Wood Stiffness Research Articles

Efeito do comprimento do corpo de prova nas propriedades mecânicas do carvão de Eucalyptus

As propriedades mecânicas do carvão são indicadoras de qualidade e influenciam no processo siderúrgico. Os ensaios de avaliação (queda e tamboramento), em geral, apresentam resultados variáveis, comprometendo sua confiabilidade. Por isso, é importante desenvolver metodologias que produzam resultados comparáveis. Esse trabalho objetivou analisar a influência do comprimento do corpo de prova na determinação da rigidez e resistência da madeira e do carvão. Foram utilizados clones de Eucalyptus urophylla, dos quais foram produzidos corpos de prova de seção transversal de 25 mm x 25 mm e comprimentos de 50 mm, 75 mm, 100 mm e 125 mm. Dez amostras de cada comprimento foram selecionadas para a realização do ensaio com madeira, e outras dez para os ensaios com carvão. O módulo de elasticidade e a resistência à compressão foram determinados em ensaio de compressão paralela às fibras. Houve efeito significativo do comprimento do corpo de prova sobre a rigidez e resistência da madeira e do carvão, sendo que os melhores resultados foram encontrados para as dimensões 25 mm x 25 mm x 75 mm. Apenas a dimensão de 25 mm x 25 mm x 50 mm se mostrou inadequada, apresentando resultados inferiores aos relatados em literatura.

Combining Homogenization, Indentation and Bayesian Inference in Estimating the Microfibril Angle of Spruce

It has been shown that the microfibril angle may severely reduce the longitudinal elastic stiffness of wood. The present paper addresses this issue by combining experimental measurements on various scales, homogenization and Bayesian statistical method. To that end, the variation of effective stiffness as a function of microfibril angle is first estimated by combining nanoindentation and homogenization. The results from a series of tensile tests carried out on thin samples of wood containing only a few growth rings are expected to give additional source of information. In the present study both types of data, microscopic as well as macroscopic measurements, are exploited in the framework of Bayesian inference to get improved, posterior, knowledge of the microfibril angle distribution. Owing to a computational demand associated with the Markov chain Monte Carlo method, as the engine of the updating process, the homogenization based on classical micromechanics is adopted.

Variation in growth, wood stiffness and density, and correlations between growth and wood stiffness and density in five tree and shrub species in the Sahelian and Sudanian ecozones of Mali

Key message Most effects of environmental variables on growth, wood stiffness, specific stiffness and density, and correlations between growth and wood stiffness, specific stiffness and density were not consistent among species.

Contribution of cellulose to the moisture-dependent elastic behaviour of wood

Wood has a hierarchical structure involving several levels of organisation. The stiffness of wood relies on its capacity to transfer mechanical stress to its stiffest element at the lowest scale, namely crystalline cellulose. This study aims at quantifying to what extend crystalline cellulose contributes to wood stiffness depending on its moisture content. The crystal strains of cellulose were measured using X-ray diffraction on wet and dry specimens of spruce, based on a previously published methodology. The comparison between crystal strain and macroscopic strain shows that, during elastic loading, cellulose strain is lower than macroscopic strain. The means ratio of crystal/macroscopic strain amounts 0.85 for dry specimens and 0.64 for wet specimens. This strain ratio cannot be explained just by the projection effect due to the difference in orientation between cellulose microfibrils and cell wall, but results from deformation mechanisms in series with cellulose. Analysis shows that this series contribution represents a non-negligible contribution to wood compliance and is strongly moisture-dependent. This contribution amounts 9% for dry specimens and 33% for wet specimens, corresponding to a 4-fold increase in compliance for the series contribution. The origin of these strains is ascribed to mechanisms involving bending or shear strain at different scales, due to the fact that reinforcing element are neither perfectly straight nor infinitely long.

