Identification of defect position in a wooden beam from the power spectrum of longitudinal vibration
Sobue, N., Shizuoka Univ. (Japan). Faculty of Agriculture | Fujita, M. | Nakano, A. | Suzuki, T.
The inverse solution procedure that enables the identification of the defect position in a beam from the resonance frequency was exploited. Resonance frequency shifts of a power spectrum due to defects in a longitudinally vibrating beam when both ends are free were investigated by both numerical and experimental analysis. Calculation by a transfer matrix method showed that the frequency shift was large when the defect position coincides with a node of vibration and that no shift occurs when it coincides with a loop of vibration. The frequency shift could be approximated by a sinusoidal curve. Calculation results agreed well with those of the experiment in which artificial round holes were drilled as the defect model. Experimental equations predicting the amount of the frequency shift in function of the defect position were obtained. In the inverse procedure, the defect position was determined by comparing the resonance frequencies between the experimental and estimated power spectra so that the coincidence factor S(x) became a minimum. The results showed the validity of the proposed method to identify the defect positions of fewer than two predominant defects.
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