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Most engineered wood components and their performance are dependent on the use of adhesives. To be able to conduct simulations, a general understanding about their mechanical behaviour under different load cases and environmental conditions is needed. Especially the temperature-dependent elasticity is of great importance for future applications as automotive components. Therefore, the tensile modulus of four common polymer-based wood adhesives (i.e., one-component polyurethane, two-component polyurethane, epoxy-silan and phenol–resorcinol–formaldehyde) at varying temperatures of −30°C, +20°C and +80°C were investigated. The aim of this study was to give fundamental insight into the elasto-mechanical behaviour of common wood adhesives. The experimental investigation showed a significant influence of the temperature on the tensile modulus. The highest tensile moduli were observed for all tested adhesives at −30°C with a significant decrease with increasing temperature. Results of previous investigations confirmed this high-temperature dependency of the polymers. [ABSTRACT FROM AUTHOR]

The use of wood in high-performance composites based on laminated veneer products, plywood or wood hybrid elements thereof requires accurate prediction of strength of each individual ply. Previous research has shown that one dominating factor influencing the strength of birch veneers is the fibre orientation. The present study investigates the validity of the failure criteria after Tsai-Hill, Hoffmann and Kollmann for thin birch veneers under tensile loading. The fibre orientation in- and out-of-plane was measured by means of wide-angle X-ray scattering. Tensile strength and threshold values were determined in laboratory experiments. Pearson correlation between the predicted strength and actual strength ranged from 0.836 up to 0.883. Best correlation (r = 0.883) was achieved for Kollmann using a combined angle between in- and out-of-plane fibre orientation. It was shown that the failure criteria commonly used for manmade fibre reinforced composites are also applicable for thin birch veneers. [ABSTRACT FROM AUTHOR]

In technical applications of wood-based composites, the predictability of elasticity and strength is important. The aim of this study was to predict the static modulus of elasticity and tensile strength of thin (0.55 mm ± 0.05 mm) birch veneers. Based on the dynamic modulus of elasticity estimated via means of wave transmission time the observed dynamic modulus of elasticity was on average 14% lower than the corresponding static modulus of elasticity. This difference could be explained by a decreased measuring area during the tensile testing or by defects within the samples. The dynamic modulus of elasticity correlated well with the static modulus of elasticity (r = 0.821). Therefore, using wave transmission time to non-destructively predict the elasticity of veneers proves to be a promising tool. The dynamic modulus of elasticity showed a significant and positive correlation with the tensile strength (r = 0.665), but this correlation was weaker than with the static modulus of elasticity. Therefore, the wave transmission time or the static modulus of elasticity must be combined with additional strength-influencing properties, such as fiber angle or density, to allow for a highly accurate prediction of tensile strength. [ABSTRACT FROM AUTHOR]

The present study investigated the effect of selected structural parameters on the mechanical performance of regenerated cellulose composites. The experimental setup comprised continuous viscose (rayon) yarns embedded in a matrix of epoxy resin. Mechanical and microscopic characterizations involved comparing the following: yarns consisting of untwisted filaments and twisted warp and weft yarns taken from a plain weave fabric, yarns with and without avivage (fiber finish), as well as yarns with and without an acrylic coating. During the epoxy treatment, samples were either prestressed or laid horizontally to preserve the original yarn structure. Tensile tests revealed that yarn crimp had a significant impact on the strength properties of composite specimens, a higher crimp ratio leading to a decrease in performance. Applying prestress to crimped yarns has proven to be an effective way to enable straight alignment in the loading direction, which is essential for the design of stiffness‐ and strength‐optimized yarn composites. Unlike an avivage, which did not markedly affect the mechanical properties of composite yarns, the application of an acrylic coating prior to resin impregnation was found to provide significantly increased extensibility and more ductile fracture behavior. [ABSTRACT FROM AUTHOR]

The currently pursued implementation of wood into novel high performance applications such as automotive parts require knowledge about the material behaviour including ultimate strength. Previous research has shown that fiber deviation seems to be the dominating factor influencing the strength of thin veneers. This study aims to further investigate and quantify the influence of fiber deviation in two dimension and different hierarchical levels on the tensile strength of thin birch veneers. The fiber deviation in- and out-of-plane as well as the micro fibril angle were assessed by means of wide-angle X-ray scattering. Tensile strength was determined in laboratory experiments. Results show a high variability for in-plane fiber deviation mainly constituted by knots and other growth influencing factors. Pearson correlations between strength and fiber deviation ranged from −0.594 up to −0.852. Best correlation (r = −0.852) was achieved for maximum in-plane fiber deviation directly followed by a combined angle of in- and out-of-plane fiber deviation (r = −0.846). Based on the results it was shown that fiber deviation in- and out-of-plane is the dominating factor influencing ultimate tensile strength of thin birch veneers. Further research in regard to non-destructive strength prediction is necessary. [ABSTRACT FROM AUTHOR]

