Use of the Roving Mass Technique and SWT to Identify and Locate Multiple Cracks in Simply-Supported Beams

The roving mass technique is used to identify and locate multiple cracks in simply-supported beams. The technique involves the traversing of an auxiliary mass along the length of the beams. At each location of the roving mass, the stiffness of the beam is different which, in turn, causes the natural frequencies of the beam to change as the mass is traversed. A plot of the natural frequencies of the beam versus the location of the roving mass results in natural frequency curves (NFCs). If a crack is present in the beam, then the dynamics of the beam is affected because the crack causes a local reduction in the stiffness of the beam. This leads to very slight reductions in the natural frequencies of the beam. However, these slight reductions in the natural frequencies cannot be observed directly from the NFCs. Identification of crack information from the NFCs is achieved by the application of the stationary wavelet transform (SWT) to the NFCs. The presence of a crack is indicated as sharp peaks in the SWT detail coefficients plots. The effects of various roving mass magnitudes on the crack detection method are investigated. It is shown that the technique is efficient in detecting double symmetric cracks about the centre of the beam as well as detecting multiple cracks.