Properties Of Clear Wood Research Articles

Determination of local mechanical properties of clear wood in relation to the local fiber deviation

Determination of local mechanical properties of clear wood in relation to the local fiber deviation

Evaluating the viscoelastic shear properties of clear wood via off-axis compression testing and digital-image correlation

AbstractHighly anisotropic materials like wood and unidirectional polymer composite structures are sensitive to shear deformations, in particular close to fixed joints. Large wooden structures in buildings and, e.g. wind-turbine blades, are designed to last for decades, and hence are susceptible to unwanted creep deformations. For improved structural design, the shear-creep properties of the material are needed. These are rarely available in the literature, possibly because of technical difficulties to achieve a well-defined shear-stress state in test specimens. For cost-efficient testing, this goal of a pure stress state necessarily needs to be compromised. In the present study, we propose a simple test method based on uniaxial compression on wooden cubes, but is equally applicable for fibre composites. The viscoelastic shear properties of Norway spruce (Picea abies) under off-axis creep compression tests have been characterised in all three directions. The tests are performed in a controlled climate chamber and the creep strains are captured using digital-image correlation.

Moisture and short-term time-dependent behavior of Norway spruce clear wood under compression perpendicular to the grain and rolling shear

ABSTRACT Material properties of wood under compression perpendicular to the grain and rolling shear are important for the engineering design of timber structures. This regards the short-term stiffness and strength, their dependence on the moisture content of wood, as well as the time-dependent behavior. Norway spruce clear wood properties in the transverse plane of wood were studied in an experimental campaign exploiting an earlier developed biaxial test setup. The moisture dependence of the stiffness and strength and the short-term time-dependent creep deformations under compression in the radial direction and under rolling shear were characterized. Loading and unloading stiffness, as well as the strength, were determined in quasi-static tests at five different moisture contents from 4% to 29%. The elastic and viscous stiffnesses were identified in creep tests at three compressive stress levels of 0.50, 0.75, and 1.00 N/mm 2 , and at two rolling shear stress levels of 0.33 and 0.50 N/mm 2 . The test data complements the existing experimental database, especially with novel data regarding the moisture dependence of the rolling shear strength, which showed less moisture dependence than the compressive strength perpendicular to the grain. The results of the creep tests revealed different material properties for the different loading and material directions of wood.

Predicting mechanical properties of clear wood from Acacia mangium provenances using ultrasound

Ultrasound was considered as a means for determining mechanical properties of clear wood in six different Acacia mangium provenances from a trial forest planted in Vietnam. A total of 30 trees (5 trees from each provenance) with no major defects were selected, and a 50-cm-long log was obtained at 1.3 m above the ground from each tree for the assessment of mechanical properties. The measured average ultrasound velocities for provenances tested in the longitudinal direction ranged from 4094 m/s to 4271 m/s. The predicted average dynamic modulus of elasticity (Ed) values varied from 7.42 GPa to 8.70 GPa among provenances. The Ed indicated significant positive correlation coefficients with modulus of elasticity (0.64 to 0.96), modulus of rupture (0.44 to 0.87), and compression strength (0.54 to 0.92) for provenances examined in this study. The results indicated that the use of ultrasound was feasible to determine the mechanical properties of A. mangium provenances planted in Vietnam.

Estimating mechanical properties of clear wood from ten‐year‐old Melia azedarach trees using the stress wave method

