Vibration peaks occurring at rational fractions of the fundamental rotating critical speed, here named Local Resonances, facilitate cracked shaft detection during machine shut-down. A modified Jeffcott-rotor on journal bearings accounting for gravity effects and oscillating around nontrivial equilibrium points is employed. Modal parameter selection allows this linear model to represent first mode characteristics of real machines. Orbit evolution and vibration patterns are analyzed, yielding useful results. Crack detection results indicate that, instead of 1 x and 2 x components, analysis of the remaining local resonances should have priority; this is due to crack-residual imbalance interaction and to 2 x multiple induced origins. Therefore, local resonances and orbital evolution around 1 / 2 , 1 / 3 and 1 / 4 of the critical speed are emphasized for various crack-imbalance orientations.
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Gómez-Mancilla et al. (2004) studied this question.
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