Crack Detection of a Beam Using the Wavelet Transform

The dynamic behaviour of a structure changes when it is subject to damage such as cracking. Recently research has been directed at employing conventional Modal Analysis techniques to investigate this change in simple structures and to study the dependency on the location and size of a crack. The use of the modeshapes to characterise the dynamic behaviour of the structure would require several accelerometers spaced across the structure. As described in this article, a technique has been developed making use of the Wavelet Transform which can be applied to detect the presence of the crack using the measurement from a single accelerometer strategically located on the structure. The method has proved mow sensitive in detecting relatively small cracks than the techniques that attempt to use the shift in resonant frrquencies in the measrxed Frequency Response Function to identify the presence of damage. The study described has been undertaken by simulating a cracked cantilever beam using a simple finite element model to provide data for the analysis. In this case the stiffness matrix, which is affected by the presence of the crack, has been derived from the integration of stress intensit,y fact.ors. The model t,akes into account the effect of crack opening and closing.