Annual Ring Structure Research Articles

Determination of dynamic elastic moduli and shear moduli of aged wood by means of ultrasonic devices

Due to ecological and environmental factors, re-using aged wood is becoming more and more important, also in applications where mechanical strength plays a central role. The aim of this study was to examine specific mechanical parameters of naturally aged and dried wood and to better understand the influence of aging on the elastic behaviour of wood. To this aim, measurements on boards and on small, clear wood specimens were carried out. Ultrasound velocities of longitudinal and, in some cases, of transversal waves were measured to determine dynamic elastic moduli and shear moduli. The measurements were performed on structural timber of aged Norway spruce (aged wood) and compared with specimens of recently cut and kiln dried timber of the same species (recent wood) as a reference with comparable density properties and average annual ring width. The measurements revealed higher values of dynamic elastic modulus for aged wood in the longitudinal and radial directions, but no significant difference was found in the tangential direction or in the shear moduli. It is supposed that the difference is more likely a consequence of variability in densities and the structure parameters (annual ring structure, microfibril angle, growth conditions) rather than a consequence of the wood age. The relation between the dynamic elastic modulus in the longitudinal direction and wood density was nearly the same for aged and recent wood specimens, so with increased prudence, grading methods developed for recent wood can also be applied for aged wood.

カラマツにおける間伐強度の違いが年輪構造や丸太のヤング係数に及ぼす影響

カラマツにおける間伐強度の違いが年輪構造や丸太のヤング係数に及ぼす影響

Microstructure–Stiffness Relationships of Common Yew and Norway Spruce

Abstract: Yew (Taxus baccata L.) exhibits among conifers a unique macroscopic elastic behaviour. For example, it shows a comparatively low longitudinal elastic modulus related to its comparatively high density. We herein explore the microstructural origin of these peculiarities, aiming at the derivation of microstructure–stiffness relationships. We measure stiffness properties of yew at different hierarchical levels and compare them to corresponding stiffnesses of Norway spruce (Picea abies [L.] Karsten). Cell wall stiffness is investigated experimentally by means of nanoindentation in combination with microscopy and thermogravimetric analysis. On the macroscopic level, we perform uniaxial tension and ultrasonic tests. Having at hand, together with previously reported stiffnesses, a consistent data set of mechanical, chemical and physical properties across hierarchical levels of wood, we discuss influences of microstructural characteristics at different scales of observation. Moreover, a micromechanical model is applied to predict trends of effects of the microstructure on the investigated stiffness properties. On the cell wall level, particularly, the amount of cellulose and its orientation – which was earlier reported to be distinctly different for yew and spruce – result in differences between the two considered species. On the macroscopic scale, model predicted effects of the annual ring structure on transverse stiffness and shear stiffness are found to be smaller than effects of the microfibril angle and mass density.

Fire History of a Douglas-Fir-Oregon White Oak Woodland, Waldron Island, Washington

The last 100 years have seen a marked decline in Oregon white oak woodlands in the Puget Sound region. Efforts to restore the woodlands cannot hope to be successful unless the role fire has played in maintaining them in the past is understood. A fire scar chronology was constructed from a Pseudotsuga menziesii—Quercus garryana community within a 155 ha study site on southeast Waldron Island, Washington. Sixty-two scars were identified on 15 crossdated Pseudotsuga samples that documented fire events between 1530 and 1908. A master tree-ring chronology was created for the period 1685 to 2004. Composite fire intervals and individual-tree fire intervals were used to characterize the fire history. Seasons of past fires were determined by analyzing fire scar position within annual ring structure. For the historical period 1700–1879, the composite mean fire return interval (FRI) was 7.4 yrs, and the mean individual-tree FRI was 18.4 yrs. The historic period mean individual-tree FRI was 18.4 yrs. In contrast, only three fires were recorded during the settlement/modern period (1880–2004), resulting in a mean individual-tree FRI of 103.8 yrs. Seasonality of past fires indicates that most fires occurred during late summer and fall. No evidence of spring or early summer burning was detected. Our study of the fire history for a site on Waldron Island shows a marked reduction in fire frequency between the historical and settlement/modern period, which we interpret as reflecting declines in Native American population size and activity and the eventual cessation of deliberate ignitions by Native Americans.

