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The plastic deformation of wood perpendicular to the grain is gaining increasing importance due to advancements in forming technologies and the densification of wood. This study investigates how two hardwood species, i.e., beech (Fagus sylvatica) and birch (Betula pendula), respond to compression in the radial direction and examines the structural changes they undergo during both elastic and plastic deformation. Stress–strain curves at different moisture contents (dry to wet) and temperature conditions (20 to 140 °C) were recorded. In-situ observations at high moisture content and temperatures by means of different microscopic techniques are practically unfeasible. Therefore, the specimens were analysed ex-situ microscopically after the test. In addition to the compression of transversely oriented fibres and vessels, special attention was paid to the deformation behaviour of the wood rays. The results suggest that the wood ray cells carry a relatively higher proportion of the load in the radial loading direction than the surrounding vessels and fibres. This observation is supported by the higher percentage of deformed vessels, seen in the microscopy, in areas where the rays developed kinks, usually in the early wood of beech and anywhere in the cross-section of birch. The weaving of rays around big vessels introduced shear strains under compressive stresses at the kinked rays' area. Thus, shear deformation is more evident in early wood than in late wood regions of wood. However, when the wood was tested at elevated moistures and temperatures, the material demonstrated a ductile response, namely the absence of localised shear deformations. Notably, wet beech and birch specimens heated to 100 °C and above exhibited pronounced thickness recovery and there was slightly irreversible buckling of rays and vessel deformations. Therefore, under such conditions, wood behaves like a "sponge" and is expected to be successfully processed without introducing clear damage to the material. This characteristic holds promise for replication in the development of bio-based energy-absorbing materials. [ABSTRACT FROM AUTHOR]

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]

Multi material mix is a promising approach to reduce weight and the carbon footprint in automotive engineering at competitive costs. As a result, automotive industry is getting more venturous, exploring and applying other materials than metals and plastics – e.g. fibre reinforced plastics (FRPs). In this context, engineered wood products (EWPs) and wood composites should be considered: Wood composites provide high stiffness, strength, excellent damping, high resistance against fatigue and a very low density at low material costs. It is hypothesized that modern wood composites are competitive to metals and artificial fibre-reinforced materials when designed and applied properly. The application of wood and wood composites in automotive engineering calls for precise and reliable material data, required for initial material selection and later in numerical simulation. In this study, a material model normally used for modelling FRPs was adopted. A material database was generated for three hardwood species, to establish the required material parameters and validate material model. Results prove that wooden components can be simulated in crash situations and the selected material model is applicable, even in full vehicle simulation. [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]