Compression Strength Of Wood Research Articles

Design and application of impact limiter for a spent fuel transport cask

As a key component of the spent fuel cask, the impact limiter can avoid the leakage of radioactive substances caused by the destruction of the container during the transport process and ensure the safe transport of nuclear spent fuel. In order to design a impact limiter that meets the engineering requirements, the effect of impact limiter size on the damping effect of the transport container was studied. The dispersity of wood compressive strength was obtained by wood compressive strength test. The 9m over center of gravity angle drop analysis of the transport container was carried out using the finite element method, and the 9m over center of gravity angle drop test was also carried out. The container acceleration and impact limiter deformation obtained by the test were consistent with the simulation results. The impact limiter of the cask is reasonably designed and can provide shock absorption and cushioning to the transport container. Generally speaking, the larger the size of the impact limiter, the more energy it absorbs but the damping effect decreases after its size exceeds a certain point. The simulation results show that when the energy absorption of the impact limiter is sufficient, the cushioning effect of wood with low compressive strength is better and the effect of wood compressive strength dispersity should be fully considered in the design.

Experimental analysis of passively and actively reinforced glued-laminated timber with focus on ductility

ABSTRACT When glued-laminated timber are subjected to bending moment, they usually fail in a brittle way in the tension zone before the compressive zone reaches the compressive strength of wood. This means that the compression strength of wood is not fully exploited. By reinforcing the tension zone, the failure mode of glued-laminated timber can be changed from tensile to compressive. As a result, by utilizing the higher compressive strength, reinforced glued-laminated timber become stronger and the failure mode becomes compressive and ductile. This paper presents experimental results of the effect of steel reinforcements in the tension zone of glued-laminated timber. Four passively reinforced beams, four actively reinforced beams, and seven unreinforced beams were tested to failure in four-point bending tests. The experimental results confirmed the brittle tension failure in the unreinforced beams as well as the ductile and compressive failure in the reinforced beams. Furthermore, the experiments revealed the increase of the passively and the actively reinforced glued-laminated timber relative to the reference beams for strengths (26% and 39%) and stiffnesses (30% and 11%). Ductilities were increased from 7.7% for the reference beams to 90% and 75% for the passively and the actively reinforced glued-laminated timber, respectively.

Phase change material impregnated wood for passive thermal management of timber buildings

The Scots pine (Pinus sylvestris L.) sapwood was impregnated with the eutectic mixture of capric acid (CA) and stearic acid (SA) as phase change material (PCM) via vacuum process for passive thermoregulation in timber buildings. The hygroscopic properties, mechanical properties, thermal energy storage (TES) characteristics and lab-scale thermo-regulative performance of wood/CA-SA composite were evaluated. The produced composite from PCM was morphologically and physico-chemically characterized by SEM, FT-IR and XRD analysis. Thermal energy storage (TES) properties, cycling chemical/thermal reliability, and thermal degradation stability of the produced composite were determined by TG/DTA and DSC analysis. The hygroscopic tests revealed that the wood/CA-SA composite showed low water absorption (WA) and high anti-swelling efficiency (ASE) after 264 hours in water. Wood treatment with CA-SA increased the bending and compression strength of wood. TG/DTA data demonstrated that the wood/CA-SA composite left higher residue of 10.31% at 800°C than that of wood with 6.87%. The DSC measurements showed that the obtained wood/CA-SA composite had a good TES capacity of about 94 J/g at 23.94°C. The cycling DSC results confirmed the eutectic PCM in wood indicated high chemical stability and storage/release reliability even though it was run 600 times melt/freeze. According to thermal performance test, the wood/CA-SA composite has ability of storing excess heat in the environment and preventing the heat flow to the environment. It can be concluded that the fabricated wood/CA-SA composite can be used for indoor temperature regulation and energy saving in timber buildings.

