Method to Enhance the Frequency Readability for Detecting Incipient Structural Damage

Vibration-based damage detection methods able to recognize cracks in the early state require accurate frequency evaluation in order to identify small modal changes. Because of higher order, the natural frequencies are rapidly damped, time history provides insufficient information if standard frequency estimations are performed. This paper introduces a method of overlaying multiple spectra achieved by iterative truncation of the original signal. In this way, the spectral bin number becomes much higher and the identification of real natural frequencies is easier. Also, an original damage detection algorithm based on the frequency shift is described that considers the first six bending vibration modes occurred due to damage. These are in direct relation to the modal strain energy stored at the damage location. The effectiveness of the detection method is proved using real structures in some damage scenarios. Thus, it was shown that even if a crack reduces the beam’s transversal cross section by only 6%, it can be clearly detected.