Determination of Young’s and shear moduli of common yew and Norway spruce by means of ultrasonic waves |
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| Authors: | Daniel Keunecke Walter Sonderegger Karol Pereteanu Thomas Lüthi Peter Niemz |
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| Institution: | (1) Institute for Building Materials (Wood Physics Group), ETH Zurich, Zurich, Switzerland;(2) Faculty of Mechanical Engineering, Department of Strength of Materials and Vibrations, University Transilvania of Brasov, Brasov, Romania;(3) Swiss Federal Laboratories for Materials Testing and Research, Electronics/Metrology, Empa, Zurich, Switzerland |
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| Abstract: | Despite the exceptional position of yew among the gymnosperms concerning its elastomechanical properties, no reference values
for its elastic constants apart from the longitudinal Young’s modulus have been available from literature so far. Hence, this
study’s objective was to determine the Young’s moduli E
L, E
R and E
T and the shear moduli G
LR, G
LT and G
RT of yew wood. For that purpose, we measured the ultrasound velocities of longitudinal and transversal waves applied to small
cubic specimens and derived the elastic constants from the results. The tests were carried out at varying wood moisture contents
and were applied to spruce specimens as well in order to put the results into perspective. Results indicate that E
L is in the same order of magnitude for both species, which means that a high-density wood species like yew does not inevitably
have to have a high longitudinal Young’s modulus. For the transverse Young’s moduli of yew, however, we obtained 1.5–2 times,
for the shear moduli even 3–6 times higher values compared to spruce. The variation of moisture content primarily revealed
differences between both species concerning the shear modulus of the RT plane. We concluded that anatomical features such
as the microfibril angle, the high ray percentage and presumably the large amount of extractives must fulfil important functions
for the extraordinary elastomechanical behaviour of yew wood which still has to be investigated in subsequent micromechanical
studies. |
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