A dynamic model of a two-span elastic rotor system with crack fault on the shaft supported on three plain journal bearings was set up. The influences of crack to nonlinear dynamic characteristics of the system were studied by mapping and continuation comprehensive method. The periodic, quasi-periodic and chaotic motions were found in the system responses. The route to chaotic motion is by periodic-doubling and explosive bifurcations, and leaving by periodic-doubling reverse bifurcation. There are many harmonic elements of 1/3, 1/2, 2/3, 1 and 2 et al within the sub-critical rotate speed range. But the 2-harmonic element decreases within the super-critical rotate speed range. There are quasi-periodic, periodic and chaotic motion in the region of ω=3ω{sub}0/2 along with the different depth of crack. It must notice to diagnosis the crack fault of the system when running within the super-critical rotate speed range.
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