Genetic Improvement of Wood Properties in Pinus kesiya Royle ex Gordon for Sawn Timber Production in Malawi

Accurate prediction of genetic potential and response to selection in breeding requires knowledge of genetic parameters for important selection traits. In this study, we estimated genetic parameters for wood properties in Khasi pine (Pinus kesiya Royle ex Gordon) grown in Malawi. Data on wood properties and growth traits were collected from six families of Pinus kesiya at the age of 30. The results show that wood density had a higher genetic control (h2 = 0.595 ± 0.055) than wood stiffness (h2 = 0.559 ± 0.038) and wood strength (h2 = 0.542 ± 0.091). The genetic correlation among wood quality traits was significantly moderate (0.464 ± 0.061) to high (0.735 ± 0.025). The predicted genetic response indicated that selection for wood density at 10% selection intensity would increase stiffness and strength by 12.6% and 8.85%, respectively. The genetic correlations between growth and wood quality traits were moderately unfavourable. However, sufficient variation exists within the breeding population to select individuals with both good growth rate and high wood quality traits. It is therefore suggested that all trees with both diameter at breast height (DBH) greater than 32.0 cm and density greater than 0.593 g/cm3 must be selected in order to increase the efficiency of the breeding programme. However, in the long term, it is recommended that the best selection strategy would be to develop a multiple-trait selection index. The selection index should be developed using optimal index weights for the advanced Pinus kesiya breeding programme in Malawi.

Load-to-grain angle dependence of the embedment behavior of dowel-type fasteners in laminated veneer lumber

Load-to-grain angle dependence of the embedment behavior of steel dowels in laminated veneer lumber, as a consequence of the anisotropic material behavior of wood, is experimentally investigated in this study. As a novel issue, in addition to the stress dependence, the displacement path of the dowel depending on the load-to-grain angle, is discussed. Full-hole embedment tests of screw-reinforced LVL specimens up to dowel displacements of two times the dowel diameter and thus, representative for highly ductile dowel connections were conducted. Tests were performed with unconstrained lateral displacement boundary conditions of steel dowels with a diameter of 12mm and 16mm. Surface deformations were monitored with a full-field deformation measurement system. Increasing the load-to-grain angle caused reduced quasi-elastic limits and loading stiffness. However, for load-to-grain angles of 60° and higher, a pronounced displacement-hardening effect, leading to high embedment stresses at large dowel displacements, was observed. For the investigated dowel diameters, surface strains and plastic deformations around the dowel indicate an almost dowel diameter independent load bearing area, which might explain higher nominal embedment stresses and consequently a more pronounced hardening effect of the smaller dowel diameter. Dowel displacements perpendicular to the initial loading direction, i.e., nonlinear displacement paths of the dowel, were related to the anisotropic stiffness of wood and densification effects close to the dowel. The established experimental dataset was compared to current European timber engineering design equations and could serve as input to analytical and numerical models of dowel connections.

Climate, location, and growth relationships with wood stiffness at the site, tree, and ring levels in white spruce (Picea glauca) in the Boreal Plains ecozone

We examined modulus of elasticity (MoE) derived from SilviScan in white spruce (Picea glauca (Moench) Voss) at the site, tree, and ring levels across the Boreal Plains ecozone in Canada. Area-weighted averages of MoE were calculated for juvenile and mature wood and were examined in relation to radial growth, climate, and location. Correlations indicated that there was a negative relationship between radial growth and MoE in the juvenile wood that was detectable at the site and tree levels; however, the relationship weakened in the mature wood, particularly at the site level. Few climate variables were correlated with MoE in juvenile wood, whereas multiple summer and fall climate variables showed a significant correlation with MOE in mature wood. A model describing the radial profile of MoE explained 58% of the variability in MoE, with 10% of the random variability attributed to between-tree differences. Elevation and summer water balance accounted for nearly all of the between-site variability. A decrease in MoE with increasing elevation was noted and has been previously linked to a decrease in cell wall thickness due to a shorter growing season at higher elevations. Integration of the MoE profile model into an individual-tree growth and yield simulator is the next logical step.

