Dynamic stiffness analysis of angular contact ball bearings based on fully coupled bearing-rotor dynamic model

A fully coupled dynamic model of a ball bearing-rotor system is developed and experimentally validated to investigate the interaction between bearing internal dynamics and rotor vibration. The model resolves bearing contact forces and moments directly from internal dynamics, enabling the dynamic stiffness to evolve naturally with rotor motion. Results show that the dynamic stiffness of angular contact ball bearings exhibits pronounced non-stationary behavior, in which low-frequency variations induced by rotor load modulation coexist with high-frequency fluctuations transmitted through the rolling elements. These stiffness fluctuations demonstrate that bearing stiffness is continuously modulated by rotor dynamics rather than being an intrinsic local property. At high rotational speeds and low axial loads, additional inertial loads induced by rotor vibration significantly degrade effective bearing stiffness and destabilize ball-raceway contacts. Based on this mechanism, a stiffness-based criterion is proposed to characterize the limiting speed governed by internal bearing dynamics. Furthermore, stiffness variations have a limited influence on low-order rotor modes but strongly affect higher-order modes, leading to shifts in hazardous operating speed ranges and modulation of rotor vibration responses.