Abstract: The chaos and the intermittent chaos motions of the Holmes type Duffing oscillator are researched. It is founded that the tiny angular frequency difference between the referential signal and the disturbing signal is the reason of the intermittent chaos. It is concluded that the oscillator phase transform is sensitive to the small signal having the tiny angular frequency difference with the referential signal but immune against the random noise and the larger interference signal having larger angular frequency difference with the referential signal. The gear off-center and the single tooth faults can be diagnosed and identified through distinguishing the intermittent chaos of the pair of oscillators.

Key words: Duffing oscillator, Fault diagnosis, Gear, Intermittent chaos