Composition of hybrid larch (Larix × eurolepis Henry) forest reproductive materials: How much does hybrid percentage affect stand performance?

The performance of hybrid larch (Larix × eurolepis) stands may be altered by the fact that the seed lots produced in hybridization seed orchards always contain a proportion of non-hybrid seeds. We studied the effect of such hybrid/non-hybrid mixtures on the productivity and quality of young plantations, through a three-step process: determination of tree species identity with cytoplasmic DNA markers, comparison of hybrid and non-hybrid tree performance, and finally, assessment of thinning impact on hybrid percentage. Overall, we analyzed progenies from eight commercial seed orchards at three sites. Huge variations in hybrid percentage were found among orchard progenies. Globally, the results concerning survival, susceptibility to drought and to Meria laricis, growth, stem form and wood stiffness were clearly in favor of hybrids. In particular, they grew faster than the non-hybrid trees and exhibited a more homogeneous growth than the mixed progenies. Hybrid superiority was highest for orchards composed of a single maternal clone of a species which was poorly adapted to the planting site. Hybrid percentage was enhanced by successive thinnings. However, a serious loss of income is expected when planting progenies characterized by low initial hybrid percentage and high hybrid superiority. Moreover, variations in hybrid percentage proved to be problematic in seed orchard testing as seed orchard ranking may change depending on whether it is based on the performance of all trees or hybrids only. These variations reduce the reliability of the recommendations typically made to forest owners. For commercial and silvicultural reasons, we suggest setting a minimal threshold level of 60–70 % for hybrid percentage in marketed forest reproductive materials.

Measurement of stiffness of standing trees and felled logs using acoustics: A review.

This paper provides a review on the use of acoustics to measure stiffness of standing trees, stems, and logs. An outline is given of the properties of wood and how these are related to stiffness and acoustic velocity throughout the tree. Factors are described that influence the speed of sound in wood, including the different types of acoustic waves which propagate in tree stems and lumber. Acoustic tools and techniques that have been used to measure the stiffness of wood are reviewed. The reasons for a systematic difference between direct and acoustic measurements of stiffness for standing trees, and methods for correction, are discussed. Other techniques, which have been used in addition to acoustics to try to improve stiffness measurements, are also briefly described. Also reviewed are studies which have used acoustic tools to investigate factors that influence the stiffness of trees. These factors include different silvicultural practices, geographic and environmental conditions, and genetics.

Genetic architecture of wood properties based on association analysis and co‐expression networks in white spruce

Summary Association studies are widely utilized to analyze complex traits but their ability to disclose genetic architectures is often limited by statistical constraints, and functional insights are usually minimal in nonmodel organisms like forest trees.We developed an approach to integrate association mapping results with co‐expression networks. We tested single nucleotide polymorphisms (SNPs) in 2652 candidate genes for statistical associations with wood density, stiffness, microfibril angle and ring width in a population of 1694 white spruce trees (Picea glauca).Associations mapping identified 229–292 genes per wood trait using a statistical significance level of P < 0.05 to maximize discovery. Over‐representation of genes associated for nearly all traits was found in a xylem preferential co‐expression group developed in independent experiments. A xylem co‐expression network was reconstructed with 180 wood associated genes and several known MYB and NAC regulators were identified as network hubs. The network revealed a link between the gene PgNAC8, wood stiffness and microfibril angle, as well as considerable within‐season variation for both genetic control of wood traits and gene expression. Trait associations were distributed throughout the network suggesting complex interactions and pleiotropic effects.Our findings indicate that integration of association mapping and co‐expression networks enhances our understanding of complex wood traits.