The objective of this study was to examine the potential of stress wave velocity (SWV) as a rapid and non-destructive method to estimate the mechanical properties of Melia azedarach wood. The SWV, dynamic modulus of elasticity (MOEd), modulus of elasticity (MOE), modulus of rupture (MOR, bending strength) and density were determined on ninety 20 ⋅ 20 ⋅ 320 mm clear wood specimens, obtained from stems of three ten-year-old M. azedarach trees, and tested at environmental equilibrium in 20°C, 60 % relative humidity (a moisture content of approximately 12 %). There was a statistically significant (0.1 % level) but weak correlation (R2 = 0.23) between the SWV and MOE, but no statistically significant correlation was found between the SWV and MOR. Much better results for prediction of static properties of M. azedarach wood were obtained when SWV and wood density (WD) were used together through calculation of MOEd in the air-dry condition (MOE: R2 = 0.76, MOR: R2 = 0.47), although in the case of MOR a model based on WD alone is slightly better (R2 = 0.58), and WD is also almost as good as MOEd for predicting MOE. It is concluded that SWV coupled with WD can be employed as a predicting parameter to evaluate the mechanical properties of M. azedarach wood during the manufacturing process, although WD alone is also effective. The SWV alone would not be useful due to MOE being almost directly proportional to WD at this moisture content.

Compression Properties of Small Clear Southern Yellow Pine Specimens Tested across Five Decades

Abstract Southern yellow pine (SYP) is one of the most used softwood species in the world. Most of this raw material come from fast-grown plantation trees. It is of interest to determine if SYP clear wood properties may have changed over the long term, in particular whether such properties may have declined. Herein, specific gravity (SG), ultimate compression strength parallel to grain (UCS‖), and UCS perpendicular to grain (UCS⊥) from three samples were compared: Sample 1 tested in 2014; Sample 2 from molding and millwork producers tested in 2017–2019; and Sample 3 from a study conducted in the mid-1960s. With respect to specific gravity (SG), the wood in Sample 1 was significantly lower than that from Samples 2 and 3. With respect to UCS‖, all three samples were statistically different. Adjusting to 12 percent moisture content had no influence on the mean separation of UCS‖. With respect to UCS⊥, no statistically significant differences were detected among the test data from any of the three samples. However, for the UCS data generated from the SG and moisture content–related model, Sample 2 was higher than Sample 3, and Sample 3 was higher than Sample 1, and these differences were statistically significant. Overall, these findings do not suggest that broad or consistent changes or declines of these wood strength properties have occurred during the past five decades.

Ultrasound to determine physical-mechanical properties of Eucalyptus camaldulensis wood

ABSTRACT The present research work had the goal of assessing the use of ultrasound for determining the physical-mechanical properties of clear wood in Eucalyptus camaldulensis from a 5-year-old forest stand located in the municipality of Sinop, Mato Grosso State, Brazil. The selection of trees was carried out according to the diameter at breast height (DBH) and height (H). Forty trees were harvested and a 2 m long log was obtained from each tree for the assessment of physical-mechanical properties. In physical properties, the specific gravity, shrinkage (radial, tangential and volumetric) and anisotropic factor were determined. The dynamic modulus of elasticity (MOE) was estimated by ultrasound applied in the longitudinal direction of the samples. The highest correlation with the mechanical test results was found for dynamic MOE, with R 2 values in the range of 0.30–0.75. Wood density was highly positively correlated with the dynamic MOE of the wood. The use of ultrasound as a non-destructive method was feasible to determine the selected physical-mechanical properties of Eucalyptus camaldulensis wood as a function of propagation speed and the MOE dynamic in most of the assays.

Physical and mechanical properties of clear wood from red oak and white oak

Red oak and white oak are common names of species that grow in the eastern United States with great economic importance. This study aimed to evaluate the visual, physical, and mechanical properties of small clear wood specimens of red oak (Quercus spp.) and white oak (Quercus spp.). The experiments were carried out on defect-free specimens extracted from boards supplied by the Stairbuilders Manufacturers Association (SMA) members. The material was obtained from sawmills located in the eastern half of the United States. A total of 181 boards (90 boards of red oak and 91 boards of white oak) were submitted for tests. Compression strength was found to be higher than the values published in past studies. Red oak exhibited higher MOE and MOR values compared to white oak. The mechanical properties for red oak and white oak have not changed substantially because the average values remain in a range that is very close to the values published in the past 100 years. Thus, the values from the Wood Handbook can still be used for engineering purposes.

