Locating Wood Defects Based on Vibration Modes

Abstract The first six lowest-order resonance frequencies, and their corresponding vibration mode displacements along the length of Larch boards, were obtained by modal analysis. Plots of the first six bending modes of these Larch specimens were obtained using measurement data. Results showed that, compared with specimens showing small area defects, specimens with larger areal defects exhibited smaller resonance frequencies. The influence of defects on the first- and second-order modes was not obvious, but the defects produced obvious deviations in the next four lowest-order modes. In regard to mode shape, sudden deviations were evident near defects. Whether a large area defect existed in a specimen can be determined using the third-order mode, and the location of wood defects is detectable using the fourth-, fifth-, and sixth-order modes.