Spatial variation of wood density, stiffness and microfibril angle along Eucalyptus trunks grown under contrasting growth conditions

Few studies have investigated the influence of environmental conditions on the within-tree variation in Eucalyptus wood traits. The genotype and environment effects and their interactions influence the wood properties. Their evaluations are crucial to estimate the genotype values and to select with efficiency. Thus, the aim of this study was to better understand the effect of ground slope and wind speed on the spatial variation of basic density (ρ), stiffness (MOE) and microfibril angle (MFA) of Eucalyptus wood. Wood discs cut along the trunk were sampled from 150 six-year-old Eucalyptus grandis x E. urophylla hybrids growing in 3 contrasting growing conditions influenced by ground slope and wind regime. Near Infrared (NIR) calibrations previously developed for ρ, MOE and MFA were used to predict in our discs. 2-D plots presenting the spatial variation of predicted wood traits were compared. The higher the ground slope, the greater the magnitude of radial variation in ρ, principally in the medium zone of the trunk. The spatial variation of wood stiffness seems to be sensitive to two environmental conditions. The MFA radial decreases were more pronounced where the wind speed was higher. At the base and top of the trees, however, there was no significant effect of growing conditions on the radial variation of the wood properties considered here.

Variation of radial wood properties from genetically improved Sitka spruce growing in the UK

There is little information about the impacts of past Sitka spruce (Picea sitchensis [Bong.] Carr.) tree breeding on wood properties because the emphasis has traditionally been on improving stem form and growth rates. This study used both SilviScan and mechanical testing to investigate the radial variations in wood stiffness, bending strength, density and microfibril angle in defect-free samples taken from the first United Kingdom progeny trial to reach merchantable size. We tested for differences in these radial patterns of variation in half-sibling progeny of three plus trees originally selected for superior growth rate and stem form against a non-selected control. Large differences in all of the properties were observed with radial position, with properties generally being less desirable in the corewood. Significant undesirable differences between the improved families and the control were found for stiffness, strength and microfibril angle. There was no significant relationship between wood density and stiffness in samples taken from the inner part of the tree, where stiffness was more closely associated with microfibril angle. Overall, previous selections for growth rate and/or stem form have compromised timber properties. It is recommended that current breeding programmes focus on corewood stiffness to prevent further degradation in the wood properties of the future timber supply.

Comparison of Stiffness and Strength Properties of Untreated and Heat-Treated Wood of Douglas Fir and Alder

This paper investigates the effect of heat treatment temperature on the stiffness and strength properties of Douglas fir (Pseudotsuga menziesii Franco) and common alder (Alnus glutinosa Gaertn.) woods. Two temperatures of heat treatment were used: 165 and 210 °C. The effects of dynamic elasticity modulus, static elasticity modulus, impact toughness, bending strength, and density were evaluated. It is already understood that the mechanical properties, primarily the bending strength, decreases with increasing temperature. In contrast to the favorable stability in shape and dimension that was achieved, the changes in the woods’ properties with temperature were mostly negative. Higher heat treatment temperatures corresponded with lower stiffness and strength properties. For higher temperature treatments, above 200 °C, deterioration of the tested properties was noticable as a result of the significant changes in the wood chemical structure. Even the positive effect of the equilibrium moisture decrease was not able to counterbalance the unfavorable changes. Moreover, it was observed that as the hemicellulose content is higher in alder wood, density, static bending strength, and toughness all decreased steadily at high temperatures, compared to Douglas fir wood.

Family variation in diameter growth and acoustic velocity in three 5‑year‑old South African‑grown Pinus elliottii×Pinus caribaea progeny trials established on three diverse sites

