Dynamic characteristics of a rod-fastening rotor system with tie rod bolt loosening

Tie rod bolt loosening is a common fault in the rod-fastening rotor (RFR) system. The preload of tie rod bolts is prone to detuning under long-time periodical alternating load during system operation. Additional moment is produced by the loose bolt and the system global stiffness is decreased, which aggravates the system motion nonlinearity. The RFR system dynamic characteristics under one tie rod bolt loosening are studied in this work. A new RFR system dynamic model is proposed, considering the piecewise linear characteristics of the interface bending stiffness under tie rod bolt loosening. The single impact of tie rod bolt loosening and the coupling effect with initial bolt preload on the system dynamics are numerical analyzed. The simulation results show that periodic-2 motion is excited by tie rod bolt loosening, and the trend of periodic-2 motion to develop into chaos becomes apparent with the decrease in the preload. Meanwhile, the frequency components complicate with the fractional frequency occurring at the same speed range. Similarly, the frequency components of the fractional frequencies increase under a smaller preload. The results obtained from the simulation are well verified by the experiment. The experimental research is conducted on a RFR system test rig with one tie rod bolt loosening under different preloads. This work provides insights into the dynamic characteristics of RFR systems under tie rod bolt loosening and contributes to the bolt loosening fault identification of RFR systems.