Defect detection in lumber including knots using bending deflection curve: comparison between experimental analysis and finite element modeling |
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Authors: | Hiroaki Nagai Koji Murata Takato Nakano |
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Institution: | (1) Division of Forest and Biomaterials Science, Graduate School of Agriculture, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan |
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Abstract: | A new method has been developed for detecting localized defects such as edge knots using a bending deflection curve. The coordinates
of a bottom edge (edgeline) of an unloaded piece of lumber are extracted from a digital image, and a bending deflection curve
is obtained from the displacement of the edgeline of the lumber using a digital image correlation (DIC) technique. Depending
on the knots within the beam, the bending deflection curve is shifted from the curve of a defect-free beam. The measured bending
deflection curve is regressed to a theoretical curve by elementary beam theory. A finite element method (FEM) model of the
beams including defects as simplified knot structure has been performed. Comparison between the bending experiment and FEM
analysis shows that cross-sectional reductions cause characteristic variations in the bending deflection curves depending
on the position of encased knots, and local grain distortions cause variations in the curves depending on the direction of
spike knots. Using the residual variance between the measured deflection curve and a polynomial regression curve, it is possible
to detect knots at which failures initiate.
Part of this article was presented at the 57th Annual Meeting of the Japan Wood Research Society, Hiroshima, Japan, August
2007 |
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Keywords: | Bending deflection curve Defect detection Knot Digital image correlation |
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