This paper discusses family differences in the stiffness of young Pinus elliottii×P. caribaea wood and how these differences relate to differences in growth rate and altitude. Trees for measurement were obtained from three 5‑year‑old progeny trials established at three diverse sites on the estate of Komatiland Forests (Pty) Ltd. The trials included the following controls: P. elliottii, P. patula, P. taeda, P. patula×P. tecunumanii and P. tecunumanii. Diameter at breast height and sound velocity (which has a direct relationship with wood stiffness) were measured on all healthy trees. Virtually all of the species and hybrids exhibited marked decreases in growth rate and velocity (stiffness) with increasing altitude; the effect on velocity was most likely partly due to the inverse relationship that normally exists between wood density and altitude in most pines. Differences in growth rate explained only a small proportion of the total variation in velocity. The average sound velocities of P. patula, P. patula×P. tecunumanii and P. tecunumanii surpassed the velocity values of most of the P. elliottii×P. caribaea crosses at all three sites. Results of Spearman rank correlations of average treatment velocity between sites suggested only some similarity in the ranking orders among sites. The inverse effect of altitude on wood stiffness suggests that trees grown at increased altitudes are likely to yield wood with higher proportions of wood not meeting the minimum stiffness requirement for structural lumber at final harvest. The wood of some P. elliottii×P. caribaea crosses would be particularly vulnerable. Considering the large variation found, presumably largely genetic, there can be little doubt that a good opportunity exists for the development of genotypes more suitable for planting at higher altitudes.

Age trend of heritability, genetic correlation, and efficiency of early selection for wood quality traits in Scots pine

To examine the efficiency of early selection for wood quality traits in the Scots pine (Pinus sylvestris L.) breeding program in Sweden, a total of 778 wood increment cores were sampled from 179 full-sib families in a single progeny trial at 40 years of age. Age trend of inheritance, age–age genetic correlation, and early selection efficiency for eight wood traits including annual ring width, wood density, microfibril angle (MFA), modulus of elasticity (i.e., wood stiffness; MOE), and fibre dimensions were studied. Heritabilities for the eight wood traits reached a plateau between age 5 years and age 15 years, with the highest heritability for radial fibre width and fibre coarseness (∼0.6) and the lowest heritability for ring width (∼0.2). Heritability reached about 0.4 for both wood density and MFA but only reached about 0.3 for MOE. Genetic correlation from early to reference age 30 years reached a very high level (&gt;0.8) for all eight wood traits at age 5 years. Early selection was effective for wood quality traits in Scots pine, and selection at age 8 years is recommended for MOE in Scots pine.

Stiffness and strength of oil palm wood core sandwich panel under center point bending

Abstract This paper presents a study of the bending's stiffness and strength of oil palm wood (OPW) core sandwich panel overlaid with rubberwood veneer under center point bending. Parameters including density and grain orientation of OPW core, rubberwood veneer thickness and span length were investigated. An experimental evaluation of some mechanical properties of OPW and the bending stiffness and strength of the sandwich beams was performed. Linear elastic beam theory was used to predict the bending performance of the panels. Results show that the linear elastic beam theory with the uses of the power law expressions of Young's moduli and shear strength of the OPW as a function of density derived within this study, adequately predicted the stiffness and bending strength of the sandwich beams. Higher OPW core density increased stiffness and strength of the beam. Failures by face fracture and core shear were observed which the latter tended to occur at low OPW core density, relatively thick veneer face and short span length. Grain orientation of OPW core little influenced stiffness and strength of the sandwich board. Finally, the stiffness and failure load equations of the OPW sandwich board were proposed for practical uses of this product.

Density Evaluation of Pinus oocarpa Submitted to Heat Treatment

To use more durable wood as a building material, thermal rectification is an alternative technique to reduce the wood decay against xylophages. The purpose of this study was to evaluate the effect of the heat treatment on the density of <i>Pinus oocarpa</i> in temperatures at 200, 220 and 240°C during 30, 60 and 90 minutes. The samples were characterized by mass loss and gravimetric yield in order to verify the variations in the density of thermally treated wood. We found that heat treatment combinations up to 60 minutes and 220°C showed little variation in the density values. For longer time and at higher temperatures, due to the thermal degradation of the wood, there was a wide variation on density values accompanied by a decreasing tendency of the density. The highest density value was obtained at a time-temperature combination of 90 minutes and 220°C and the lowest at 60 minutes and 240°C. These results suggest that to apply the heat treated wood in construction purposes, better results were observed for thermal rectification that had little loss of density, since this property is directly related to less variation in strength and stiffness of wood.