Evaluation of a modified Iosipescu shear test method for determining the shear properties of clear wood

A modified Iosipescu shear test method is proposed as an alternative for measuring the shear properties of clear wood. The method adopts four-point asymmetric loading procedure in the Iosipescu shear test but with the loading positions shifted to the neutral axis of the specimen. The original V-notched specimen is replaced by a combination of polyvinyl chloride blocks at two ends and a bow-tie-shaped wood specimen in the middle to provide a better stress pattern at failure. The measured shear strength and shear moduli are compared with results from compression test and off-axis tension test. Finite element analysis is also carried out to study the stress distribution in the wood specimen. Results show that the new shear test setup can provide close-to pure shear stress state in the specimen yielding better estimates of the shear properties of wood. The shear strength obtained by the new test setup is slightly lower than that from the off-axis tensile test which is probably due to the relatively thick specimen chosen in this study.

Ecogeographic variation in black spruce wood properties across Quebec’s boreal forest

Ecogeographic variation in black spruce clear wood properties was investigated for the two main vegetation types of the managed boreal forest of the province of Quebec, Canada. In total, 409 co-dominant and dominant trees from 82 mature stands were sampled. Basic wood density, modulus of elasticity and microfibril angle were measured using SilviScan. Mature fiber length was determined using a high-resolution Fiber Quality Analyzer. Wood growing in pure black spruce stands had longer mature fibers, a significantly denser wood with better mechanical characteristics than the wood growing in mixed stands with balsam fir. All wood properties were clearly influenced by radial growth and species composition.Given the limited number of sample plots for mapping purposes, a two-stage modeling approach was assessed to predict stand-level estimates of black spruce clear wood properties. This scaling-up method, based on field measurements and ring data from 3350 inventory plots, has improved the performance of all models. Stand-level models explained 47%, 57%, 63% and 63% of variance in wood density, modulus of elasticity, microfibril angle and mature fiber length respectively with estimated root mean square errors of 8.9kg/m3, 0.52GPa, 0.60° and 0.06mm.An east-west gradient in black spruce clear wood properties was revealed as possibly the by-product of the change in relative proportions of both studied vegetation types across the study area. The results indicate that the black spruce wood from western regions of the managed boreal forest has a better potential for producing pulp and paper, lumber or engineered products due to its longer mature fibers and higher mechanical properties.

Quantifying the influence of live crown ratio on the mechanical properties of clear wood

Conceptual models of wood formation suggest that trees with large crowns produce wood with reduced mechanical properties due to enhanced auxin production, but few studies have explicitly examined the relationship between crown dimensions and wood properties. Using white spruce (Picea glauca (Moench) Voss) trees harvested from spacing and thinning trials in central Ontario, Canada, this study examines how live crown ratio influences the strength and stiffness of wood. Modulus of rupture (MOR) and modulus of elasticity (MOE) were measured by conducting three-point bending tests on small (150 ×10×10 mm) defect-free samples selected from different radial positions at three heights within the stems. MOR and MOE were strongly and positively related to cambial age, and also increased slightly with sampling height. In addition, MOR showed a significant decrease with increasing live crown ratio ‐ calculated as the ratio of crown length to tree height ‐ in both the spacing and the thinning trials. However, MOE decreased significantly with live crown ratio only in the spacing trial, where the younger trees had a larger range of crown ratios. These results provide tentative support for models of wood formation that link wood quality with crown development, suggesting that crown metrics could be used to predict wood properties before harvest, but doing so may be problematic in mature stands that exhibit less variability in crown dimensions.

