Strength Parallel Research Articles

Changes in surface and mechanical properties of heat treated wood during natural weathering

In this study, it was aimed to investigate the changes in moisture content, color, surface roughness, compression strength parallel to grain, modulus of rupture and modulus of elasticity of heat treated ash, iroko, Scots pine and spruce wood species during natural weathering for two years. Samples were removed at 6-month intervals for performance evaluation, and test results were compared with the controls. Moisture content of heat treated samples was found to be lower than that of control samples for all exposure periods. Heat treatment significantly changed original wood color as well as weathering factors. Wood surfaces become rougher within longer weathering exposure period. Natural weathering factors caused a decrease for all strength properties. Reduction rate for strength properties of heat treated samples was relatively lower than that of control samples. Heat treatment also seemed to improve color stability and surface quality of samples after weathering.

Water Retention Characteristics and State-Dependent Mechanical and Petro-Physical Properties of a Clay Shale

A series of clay shale specimens in equilibrium with various humidity conditions were used to establish the water retention characteristics, the influence of suction on ultrasonic p-wave velocity and rock mechanical properties such as Young’s modulus, Poisson’s ratio, onset of dilatancy, unconfined compressive strength and Brazilian tensile strength. Opalinus Clay, a clay shale considered as host rock for the disposal of nuclear waste in Switzerland was utilized. The results showed that the p-wave velocity normal to bedding (vp,n) dropped sharply upon desaturation until suction approached the air-entry value. The sharp decrease was associated with desiccation cracks solely oriented parallel to bedding. For suction in excess of the air-entry value, vp,n was constant, indicating no further desiccation damage. The suction at the shrinkage limit and at the air-entry point is similar in magnitude. The p-wave velocity parallel to bedding (vp,p) remained constant in the entire range of suction investigated in this study. The constant vp,p with increasing suction might be associated with the disproportional decrease in the Poisson’s ratio and Young’s modulus and its opposing effect on p-wave velocity. An almost linear increase in unconfined compressive strength, Brazilian tensile strength, stress at the onset of dilatancy and Young’s modulus with increasing suction was observed up to a suction of 56.6 MPa. For suction larger than 56.6 MPa, relatively constant strength and stiffness was observed. The increase is associated with the net contribution of suction to strength/stiffness, which decreases nonlinearly with decreasing volumetric water content. The rate of increase in tensile strength and unconfined compressive strength with increasing suction is different depending on the rock anisotropy. Compared to the strength values (Brazilian tensile and uniaxial compressive strength) obtained from specimens loaded parallel to bedding, the tensile strength parallel to bedding and the unconfined compressive strength obtained from specimens loaded normal to bedding are considerably more affected by increasing suction or decreasing water content. The reasons for the different rates in strength increase are considered to be related to local variations in suction (i.e., local suction) as a consequence of zones of contrasting pore-size distribution. These variations may influence the effect of suction on strength, especially when the load is applied parallel to bedding and crack growth occurs predominately along bedding layers with comparably low suction.

Physical and Mechanical Properties of Woods from Three Native Fast-Growing Species in a Secondary Forest in South Kalimantan, Indonesia

Abstract Growth characteristics and basic wood properties of three native fast-growing species, terap (Artocarpus elasticus Reinw. ex Blume), medang (Neolitsea latifolia (Blume) S. Moore), and balik angin (Alphitonia excelsa (Fenzel) Reissek ex Benth), were investigated. All three species are grown in a secondary forest in South Kalimantan, Indonesia. No significant correlations between growth characteristics (stem diameter and tree height) and stress-wave velocity of the stems were found. The mean basic density (BD) for whole trees of terap, medang, and balik angin were 0.34, 0.55, and 0.39 g cm−3, respectively. The BD in medang wood was similar in both radial and longitudinal directions. On the other hand, the BD gradually increased from pith to bark, decreased from 1 to 3 m above the ground, and then gradually increased to the top of the tree in terap and balik angin. Significant positive correlations between radial and tangential shrinkages and BD were found. Compressive strength parallel to grain and air-dry density also showed high positive correlations for all species. Analysis of variance showed significant differences in wood properties among the five sample trees in each species.