A 3D multilevel model of damage and strength of wood: Analysis of microstructural effects

A 3D hierarchical computational model of damage and strength of wood is developed. The model takes into account the four scale microstructures of wood, including the microfibril reinforced structure at nanoscale, multilayered cell walls at microscale, hexagon-shape-tube cellular structure at mesoscale and annual rings at the macroscale. With the use of the developed hierarchical model, the influence of the microstructure, including microfibril angle (MFA), the cell shape and the wood density (annual ring structure), differences between earlywood and latewood as well as microstructural arrangements and cellulose strength distributions on the tensile strength of wood is studied numerically. Good agreement of the theoretical results with experimental data has been obtained.

Delamination in Wood, Wood Products and Wood-Based Composites

<i>Delamination in Wood, Wood Products and Wood-Based Composites</i>

Evaluating the dendroclimatological potential of central Appalachian Table Mountain pine (Pinus pungens LAMB.)

Table Mountain pine (Pinus pungens Lamb.) is an Appalachian endemic that occurs in a patchy distribution from Georgia to Pennsylvania on xeric, fire-prone sites. Beginning in the 1990s, Table Mountain pine first showed usefulness in reconstructing fire regimes in these xeric Appalachian forests. The next step in Table Mountain pine research, the relationships between fire occurrence and climate variables, cannot happen until the dendrochronological potential of the species has been proven. This research investigates the annual ring structure and formation, relationship between climate and growth, and dendrochronological dating between trees in the same stands to prove the species’ effectiveness in climate reconstructions. Table Mountain pine cores and cross-sections were collected from four sites in the Virginia Appalachian Mountains. Results indicate that the species is sensitive to climate (monthly precipitation and temperature, PDSI and PHDI). Climate analyses revealed that Table Mountain pine growth is reduced when the previous year’s September is drier than normal, the current year’s February is wetter than average, and the winter is colder than average. Results of these climate analyses illustrate a regional climate signal in Table Mountain pine stands; however, results from individual sites provided more significant details on the influence of climate on the species. Published by Elsevier GmbH.

Functional gradient effects explain the low transverse shear modulus in spruce – Full-field strain data and a micromechanics model

An important failure mechanism in glulam beams is cracking caused by out-of-plane transverse loads. It has been demonstrated that the low transverse shear modulus G RT in spruce contributes to large transverse strain inhomogeneities due to the annual ring structure in combination with shear coupling effects. In the present study, improved understanding of annual ring effects is achieved by the development of a micromechanical model. It relates the functional density gradient in spruce annual rings to shear modulus G RT . The geometrical basis is a hexagonal cell model, and in shear it is demonstrated to deform primarily by cell wall bending. Full-field strain measurements by digital speckle photography (DSP) show very strong correlation with predicted shear strains at the annual ring scale. Predictions are obtained by implementation of the micromechanics model in a finite element (FE) model developed for the single cube apparatus shear specimen. The low G RT of spruce is due to the strong dependence of G RT on relative density ρ / ρ s ( G RT ∝ ( ρ / ρ s ) 3 ) . This is particularly important in spruce. Even though average density is typically quite high, the functional gradient structure includes local densities as low as 200 kg / m 3 .

Untersuchungen zu ausgewählten Eigenschaften von Fichtenklangholz aus Graubünden

This survey focuses on the mechanical properties of spruce tonal wood from three different locations in the canton of Grisons, Switzerland. In addition, the material from one location was stored under water for three months in order to test the influence of extractives. The tests included the analysis of the annual ring structure, measurements of the sound velocity with longitudinal and transverse waves in the three main directions, bending strength, bending modulus of elasticity (MOE), eigenfrequency, logarithmic decrement of the damping, sorption and swelling. Single specimens were taken to measure the extractives content. The tested wood properties suggest tonal wood of high quality for all the locations. No significant differences of the wood properties, except density-related ones, were found between the three locations. The water storage resulted in the removal of extractives, but no significant change in properties could be found.

