Specific dynamic shear modulus of drilled beech wood

In this research, specific dynamic shear moduli in plane with LR and LT surface of 22 rectangular clear beams of beech wood (Fagus orientalis) were evaluated in “free flexural vibration of a free-free bar” method with and without the presence of drilled holes on the tangential surface. The drilling was done exactly at the middle of the bar, on the node of the 2nd mode of vibration. Stepwise hole widening from zero to 3, 5, 8, and 10 mm, visible on two opposite tangential surfaces were used. Beech timbers were converted to nominal dimensions of 20×20×360 mm R×T×L. After measuring the dimensions and calculating the density () of the specimens, for both radial and tangential impacts of hammer in which the beam was vibrated in LT and LR plane, respectively, two specific shear moduli (specific GLR and specific GLT) were evaluated in Timoshenko beam theory, considering the three initial modes of vibration. When the bar was excited from its tangential surface by a percussion (vibrated in LR plane), stepwise drilling raised the estimated value for specific shear modulus in LR plane (Specific GLR). However, in LT vibrations, the specific GLT remained statistically constant. It is clear that the specific shear moduli as material property are not affected by artificial manipulation, but the responses of the bars would be affected. So the obtained result has been discussed due to neutral axis related to the hole localization. The finding of this paper may be used as an indicator for recognition of a hidden hole, perpendicular to the growth rings.