Variation of wood density and mechanical properties of blackwood (Acacia melanoxylon R. Br.)

The variation of wood density and mechanical properties with site, tree and within tree (longitudinal and radial) were studied for blackwood (Acacia melanoxylon R. Br.) grown in four sites in Portugal. Twenty trees were randomly selected (40cmdbh class, 33–51years of age), sampled at three stem height levels (5%, 35% and 65% of tree height) and three radial positions (10%, 50% and 90% of radius). They were further tested for air-dry density at 12% moisture content, bending strength (MOR), modulus of elasticity (MOE) and compression strength parallel to grain (CS), using ISO standards.The overall mean properties of blackwood were: 654kgm−3 density, 139Nmm−2 MOR, 141×102Nmm−2 MOE and 61Nmm−2 CS. Site was not a significant source of variation for all wood properties. The variation between individual trees was the most important. Within the tree, the radial variation was highly significant for all traits, while the longitudinal variation was only significant for density. The correlation of density with the mechanical properties was moderate.Blackwood showed potential for being an alternative species to supply the industry with valuable hardwood timber. The significant differences found between the trees demonstrate the possibility of selection and improvement for increased wood quality.

Influence of veneer thickness on the properties of LVL from Paricá (Schizolobium amazonicum) plantation trees

The work aimed at evaluating the influence of the veneer thickness on physical and mechanical properties of laminated veneer lumber (LVL) boards made from Schizolobium amazonicum plantation trees. It is a fast growing species (20 m3/ha/year), having a straight trunk almost without any branch and producing a white-yellowish low density hardwood: usually <0.40 g/cm3. The boards were manufactured with the following thicknesses: 1.54, 2.32 and 2.71 mm. Seven LVL boards were produced for each thickness, totaling 21, all according to the following characteristics: PVAc adhesive (200 g/m2), pressed (1.0 N/mm2) at room temperature for 12 h. The following mechanical and physical properties were then evaluated: static bending modulus of elasticity (EM), modulus of rupture (fM), compression strength parallel to grain (fc,0), shear strength parallel to glue-line (fv,0), shear strength perpendicular to glue-line (fv,90), water absorption and thickness swelling for 2 and 24 h of water immersion. The results pointed out that the utilization of thinner veneers implied improving mechanical properties, while thicker veneer reduced the water absorption. Nevertheless, in contrast, the efficiency was lower than that observed when thicker veneer was used.

Mechanical properties of wood from Pinus sylvestris L. treated with Light Organic Solvent Preservative and with waterborne Copper Azole

Aim of study: To determine the effect on wood from Pinus sylvestris of treatment with preservatives on mechanical properties and to establish the relation between the penetration and compression strength.Area of study: SpainMaterial and Methods: 40 samples of defect-free wood from Pinus sylvestris L. were treated with Light Organic Solvent Preservative (Vacsol Azure WR 2601) and 50 with waterborne Copper Azole (Tanalith E 3492). 40 control samples were not treated (water or preservative). Mechanical resistance to static bending, modulus of elasticity and compression strength parallel to the grain were compared with untreated wood. Regression analysis between the penetration and compression strength parallel was done with the samples treated with waterborne preservative.Main results: The results indicate that the treated wood (with either product) presents a statistically significant increase in mechanical resistance in all three mechanical characteristics. The results obtained differ from earlier studies carried out by other authors.There was no correlation between parallel compression strength and the degree of impregnation of the wood with waterborne Copper Azole . The most probable explanation for these results concerns changes in pressure during treatment.The use of untreated control samples instead of samples treated only with water is more likely to produce significant results in the mechanical resistance studies.Research highlights: Treated wood presents a statistically significant increase in MOE, modulus of rupture to static bending and parallel compression strength.There was no correlation between parallel compression strength and the degree of impregnation with waterborne preservative.Keywords: Light Organic Solvent Preservative; MOE; parallel compression; static bending; waterborne Copper Azole; wood technology.

