Detection of knot using distribution of bending deflection: Measurement with laser displacement sensor
2010
Nagai, H., Kyoto Univ. (Japan) | Murata, K. | Imoto, M.
In this study, we propose a new method for detecting a knot, a parameter that determines the strength of timber. This method involves the measurement of the deflection distribution of bending wood specimen. A laser sensor is placed below a wood specimen to measure the one-dimensional shape of the specimen. A defect-free specimen and a knotty specimen were tested in three point bending. The distributions of the local Young's modulus was obtained from the deflection distributions. In the case of the defect-free specimen, a fluctuation in displacement was observed, but the local elastic modulus of the specimen was uniform. In the case of the knotty specimen, the local Young's modulus of the knotty area including a death knot was less than that of the defect-free area. A knot that looked like a death knot on one side and a live knot on the other side couldn't be detected by the difference of local Young's modulus. When a death knot was present on the edge of the tension side of a specimen, the Young's modulus of the area around the knot was observed to be less than that on the edge of the compression side.
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