Structural Fatigue Crack Localization Based on EMD and Sample Entropy

During structural vibration, fatigue cracks, especially at their initial stage, introduce a repetitive crack open-close breathing-like phenomenon. Breathing cracks cause irregularities, bi-linearity, or perturbations in the vibration response of a structural system. Entropy can be used to quantify the irregularity or bi-linearity in those responses, and the crack position can be determined since on the two sides of the breathing crack, there is an apparent variation of entropy values. Here, we present a new breathing crack localization method based on a spatially distributed entropy approach coupled with the empirical mode decomposition (EMD). EMD is used as a pre-processing tool to extract the characteristics caused by breathing phenomenon in the vibration signal, and the reconstructed signal is used for entropy calculation. The location of the crack can be estimated by entropy values at different positions of the test structure. To verify the accuracy of the proposed method in localizing the breathing crack, the results were compared with a series of laboratory experiments in a beam. It is concluded that the proposed approach can be effectively used for breathing crack localization in a structural system.