Detection of a crack and its location and development of diagnosis system by modal analysis and wavelet

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The early detection of a crack is very important because it causes a serious accident. In this research, we investigated the means to find the occurrence and the location of a crack. The contents are classified into two subjects.First, the changes of resonance curves or responses of steady-state oscillations and nonstationary oscillations due to the magnitude and the direction of the unbalance are investigated theoretically and experimentally. As a result, it is clarified that a remarkable change, such as, the occurrence of unstable range, occurs in a steady-state oscillation of a cracked shaft. It is also found that the response curve of a nonstationary oscillation of a cracked shaft changes depending on the location of a crack.Secondly, the means to find a crack by sweeping the frequency of the external excitation besides unbalance force is investigated. By experiments, it is clarified that new resonances occur due to a crack. By FEM analysis, it is clarified that the kinds and magnitudes of resonance, the kinds of predominant frequency spectrums changes due to the location of a crack. This result suggests that it is possible to specify the occurrence and the location of a crack if these data are analyzed totally.