Characterization of Cross-Sections from Old Chestnut Beams Weakened by Decay

This work aims to experimentally assess the material properties of old chestnut (Castanea sativa Mill.) cross-sections weakened by decay. Specimens were taken from critical zones of twenty floor beams, mostly corresponding to their ending parts, in contact with granite masonry walls. These specimens were compared with clear wood specimens taken from non-decayed parts. The experimental campaign comprised of visual inspection, non-destructive testing (ultrasound, impact penetration and drilling resistance tests) and uniaxial compression tests, parallel to the grain. Pin penetration test evidenced a depth of penetration 36% higher for decayed specimens compared to non-decayed specimens, proving the loss of capacity in the superficial decayed layer. The results of decayed specimens exhibited a decrease of approximately 30% in the compressive strength parallel to the grain. A reduction of approximately 5% was found for the dynamic and elastic moduli. The coefficients of variation for decayed specimens are significantly higher than for sound specimens. Different decay models are considered and compared aiming at analyzing decay evolution along time and determining the decrease of load bearing cross-section. Finally, the results were used to calibrate a bi-parametrical decay model for above ground timber structures, considering a linear relation between time and decay depth.

Microwave Radiation Effect on Axial Fluid Permeability in False Heartwood of Beech (Fagus sylvatica L.)

This study evaluated the effect of microwave radiation on the fluid permeability and compression strength parallel to the grain of beech false heartwood. European beech (Fagus sylvatica L.) was selected, and samples of false heartwood with dimensions of 30×20×20 mm3 were used. The microwave treatment was carried out in a laboratory device at a frequency of 2.45 GHz. The testing samples were divided into three groups (untreated, treated at 20-s intervals, and treated at 30-s intervals). The permeability was measured in the axial direction using distilled water. The coefficient of specific permeability was calculated using Darcy’s law. The results showed that the coefficient of specific permeability increased by up to 159% in comparison with untreated samples. The compression strength parallel to the grain decreased by up to 15%.

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.

Combined treatment of green pitch pine wood by heat and superheated steam and the effects on physical properties of the products

Abstract Pitch pine (P. rigida) wood was treated with superheated steam (SHS) and the subsequent effects due to drying and heat treatment (HT) were observed. The following treatment parameters were tested: 180°C air HT, 220°C air HT, 0.1 MPa–180°C SHS HT, 0.1 MPa–220°C SHS HT, 0.5 MPa–180°C SHS HT, and 0.5 MPa–220°C SHS HT. No drying checks were observed in the specimens (500×150×50 mm3) treated at 0.5 MPa–220°C SHS and with these treatment parameters, equilibrium moisture content (EMC) was the lowest. Low EMC has an effect on physical properties such as shrinkage, compressive strength parallel to the grain, bending strength, hardness, and decay resistance. Based on the results, it is expected that the green wood in a large scale is possible to be simultaneously dried and heat-treated without occurrence of checks by the SHS HT process.

Variation throughout the tree stem in the physical-mechanical properties of the wood

This study analyses the variation of main physical-mechanical properties of wood along the longitudinal and radial directions of the tree for Abies alba Mill. growing in the Spanish Pyrenees. Smallclear specimens were used to study the properties of volumetric shrinkage (VS), density (ρ), hardness (H), bending strength (MOR), modulus of elasticity (MOE), maximum compressive strength parallel to the grain (MCS) and impact strength (K). Several models of properties variation in the longitudinal and radial directions were analyzed. Main trends of variation of properties throughout the tree stem were identified although none of them could be fitted to predictive statistical models. Along the longitudinal direction, the properties studied followed a downward trend from the base to the crown, which was not significant in all cases, indicating that no differences in quality existed. Throughout the radial directionthe trend is upward for the first 40-50 growth rings, after which it slopes downwards, more gently at first until rings 70-75 and then more steeply. This behaviour is related to variation in wood structure from the pith to the bark, depending on whether the wood is juvenile, sapwood or heartwood, and to wood maturityand microfibril angle. Authors encourage carrying further studies on other populations of A. alba in the Spanish Pyrenees to check if the trends found in this study apply to other provenances.

