Moisture-dependent elastic and strength anisotropy of European beech wood in tension

While the general mechanical behaviour of wood is known, its moisture-dependent elastic and strength anisotropy remains little studied. Given the anisotropic and hygroscopic nature of wood, a characterisation of wood mechanical behaviour will require knowledge of its moisture-dependent properties in relation to the three principal axes of anisotropy. The present study examines the influence of the moisture content (MC) on the elastic and strength anisotropy of beech wood (Fagus sylvatica L.). Selected elastic and strength parameters, including the anisotropic Young's moduli, Poisson's ratios, yield and ultimate stress values and the fracture toughness in the TR, TL, RT and RL directions, are determined in uniaxial tension and compact tension tests at different moisture conditions. A distinct moisture dependency is shown for the elastic and strength behaviour of beech wood. With the exception of some Poisson's ratios, all investigated elastic and strength parameters are shown to decrease with increasing MC. The two- and three-dimensional representation of the compliance matrix, and the two-dimensional visualisation of a yield surface, provides a valuable overview on the moisture-dependent elastic and strength anisotropy of beech woo

Moisture-dependent orthotropic tension-compression asymmetry of wood

The influence of moisture content (MC) on the tension-compression (Te-Co) asymmetry of beech wood has been examined. The elastic and strength parameters, including Te and Co Young's moduli, Poisson's ratios, and ultimate and yield stress values, were determined and compared in terms of different MCs for all orthotropic directions. The results reveal a distinctive Te-Co strength asymmetry with a moisture dependency that is visualized clearly by the Te to Co yield stress ratio. The Te-Co asymmetry is further shown by the inequality of the elastic properties, known as the "bimodular behavior”. The latter is proven for the Young's moduli values in the radial and tangential directions and for individual Poisson's ratios. Although the bimodularity of the Young's moduli is significant at low MC levels, there is no evidence of moisture dependency on the Te-Co asymmetry of the Poisson's ratio

Determining moisture-dependent elastic characteristics of beech wood by means of ultrasonic waves

The present study investigates the influence of moisture content on the elastic characteristics of beech wood (Fagus sylvatica L.) by means of ultrasonic waves. A set of elastic engineering parameters (i.e. three Young's moduli, three shear moduli and six Poisson's ratios) is determined at four specific moisture contents. The results reveal the significant influence of the moisture content on the elastic behaviour of beech wood. With the exception of some Poisson's ratios, the engineering parameters decrease with increasing moisture content, indicating a decline in stiffness at higher moisture contents. At the same time, wood anisotropy, displayed by the two-dimensional representation of the velocity surface, remains almost unchanged. The results prove that the ultrasonic technique is suitable for determining the elastic moduli. However, non-diagonal terms of the stiffness matrix must be considered when calculating the Young's moduli. This is shown experimentally by comparing the ultrasonic Young's moduli calculated without, and allowing for, the non-diagonal terms. While the ultrasonic technique is found to be reliable to measure the elastic moduli, based on the measured values, its eligibility to measure the Poisson's ratios remains uncertai

Moisture dependent physical-mechanical properties from beech wood in the main directions

Hardwood is increasingly trying to get established in the building industry in order to realise a larger material output and to take advantage of the superior mechanical properties of hardwood in comparison to softwood for structural applications. For calculations of stress and strain in boards and glued-laminated timbers it is essential to know the specific values of wood in the main directions: longitudinal, radial and tangential. Therefore, the specific values of Young’s modulus, shear modulus, Poisson’s ratio, the specific values of strength and also these of mass and heat flux (diffusion coefficient, thermal conductivity) were determined on European beech

Evaluating the use of calcium hydrogen phosphate dihydrate as a mineral-based fire retardant for application in melamine-urea-formaldehyde ( MUF )-bonded wood-based composite materials

Calcium hydrogen phosphate dihydrate (DCPD) was evaluated for its potential as a mineral fire retardant (FR) for application in melamine-urea-formaldehyde (MUF)-bonded wood composites. The efficacy as FR was studied in melamine-urea-formaldehyde (MUF)-bonded three-layer particleboard as a function of addition quantities of 10-, 20- and 30¿wt%. Resistance to fire and mechanical properties were determined by measuring the self-extinguishing time after flame exposure and internal bond strength, respectively. Combustion behavior was examined on samples with 20¿wt% DCPD addition by performing cone calorimetry experiments. The efficacy of DCPD was evaluated by determining the heat release, total heat release rate, smoke production, and smoke production rate and compared to another promising mineral-based fire-retardant composition (FRC) based on hydroxyapatite (HA) with deliquescent salt and HA alone. The effect of FR on the curing behavior of MUF in relation to mechanical properties was determined through viscosity measurements of MUF with 10 wt% addition of FR. The results confirmed the fire-retardant characteristics of DCPD in wood composites, albeit at higher application rates when compared to the FRC, however with no negative impact on resin curing time or mechanical strength. Based on the demonstrated compatibility in MUF, DCPD is considered a promising mineral extender of other FRs for application in UF-based wood composites.Peer ReviewedPostprint (author's final draft

Investigations on the physical and mechanical behaviour of sycamore maple ( Acer pseudoplatanus L.)

