Cracked Shaft Damage Identification via Symmetry Breaking Active Magnetic Bearing Control and Interrogation

A new vibration-based damage identification methodology for cracked rotor systems with periodically time-varying dynamics is developed and demonstrated on a shaft-disk system. This approach is based Floquet theory and utilizes measured changes in the system natural frequencies to estimate the severity and location of shaft structural cracks during operation. The damage identification is enhanced through the use of an Active Magnetic Bearing with adjustable support stiffness and acceleration feedback. Here, a novel symmetry-breaking closed-loop control is employed during the iterative damage identification process to enrich the data set by removing the Eigen degeneracy of the symmetric shaft structure. This approach enables full damage identification from a single sensor and hence without requiring measured modeshape information. The dynamical model of system is built based on the Lagrange principle and the assumed mode method while the crack model is based on fracture mechanics. The method is synthesized via harmonic balance and numerical examples for a shaft/disk system demonstrate the effectiveness in detecting both location and severity of the structural damage.