SIMPOLE — Simulation of wood poles mechanical behaviour

Generation of virtual poles, based on the statistical distribution of selected visual and physical properties, and the estimation of their mechanical properties are of great help for predicting the quality of the roundwood that a forest stand can provide. With this objective in mind, an algorithm, SIMPOLE (SIMulator of POLEs), was developed. This algorithm allows the generation of pole’s geometry, as well as the mechanical properties of clear wood and the distribution of knots along its length. This generation is made through statistical distributions. The generated poles are simulated, either according to standard EN14251 or according to EN14229, for testing with simple supported beam conditions or with cantilever beam conditions, respectively. The algorithm outputs are: the bending strength, the modulus of elasticity, the location, and cause of failure. The algorithm was calibrated with a sample of 56 maritime pine utility poles and validated with another sample of 57 small diameter maritime pine poles. The results for the validation sample show: for bending strength, a mean error of 16.9%, and for modulus of elasticity, a mean error of 17.2%. Based on these results, the algorithm shows potential to estimate mechanical characteristics of small diameter poles from a forest.

CHARACTERIZING CHANGBAI LARCH THROUGH VENEERING. PART 1: EFFECT OF STAND DENSITY

Changbai larch (Larix olgensis Henry) is one of the main plantation species in the northern part of China, but so far its utilization has been limited to solid wood, pulping, and paper products. As part of a national initiative, the objective of this work was to develop a good understanding concerning how stand management practices affect larch wood and veneer properties. To cope with the variation of initial and final stand density, the term “relative thinning intensity (RTI)” was introduced to describe the effect of stand thinning on the resulting wood and veneer properties. Nine representative sample trees each from four stands were harvested, then trimmed and bucked. Six 1.25 m long bolts along the entire tree stem were systematically cut to peel 2.6 mm thick veneers. Clear wood specimens were also sawn from matched bolts for mechanical testing for the purpose of comparison and validation. The correlation between the main tree variables and properties of clear wood and veneer was analyzed, and the influence of RTI on key wood and veneer properties was examined and compared. A good correlation was found in density and modulus of elasticity (MOE) between larch clear wood and veneer, giving an R2 of 0.75 and 0.71, respectively. This indicates that veneering can be potentially used to characterize this larch species. The stand with the lowest RTI had the shortest rotation but yielded the best properties of both clear wood and veneer, which highlights the importance of stand management in terms of thinning.

A semi-destructive tension method for evaluating the strength and stiffness of clear wood zones of structural timber elements in-service

The paper presents a new semi-destructive method for obtaining a prediction of the tension parallel to the grain properties of clear wood of structural timber members. This method is less intrusive than other existing methods and consists in extracting four small specimens along the length of the timber members. The tension strength and stiffness obtained is intended to be used as input data for the assessment of timber members in situ. Since the method only provides information regarding clear wood, it will have to be used together with other non- or semi-destructive methods that could accommodate the effect of defects on the loss of clear wood properties. The validation of the method was carried out by a comparison with results obtained from a standard method used for determination of clear wood properties. The results show a good agreement between stiffness values but a medium agreement in the case of tension strength.

Measurement of the shear properties of clear wood by the Arcan test

AbstractIn this work, the identification of the shear properties of maritime pine (Pinus pinasterAit.) wood was investigated by applying the Arcan test method. For this purpose, an ad hoc Arcan fixture was designed for which clear wood samples could be tested along all the material planes of symmetry –LR,LTandRTplanes. For the accurate evaluation of the shear moduli, correction factors taking into account the non-uniformity of the shear stress and the shear strain distributions at the gauge section were determined with finite element analyses. Experimentally, two 0/90 rosettes were glued on both frontal and back surfaces of the specimens in order to take into account any through-to-thickness shear strain variation. It was found that the Arcan test is suitable for the identification of the shear moduli of wood in all its natural planes. The failure of the Arcan specimens systematically occurred under a concentrated stress state nearby the V-notches. Nevertheless, it was shown that an accurate estimation of the shear strengths of wood can be achieved by the Arcan test.

