  This paper investigated the friction-induced vibration (FIV) behavior under
the running-in process with oil lubrication. The FIV signal with periodic
characteristics under lubrication was identified with the help of the squeal
signal induced in an oil-free wear experiment and then extracted by the
harmonic wavelet packet transform (HWPT). The variation of the FIV signal from
running-in wear stage to steady wear stage was studied by its root mean square
(RMS) values. The result indicates that the time-frequency characteristics of
the FIV signals evolve with the wear process and can reflect the wear stages of
the friction pairs. The RMS evolvement of the FIV signal is in the same trend
to the composite surface roughness and demonstrates that the friction pair goes
through the running-in wear stage and the steady wear stage. Therefore, the FIV
signal with periodic characteristics can describe the evolvement of the
running-in process and distinguish the running-in wear stage and the stable
wear stage of the friction pair.
