Abstract: This paper investigated the bifurcation and chaotic behaviors of the forced unbalance responses of a flexiblerotor-squeeze film damper system, which is commonly used in aero-engines. The system is a highly nonlinear systemwith 8 degrees of freedom and 16 orders. By analyzing the response orbit, bifurcation map and Poincare map, it wasfound that there exist many kinds of periodic (synchronous, sub-and super-synchronous) and non-periodic (quasi-periodic and chaotic) responses in the system, and the periodic and non-periodic responses were interlaced in the rotating speed range. The bifurcation forms of the response are the quasi-periodic bifurcation and the double periodic bifurcation. It was also found in this paper that the routes to chaos of the system response are the route of double periodic bifurcation to chaos, the route of quasi-periodic bifurcation to chaos and the route of intermittence to chaos,while the route out of chaos are the double periodic bifurcation and the quasi2periodic bifurcation.

Key words: rotor dynamics, bifurcation and chaos, nonlinear vibration, squeeze film damper