Investigations on the sorption behaviour of selected wood species from cameroon

The sorption isotherms during adsorption and desorption of 25 wood species from Cameroon (included 3 species from plantation in Togo) were determined. In addition, the chemical compositions of these wood species were tested. The equilibrium moisture contents in a normal climate varied between 10,55 % and 15,6 %. A clear influence of the proportion of extractives can be seen. The maximum differences between adsorption and desorption varied between 2,3 % and 3,6 %

Time dependence of the orthotropic compression Young's moduli and Poisson's ratios of Chinese fir wood

The time dependency of the orthotropic compliance for Chinese fir wood [Cunninghamia lanceolata (Lamb.) Hook] has been investigated by performing compressive creep experiments in all orthotropic directions. Time evolution of the creep strain in the axial and lateral directions was recorded by means of the digital image correlation (DIC) technique, to determine the diagonal and nondiagonal elements of the viscoelastic compliance matrix. The results reveal the significant influence of time on the mechanical behavior. The orthotropic nature of the viscoelastic compliance is highlighted by the different time dependency of the Young's moduli and the Poisson's ratios obtained for the individual directions. Differences among the time-dependent stress-strain relationship determined at the 25, 50, and 75% stress levels indicate that the viscoelastic behavior of wood is also load-dependent. A Poisson's ratio values, which are increasing with time in νLR, νLT, νRT, νTR, and decreasing in νRL and νTL, demonstrate that the creep strain is influenced by loading directions. The substantially different time dependency of the nondiagonal elements of the compliance matrix further reveals the orthotropic compliance asymmetry and emphasizes the complexity of the viscoelastic character of wood

Flax, Basalt, E-Glass FRP and Their Hybrid FRP Strengthened Wood Beams: An Experimental Study

In this study, the structural behavior of small-scale wood beams externally strengthened with various fiber strengthened polymer (FRP) composites (i.e., flax FRP (FFRP), basalt FRP (BFRP), E-glass FRP ("E" stands for electrical resistance, GFRP) and their hybrid FRP composites (HFRP) with different fiber configurations) were investigated. FRP strengthened wood specimens were tested under bending and the effects of different fiber materials, thicknesses and the layer arrangements of the FRP on the flexural behavior of strengthened wood beams were discussed. The beams strengthened with flax FRP showed a higher flexural loading capacity in comparison to the beams with basalt FRP. Flax FRP provided a comparable enhancement in the maximum load with beams strengthened with glass FRP at the same number of FRP layers. In addition, all the hybrid FRPs (i.e., a combination of flax, basalt and E-glass FRP) in this study exhibited no significant enhancement in load carrying capacity but larger maximum deflection than the single type of FRP composite. It was also found that the failure modes of FRP strengthened beams changed from tensile failure to FRP debonding as their maximum bending load increased

Thermal Stability, Fire Performance, and Mechanical Properties of Natural Fibre Fabric-Reinforced Polymer Composites with Different Fire Retardants

In this study, ammonium polyphosphate (APP) and aluminum hydroxide (ALH) with different mass contents were used as fire retardants (FRs) on plant-based natural flax fabric-reinforced polymer (FFRP) composites. Thermogravimetric analysis (TGA), limited oxygen index (LOI), and the Underwriters Laboratories (UL)-94 horizontal and vertical tests were carried out for evaluating the effectiveness of these FR treatments. Flat-coupon tensile test was performed to evaluate the effects of FR treatment on the mechanical properties of the FFRP composites. For both fire retardants, the results showed that the temperature of the thermal decomposition and the LOI values of the composites increased as the FR content increases. Under the UL-94 vertical test, the FFRP composites with 20% and 30% APP (i.e., by mass content of epoxy polymer matrix) were self-extinguished within 30 and 10 s following the removal of the flame without any burning drops, respectively. However, the mechanical tensile tests showed that the APP treated FFRP composites reduced their elastic modulus and strength up to 24% and 18%, respectively. Scanning electronic microscopic (SEM) for morphology examination showed an effective coating of the flax fibres with the FRs, which improved the flame retardancy of the treated composites

