Abstract: Based on fractal theory, the fractal features of running-in surface are discussed. Experiments show that running-in surface within a limited dimension has remarkable fractal feature. Two methods of defining the running-in period are unprecedentedly introduced and explained, namely①defining by the changing of fractal dimension of running-in surface. ②defining by the difference of the fractal dimensions between two running-in matching surfaces. Also, a fractal curve of running-in surface conclude from experiments is clearly illustrated, which is virtually the foundation of the two hypothetical ways.

Key words: Fractal dimension, Fractal feature, Profile of matching surface, Running-in, Cam lift error, Eccentricity correction, Non-circular contour, Tracing measurement