Anisotropy of Dynamic Young's Modulus and Internal Friction in Wood

The dynamic Young's modulus E and the internal friction Q -1 in three principal directions were measured from the longitudinal vibration in several species of softwood and hardwood. The modulus E in the radial ( R ) and tangential ( T ) directions was much lower than that in the longitudinal ( L ) direction regardless of the wood species, and the order of magnitude was E l ≫ E r > E t , whereas the friction Q -1 showed exactly the opposite tendency, i.e., Q l -1 ≪ Q r -1 < Q t -1 . An investigation of the relationship between the values showed that the internal friction could be expressed by an exponential equation of the specific Young's modulus E /γ regardless of the direction and wood species, and that the exponent in three principal directions was slightly lower than that in the L direction. Furthermore, the differences in the values ( E and Q -1 ) and exponents between directions were considered from the structural aspect, and it was found that the causes were the same and could be explained well by the difference in the structural factors.