Physical and Mechanical Properties of Paricá Wood Species Treated with CCB Preservative

Wood of Paricá species <i>(Schizolobium amazonicum</i>) is highly susceptible to degradation by decay microorganisms. Due to its increasing production in the northern region of Brazil, about 85 thousand hectares, and later use both for structural purposes and for the furniture industry, the need of extending life of Paricá wood applying chemical preservatives arises. One current alternative is the treatment by autoclave using CCB (Copper Chrome Boron). The aim of this study was to evaluate the influence of treatment with CCB in the properties: apparent density, parallel and perpendicular hardness to the grain, strength to shear and in the compression parallel to the grain of the <i>Schizolobium amazonicum</i> wood species, comparing the results with untreated wood. We observed that treatment with CCB did not change the properties of apparent density, shear strength, perpendicular hardness, strength and stiffness in compression parallel to the grain. For the hardness strength parallel to the grain was decreased in 28.9%.

Prospects for the use of municipal tree pruning wastes in particleboard production

The purpose of this study was to evaluate the physical and mechanical properties of particleboard made with pruning wastes from Ipê (Tabebuia serratifolia) and Chapéu-de-Sol (Terminalia catappa) trees. Particleboards were prepared with both wood species, using all the material produced by grinding the pruning wastes. The particleboards had dimensions of 45 × 45 cm, a thickness of approximately 11.5 mm and an average density of 664 kg/m3. A urea-formaldehyde adhesive was used in the proportion of 12% of the dry particle mass. The particleboards were pressed at a temperature of 130°C for 10 mins. The physical and mechanical properties analyzed were density, moisture content, thickness swelling, percentage of lignin and cellulose, modulus of resilience, modulus of elasticity and tensile strength parallel to the grain, accordingly to the standards NBR 14810 and CS 236-66 (1968). The particleboards were considered to be of medium density. The particle size significantly affected the static bending strength and tensile strength parallel to the grain. Ipê presented better results, demonstrating a potential for the production and use of particleboard made from this species.

Probabilistic characterisation of the length effect for parallel to the grain tensile strength of Central European spruce

The paper presents a probabilistic model characterising tensile strength parallel to grain of Central European spruce boards without longitudinal joints. The effect of length of members on strength is considered explicitly by considering a member by a serial arrangement of weak sections triggered by major knots of knot clusters. In order to demonstrate the applicability of the proposed model the model parameters are calibrated based on the analysis of three samples of spruce of Switzerland (Mischler-Schrepfer, 2000 [25]) and Austria (Schickhofer and Augustin, 2001 [28]), in total 460 boards tested in full size. This model might serve as basis for studies concerning the length effect of boards relevant for solid timber structures as well as basis for judging the length effect of finger jointed construction timber and glulam, and as starting point for modelling the process of proof loading.

Mechanical Characterization of Lumber of Small-Diameter Hardwood Species after Different Drying Schedules

The influence on the drying behavior as well as the mechanical properties of lumber of small-diameter hardwoods at different low-temperature convection kiln dryings was investigated. Standard test methods in three-point-bending and the modulus of elasticity in three-point-bending, compression tests parallel and perpendicular to the grain, as well as Brinell hardness tests were performed in order to assess the drying quality. Furthermore, non-standard tensile tests perpendicular to the grain and fracture energy tests in radial/longitudinal and also in tangential/longitudinal crack propagation systems were carried out as a most sensitive test method. The results showed significant changes of the specific fracture energy, bending strength, compression strength parallel and perpendicular to the grain, and the Brinell hardness with good drying performance at the same time.

Bending and Compression Properties of Malaysian Medium Hardwood in Orthotropic Directions Kelat (&lt;i&gt;Syzygium spp&lt;/i&gt;.)

Wood behaves differently in three independent orthotropic directions, namely radial, tangential and longitudinal. Determination of mechanical properties of wood and the study on the orthotropic behavior could enhance effective utilization of wood as construction material. Kapur and Kelat are two commercial medium hardwoods that are found abundantly in the east-coast of Malaysia. The purpose of the study is to determine the variation of bending and compression strength properties of Kapur and Kelat in three different anatomical directions. Bending and compression tests on small clear specimens were carried out according to BS373:1987. The result shows that Kapur is higher in bending and compression strength compares to Kelat. Bending strength properties for Kapur and Kelat were found to be significantly higher on the radial direction compared to tangential direction. In compression, the strength properties are higher on the longitudinal directions that are parallel to the grain. This is followed by radial and tangential direction for both Kapur and Kelat. The result also shows that compression strength parallel to the grain for both wood species to be significantly different from those perpendiculars to the grain.