Mechanical properties and water resistance of Vietnamese acacia and rubberwood after thermo-hygro-mechanical modification

Low density and poor mechanical performance often limit utilisation of sawn wood from fast-growing plantation forests. Thermo-hygro-mechanical modification (THM) of timber is one innovation for improving the properties of light-weight wood species. The objective of this study was to determine the effects of THM and subsequent thermal treatment on dry density, modulus of elasticity (MOE), compression strength, Brinell hardness, and swelling behaviour in immersion tests on two fast-growing Vietnamese species, acacia (Acacia mangium) and rubberwood (Hevea brasiliensis). Test boards were modified in an industrial kiln, in which a tangential thickness compression of 14% and 12% were aimed for acacia and rubberwood, respectively, either with or without subsequent thermal treatment at 210 °C. Dry density, MOE, Brinell hardness, compression strength, and dimensional changes in water immersion tests of specimens were measured from the modified and unmodified reference materials, the latter ones being kiln dried at 50 °C. The results showed that the responses of the mechanical properties were more evident for rubberwood than for acacia. In rubberwood, the MOE and compression strength of wood thermo-hygro-mechanically modified with or without thermal treatment were higher than those of kiln-dried reference specimens throughout the thickness profile. In case of acacia, similar differences between the modified and reference specimens were observed only in the surface layer. Density and Brinell hardness of thermo-hygro-mechanically modified rubberwood were higher than those of reference specimens, but after thermal treatment they did not differ from (acacia) or were lower (rubberwood) than those of THM specimens. Post-compression thermal treatment increased the hydrophobicity of THM specimens.

Prediction methodology for wood compression strength based on particle-filtered near-infrared spectroscopy

The measurement of wood mechanical properties is important for engineering design and applications. This study investigated near-infrared (NIR) spectroscopy coupled with particle filter (PF) and partial least-squares (PLS) methods to predict wood compression strength. Three structural timbers (Acer mono, birch, and toothed oak) were studied. The NIR spectra were collected from 900 to 1700 cm-1 and preprocessed by a standard normal variate transformation combined with Savitzky-Golay filtering. The prediction model coefficient matrix and standard variance were obtained by a PF iterative process, and their ratio was used to select the NIR feature wavelength points. A PLS prediction model based on NIR spectroscopy was established to predict the wood compression strength. Compared with the successive projection algorithm (SPA) and Kalman filtering (KF), the PF-PLS prediction model outperformed the other models in all three wood samples, resulting in a high correlation coefficient (r) of 0.89, 0.92, and 0.90, a low root-mean-square error of prediction (RMSEP) of 6.30, 10.60, and 9.71, and a fast average detection speed of 0.28 s, 0.46 s, and 0.33 s, respectively. The optimal PF selection can effectively reduce the redundant information of the NIR matrix and improve the accuracy and efficiency of the prediction model.

The variability of wood density and compression strength of Norway spruce (Picea abies/L./Karst.) within the stem

This study relates to the variability of wood density and compression strength parallel to grain within the stem of spruce trees (Picea abies/L./Karst.). The sample tree originated from the Giant Mountains and was an adult autochtonous mountain spruce. The properties were analysed for wood that formed between 1850 and 1990 along (1) the north-south oriented radius and along (2) the stem height on test specimens with the following dimensions: 20×20×30 mm, prepared from logs taken from the stem base at distances of 2, 4, 6, 10, 14, 20, 22, 24 and 26 m. In individual sections, the properties of the samples oriented in the north or south direction did not differ, while the effect of different ages on the properties showed statistically significant differences at each orientation (p < 0.05). Along the radius, the properties showed an increasing trend in tree-rings that developed between 1850 and 1940 with a slight decrease in the following years. The coefficient of variation in various decades was 1–7 % (wood density) and 3–15 % (wood compression strength). Along the stem height, the properties gradually increased to a height of 20 m, while the increase in values ​​was more pronounced in the 22–26 m interval. The variability of the wood properties along the stem height corresponded to the variability of the properties along the stem radius. A linear dependence between wood strength and density was demonstrated. Compared to what had been previously written, wood density showed a greater impact, probably due to the biomechanical optimization of the stem with regard to mechanical wind and snow loads in the mountains.

Effect of microwave heating on compressive strength of beech wood (Fagus sylvatica L.) parallel to grain

ABSTRACTThis article deals with the changes of strength of beech wood (Fagus sylvatica L.) when compression load is applied parallel to grain and the wood is heated using microwave (MW) energy for a time period determined by two variants of drying. The elasticity modulus and compressive strength parallel to grain were measured using a universal testing machine in accordance with a relevant technical standard. Regression equations describing the dependence of compressive strength on wood density were determined for both variants of heating with a given load. Furthermore, a three-factor analysis of variance was performed to verify the significance of possible factors influencing changes of wood strength and elasticity. Possible hypotheses of changes caused by MW heating and the significance of discovered factors are also discussed. The results showed reduction of average values of wood compressive strength parallel to grain. The values were reduced by 35% in variant 1 and by 41% in variant 2 as opposed to wood to which no MW energy was applied. The difference in strength between the variants was nearly 9%.