Selected mechanical and physical properties of cherry and walnut wood

Comprehensive work is in progress to preserve wood cultural assets in, for example, museums. Numerical simulation, namely finite element method (FEM), is performed to model the impact of climate change to avoid unnecessary damage in the objects. Material parameters for adhesives and coating materials, and mechanical properties along the three main axes (longitudinal, radial and tangential) of wood are then required for the modelling. In the present work, the modulus of elasticity, shear modulus, Poisson’s ratio and ultimate strengths, in the three main directions and in various moisture conditions were experimentally estimated for cherry (Prunus avium L.) and walnut (Juglans regia L.) wood, which are common species used in cultural assets and furniture. Characteristic values for Norway spruce (Picea abies L.) were also listed for comparison. Based on these data, orthotropic elastic deformation bodies were calculated. Furthermore, the sorption behaviour, the swelling and the diffusion resistance (dry and wet cup method) were also determined.Funder: Swiss National Science Foundation (SNF);ISBN för värdpublikation: 978-963-334-446-0</p

Determination of mode I and mode II fracture toughness of walnut and cherry in TR and RT crack propagation system by the Arcan test

Two specimen types, each from walnut and cherry wood, were prepared for tangential-radial (TR) and radial-tangential (RT) crack propagation systems at 65% of RH and 20°C before mode I and mode II fracture toughness was determined through Arcan tests. It was found that fracture toughness in mode I is in agreement with literature data. In the mode II test, however, the crack propagated in the direction normal to the shear plane and not parallel to it. The release rate of strain energy in terms of the opening failure in mode II was lower than that in mode I. It can be concluded that it is difficult to determine the fracture toughness of RT or TR propagation in hardwood specimens in mode II

Selected mechanical and physical properties of cherry and walnut wood

Comprehensive work is in progress to preserve wood cultural assets in, for example, museums. Numerical simulation, namely finite element method (FEM), is performed to model the impact of climate change to avoid unnecessary damage in the objects. Material parameters for adhesives and coating materials, and mechanical properties along the three main axes (longitudinal, radial and tangential) of wood are then required for the modelling. In the present work, the modulus of elasticity, shear modulus, Poisson’s ratio and ultimate strengths, in the three main directions and in various moisture conditions were experimentally estimated for cherry (Prunus avium L.) and walnut (Juglans regia L.) wood, which are common species used in cultural assets and furniture. Characteristic values for Norway spruce (Picea abies L.) were also listed for comparison. Based on these data, orthotropic elastic deformation bodies were calculated. Furthermore, the sorption behaviour, the swelling and the diffusion resistance (dry and wet cup method) were also determined.Funder: Swiss National Science Foundation (SNF);ISBN för värdpublikation: 978-963-334-446-0</p

Comparison of moisture-dependent orthotropic Young’s moduli of Chinese fir wood determined by ultrasonic wave method and static compression or tension tests

Wood with distinctively different properties in the longitudinal, radial and tangential directions exhibits a strong moisture-dependent material characteristic in the elastic range. The purpose of this study was to analyze the orthotropic elastic properties of Chinese fir wood [Cunninghamia lanceolata (Lamb.) Hook] determined at different moisture conditions using an ultrasonic wave propagation method. The results were compared with those obtained by the traditional static compression or tension tests. The results confirm that the stiffness coefficients obtained by the ultrasound without considering the complete stiffness matrix show significantly higher values than the compression or tension Young’s moduli in all the three anatomical directions at each specific MC. The differences between stiffness coefficients and Young’s moduli were significantly reduced by corrections with Poisson ratio. Only in tangential direction, the Young’s moduli with Poisson ratio correction are statistically equivalent to the Young’s moduli obtained by compression and tension.ISSN:0018-3768ISSN:1436-736

Investigations on the sorption behaviour of selected wood species from Cameroon

The sorption isotherms during adsorption and desorption of 25 wood species from Cameroon (included 3 species from plantation in Togo) were determined. In addition, the chemical compositions of these wood species were tested. The equilibrium moisture contents in a normal climate varied between 10,55 % and 15,6 %. A clear influence of the proportion of extractives can be seen. The maximum differences between adsorption and desorption varied between 2,3 % and 3,6 %