Although hardwood building materials are mainly produced from the tree stem, the branches of deciduous trees make up a significant proportion (20–50%) of their above-ground biomass. Regrettably, the mechanical properties of branches are largely unknown and they are mainly used as fuel, overlooking their potential as valuable construction materials. Therefore, we conducted quasi-static tests on branch and stem wood from beech, oak, and poplar trees, evaluating wood density, tensile, compression and bending strength, and elastic properties. The mechanical properties were correlated with precise positional data from 3D point clouds of the sample trees. Our findings revealed significant differences between branch and stem wood, most notably in density and tensile strength. The linear regression models revealed that bending strength depends primarily on density and branch slope, and secondarily on branch top side and diameter. Applying laser scanning technology can help to better understand the variability and predict the performance of branch wood, enabling more resource- and carbon-efficient processing into building materials. [Display omitted] • Mechanical material properties of branch wood are combined with precise positional data from close-range laser scanning. • Branch wood of beech has a higher density but up to 20% lower tensile strength than stem wood. • Branches that have grown at a steeper angle have a higher bending strength than flat branches. • The bending performance of oak branch wood can be predicted when density and position parameters are considered. [ABSTRACT FROM AUTHOR]

EN 302-1 and EN 205 are among the most commonly used standards for the approval as well as research of wood adhesives to evaluate bond strength. The present study investigates the sensitivity of the lap-joint samples to a possible error in groove cutting as well as the influence of using steam-treated and untreated beech wood on tensile shear strength. The lap-joint specimens cut with 0.5 mm too shallow and 0.5 mm too deep grooves was compared with samples cut precisely within the tolerances mentioned in the standards. A comparison of tensile shear strength between the joints manufactured out of steam-treated and untreated beechwood has been made. The results show a significant influence of groove depth on the resulting tensile shear strength. While deep groves (+0.5 mm) underestimate, shallow grooves (−0.5 mm) overestimate it dramatically. Additionally, the joints with steam-treated beech wood delivered lower tensile shear strength than those of untreated beech wood bonds when there is a considerable wood failure percentage. When the ultimate tensile shear strength of the adhesive bond approaches the shear strength parallel to the grain of wood, the impact of steam-treated beech wood on the estimation of adhesive bond strength is higher. [ABSTRACT FROM AUTHOR]

Birch (Betula pendula Roth.) and beech (Fagus sylvatica L.) solid wood and plywood were overmolded with polyamide 6 (PA 6) and polypropylene (PP) to investigate their mechanical properties and interfacial adhesion. In the case of PA 6, maximum tensile shear strengths values of more than 8 to 9 MPa were obtained for birch and beech, respectively. The values are comparable to bond strengths of commercial joints bonded with formaldehyde-containing amino-plastics. Perpendicular to the wood elements, bond strength values of 3 MPa was achieved for PA 6. The penetration of the polymers into the wood structure results in a non-densified interphase and subsequent plastic deformation of the wood structure beyond the interphase. These compressed areas influenced the interfacial adhesion and mechanical interlocking. SEM and XPS analysis revealed different interpenetration behavior of the polymers into the wood structure, with chemical interaction confirmed only for wood and PA 6 but not PP. [ABSTRACT FROM AUTHOR]

Golf tees with a plastic head and wooden shaft were prepared by back injection moulding of a beech wood (Fagus sylvatica) shaft with different polymers (i.e. ionomer, polypropylene, and polyamide). In order to facilitate adhesion between the polymer melt and the wood surface, the wooden shafts were pre-treated with different primer substances, including a commercially available primer for ABS edges, a 10% solution of alkyl ketene dimer (AKD) in toluene and tumbling lacquer. The mechanical strength of the wood-plastic interphase was characterized by applying a pull-out test. Bond strength values of more than 9 N/mm² were observed for polyamide, whereas ionomer and polypropylene specimens achieved values between 0.7 and 3.8 N/mm². Surprisingly, the used primers failed to improve interfacial adhesion with the exception of the ionomer sample pre-treated with the commercial ABS-primer. Although light microscopy and SEM revealed some differences in the penetration behaviour of the different polymers as well as in the extent of plastic wood deformation imposed during injection moulding, the chemical nature of the polymer seems to be the most important determinant for the bond strength of wood-plastic hybrid components. [ABSTRACT FROM AUTHOR]