Strength Parallel Research Articles

Evaluation of xylem maturation and the effects of radial growth rate on anatomical characteristics and wood properties of Azadirachta excelsa planted in Indonesia

The xylem-maturation process and the effects of radial growth rate on anatomical characteristics (vessel and fibre morphologies) and wood properties (basic density and compressive strength parallel to grain) were studied for 4-year-old Azadirachta excelsa planted in Indonesia. Mean values were 121 µm, 8.1 vessels/mm2, 16 µm, 1.4 µm, 0.33 mm, 0.98 mm, 0.40 g/cm3, and 27.3 MPa for vessel diameter (VD), vessel frequency, fibre diameter, fibre wall thickness, vessel element length, wood fibre length, basic density, and compressive strength parallel to the grain at green condition, respectively. With a few exceptions, no significant correlations were found between the stem diameter and the anatomical characteristics or wood properties, indicating that radial growth rate does not always affect the characteristics and properties of this species. On the other hand, almost the same radial variation patterns in VD were found in trees of a different stem diameter, suggesting that xylem maturation in this species might depend on diameter growth rather than cambial age.

Impact of laminations and natural fractures on rock failure in Brazilian experiments: A case study on Green River and Niobrara formations

Natural fractures and laminations are common features in many unconventional resources which require hydraulic fracturing for economic production. To better understand the effect of such features on rock failure, we have conducted indirect tensile or Brazilian testing on several rock samples from Green River and Niobrara formations. Brazilian experiments were conducted at various orientations of laminations or natural fractures with respect to the loading direction. In contrast to isotropic rocks, we observed that rock failure can occur away from the vertical central line of rock parallel to lamination or natural fracture when the approaching angle between the lamination and loading direction is less than 30° in the tested samples. It was also determined that the tensile strength parallel to laminations or calcite-filled fractures is lower than the tensile strength perpendicular to lamination and/or the natural fractures; for instance the tensile strength of Niobara calcite-filled fractures were almost one third of the rock matrix.

Effect of Vacuum and Pressure Treatments on the Mechanical Properties and Moisture Balance of Wood from Pinus sylvestris

Several works have analyzed the alteration in the mechanical strength of wood after the application of protective substances. However, it remains unclear whether the significant differences obtained are caused by the protective substances, the pressure and vacuum conditions used in the treatment, or the simultaneous effect of both. In this study, 123 wood samples from Pinus sylvestris were tested for bending, and 85 samples were tested for compression strength parallel to the grain. These samples were randomly distributed in three groups (treated with water pressure, water vacuum, and control samples simply submerged in water). The results indicated that there was no difference in mechanical properties between the treated and untreated samples. In contrast, significant differences were detected in equilibrium moisture after a prolonged drying process.

Mechanical Properties of Impregnated and Heat Treated Oriental Beech Wood

The main purpose of this study was to investigate mechanical properties such as the modulus of rupture (MOR) and compression strength parallel to grain (CSPG) of impregnated and heat-treated Oriental beech (Fagus orientalis L.) wood. Some copper and boron containing impregnation chemicals such as Wolmanit CX-8 (WCX-8) and Celcure AC-500 (CAC-500) were used. Wood specimens were impregnated 2% aqueous solution of the chemicals according to ASTM D1413-07e1 standard. The wood specimens were heated at 150 and 175 °C for 4 and 8 h, respectively. Results showed that both impregnation and heat treatment decreased the MOR and CSPG of Oriental beech wood. The MOR losses of Oriental beech after both treatments were higher than CSPG losses. The largest reduction of MOR and CSPG were observed with 51.5% and 15.5% for CAC-500 impregnated and heated at 175 °C for 8 h. Except for WCX-8 impregnation and heat treatment at 150 °C for 4 and 8 h, the MOR values of impregnated and heat-treated Oriental beech wood were lower than only heat-treated Oriental beech wood. It was also found that the CSPG values of impregnated and heat-treated Oriental beech wood were higher than only heat-treated Oriental beech wood, except for impregnation and heat treatment at 175 °C for 8 h.