Physical and mechanical properties of sycamore maple (Acer pseudoplatanus L.) were extensively investigated as basis for three-dimensional material modelling for structural simulations (e.g., with finite element method) based on this species. The physical properties of swelling, water absorption, water vapour resistance and thermal conductivity were tested and the mechanical properties of tensile, bending and compression strength and of Young's modulus (static and dynamic) as well as of Poisson's ratio, shear strength, shear modulus and fracture toughness were determined. The tests were carried out for most of the features depending on moisture content and also in all three anatomical main directions: longitudinal, radial and tangentia

Structural mechanism of JH delivery in hemolymph by JHBP of silkworm, Bombyx mori

Juvenile hormone (JH) plays crucial roles in many aspects of the insect life. All the JH actions are initiated by transport of JH in the hemolymph as a complex with JH-binding protein (JHBP) to target tissues. Here, we report structural mechanism of JH delivery by JHBP based upon the crystal and solution structures of apo and JH-bound JHBP. In solution, apo-JHBP exists in equilibrium of multiple conformations with different orientations of the gate helix for the hormone-binding pocket ranging from closed to open forms. JH-binding to the gate-open form results in the fully closed JHBP-JH complex structure where the bound JH is completely buried inside the protein. JH-bound JHBP opens the gate helix to release the bound hormone likely by sensing the less polar environment at the membrane surface of target cells. This is the first report that provides structural insight into JH signaling

Influence of biostimulant application in containerized Eucalyptus globulus Labill. seedlings after transplanting

The use of biostimulants (amino acid containing protein hydrolysate) in forestry field has re- ceived much less attention so far than in agriculture. Promising evidences were reported in literature with useful application for nursery activities, stimulating early growth and reducing transplanting stress. This study investigates the potential benefits induced by an amino acid-based animal-derived protein hydro- lysate biostimulant (Siapton® by Isagro) in containerized Eucalyptus globulus seedlings following transplant- ing. Foliar and soil drench applications were applied using two different concentrations each (2.5 ml.l−1 and 5.0 ml.l−1 for foliar, 10 ml.l−1 and 20 ml.l−1 for soil). Measures on seedling height, apical shot formation, total aboveground (dry weight of leaves and stem) and belowground biomass (dry weight of roots) 120 days after transplanting were made to quantify the effect on growth. The contrasts analysis on results revealed a positive effect of the biostimulant on many of the measured parameters, especially with foliar application using the lowest concentration (2.5 ml.l−1). The foliar application was overall suggested as more efficient than soil drench also allowing lower inputs (i.e. biostimulant quantity). The main consequence of the treatment was an increased biomass allocation in the stem (above ground biomass) due to a stimu- lated leaves production which might suggest an increased photosynthetic activity and growth. Conversely no influence was detectable on total height of seedlings neither on the collar diameter. The biostimulant treatment on containerized Eucalyptus globulus positively influenced some features of seedlings’ growth after transplanting and the use of biostimulant with foliar application during the hardening phase in the nursery, appears to be a promising technique to potentially improve seedling growth after transplanting. An inter- esting impact from application of biostimulant on biomass accumulation following transplanting was here demonstrated. Anyway, further research to verify the results on different tree species as well as under open field conditions is envisioned

Moisture-dependent elastic and strength anisotropy of European beech wood in tension

ISSN:0022-2461ISSN:1573-480

Moisture-dependent orthotropic tension-compression asymmetry of wood

Abstract The influence of moisture content (MC) on the tension-compression (Te-Co) asymmetry of beech wood has been examined. The elastic and strength parameters, including Te and Co Young’s moduli, Poisson’s ratios, and ultimate and yield stress values, were determined and compared in terms of different MCs for all orthotropic directions. The results reveal a distinctive Te-Co strength asymmetry with a moisture dependency that is visualized clearly by the Te to Co yield stress ratio. The Te-Co asymmetry is further shown by the inequality of the elastic properties, known as the “bimodular behavior”. The latter is proven for the Young’s moduli values in the radial and tangential directions and for individual Poisson’s ratios. Although the bimodularity of the Young’s moduli is significant at low MC levels, there is no evidence of moisture dependency on the Te-Co asymmetry of the Poisson’s ratios.</jats:p