The dendrochronology of Callitris intratropica in northern Australia: annual ring structure, chronology development and climate correlations

In this study we demonstrate the significant dendrochronological potential of Callitris intratropica, a native conifer distributed across much of the seasonal tropics of northern Australia. We developed two rigorously cross-dated chronologies from sites in the Northern Territory, Australia. The first chronology (1965–2004) was developed from plantation C. intratropica of known-age at Howard Springs and was heavily replicated both within and among trees to evaluate the quality of cross-dating for the species. The second chronology (1847–2006) was developed from trees growing naturally near Pine Creek and compared with long-term instrumental climate records to assess the potential for dendroclimatic reconstructions. Both chronologies had mean interseries correlations &gt;0.65, the highest reported for a tropical tree species. The Howard Springs chronology demonstrated that C. intratropica produces anatomically distinct annual growth rings with the consistent ring-width variation within and among trees necessary for rigorous dendrochronological studies. The Pine Creek chronology exhibited statistically significant correlations with rainfall and the Palmer Drought Severity Index (PDSI; integrated measures of plant water stress), and to a lesser extent temperature. The strongest correlations between the climate data and tree-ring width indices were for early monsoon rainfall (October–December; Pearson’s r = 0.53) and late monsoon PDSI (May; Pearson’s r = 0.41). Our study demonstrates the significant potential of high-quality dendrochronological research on mainland Australia in general, and of C. intratropica, specifically, to reconstruct historical variation of the Australian monsoon system. In addition, C. intratropica may be able to provide novel insights into the dynamics of forests in the seasonal tropics of northern Australia and the role of disturbances, such as fire and cyclones, on these ecosystems.

Shear coupling effects on stress and strain distributions in wood subjected to transverse compression

The mechanical behaviour of a wood board subjected to transverse compression is relevant to the performance of glulam beams and solid wood structures. The wood material can be described as polar orthotropic, due to the annual ring structure and to the differences in moduli in different directions in the radial–tangential plane. Strain measurements are performed on single wood boards using a whole-field digital speckle photography technique. Finite element analysis is performed and compared with experimental data. Good agreement in terms of strain fields and apparent moduli is observed between predictions and data. The experimental data show strong variations in local strain due to the polar orthotropic behaviour of wood in this plane, and the extremely low value for shear modulus G rt as compared with the other moduli. This leads to shear coupling effects resulting in large local shear deformation and correspondingly low effective stiffness under transverse global loading.

Preparation and Characterization of Three Dimensions Chitosan Rods with Biomimetic Layered Structure Similar to Annual Ring

Inspired by the annual ring structure of wood, a cylindrical semi-permeable chitosan gel membrane was chosen as a template to separate chitosan solution from NaOH coagulation solution. Three dimensions (3D) chitosan (CS) rods (Φ5×80 mm) with layered structure similar to annual ring of wood were prepared via a novel and simple in-situ intermittently precipitating method. These chitosan rods presented quite good mechanical properties with bending strength and shear strength of 102MPa and 31MPa respectively. The concentric circles layered structure was approved by SEM characterization, the mechanism of preparation and the relationship between structure and properties of chitosan rods were also discussed.