Experimental Study on Tensile and Compressive Strength of Bamboo Scrimber

The objective of this study was to provide fundamental parameters for the utilization of bamboo scrimber in the building structure field as a green building material. Both static tensile and compressive tests were conducted on bamboo scrimber, with 180 specimens for compressive tests and 173 specimens for tensile tests. The normal and lognormal distributions were selected to fit the experimental data. The design values were calculated according to the Chinese allowable stress design method and ASTM D2915 (2003). The results showed that both tensile strength (UTS) and compressive strength (CS) parallel to the fiber of bamboo scrimber were significantly higher than those of wood and other bamboo-based composite materials. Kolmogorov-Smirnov and chi-squared test results indicated that a lognormal distribution was a good fit for the UTS and CS except for the fitting result of UTS by the chi-squared test. The calculated design values of UTS and CS using ASTM D2915 (2003) were higher compared with those found using the Chinese allowable stress design method.

Assessing the destructive behaviors of two white-rot fungi on beech wood

This research assessed the destructive behaviors of two white-rot fungi, Pleurotus ostreatus and Trametes versicolor and compared their degradation capabilities on solid oriental beech wood (Fagus orientalis Lipsky). Beech wood specimens were exposed to both fungi for a period of 120 days based on the specifications in the EN-113 standard. Mechanical properties and chemical composition of the specimens were measured every 15 days. Mass loss (ML) caused by the two fungi were not significantly different at the last stage of exposure, although T. versicolor showed higher ML at the middle exposure intervals. Compression strength parallel to grain, hardness, and impact bending values were higher in specimens exposed to P. ostreatus, although differences were not statistically significant. Microscopic images showed nearly the same decay patterns for both fungi. The results of the chemical assessment indicated that degradation of cell wall components was approximately the same for both fungi, but in some case T. versicolor showed a slightly higher potential to decay compared to P. ostreatus, especially in the early stages of exposure. The two fungi differed in their ability to reduce degree of polymerization (DP) holocellulose of beech wood. It was concluded that the destructive behaviors ability of both fungi was considerable.

Temperature reduction factor for compressive strength parallel to the grain

The aim of this work is to evaluate the effect of the temperature on the compressive strength parallel to grain of Schizolobium amazonicum, Eucalyptus saligna and Pinus taeda from cultivated forests. The Schizolobium amazonicum sample was formed by 105 clear specimens assembled in 15 groups, the Eucalyptus saligna and Pinus taeda were formed by 150 clear specimens assembled in 15 groups each. Each group of samples was formed by 7, 10 and 10 specimens, respectively. The specimens were tested in a temperature range from 20 to 230°C. The Schizolobium amazonicum, Eucalyptus saligna and Pinus taeda samples present a decrease in the compressive strength, reaching 70%, 79% and 62% of the compressive strength at room temperature, respectively. The compressive strength decrease of the samples can be associated to the thermal degradation of wood polymers and the moisture content.

Effects of Temperature on the Compressive Strength Parallel to the Grain of Bamboo Scrimbe

The objective of this study was to investigate the compressive strength parallel to the grain of bamboo scrimber during and after exposure to various temperatures, in a range from 20 to 225 °C. These data were used to provide a basis for the evaluation of the fire performance of bamboo structures. A total of 152 specimens, assembled as group “during-fire” and “post-fire”, were tested during and after exposure to high temperatures. The experimental results indicated that there were significant differences in compressive properties between the “during-fire” and “post-fire” groups. At one temperature level, the compressive strength and modulus of elasticity of the “post-fire” group were significantly higher than those properties of the “during fire” group, but the ductility coefficient was reversed. FTIR analysis results showed that 175 °C was a key turning point, at which thermal decomposition occurred in the cellulose of the bamboo and phenolic resin.

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%.

Effect of Glass Wool and Stone Wool Additives on Some Mechanical Properties of Wood Composites

Mechanical properties of wood composites made from multiple wood species (50% Crimean pine, 30% Eastern Black Sea oak, 15% quaking aspen, and 5% wood machining residues) were evaluated using various amount of glass wool (GW) and stone wool (SW) additives. A total of 70 experimental panels were produced with a target density of 640 kg/m3. The bending strength, modulus of elasticity, tensile strength parallel to the surface of boards, tensile strength perpendicular to the surface of boards (internal bond), and cutting (shear) strength parallel to the surface of boards were determined. After statistical analysis, the results indicated that the SW and GW additives decreased the bending strength and modulus of elasticity by 49% in almost all boards. The addition of SW resulted in a 6% reduction in the tensile strength parallel to the surface. Relative to SW, GW resulted in an additional 8% reduction in shear strength, a 3% reduction in the screw tensile strength perpendicular to the surface, and a 6% reduction in the tensile strength parallel to the surface. Thus, the SW and GW additives decreased all the selected mechanical properties of wood composites.