On the use of NDT data for reliability-based assessment of existing timber structures

The objective of this paper is to address the possibilities of using non-destructive testing (NDT) data for updating information and obtaining adequate characterization of the reliability level of existing timber structures and, also, for assessing the evolution in time of performance of these structures when exposed to deterioration. By improving the knowledge upon the mechanical properties of timber, better and more substantiated decisions after a reliability safety assessment are aimed at.Bayesian methods are used to update the mechanical properties of timber and reliability assessment is performed using First Order Reliability Methods (FORM). The results show that different degrees of belief in the updating data may significantly influence the reliability level. The updating data to be used are NDT results obtained with ultrasound, resistance drilling and pin penetration equipments. The tests were conducted on chestnut wood (Castanea sativa Mill.) specimens, and were combined with tests to determine the compressive strength parallel to the grain. The uncertainty of the different NDT results is modeled by Maximum Likelihood estimates. Resistance distributions functions are considered to analyze the difference before and after updating by NDT, showing that lower variations may typically be obtained with the new information. Moreover, updating of the parameters in different deterioration models is considered in order to be able to evaluate the time dependency of the reliability, and information of NDT is also used to calibrate these models.The proposed approach is used for reliability assessment of different structural timber systems. Reliability of the structural system is assessed regarding the failure consequences of individual elements defined as key elements which were determined by their influence on the cross section loss. The results given by the pin penetration tests were the most similar to the reference experimental model with statistic parameters given by the results of destructive tests. The resistance drilling and ultrasound updating schemes led to higher level of reliability than the reference model values, therefore these updating data should be considered with caution, as they can result in unsafe results for the reliability compared to the reference models.

Mechanical properties of MMA-hardened hybrid poplar wood

Wood of fast-growing hybrid poplars, consisting of six 6-year-old clones in one plantation in Quebec, was impregnated with methyl methacrylate (MMA) and then polymerized by heat/catalyst method. The mechanical properties (static bending and compressive strength) of poplar clones and its MMA-hardened wood were investigated. Significant differences were observed among clones in bending and compression strength parallel to grain. Hardening treatment has also considerably improved all strength properties except for strain at rupture in static bending. The effects of density on mechanical properties were inconsistent, especially for hardened wood. Density was not the most important factor affecting strength properties. The improved properties of MMA-hardened hybrid poplar were comparable to some commercial hardwood species.

Relationship between Mechanical Properties of Vitex doniana, a Lesser Known Species and Implications for Utilization

Relationship between the mechanical properties of Vitex doniana, a lesser known wood species was investigated towards determining its potentials for utilization. Four trees obtained from the free area of Olokemeji Forest Reserve, Ogun State, Nigeria were sampled at butt (50cm above the ground) and at 10%, 30%, 50%, 70% and 90% of merchantable height (MH) The samples were also partitioned into corewood, middlewood and outerwood. Impact Bending (IMB), Modulus of Rupture (MOR), Modulus of Elasticity (MOE) and Maximum Compressive Strength Parallel to Grain (MCS//) were determined. Relationship between the mechanical properties was determined using regression equation. Results showed that Mean IMB, MOR, MOE and MCSS// were 0.69m, 85.4 N/mm 2 , 6380N/mm 2 and 40.8N/mm 2 respectively. The best relationship existed between IMB and MCS// (R 2 = 0.75) followed by between MOR and MOE (R 2 =0.71) while the least relationship (R 2 = 0.43) existed between MOR and MCS//.

The combined effects of copper sulfate and rosin sizing agent treatment on some physical and mechanical properties of poplar wood

This aim of this study was to determine the effect of rosin upon some physical and mechanical properties of poplar wood treated with mixtures of 3%CuSO4 and 1.0%, 2.0%, or 4.0% rosin sizing agent. Rosin–copper treatments decreased the moisture absorption, water absorption and swelling properties of wood, whilst increasing water repellent efficiency and anti-swelling efficiency to approximately 40% after 30-day immersion in water. In general, rosin–copper treatments increased the compression strength parallel to grain and Brinell hardness compared to controls, but the MOR and MOE were lower than that of control.