Improving the permeability of Douglas-fir (Pseudotsuga menziesii) containing compression wood by Physisporinus vitreus and Xylaria longipes

The bioincising impact of Physisporinus vitreus and Xylaria longipes on the porous structure, and permeability of Douglas-fir containing compression wood was investigated. Fungal cultivation was carried out at 25°C and 85% relative humidity in an incubator for three time periods, namely, 15, 30 and 45 days. Safranin solution was injected into wood specimens to evaluate liquid permeability whereas air permeability was measured by the falling-water method. Wood exposure to both fungi enhanced permeability by increasing incubation period. However, the parallel compression strength of wood reduced. Microscopic imagery revealed degradation of bordered pits, bore-hole formation through tracheid walls as well as ray damage which are thought to be main reasons for improvements in air and liquid permeability. No pronounced differences were found between the fungi in their effects on permeability. Parenchyma rays were also shown to play an important role in the radial permeability of Douglas-fir compression wood.

Assessing the wood compressive strength in pile foundations in relation to diagnostic analysis: The example of the Church of Santa Maria Maggiore, Venice

Foundation piles are a noteworthy example of waterlogged wood still constituting load bearing structures. Micromorphological analysis, investigation of physical properties (water content, residual basic density), compressive tests in wet conditions and chemical analyses (lignin, holocellulose) were carried out on samples taken in Venice. Obtained results demonstrated that both mass and strength were lost due to decay, but the residual strength loss was greater than the residual mass. It is also shown that this occurrence was due to the holocellulose decrease. Present results point out that basic density and holocellulose amount could be used as possible predictors of woodpiles residual strength.

Hygro-mechanical behavior of thermally treated beech subjected to compression loads

The physical and mechanical properties of beech wood (Fagus sylvatica L.) were determined after industrial thermal treatment in a steam atmosphere. Parallel clear uniaxial compression specimens (20×20×20mm) were made from control and thermally treated wood, conditioned in a series from an oven dry to saturated atmosphere (20°C) and compression loaded parallel and transverse to the grain. The reduced density of thermally treated beech was reflected in the decreased stiffness and, especially, strength of wood transverse to the grain. No impact of thermal treatment on the longitudinal compression strength of wood was confirmed. Lower hygroscopicity was additionally detected with thermo-modified wood, whereas the relationship between wood moisture content and stiffness (MOE/MOE0), as well as strength (σ/σ0), along and transverse to the grain of the beech wood remained identical.

Influence of wood treatments on mechanical properties of wood–cement composites and of Populus Euroamericana wood fibers

Wood–cement composites are interesting materials for structural and isolation purposes. Dimensional stability, economic factors and resistance to environmental degradation are features that can be exploited for housing components. The main inconvenient affecting its manufacture is the incompatibility between wood and cement, caused by setting inhibitory substances present in woods. Wood treatments are multivariable processes required for the appropriate cement setting reaction on wood surfaces. Treatment conditions affect the mechanical properties of the resulting composites. This work evaluates the simultaneous influence of the variables ruling three widely used wood treatments – water extraction, degradation by alkaline hydrolysis and retention of inhibitory substances – on the mechanical properties of wood fibers and of resulting wood–cement composites. Populus Euroamericana wood fibers and Portland cement were selected as case materials. The alkaline hydrolysis was found as the most effective treatment for the suppression of inhibitory substances and the highest decrease on mechanical properties of resulting composites. Empirical relationships describing the dependence of the compressive modulus of elasticity and compression strength of wood–cement composites with the wood treatment variables are presented.

