Influence of experimental setups on wood loss factor measured by means of forced flexural vibration

The forced flexural vibration method is widely used to measure the loss factor of wood, providing valuable insights into its viscoelastic properties. Although the accuracy of this method strongly depends on the experimental setups, systematic research in this area remains limited. In this study, a spruce specimen was vibrated by electromagnetic excitation, and the influence of experimental parameters was investigated to optimize the forced flexural vibration method. The results showed that sampling rate is a critical parameter determining the accuracy of the vibration signals. Only when the sampling rate exceeded 10k × 2.56 Hz could the relative measurement error be reduced to less than 0.50%. Fitting the vibration response function to the data could yield more accurate results than the linear interpolation method over a wider range of frequency resolutions. In the manual point-by-point excitation mode, the excitation intensity had a significant impact on the loss factor. In contrast, the sweep excitation mode could effectively reduce the influence of excitation intensity through filtering functions in signal processing. The increase of the mass attached to the specimen resulted in the linear increase of the loss factor. In fast Fourier transform, the flattop window function was found to give more accurate loss factor values.