Structural damage detection in beams by wavelet transforms

Abstract

The use of a laser-based optical system and wavelet transforms is explored for the detection of changes in the properties of cantilevered aluminum beams as a result of damage. The beams were modeled using the ANSYS 5.3 finite-element method and the first six mode shapes for the damaged and the undamaged cases obtained. Damage was simulated by a reduction in the stiffness of one element. Gaussian white noise was added externally to simulate field conditions. The results show that a spatially-localized abnormality in the mode shape could be represented uniquely by a small set of wavelet coefficients while the white noise was uniformly spread throughout the wavelet space. It was observed that the damage clearly manifested in the sixth-order detail of certain modes only. A different finite-element model was used as a test beam to validate the proposed method. An actual aluminum beam, fabricated with dimensions similar to the test beam, was excited and the mode shapes recorded with the scanning laser vibrometer. Damage was created by machining a notch in the beam of the same dimensions as the finite-element test beam. An image of the damage location was obtained from the continuous wavelet transform coefficients. The magnitude of the wavelet coefficients at the damage location showed a close correlation to the severity of damage. It was observed to increase with increasing damage. The finite-element test beam results showed a close correlation to the corresponding experimental beam results. The method benefits from the fact that the undamaged mode shapes were not used to evaluate the condition of the beam, which in most field conditions is not feasible.

An investigation into the acceleration response of a damaged beam-type structure to a moving force

“…The wavelet transform has obvious advantages when trying to detect these features from mode shape data due to its ability to analyze a local portion of a larger signal [11][12][13][14].…”

A Bridge-Vehicle Interaction Based Experimental Investigation of Damage Evolution

“…Computationally inexpensive lumped crack model of such damage is also popular among many researchers [22,24,51,39,52,31] for simulation. All of these models contain a singularity in their modeshape, static or dynamic deflected shape, or in any of their derivatives.…”

“…While these experimental studies deal with the identification of the location of damage comparatively well, very few of them investigate the evolution of the extent of damage [24,29]. A large number of studies have been devoted to the problem of an open crack in a simply supported beam [22,31] in this respect and the use of wavelet analysis on the damaged modeshapes [23] or static deflected shapes [28] has successfully illustrated the potential of wavelet based analyses in identifying damage without a pre-existing benchmark.…”

Wavelet Based Experimental Damage Calibration using Beam-Moving Load Interaction Model

“…Successful experimental detection of static and dynamic modeshapes and deflected shapes of beams with open cracks and consequent wavelet based identification of damage have been reported by a number of researchers in recent times. Scanning Laser Vibrometer (SLV) device has been used to identify open cracks in beams through wavelet analysis by a number of researchers (Khan et.al [2], Okafor and Dutta [3], Vanlanduit et.al [4]). However, the cost and accessibility of such sophisticated devices can sometimes be prohibitive.…”

“…Comparatively less expensive and accessible digital camera based methods in conjunction with image processing techniques have successfully detected damage in beams with open cracks in recent times (Poudel et.al [5], Rucka and Wilde [6], Patsias and Staszewski [7], Pakrashi et.al [8,9,10]). Very few of these experimental studies investigate the prediction of the extent of damage (Okafor and Dutta [3], Pakrashi et.al [9]), although the successful identification of the location of damage has been comparatively well dealt with. The presence of damage in a structure usually introduces a local and sharp change in the stress, strain and the displacement fields in the damage region and the change is usually translated as singularities in the derivatives of the modeshapes and the deflected shapes (Bovsunovsky and Matveev [11], Narkis [12], Carneiro and Inman [13]).…”