Application of modal analysis by the transfer function to nondestructive testing of wood, 3: Detection of knots and estimation of elastic modulus distribution in wood by the curvature ratio of the flexural vibration wave shape
2002
Yang, X. (Kyoto Prefectural Univ. (Japan). Faculty of Agriculture) | Ishimaru, Y. | Iida, I.
The objective of this study was to detect nondestructively defects such as intergrown knots, dead knots, loose knots and deviations of the fiber direction in wood by using curvatures of the flexural vibration wave shape at the first mode measured by modal analysis. Furthermore, the dynamic modulus of elasticity of the area containing the defect was estimated from the plot of relative elastic modulus, and the distribution of elastic modulus in wooden beams was discussed. The results are summarized as follows : (1) The higher density of knots had very little effect on the distribution of relative elastic modulus as obtained from the curvature of the wave shape. (2) If a wooden beam contains a defect with a lower dynamic modulus of elasticity, such as an intergrown knot, a dead knot, or a loose knot, the defect can be detected by the plot of relative elastic modulus calculated from the curvature of the flexural vibration wave shape at the first mode. (3) If a wooden beam contains several knots, the curvature plot of the wooden beam would show a peak for each knot. (4) The dynamic modulus of elasticity measured by longitudinal vibration was highly correlated with the elastic modulus estimated from the curvatures of the flexural vibration wave shape. (5) From these results, it is possible to determine the position of defects and estimate the distribution of elastic modulus in wood.
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