The mechanism of stiffness increase phenomenon of a rubbing disk

The phase characteristic of a disk rubbing with a ring supported elastically is investigated and used to explain the mechanism of stiffness increase phenomenon. As long as the rubbing is maintained, the averaged phase difference between the disk and the rotating mass on the disk is definitely less than π/2. When the rubbing finishes, the phase difference quickly approaches to π. This behavior is independent of the physics parameters of the rubbing system. The theoretical results are qualitatively verified with experiments.