Comparison of physical and mechanical properties of Dendrocalamus asper Backer specimens with and without nodes

This study investigated the effects of nodes on some of the physical and mechanical properties of Dendrocalamus asper Backer (D. asper Backer). Two types of D. asper Backer specimens, with and without nodes, were prepared from the bottom and top parts of the bamboo culms for testing of their physical (density, water uptake, shrinkage and swelling) and mechanical (shear strength parallel to the grain, tensile strength parallel to the grain, modulus of rupture and modulus of elasticity) properties. The results obtained for the two types of specimens were then compared. The results showed that the radial swelling and shrinkage properties, the tensile strength parallel to the grain and the modulus of rupture values of specimens with nodes were significantly lower than those of specimens without nodes at both culm height positions examined. The other properties along the culm’s height were not significantly different for the two specimen types. The results indicate that node effects should be considered as part of the practical design of D. asper Backer bamboo products, especially when bamboo with nodes is used.

ESTIMATIVAS DAS PROPRIEDADES FÍSICO-MECÂNICAS DE COMPOSTOS LVL CONFECCIONADOS COM PARICÁ POR MEIO DE ULTRASSOM

http://dx.doi.org/10.5902/1980509821118No presente estudo buscou-se avaliar as propriedades físicas e mecânicas de compostos LVL produzidos com a madeira de paricá (Schizolobium amazonicum Huber ex. Ducke) por meio do ultrassom. Para isso, foram utilizados LVL produzidos em laboratório e destes retiradas amostras para realização dos ensaios não destrutivos. Posteriormente, as mesmas amostras foram destinadas para realização dos ensaios físicos (absorção de água; inchamento em espessura e inchamento residual) ou mecânicos (resistência e rigidez à flexão estática flatwise; resistência e rigidez à flexão estática edgewise; resistência à compressão paralela e resistência ao cisalhamento paralelo e perpendicular). Os dados da velocidade de propagação de ondas e do módulo de elasticidade dinâmico obtidos nos ensaios não destrutivos foram utilizados no ajuste de equações para estimar as propriedades avaliadas. Os resultados obtidos apontaram o uso do ultrassom como uma ferramenta eficaz para a predição da maior parte das propriedades avaliadas. Dentre as variáveis independentes avaliadas, o módulo de elasticidade dinâmico obteve os melhores resultados quando comparado à velocidade de propagação das ondas.

Some physical, mechanical and anatomical characteristics of stemwood and branchwood of two hardwood species used for structural applications

Interest in branchwood utilization is gradually increasing on account of increasing demand for wood for construction and furniture production. However, wood quality assessment involves consideration of physical, mechanical and anatomical characteristics. This present study compared density, MOE and MOR, and compressive strength at 17 ± 3 %MC and 10 ± 4 %MC and some anatomical characteristics of Khaya ivorensis and Entandrophragma cylindricum by following BS (British Standard) 373, Strength properties of timber 1–24, 1957; ISO (International Standard) 3131, International Standard; wood-determination of density for physical and mechanical tests, 1975) and IAWA committee protocol of 1989. Branchwood and stemwood samples were extracted from two natural forest reserves. Results indicated that branchwood of the species dried to 17 %MC and 10 %MC proved to be as good materials as their stemwood counterparts in terms of bending and compressive strength parallel to the grain. Branchwood had significantly (p < .01) higher density than stemwood but such high densities did not translate into significant higher strength values. Moisture content and wood types (stemwood or branchwood) had significant effect (p < .001) on density, MOE, MOR and compressive strength. Fibre and axial parenchyma quantities were, respectively, the highest and lowest in both stemwood and branchwood of the two species. Fibre proportions in stemwood and branchwood correlated positively with density, MOE, MOR and compressive strength. Compared to bending strength, compressive strength was less influenced by anatomical properties of stemwood and branchwood. It was concluded that branchwood of E. cylindricum and K. ivorensis are not inferior to their stemwood and therefore could be used for structural applications. Further studies including shear strength, adhesive bonding, and finishing properties should be carried out to confirm the possibility of utilising branchwood for structural applications.

