Identification of damaged shafts using active sensing-Simulation and experimentation

Rotating machines are susceptible to fatigue failures if transverse cross-sectional cracks form in shafts. Early detection of cracks is essential to avoid a catastrophic event and the associated costs. In this work, a detailed physics-based three-dimensional model of an experimental Machinery Fault Simulator^® apparatus is developed using ANSYS^® with beam elements based on Timoshenko beam theory. Different kinds of faults such as transverse cracks, imbalance, misalignment, bent shafts, and combinations thereof are considered. Off-line and on-line experimental tests are carried out. Different types of external excitation with piezoelectric actuators are introduced and the vibration responses in several dimensions are measured. Numerical and experimental results demonstrate that there are only subtle changes in the passive vibration natural frequencies and mode shapes due to cracks in the shaft; therefore, active sensing is necessary to detect damage. It is also shown that torsional and axial responses that are measured using active vibration sensing are highly sensitive to cracks in the shaft.