Active health monitoring in a rotating cracked shaft using active magnetic bearings as force actuators

We consider the active health monitoring of rotordynamic systems in the presence of breathing shaft cracks. The shaft is assumed to be supported by conventional bearings and an active magnetic bearing (AMB) is used in a mid-shaft or outboard location as an actuator to apply specified, time-dependent forcing on the system. These forces, if properly chosen, induce a combination resonance that can be used to identify the magnitude of the time-dependent stiffness arising from the breathing mode of the shaft crack.