Vibration characteristics of a rub-impact rotor system supported on oil film bearings are investigated. Oil film forces are obtained from the short bearing approximation. Elastic impact and the Coulomb type of frictional relationship are assumed in the analysis. A nonlinear mathematical model with piecewise linear stiffness is used. Rotating speed, the system damping and unbalance are used as control parameters to observe various forms of periodic, quasi-periodic and chaotic vibrations. Four different routes to and out of chaos, that is, periodic, quasi-periodic, intermittent and period doubling bifurcation routes, are found. It is shown that the system can exhibit very rich types of periodic, quasi- periodic and chaotic vibrations. These forms of vibrations and relevant phenomena can be effectively used to diagnose the rub-impact fault in rotating machinery.
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