Effects of elevated CO2 concentration on growth, annual ring structure and photosynthesis in Larix kaempferi seedlings

We evaluated the effects of elevated carbon dioxide concentration ([CO2]) and two nutrient regimes on stem growth rate, annual ring structure and temporal variations in photosynthetic characteristics of seedlings of Japanese larch (Larix kaempferi (Lamb.) Carr.). Seedlings were grown in phytotron chambers in an ambient (360 ppm) or an elevated (720 ppm) [CO2] in two nutrient regimes for one growing season. Elevated [CO2] reduced stem height and increased stem basal diameter compared with ambient [CO2]. The effect of elevated [CO2] on growth tended to be greater at high-nutrient supply than at low-nutrient supply. Elevated [CO2] had no significant effect on ring width or the number of tracheids per radial file. There was no obvious difference in cell wall thickness or the relative area of the cell wall between seedlings grown in ambient or elevated [CO2]. Although growth in elevated [CO2] resulted in a slight increase in cell diameter, the increase had a relatively minor effect on the relative area of the cell wall. Net assimilation rate increased in response to elevated [CO2]; however, the increase in whole-crown photosynthetic rate (Total Agrowth) in seedlings in the elevated [CO2] treatment was minimal because of the smaller specific needle area and acclimation of the photosynthetic characteristics of the needles to the growth [CO2]. In conclusion, we observed no obvious enhancement in the capacity for carbon fixation in Japanese larch seedlings grown in the presence of elevated [CO2] that might be attributable to changes in stem growth. However, elevated [CO2] caused changes in the temporal pattern of stem growth and in some anatomical features of the tracheids.

A stable isotope-based approach to tropical dendroclimatology

We describe a strategy for development of chronological control in tropical trees lacking demonstrably annual ring formation, using high resolution δ 18O measurements in tropical wood. The approach applies existing models of the oxygen isotopic composition of alpha-cellulose (Roden et al., 2000), a rapid method for cellulose extraction from raw wood (Brendel et al., 2000), and continuous flow isotope ratio mass spectrometry (Brenna et al., 1998) to develop proxy chronological, rainfall and growth rate estimates from tropical trees lacking visible annual ring structure. Consistent with model predictions, pilot datasets from the temperate US and Costa Rica having independent chronological control suggest that observed cyclic isotopic signatures of several permil (SMOW) represent the annual cycle of local rainfall and relative humidity. Additional data from a plantation tree of known age from ENSO-sensitive northwestern coastal Peru suggests that the 1997–8 ENSO warm phase event was recorded as an 8‰ anomaly in the δ 18O of α-cellulose. The results demonstrate reproducibility of the stable isotopic chronometer over decades, two different climatic zones, and three tropical tree genera, and point to future applications in paleoclimatology.

画像相関法による針葉樹の横圧縮ひずみ分布解析

Strain distributions on a cross section of softwood under transverse compression were analyzed in detail using digital image correlation method. We discussed the relationship between compression strain distributions in an annual ring and anatomical structure (earlywood and latewood). In radial compression, local large shear strains were observed in the edge of earlywood near annual ring boundary where mechanical properties change abruptly along radial direction. In a plastic region of stress-strain curve we found a row of large compression strain that is thought to be cell-wall collapse in earlywood. A start point of the row of large compression strain was the edge of earlywood in which the large shear strain were observed, because the radial wall of sheared cell are easily buckled. In the case of 45 degree compression, large compression strain along loading direction was observed in earlywood. Large expansion strain across the loading direction was also observed in the same area because of Poisson's ratio effect. As the strains were transformed to radial-tangential coordinate system, large shear strain and little normal strain were observed in early wood. The shear strain under 45 degree compression was larger than that under radial compression. The former is the shear strain that is usually called rolling shear.

Growth and annual ring structure of Larix sibirica grown at different carbon dioxide concentrations and nutrient supply rates.

We compared effects of ambient (360 vpm) and elevated (720 vpm) carbon dioxide concentration ([CO2]) and high and low nutrient supply rates on stem growth, annual ring structure and tracheid anatomy of Siberian larch (Larix sibirica Ledeb.) seedlings over two growing seasons. Elevated [CO2] had no significant effect on either stem height or diameter growth; however, both stem height and diameter growth were enhanced by the high nutrient supply rate, and these increases were stimulated by elevated [CO2]. Elevated [CO2] tended to increase the width of the annual xylem ring, the number of cells in a radial file spanning the ring, and tracheid lumen diameter, whereas it tended to reduce cell wall thickness, although there were no statistically significant CO2 effects on tracheid anatomy. Changes in tracheid cell morphology seemed to be dependent on changes in shoot elongation rates.

