Dynamic modeling of rod-fastening rotor systems with rub-impact and rod loosening

• A mechanical model characterizing preload detuning is established. • Coupled effects between tie-rod detuning and rub-impact are incorporated. • A nonlinear rotor dynamics model with tie-rod detuning is proposed. • Frequency shift phenomena induced by preload reduction are investigated. Rod-fastening combined rotor (RFCR) systems are extensively utilized in aerospace and industrial machinery due to their high strength and modular design. However, the compact configuration of gas turbines makes rotor–stator rub-impact more likely to occur during operation. Moreover, the relaxation of interfacial preload under cyclic loading further exacerbates the situation by introducing structural looseness. These combined effects give rise to complex nonlinear dynamic behaviors, such as bifurcations, subharmonic resonances, and instability near critical speeds. To investigate these phenomena, this study develops a detailed dynamic model of the RFCR system, incorporating tie-rod preload detuning and rub-impact effects using Timoshenko beam theory and finite element discretization. The system response is analyzed using the Newmark- β numerical method, and the nonlinear dynamic characteristics such as bifurcations, subharmonic resonance, and fractional frequency components are examined. Simulations reveal that preload detuning induces higher-order periodic responses, reduces the threshold for quasi-periodic motion, and broadens the vibration instability region. These findings are further validated through experimental tests on a custom RFCR test bench. The results demonstrate a strong correlation between preload degradation and the evolution of nonlinear behaviors, such as early-onset rub-impact and critical speed shifts. This study provides a theoretical and experimental framework for understanding and diagnosing preload-induced faults in rotor systems, offering valuable guidance for structural health monitoring and reliability design in turbomachinery applications.