Experimental study of torsional vibration of wooden bars by plate theories

The resonance frequencies of higher torsional vibration modes for wood bars were measured and compared with the frequencies by St. Venant's torsion theory, and by the thin-, and thick-plate theories considering different elastic constants. The thick-plate theory with the Ritz method precisely predicted the frequencies. The in-plane shear modulus was predominant up to the 2nd order. For the higher modes, the terms for the other elastic modulus affected the vibrations of the bars. The shear modulus values by the side plane rigid torsion theory were almost the same as those by the thick-plate theory in cases where the width of a bar approached its length. The frequency dependence of the loss tangent (the internal friction) of torsinally vibrating bars became more apparent after correcting the effect of the interactions of the different loss tangent parameters.