A novel way to detect transverse surface crack in a rotating shaft

This paper presents a novel way to detect fatigue transverse cracks in rotating shafts. The proposed detection methodology exploits both the typical nonlinear breathing phenomenon of the crack and the coupling of bending–torsional vibrations due to the presence of crack for its diagnosis. A transient torsional excitation is applied for a very short duration at specific angular orientation of the rotor and its effect in the lateral vibrations is investigated. Wavelet transforms (WTs) is used in revealing the transient features of the resonant bending vibrations, which are set up for a short duration of time upon transient torsional excitation. Variation of peak absolute value of wavelet coefficient (of the transient lateral vibration response) with angle at which torsional excitation is applied is investigated. The correlation of this variation with the breathing pattern of the crack is studied. The sensitivity of the proposed methodology to the depth of crack is investigated. The detection methodology gives a vibration response signature that closely correlates with and is very specific to the behaviour of the transverse surface crack in a horizontal rotor. The response features are not likely to be exhibited by other common rotor faults under similar excitation conditions making the proposed detection methodology unambiguous. The fact that the rotor is not required to stop and that the detection process is applied for a rotating shaft with only a short period transient external excitation makes the methodology more convenient.