Oil Uptake Percentage in Oil-Heat-Treated Wood, its Determination by Soxhlet Extraction, and its Effects on Wood Compression Strength Parallel to the Grain

Oil heat treatment can effectively improve the dimensional stability and bio-durability of wood. However, the characteristics of high oil uptake (50 percent or higher) and high susceptibility to leaching from wood have an adverse effect on subsequent manufacturing processes of wood product and production costs. A solvent extraction (100% ethanol) process was used to extract the surplus oil from the treated wood. Because the making of powder specimens from high oil uptake wood would result in experimental error, a new method of determination of oil uptake percentage was proposed by two step Soxhlet extraction with ethanol. The oil uptake percentage of oil-heat-treated poplar wood at 180 oC for 2 h with this method was determined to be 113.29%. Additionally, the average oil uptake percentage (OUP) of oil-treated poplar after the oil extraction process for 2 and 6 h was 54.82% and 29.11%, respectively. Moreover, the average oil extraction percentage (OEP) of specimens with the oil extraction process at the first step (wood sticks) in the Soxhlet extractor apparatus was larger than that of oil-heat-treated poplar specimens. Due to the combined effect of chemical changes in the wood at high temperatures and of oil uptake by the wood, the compression strength parallel to the grain changed at different OUP levels.

Mechanical behaviour of pine wood chemically modified with a homologous series of linear chain carboxylic acid anhydrides

The work described in this paper demonstrated that acetylation of pine wood up to 16.4 weight percent gain has a positive effect on the compression strength. Higher modification levels resulted in a reduction of the compression strength of wood, compared to the untreated wood. A comprehensive investigation of the effect of molecular size of the substituent group of softwood modified with linear chain carboxylic acid anhydrides, namely acetic, propionic, butyric, valeric, hexanoic, upon the compression strength has also been performed. It was found that the improvement of compression strength imparted by chemical modification is independent of the degree of bulking of the cell wall, but correlates well with the degree of substitution of the cell wall hydroxyl groups.

Variability of spruce (Picea abies [L.] Karst.) compression strength with present reaction wood

The aim of research was to find out the variability of spruce (<I>Picea abies</I> [L.]) Karst.) wood compression strength limits in the direction parallel to grain. The wood strength was examined using samples from a tree with present reaction (compression) wood. The strength was found out for individual stem zones (CW, OW, SWL and SWR). The zone with present compression wood (CW) demonstrated slightly higher values of wood strength limits. The differences in the limits of compression strength parallel to grain in individual zones were not statistically significant. All the data acquired by measuring were used to create 3D models for each zone. The models describe the strength along the radius and along the stem height. The change of strength along the stem radius was statistically highly significant. There was an obvious tendency towards an increase in the strength limit in the first 40 years. With the increased stem height, there is a slight decrease in wood strength.

Effect of wood species and glue type on contact stresses in a mortise and tenon joint

New technologies for wood building construction continue to employ various profile-adhesive joints, with mortise and tenon joints being the most popular. Their strength depends both on the wood species and type of the applied glue, as well as the execution accuracy of individual elements. The aim of the performed experiments was to determine the size of normal stresses in places of mutual pressures of the tenon and mortise and the impact of the change of wood species and the type of glue (or lack of glue) applied to the joint on the value of those stresses. It was established, on the basis of numerical calculations, that the phenomena of the tenon and mortise contact are caused both by the bending of the tenon as well as by the torsion of the glue bond. Stresses in the direction perpendicular to the fibre course generating pressures exceeding wood compression strength turned out to be the most dangerous for the tenon and mortise joint. The value of the linear elasticity modulus of the glue bond exerts a decisive influence on the stress values caused by the mutual pressures of the elements of the examined joint.

Does growing on a slope affect tree xylem structure and water relations?