Effect of growth on wood properties for Japanese larch (Larix kaempferi): Differences of annual ring structure between corewood and outerwood

To investigate the relations between growth and the wood properties of Japanese larch (Larix kaempferi), six sample trees of varied ages and radial growth were felled and the ring width, ring density, percentage of latewood, and some other factors were determined. There were significant differences in ring density and percentage of latewood between sample trees with vigorous growth and those with poor growth. In corewood the ring density decreased with increasing ring width for all sample trees, whereas in outerwood this trend did not appear. Moreover, the latewood width increased with the increment of ring width only in outerwood, whereas there was almost no change in the corewood. The variation in patterns of ring width, ring density, and percentage of latewood in the radial direction and the relation with height was also studied.

A preliminary study on unbiased volume estimation of resin pockets using stereology to interpret CT-scanned images from one spruce log

Stereological methods for the volume estimation of resin pockets in saw logs were studied using computed tomography (CT) and image analysis. The Cavalieri theorem was applied for transverse sections and the Pappus theorem was applied for longitudinal radial sections. Stereology applied on wood has to consider both the linear orientation of tracheids and rays, and the circular, lamellar oriented structure of annual rings. The precision of the estimates is illustrated with varying step length between sections, i.e. varying sample size and sampling intensity. To estimate the volume of resin pockets in one log with a coefficient of error of less than 10% requires a step length of 80 mm between transverse sections or ten radial longitudinal sections 18 degrees apart. Here, the resolution of 1.37 x 1.37 x 5 mm overestimated the true volume of resin pockets. Large resin pockets can be detected, whereas detection of small resin pockets, which involved differentiation between resin pockets and compression wood, was difficult with the CT-scanner. This study proves that implementation of stereology on wood can be a good tool for quantitative analysis of resin pockets, which also means that the methods are suited for effective quality control of resin pockets in sawn timber

The influence of inhomogeneity on the propagation of ultrasound in wood

The use of ultrasound for determining the elastic constants of materials is a well-established science for homogeneous materials such as metals. However, its extension to anisotropic, inhomogeneous materials such as wood has proved more problematic. Wood is modelled as an orthorhombic material with the influence of inhomogeneities generally being neglected. For this paper the potential influence of inhomogeneities on waves propagating in the radial direction was considered. Within ring density and ultrasonic velocity measurements were made. A model for ultrasound propagation in the radial direction was then constructed which treats the annual ring structure in the radial direction as a layered structure and predicts the occurrence of stop bands in the frequency domain. Evidence for the existence of such stop bands is considered.

EFFECT OF COMPOSITE STRUCTURE ON STRAIN AND FAILURE OF LAMINAR AND WAFER COMPOSITES

The effect of composite structure on the distribution of strain and failure modes in wood laminar and wafer composites was investigated. Mechanical testing was performed using bending tests of solid wood, plywood, and oriented strandboard specimens (OSB) in accordance with ASTM D143-83, Standard Methods of Testing Small Clear Specimens of Timber [1], and ASTM D3043-83, Standard Method of Testing Structural Panels in Flexure [2], The strain distributions were measured using a new technique, the digital image correlation technique Strain distributions from bending tests on small, clear specimens of solid wood indicated close agreement with conventional beam theory and exact correlation with the failure patterns oflht specimens. The layered annual ring structure of the solid wood controlled the path of the tension cracks. Neither composite board followed conventional beam theory entirely. Of the two composites investigated in this study, the laminated veneer board exhibited behavior closer to conventional theory and exhibited the least correlation with composite structure. The wafer composite exhibited strain patterns most closely related to the arrangement of the composite strands.