Abstract: Fractal dimension and scale coefficient of surface profiles are calculated using structure function method. Studies show that there is the imperfection of fractal dimension or scale coefficient in characterizing rough surfaces. In consideration of this case, combing profile fractal dimension and scale coefficient puts a new fractal parameter called characteristic roughness forth. Its definition and calculation expression are given. Friction and wear tests were conducted by using thrust type tester and surface topographies were measured in the same place of the test specimen at different wear time. It’s found that it is not only more sensitive but also more regular for characteristic roughness to characterize rough surface during running-in process than fractal dimension or scale coefficient to do.

Key words: Characteristic roughness, Fractal, Friction, Running-in, Surface topography, Wear