load to alternating symmetrical cyclic stresses (Figure 1a). Archit. All authors have read and agreed to the published version of the manuscript. Short-term mechanical behaviour of softwood in high-stress-level compression parallel to grain; Proceedings of the Fourth International Conference on the Development of Wood Science, Wood Technology and Forestry; Missenden Abbey, UK. Konstantinov A.Y., Lomunov A.K., Iuzhina T.N., Gray G.T., III Investigation of wood anisotropy under dynamic loading. The degree of bending depends on the grain of the wood and on its modulus of elasticity. The charring rate is around 0.51.0 mm per minute. Users requiring more precise data for scientific or engineering
In this study, axially symmetrical cyclic loads (traction-compression) samples of pine wood in the direction parallel to the grain were tested. Higher levels of thermal radiation are required for ignition without a naked flame. 1) Does not fall into class E and must not be used in buildings under Boverkets Building Regulations (BBR). Figure 2 shows the experimental equipment and some details from tests.
Forest products reduce our climate footprint, Climate-positive products that build the future, Working environment and living environment, Wood construction systems in the building process, Factory-painted and quality-assured external cladding, Moroccan designers explore the potential of Swedish pine. The second category of pine specimens denoted with A10; B10; C10 was subjected at a speed of 10 mm/min, having similarly to the first category, three sets of samples tested at different intensities of the applied load. All the values relate to wood with 12% moisture content. Based on the Boltzmann superposition principle, which describes the response of a material to different loading histories and fitting the deformations peaks for each cycle [21,22], in Figure 5af are graphically represented the master curves covering the accumulated peak deformations in tensile (Figure 5a,c,e) and compression tests (Figure 5b,d,f). and M.D.S. Brownian dynamics investigation of the Boltzmann superposition principle for orthogonal superposition rheology. error. If you dont want to accept all cookies, you can change your settings by clicking Manage settings. ASTM D143-14 Standard Test Method for Small Clear Specimen of Timber. Fig. Fractures may be gradual or brittle. Regarding the behaviour of Scots pine (Pinus sylvestris) as control samples and thermally modified subjected to cyclic bending, Sharapov et al. Comparison of strains in cases of different load speeds and intensity: (a) tensile and compression strains; (b) total true elastic and plastic strain range after a complete cycle. Visiting address: No vendors are listed for this material. and V.S. Ferreira D., Fonseca E., Pinto C., Borges P. Tensile strength of pine and ash woodsexperimental and numerical study; Proceedings of the 6th International Conference on Mechanics and Materials in Design; Ponta Delgada, Azores. The total strain range (the strains from A to C points) is calculated as total of tensile strain and compression strain containing both elastic and plastic strains. In the centre of the stems cross-section sits the pith, which runs through the whole tree and terminates at the top with a bud.
They noticed that at a low strain rate, the damage to the specimen was seen to be insignificant, while at a high strain rate the integrity of the specimen was exceeded leading to sample failure. The width of growth rings and the proportion of summerwood varies within the stem. As such, it is possible to see indicators of good and poor growth years, and how the conditions for growth have been affected by different silviculture measures. The fibre direction deviates from the direction of the forces at knots and when the fibres are not parallel with the edge of the wood. The specimens were loading with a constant speed of 1 mm/min and then 10 mm/min, being subjected successive to 1 cycle, 10 cycles and 20 cycles. Feio A., Machado J., Lourenco P. Parellel to the grain behavior and NDT correlations for chestnut wood (Castanea sativa Mill); Proceedings of the International Conference Conservation of Historic Wooden Structures; Florence, Italy. Thus, after 20 alternately symmetrical cycles, the longitudinal modulus of elasticity decreases by approximately 28%, and with the increase of the loading speed, for some cases, there was even destruction of the samples. Summerwood, which weighs 900 kilos per cubic metre dry wood, is three times denser than springwood, which weighs 300 kilos per cubic metre dry wood. Some studies analyze the fatigue behavior of chemically or thermally modified wood compared to control samples, finding that both the modulus of bending elasticity (MOE) increased by about 21% in the case of pine wood modified by impregnation with phenol formaldehyde resin [10]. With pine there is a clear difference between the darker heartwood and the sapwood. An application to Bridgman experiments. A brittle fracture is sudden and occurs without warning. ; software, H.D.T. Force required to imbed a 0.444 inch steel ball to one-half its diameter, Side. In the radial section, can be noticed the axially aligned tracheid cells with different sizes in late wood and early wood (Figure 9c). Similar to the composite materials and kinking fibres of them studied by Pinho et al.
The density is therefore low in the wood near the pith, compared with the mature wood further out along the radius of the stem. The 18th cases as combination between loading intensity, number of cycles and speed of loading were analyzed on samples of solid wood of Scots pine cut radially, having the nominal dimensions of length L = 150 mm, width b = 15 mm, thickness h = 5 mm (Figure 2a).