Application of modal analysis by transfer function to nondestructive testing of wood I. Determination of localized defects in wood by the shape of the flexural vibration wave

This study intended to detect nondestructively some defects such as knots a nd grain deviations in wood by using modal analysis. The shapes of flexural vibration waves at the first mode generated by tapping of wooden beams wer e determined by using the transfer function. The wave shapes obtained were compared with the theoretical wave shape for a uniform material, and the po ssibility of detecting defects in wood was discussed. The results were summ arized as follows: (1) The shapes of flexural vibration waves at the first mode of wooden beam s free of defects coincided almost completely with the theoretical wave sha pe. (2) The shapes of flexural vibration waves of wooden beams containing defec ts such as knots clearly differed from the theoretical wave shape, especial ly in the position near the defect. (3) From these result, it should be possible to detect presence of defects and to determine their locations in wood.