Crack detection in a rotor by operational deflection shape and kurtosis using laser vibrometer measurements

High speed rotating machinery operating with higher load capacity in extreme working conditions can induce fatigue crack into the systems. To avoid failure of the system, it has to be monitored continuously for cracks before it becomes critical. There is a need for the newer techniques that can detect even small cracks. The aim of the present work is to identify the crack in a rotor-bearing system using the concept of operational deflection shape and using kurtosis of vibration response. In the literature kurtosis is used for identifying bearing and gearbox defects. Higher kurtosis means more of the variance is due to infrequent extreme deviations, as opposed to frequent modestly sized deviations. In this study kurtosis deviation curve and amplitude deviation curves are also used for shaft crack detection. It has been noted that the kurtosis changes are significant when the crack is closer to the bearing locations. Single cracks and two cracks have been identified. The rotational laser vibrometer has been used to measure the response from the rotating system. The simulation results of crack detection compare well with experimental results.