The changes of fractal dimensions of frictional signals in the running-in wear process

The running-in wear experiments were preformed on the pin-on-disc tester. Time series signals of both frictional force and vibration were distilled by the computer data-collecting system, at the same time the fractal dimensions of the signals were obtained by the correlation-dimension method. It was found that the signals had an apparent fractal nature. Their fractal dimensions altered with the change of friction time, that is, increased gradually with the running-in procedure going on to reach its maximum ultimately. This indicated that the running-in process was ended from the initial friction of two surfaces to their fitted state (i.e. running-in state). In addition, the fractal dimension of friction signals was consistent with the fractal dimension of worn surfaces in the running-in process. So we can predict the progress of running-in wear process and identify the running-in state of a friction pair by the change of fractal dimension of frictional signals.