Mechanical Grading of Round Timber Beams

Current procedures used to sort round timber beams into structural grades rely on visual grading methods and property assignments based on modification of clear wood properties. This study provides the technical basis for mechanical grading of 228 mm (9 in.) diameter round timbers. Test results on 225 round Engelmann spruce–alpine fir–lodgepole pine beams demonstrate the conservative nature of current timber strength assignments. A good correlation was obtained between static bending strength and static modulus of elasticity (MOE), and between bending properties and dynamic MOE determined in transverse vibration. Relationships were also developed between compressive strength parallel to grain, bending strength, and MOE by transverse vibration. The property relationships developed in this study were used to propose grading criteria consistent with procedures used with mechanically graded softwood dimension lumber. Estimated grade yields obtained using the proposed criteria show that significant increases i...

Influence of silvicultural regime on wood structure characteristics and mechanical properties of clear wood in Pinus sylvestris

The objective of the study presented here was to evaluate the influence of two contrasting silvicultural regimes on the structural characteristics and mechanical properties of different wood tissue types at different heights in Scots pine (Pinus sylvestris L.) trees, and reasons for these differences. Wood samples were taken from two stands (a dense 85-year-old stand established by direct seeding and a 56-year-old widely spaced stand established by planting, designated SDR and PWR, respectively in the boreal zone of Sweden). The wood properties associated with the examined silvicultural regimes differed, in terms of both structural characteristics (with up to fivefold differences between SDR and PWR) and mechanical properties (with up to almost threefold differences between SDR and PWR). Differences between the regimes were highest for stiffness, followed by strength and hardness properties and lowest for relative stiffness after 1000 h of loading (creep) (with higher parameter values for SDR than for PWR in each case). The rankings could be explained by differences among the mechanical properties in their sensitivity to maturation of wood characteristics. In conclusion, silvicultural regimes have great potential to regulate wood structural characteristics and mechanical properties, apparently due to the influences of the green crown and growth rate on the vascular cambium, the strength of which vary throughout the rotation period. A silvicultural regime could therefore be seen as a tool that can be used to select material qualities and to make wood a more homogenous material for engineers.

Determination of elastic properties of clear wood by the homogenization method in two dimensions

A two-dimensional homogenization model for determining elastic properties of clear wood is described. It is based on the elastic properties of the chemical constituents of the wood and the known geometry of the fibers. The model is valid for clear wood and can be used to determine the state of stresses at both micro and macrostructural levels. Stress and displacement analysis were made with the finite element method. Experiments in bending, compression parallel- and perpendicular-to-grain were made with six different Mexican wood species, including softwoods, temperate climate hardwoods and tropical hardwoods using small clear wood specimens. Such tests were made at various moisture content levels and the results of the model match closely with experimental data. The analytical technique can be readily extended to three dimensions. The data generated with this model can be used in further studies for material and structures optimization purposes.

Estimation ofPinus radiata D. Don clear wood properties by near-infrared spectroscopy

The use of calibrated near-infrared (NIR) spectroscopy for predicting of a range of solid wood properties is described. The methods developed are applicable to large-scale nondestructive forest resource assessment and to tree breeding and silviculture programs. A series ofPinus radiata D. Don (radiata pine) samples were characterized in terms of density, longitudinal modulus of elasticity (E L), and microfibril angle (MFA). NIR spectra were obtained from the radial/longitudinal face of each sample and used to generate calibrations for the measured physical properties. The relations between laboratory-determined data and NIR fitted data were good in all cases, with coefficients of determination (R 2) ranging from 0.68 for 100/MFA to 0.94 for densitystrip. A good relation (R 2 = 0.83) was also obtained forE L estimated using data collected by SilviScan-2. The finding suggests that an NIR instrument could be calibrated to estimate theE L of increment cores based on SilviScan data. In view of the rapidly expanding range of applications for this technique, it is concluded that appropriately calibrated NIR spectroscopy could form the basis of a testing instrument capable of predicting a range of properties from a single spectrum obtained from the product or from the raw material.