Vibration analysis of an inhomogeneous string for damage detection by wavelet transform

In this paper we present a new method based on the wavelet transform for the detection of structural damage. It is assumed that the vibration signal of the original structure without any defect is already known. In the case when defects are present, the vibration signals of the defected structure are then recorded. After comparing the discrete wavelet transforms of these two sets of vibration signals in the space domain, we are not only able to detect the presence of defects, but also their number and location as well. To test the effectiveness of the proposed method, we use a uniform string as the original undamaged structure. To simulate the defects of the structure, we attach several point masses and springs on the string. Numerical result shows that even a minor localized defect can induce significant changes in the wavelet coefficients of the vibration signals. Furthermore, the maximum change of the wavelet coefficients occurs in the proximity of the defect. These results indicate that the proposed method could potentially be an alternative tool in the structural damage detection.