The Delignification Pattern of Ailanthus excelsa Wood by Inonotus hispidus (Bull.: Fr.) P. Karst.

In vitro laboratory decay tests on Ailanthus excelsa Roxb. wood revealed that I. hispidus exhibits a combination of both white-rot and soft-rot patterns of wood decay. Early stages of wood decay showed dissolution of the middle lamella as well as defibration and localized delignification of fiber walls; vessels, axial, and ray parenchyma remained unaltered. Delignification commenced from the middle lamellae at the cell corners without any marked effect on the primary and secondary wall layers. In later stages of growth, the species produces typical soft-rot decay pattern by forming erosion channels through the S2 layers of fiber walls, transverse bore holes in the cell walls, and erosion channels alongside/following the orientation of cellulose microfibrils. The rays showed signs of cell wall alterations only after the extensive damage to the fiber walls. After 120 days of incubation, the vessels also showed localized delignification, the erosion of pits, and separation from associated xylem elements. The extensive weight losses under natural and in vitro decayed wood as well as the very soft nature of severely degraded wood indicate that I. hispidus alters wood strength and stiffness.

Heritability estimates for wood stiffness and its related near-infrared spectral bands in sugi (Cryptomeria japonica) clones

Rapid and cost-effective methods of evaluating the properties of wood are required for forest-tree breeding programs. In this work, we first attempted to develop a calibration model for predicting the stiffness of wood using near-infrared (NIR) spectroscopy. Wood samples were collected from three stands of sugi (Cryptomeria japonica) plus-tree clones aged from 34 to 36 years old. Two to three sample trees were harvested from each clone, yielding a total of 129 sample trees. Partial least-squares analysis was performed to predict the dynamic modulus of elasticity (Efr). A reasonable calibration model that allowed Efr to be predicted with a correlation coefficient of 0.69 and a root mean square error of prediction of 0.82 GPa was obtained. Second, in a novel approach, we tried to select the NIR spectral bands that were the most strongly related to wood stiffness, and we examined the degree to which these bands were genetically controlled. The heritability estimates (h2) for the NIR absorbance values at 7,320 and 6,281 cm−1, which were found to be the most important bands for predicting Efr, were 0.48 and 0.57, respectively. Although the genetic control of the NIR spectral bands was weaker than the genetic control associated with the actual measurement of Efr (h2 = 0.74), the results imply that the NIR spectral bands are under moderate genetic control. Assuming that the NIR spectral bands are the dissected components of the target trait (Efr), the results should provide useful information when attempting to perform genomics-based breeding.

Incorporating economic weights into radiata pine breeding selection decisions

This article introduces the concept of “robust selection”, which proposes tree selection based on the stochastic simulation of economic values to account for the inherent uncertainty of economic weights used in tree selection for breeding programs. The proposed method uses both median ranking and ranking variability as criteria for breeding selection. Using consensus genetic and economic parameters from the New Zealand Radiata Pine Breeding Company program, we compare three selection strategies: deterministic application of economic weights from a vertically integrated bioeconomic model, an equal-weight index often used in operations, and robust selection. All strategies aim to increase value for a breeding objective that includes four traits, i.e., volume, stem sweep, branch size, and wood stiffness (measured as modulus of elasticity), based on a selection index that considers five criteria, i.e., stem diameter at breast height (1.3 m), straightness, branching score, wood density, and modulus of elasticity. Two-thirds of the selected trees were unique for each of the selection strategies. Robust selection achieved the best realised gain for three of the four selection criteria and was the middle performer in the last selection criteria. Considering the high intrinsic uncertainty of economic weights, we suggest that the relevant criterion for the selection of individuals is the maximum median ranking, subject to an acceptable level of variation in that ranking, rather than their narrow performance under a single economic scenario. This will lead to tree selections that perform well under a wide range of economic circumstances.