Damage detection using modal frequency curve and squared residual wavelet coefficients-based damage indicator

- The theoretical basis of the modal frequency curve method is established.
- Extraction of defect features from frequency curve via wavelet decomposition shown.
- New multiple-mode wavelet-based squared residual damage indicator is proposed.
- Damage size estimator based on standard deviation of the indicator is presented.
- Damage indicator gives a more robust and unambiguous damage identification.

A theoretical and experimental study of the frequency-based damage detection method has been presented in this paper. Based on the eigenvalue problem and perturbation assumption of defect in modal response, the theoretical basis of the modal frequency curve method is established. The extraction of defect characteristics from the modal frequency curve via discrete wavelet transform is illustrated. The above background leads to the development of a new multiple-mode damage indicator for damage localisation and a damage estimator for size prediction. Then, the proposed method has been applied to aluminium samples with pre-defined damage sections. Finite element modelling and experimental testing results are presented to demonstrate the performance of the method. Additionally, detectability with respect to the various mass ratios is investigated to support the ability of the method in real applications. The numerical and experimental results suggest that the use of the damage indicator provides a more robust and unambiguous damage identification than the sole use of the wavelet coefficients of the modes investigated. In addition, the damage estimator predicts the defect size to a satisfactory level.