Micromechanical properties of common yew (Taxus baccata) and Norway spruce (Picea abies) transition wood fibers subjected to longitudinal tension

Abstract

The longitudinal modulus of elasticity of common yew is astonishingly low in light of its high raw density. At least this was found for specimens examined at the solid wood level and at the tissue level. However, to reveal if this low axial stiffness is also present at the cellular level, tensile tests were performed on individual yew fi bers and on spruce fi bers for reference. The results revealed a low stiffness and a high strain to fracture for yew when compared with spruce. This compliant behavior was ascribed to a relatively high microfi bril angle of yew measured by X-ray scattering. It can be concluded that the high compliance of yew observed at higher hierarchical levels is obviously controlled by a structural feature present at the cell wall level. In future studies, the biomechanical function of this compliant behavior for the living yew tree would be of particular interest.

Fracture tolerance of reaction wood (yew and spruce wood in the TR crack propagation system)

“…This fracture mode consumes more energy, and thus leads to reduced crack propagation in comparison with pure tensile fractures of cells with a small fiber angle (Reiterer et al, 2001). As reported earlier (Keunecke et al, 2007(Keunecke et al, , 2008aKeunecke and Niemz, 2008;Keunecke et al, 2009), the microfibril angle of yew is rather high and that of reaction wood is even higher. Therefore, loading of yew compression wood in the TR direction may be more highly influenced by the microfibril angle than expected, so that this microstructural feature may also contribute to the higher fracture tolerance of yew and even more of yew compression wood.…”

Modelling time-dependent mechanical behaviour of softwood using deformation kinetics

“…Young's moduli for the entire cell based on its gross crosssection are in the ranges 5.2-12.4 GPa. Experimental results for spruce fibres, tissues and solid wood with MFAs in the range 0-58 at around 12% moisture content (MC) was 9.9-12.1 GPa and 26.2-29.4 GPa for the gross and the actual cross-sectional area, respectively (Keunecke et al 2008). The reason why the current model predicts a modulus of 12.4 GPa for MFA of 158 could be partly due to a swelled cross-sectional area at 12% MC, which is not accounted for in the current model.…”

Synchrotron-based tomographic microscopy (SbTM) of wood: development of a testing device and observation of plastic deformation of uniaxially compressed Norway spruce samples

“…On the mesoscopic scale, a growth ring is composed of thin-walled earlywood (EW) tracheids and thick-walled latewood (LW) tracheids. The composition of wood is inhomogeneous, and the spatial distribution of the different cell types (and their size) may vary, thus the physical properties of wood observed at the macroscopic level vary signifi cantly even within the same species (Keunecke et al 2008). This is a reason why the simulations of the mechanical behavior of wood are diffi cult (Hofstetter et al 2005 ).…”