Detection, discrimination and real-time tracking of cracks in rotating disks

The purpose of this effort was to develop a system to detect, discriminate and track fatigue cracks in rotating disks. Aimed primarily at jet engines in flight applications, the system also has value for detecting cracks in a spin pit during low cycle fatigue testing, and for monitoring the health of steam turbines and land-based gas turbine engines for maintenance purposes. The results of this effort produced: a physics-based model that describes the change in the center of mass of a rotating disk using damping ratio, initial unbalance and crack size as parameters; the development of a data acquisition and analysis system that can detect and discriminate a crack using a single cycle of data; and initial validation of the model through testing in a spin pit. The development of the physics-based model also pointed to the most likely regimes for crack detection; identified specific powers of ω to search for in specific regimes; dictated a particular type of data acquisition for crack discrimination; and demonstrated a need for a higher signal-to-noise ratio in the measurement of the basic vibration signal.