Effect of a Longitudinal Cut on the Mechanical Properties of Small-Diameter Roundwood of Pinus nigra Arnold

The use of roundwood in structures has drawbacks that include tapering and lack of flatness, which can be overcome by making a longitudinal cut to flatten one side. The aim of this work was to compare the mechanical behavior of roundwood vs. roundwood with one flat face, comparing pieces of small-diameter roundwood from young trees of Pinus nigra Arnold. Half the samples were given a longitudinal cut. Specimens taken from these pieces were tested for bending and compression parallel to the grain to determine their modulus of elasticity and strength. The modulus of rupture by bending was 22% lower in roundwood with one flat face (59.0 MPa) than in roundwood (75.6 MPa). It has been observed that the smaller cross section in the roundwood with one flat face is not the only explanation for the decrease in the bending strength. In contrast, no significant differences were observed for the other three mechanical properties studied (compression strength parallel to the grain and modulus of elasticity in bending and compression).

Compressive strength parallel to the fiber of spruce with high moisture content

The research aimed to derive substantiated reduction factors for compressive strength and modulus of elasticity parallel to the fiber for structural sized spruce and fir (round) wood with moisture contents at and beyond fiber saturation. Such values, which at present are not given in Eurocodes 5 and 7, are essential in order to perform a reliable design of water/soil immersed piles as well as structural assessment of piles in embankments and foundations of historic, cultural heritage buildings and bridges. The experimental investigations, preceded by a comprehensive literature evaluation, comprised a total of 17 pairs of matched structural sized spruce (Picea abies) pile specimens with mid-length diameters of about 200 mm, with each pair being cut successively from individual logs. From each pair, one specimen was tested in the dry state (MC = 12%), and the other in the wet/green state (MCmean = 90%) according to EN 408 (2010). Further, for calibration purposes, matched small clear specimens with two different aspect ratios were sampled close to the sections from which the structural sized piles were cut. At the mean strength level, the pile compression tests parallel to the fiber gave a moisture reduction factor of $$k_{moist, green, mean}$$ = 0.57, conforming well with the condensed result (0.54) of the literature evaluation on clear wood data, whereas the conducted matched clear wood reference tests gave a 15 % lower reduction factor. The moisture reduction at the 5 % quantile level of the pile compressive strength $$k_{moist, green, 05}$$ = 0.65 was less expressed, and 30 % lower than that obtained for the small clear specimens. The moisture modification factor for the modulus of elasticity in compression parallel to fiber from dry to green state was found to be 0.89 for the pile specimens, which conforms closely to literature data on small clear specimens. Based on the experimental results for the moisture reduction and the present implicit provisions of EC 5 on duration of load, a modification factor $$k_{mod}\;=\;0.65 \times 0.6\;=\;0.4$$ is proposed for structural sized spruce/fir piles as well as sawn lumber subjected to permanent load in the water saturated state.

In vitro wood decay of teak (Tectona grandis) by Rigidoporus cfr. microporus (Meripiliaceae, Polyporales, Basidiomycota)

The use of exotic species like teak for industry demands has increased over the last decades in Central America, however its vulnerability to decay by saprophytic fungi has not been well studied. Among these fungi, Rigidoporus spp. have been described as white rotters of dead hardwoods and conifers worldwide. In Costa Rica, R. microporus has been found growing on teak stumps. The aim of this study was to determine the effects of this white rot fungus on the chemical, mechanical and physical properties of teak wood from trees of different ages. Six and ten year old sapwood and heartwood samples were used in the assays. Severe anatomical damage and the highest weight and resistance losses were observed on 6 yr. old sapwood samples. There was an increase in the quantity of soluble materials in 1% NaOH (relative values) and lignin content in all the samples analyzed, after 3 months exposure and up to the end of the experiment. Mass loss reduction and increased resistance of wood to compressive strength parallel to the grain were related to both the type of wood and the age of the tree. Knowledge of the potential damage that this fungus can cause to teak wood might help in a better selection of wood and developing more effective protection measures against decay in the field or in construction wood.

The effect of growth conditions in specific areas of Croatia and the Czech Republic on the physical and mechanical properties of black alder wood (Alnus glutinosa Gaertn.)

