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 wood.

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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.

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 uncertain.

A flame retardant composition (FRC) composed of a surface-treated calcium carbonate-based mineral, having high porosity and loaded with deliquescent calcium chloride, was assessed for its potential as a flame retardant. Two FRCs with 16% and 26% calcium chloride (dry solid) stored in the pore structure, respectively, were studied with respect to their ability to absorb and release free water and their efficacy in melamine-urea-formaldehyde (MUF)bonded wood composites was investigated. Water absorption capacity was determined by performing absorption tests at a temperature of 20°C and relative humidity (RH) of 65% and 95% and the water release behaviour was studied by performing thermogravimetric analysis. The FRCs have the capacity to hold substantial amounts of water (up to 60 wt. %), however still behave as a free-flowing powder. The influence of addition of 10 and 20 wt.% FRC in wood composites on reaction to fire and strength properties was determined by measuring the selfextinguishing time after flame exposure and internal bond strength, respectively. These effects were evaluated by comparing to ground calcium carbonate (GCC) and commercially available nitrogen containing phosphorus based fire retardant. Although the FRCs had a negative impact on internal bond strength, the results confirmed their flame retardant potential and showed that 10-15 % by weight of the flame retardant would be a good compromise, in terms of the trade-off between flame retardancy and mechanical properties. The synergistic effects of multiple flame retardancy reaction mechanisms due to the presence of inorganic minerals and a hygroscopic agent, CaCl2, are also discussed. The unique properties of the FRC, which allow to exploit the fire retardant potential of CaCl2 while at the same time eliminating the risk associated with the emission of hydrogen chloride gas during combustion, is confirmed by the results of FTIR spectroscopic analyses of the flue gas.

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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 tangential. Untersuchungen zum physikalischen und mechanischen Verhalten von Bergahorn (Acer pseudoplatanus L.) Zusammenfassung Die physikalischen und mechanischen Eigenschaften von Bergahorn (Acer pseudoplatanus L.) wurden eingehend untersucht, um eine Grundlage für eine dreidimensionale Materialmodellierung für Struktursimulationen (z.B. mit der Methode der finiten Elemente), basierend auf dieser Holzart, zu schaffen. Bei den physikalischen Eigenschaften wurden das Quellen, die Wasseraufnahme, der Wasserdampfdiffusionswiderstand und die Wärmeleitfähigkeit geprüft sowie bei den mechanischen Eigenschaften die Zug-, Biege-und Druckfestigkeit, der Elastizitätsmodul (statisch und dynamisch), die Poissonzahl, die Scherfestigkeit, der Schubmodul und die Bruchzähigkeit bestimmt. Die Untersuchungen wurden in den meisten Fällen feuchteabhängig durchgeführt und ebenso in allen drei anatomischen Hauptrichtungen: längs, radial und tangential.