Detection of defects in timber using dynamic excitation and vibration analysis

Abstract: This thesis evaluates the possibility to detect natural defects, such as knots, in timber boards using dynamic excitation test and ABAQUS software. In the study the edgewise bending direction were compared with axial direction. Dynamic excitation and modal analysis were used to extract the natural frequencies of several sound and artificially defected boards with the help of Signalcalc. Mobylizer software. By using the first edgewise natural frequency, modulus of elasticity (MOE) was calculated. An ABAQUS 2D Finite Element model was utilized to model the board and to extract the frequencies for the six first mode shapes in both axial and edgewise directions. The extracted frequencies from the model were compared with the frequencies from the tests. The analytical and experimental results, from the homogeneous boards, in edgewise direction has similar frequency variations. The defects in the timber boards decreased the natural frequencies. The bending modes with more curvature at the location of the artificial defect displayed more frequency deviation in that mode. The variation in response frequencies for uniform and defected boards was more noticeable in edgewise bending modes than in longitudinal modes.