Crack detection in simply supported beams using stationary wavelet transform of modal data

摘要

A new approach, using stationary wavelet transform (SWT), is proposed for crack detection in beam-likenstructures. SWT is a redundant transform that doubles the number of input samples at each iteration,nwhich can provide a more accurate estimation of the variances and facilitate the identification of salientnfeatures in a signal, especially for recognizing noise or signal rupture. The mode shape of a cracked beamnwith a small crack depth, while apparently a single smooth curve, actually exhibits a local peak orndiscontinuity in the region of damage. The mode shape ‘signal’ can be approximately considered as that ofnthe intact beam contaminated by ‘noise’ which consists of response noise and the additional response duento the crack. The signal can be decomposed by SWT into a smooth curve, called approximation coefficient,nand a detail coefficient curve, which includes crack information, respectively. In this paper, the modalnresponses of damaged simply supported beams are computed using the finite element method innconjunction with some experimental tests. The effect of noise on the proposed method is also studied. It isnshown that SWT of the modal data of cracked simply supported beams provides a better crack indicationnthan conventional discrete wavelet transform. The relationship between SWT detail coefficient and cracknsize (depth and width) are also discussed. A new method based on the average difference of the SWT detailncoefficient of vibration bending modes of a cracked beam and an intact beam is proposed as a damagenindex and verified. Copyright r 2009 John Wiley & Sons, Ltd.