On the gear testing device of the LIS laboratory (Grenoble, France), a total of 20 signals are synchronously recorded including shaft acceleration signals in several positions, torque, rotation speed, optical encoder signal of both shafts and currents and tensions of the non-synchronous training motor. After about 3500 hours of using this device, the driving gear shaft broke at the gear coupling position with the training motor shaft, which created an impressive helicoidal crack. This failure could be due to a flexion strain caused by a misalignment of the two shafts, but this fault was not detected before. In this paper we compare results of different signal processing methods for the detection of this fault. Particularly, we use the phase spectrogram whose advantage is to be able to highlight a slight phase modulation in signals that is not detectable on the amplitude spectrogram. We also attempt to detect the fault using spectral analysis, a non-stationary modelling based on Prony's model and comparison of signals recorded at different times before the crack: the acceleration signals, the torque, and the torsional vibration signal obtained from the shaft encoder signal. The detection results are compared and discussed between the different methods.
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