Vibration-based crack-induced damage detection of shaft-disk systems

The objective of this dissertation is development of vibration-based crack detection strategies for on-line condition monitoring of rotordynamic systems. The dynamic response of a cracked Jeffcott rotor passing through the critical speed at constant acceleration is investigated analytically and numerically. The results of parametric studies of the effect of the crack depth, unbalance orientation with respect to crack, and the rate of acceleration on the rotor's response are presented. The dynamic behavior of the cracked rotor passing the resonance under a constant driving torque is analyzed by incorporating the coupling between the bending and torsional degrees of freedom. The effect of the crack depth on "stalling" of the rotor is investigated in details. The analysis of vibrational response of the cracked rotor employed nonlinear dynamics tools. The considered model accounts for nonlinear behavior of the crack and dynamic modes coupling. The finite element analysis of coupled lateral-torsional dynamic behavior of a rotor with two breathing cracks has been conducted for frequency analysis and response to excitation forces such as an externally applied torque. The variation of the stiffness matrix over the full shaft revolution is represented by Fourier series decomposition. The Fourier coefficient matrices are calculated from the stiffness matrices of the cracked shaft with the crack located at discrete angular locations based on fracture mechanics.