Effect of artificial inhomogeneity of density on dynamic shear modulus of Oak wood (Quercus castaneifolia)

In this study, the effect of artificial inhomogeneity of density in the initial and middle of Oak wood beams (Quercus castaneifolia) by the changes in the dynamic shear modulus values obtained from the free vibration in free-free beam method have been investigated. For this purpose, 10 specimens of Oak wood species with a dimension of 720×40×20 mm (longitudinal, radial, and tangential) were tested by the free flexural vibration method to determine the shear modulus in the solid wood beams. After that, the samples were divided into two groups and from the first group, the blocks with a dimension of 40×40×20 mm from the initial part, and from the second group, the blocks with the mentioned dimension were extracted from the middle part of the solid beams, and jointed to each other by polyvinyl acetate adhesive. After the jointing, the free bending vibration test was performed on both groups again. Afterward, the Oak blocks were removed from the junction and in two stages, blocks of two species of Poplar wood (Populus nigra) and Iron wood (Parrotia persica) were replaced and in order to the effect of artificial inhomogeneity created by each of the replaced blocks on the values of the shear modulus, the flexural vibration test was performed on them. The results showed that the development of artificial inhomogeneity of density in the initial area of the beam by all three species of Oak, Poplar, and Iron wood did not have a significant effect on the values of dynamic shear modulus, while creating inhomogeneity in the middle of the beam has caused a significant drop in the values of this factor. Heterogeneous beams by Iron wood species had the highest, and heterogeneous beams by Oak wood species had the lowest percentage decrease in dynamic shear modulus values.