Variations in slope, exposure, relief and substrate over a short distance and their influences on plant function are poorly understood. We investigated the influences of soil hydrological characteristics on internal stem structure and hydraulic properties of downy oak (Quercus pubescens Willd.) growing along a hill slope. Increment wood cores were extracted from the base and at breast height (BH) of tree stems. Relative wood water content (W(c)) and wood density (D(w)) were measured in the sapwood. Wood compression strength (delta) in the longitudinal direction was measured with a fractometer. Thin sections were cut from the transversal face of each core and vessel lumen area (V(A)) was measured and xylem theoretical hydraulic conductivity (L(th)) estimated over the sapwood. Topsoil volumetric water content (theta(v)) was determined around trees and the hydrological behavior of the slope was studied through field surveys. Data were used as input to a hydrological model to simulate topsoil water distribution along the slope. Results showed that theta(v) tends to decrease with increasing altitude. Groundwater levels were lower upslope than downslope, and results from the hydrological model confirmed these trends. Mean W(c) at the base of each tree decreased significantly with increasing altitude, whereas at BH, no differences were found along the slope. There was a significant positive relationship between W(c) measured at the tree base and theta(v) along the hill slope, but not for W(c) measured at BH. Values of D(w) and delta measured at both stem positions increased significantly with increasing altitude and decreasing theta(v). Significant negative relationships were found between delta and theta(v) measured at the stem base and at BH. At both stem positions, delta was closely related to D(w) and L(th). Vessel lumen areas at BH and the stem base were significantly regressed with altitude, theta(v), D(w) and delta. Xylem theoretical hydraulic conductivity at both stem positions was negatively related to altitude and soil theta(v), but only L(th) measured at the stem base was negatively regressed with D(w). The results are discussed in the context of how tree position along a hill slope influences water uptake and internal xylem structure.

Axial compression strength of Norway spruce related to structural variability and lignin content

Variability in the axial tensile strength and Young's modulus of wood is mostly due to changes in the main orientation of the cellulose microfibrils with respect to the cell axis. By contrast, the causes of variability in the axial compression strength of wood are less well understood. Therefore, the axial compression strength and density as well as microfibril angle and lignin content of Norway spruce specimens were examined. 84% of the variability of compression strength could be explained by density. After normalisation of compression strength for density, the experimental results showed that variability in the microfibril angle in the secondary cell wall is not responsible for variability in the axial compression strength of the cell wall. This finding is supported by theoretical considerations using a composite failure criterion. Deviations of the microfibrils from a strictly axial alignment in the vicinity of rays are most probably the cause for the initiation of compression failure in Norway spruce. The lignin content of the secondary cell wall showed a positive relationship at low statistical significance with the compression strength of the cell wall. A positive effect of increasing lignin content on compression strength seems therefore possible, but very weak.

Strength of profile-adhesive joints

The current article presents an attempt to describe the strength of profile-adhesive joints. Its main objective was to develop mathematical models describing phenomena occurring in bent mortise joints prevalent in constructions of skeleton furniture, but also to determine factors influencing the strength of profile-adhesive joints. The presented cases of gluing of a mortise joint reveal that mutual interactions of compressed wood surfaces influence significantly the strength of the developed node. In extreme cases, when a glue bond fails to form on surfaces of elements, the strength of the joint will depend only on the compression strength of wood. That is why, despite the impairment of the adhesive bond, the construction will still be able to carry considerable outside loads. However, the best situation is when well fitted elements of the joint, compressing one another, reduce stresses in the glue bond and increase its strength above the value of outside loads exceeding greatly the shear strength of the glue.

Elevated atmospheric CO2 alters wood production, wood quality and wood strength of Scots pine (Pinus sylvestris L) after three years of enrichment

AbstractScots pine (Pinus sylvestris L.) trees were grown in open top chambers for three years under ambient and elevated CO2 concentrations. The trees were aged 3 y at the beginning of the CO2 exposure, and the effects of the treatment on total stem volume, stem wood biomass, wood quality and wood anatomy were examined at the end of the exposure. The elevated CO2 treatment lead to a 49% and 38% increase in stem biomass and stem wood volume, respectively. However, no significant effects of the elevated CO2 treatment on wood density were observed, neither when green wood density was estimated from stem biomass and stem volume, nor when oven‐dry wood density was measured on small wood samples. Under elevated CO2 significantly wider growth rings were observed. The effect of elevated CO2 on growth ring width was primarily the result of an increase in earlywood width. Wood compression strength decreased under elevated CO2 conditions, which could be explained by significantly larger tracheids and the increased earlywood band, that has thinner walls and larger cavities. A significant decrease of the number of resin canals in the third growth ring was observed under the elevated treatment; this might indicate that trees produced and contained less resin, which has implications for disease and pest resistance. So, although wood volume yield in Scots pine increased significantly with elevated CO2 after three years of treatment, wood density remained unchanged, while wood strength decreased. Whilst wood volume and stem biomass production may increase in this major boreal forest tree species, wood quality and resin production might decrease under future elevated CO2 conditions.