In this paper, static bending (modulus of rupture, MOR, and modulus of elasticity, MOE) and compression strength parallel to grain (σ cǀǀ ) of black alder wood (Alnus glutinosa Gaertn.) were investigated. For experimental testing, we used black alder wood from two different areas: Crni Jarci, Croatia, and Mala Bystřice, Czech Republic. Experimental tests were carried out according to the Czech national standards: CSN 49 0115 and CSN 49 0116 for static bending and CSN 49 0110 for compression strength. The samples from Mala Bystřice showed lower values of MOR (~14%), MOE (~30%), and σ cǀǀ (~4%), when compared to the samples from Crni Jarci. The relationship between density and strength was investigated. The difference between the studied groups at the 0.05 significance level was confirmed. The average linear correlation was found between density and the observed mechanical properties (for σ cǀǀ ). The average density was 549 kg m -3 for samples from Crni Jarci and 469 kg m -3 for samples from Mala Bystřice. The results were compared with values indicated in similar studies.

The bearing strength capacity perpendicular to grain of norway spruce – Evaluation of three structural timber design models

The perpendicular to grain compressive strength of timber is known to be much lower than the strength parallel to grain. Many timber structures, however, rely on this property especially in bearings that occur frequently in building practice. The linear elastic–plastic behaviour of structural timber loaded perpendicular to grain has been a problematic issue for decades which is reflected in the differences between the prediction models in structural design codes over the world. This article concentrates on the evaluation of the strength predictive ability of three of the latest bearing models having an empirical, semi-empirical or physical background. On the bases of a large database of over 1000 test results covering eight practical load cases, it is shown that the accuracy and consistency of the physical model is the best, which makes it a potential candidate for the new generation timber design codes.

Получение модифицированной древесины химико-механическим способом и исследование ее свойств

The best method of hardening of low-value wood is pressing her to the extent of 40-50 %. About 2 times its volume decreases and, respectively, but the output of the modified wood. As hardener can be used on-nofibrillyarnuyu cellulose (NFP) in the form of a 2 % hydrogel magnetically activated. Completely replace the pressing NFP is impossible, since hydrogel has a very small concentration of NFP and receive content over 1 % in relation to dry wood impossible. Technology for producing modified wood involves activation of a 2 % hydrogel magnetization in STEL-49 to obtain the analyte with a potential of 600-800 mV and the pH = 2.5. In a 30 % aqueous urea solution was added 20 % activated hydrogel NFP stabilizer and 15 % the size of the particle board - UREAFORMALDEHYDE oligomer aqueous solution (UFC). The resulting mixture is impregnated with crude wood aspen or birch end under pressure to ensure through impregnation. The content of the mixture in the impregnated wood of 40-60 % by weight of the wood. The impregnated wood is dried with simultaneous compression to the extent of 20-25 %. The resulting wood has a moisture content 6-8 %, the density of 800-900 kg / m3, compressive strength parallel to the grain of 100-150 MPa. Due to the presence of urea loss on fire test is reduced 5 times. Biostability modified wood increases from baseline in 2-3 raza.Posle processing wood according to the procedure described obtained modified wood having a degree of compaction of 15 % birch and 25 % aspen, i.e. Use of the method reduces the degree of compaction is twice as compared with the known method, thus also increasing the yield of the resulting material. Reducing pressing for birch from 30 to 15 % increases the yield of modified wood by 15 %, ie 1 m3 with savings of 0.15 m3, with 1000 m3 -150 m3, When the selling price of the modified birch 30 thousand rubles. 1 m3 for savings of 150x30 = 4500 rubles. Reducing the degree of compaction of the aspen from 50 to 25 % increases the yield of modified wood by 25 %, i.e. 1 m3 with savings of 0.25 m3, with 1000 m3 -250 m3. When the selling price of the modified aspen wood 25 thousand rubles. 1 m3 for savings of 250x25 = 6250 rubles.

Effects of Heat Treatment under Vacuum on Properties of Poplar

The influences of heat treatment under vacuum on the mechanical properties and corrosion resistance of untreated poplar wood were investigated in this study. Wood samples were heated in a vacuum atmosphere in laboratory conditions at 140 to 200 °C for 1 to 3 h. The color of the poplar’s surface after heat treatment was deeper than that of the untreated wood, and the dimensional stability of poplar was improved by increasing the temperature and time. However, the compressive strength parallel to the grain of heat-treated samples was slightly lower than that of the control samples. The modulus of rupture of samples heat-treated at 200 °C for 3 h decreased 41.25% compared with the untreated samples. The corrosion resistance of heat-treated poplar increased with increasing temperature and time. The white-rot fungus resistance of the treated poplar was better than its resistance to brown-rot fungus.