Multifractal analysis of three-dimensional surface topographies of GCr15 steel and H70 brass during wear process

The variation of three-dimensional topographies of GCr15 steel and H70 brass during wear process was studied by multifractal method. A multi-stage test method was proposed to obtain the worn surfaces of friction pair at different wear time. The tests were performed on a ring-on-disc tribometer. The three-dimensional (3D) topographies of ring and disc were measured by laser confocal microscopy. Box-counting method was applied to compute multifractal spectrum, spectrum width Δα and spectrum difference Δf(α) of counter surfaces. All the spectra of mating surfaces are presented as parabolic curve, which indicates that the worn surfaces have the characteristics of multifractal. The Δα and Δf(α) of disc surfaces decrease at first, then stabilize at a small value and finally increase rapidly. Those of ring surfaces increase at first, then maintain at a small value and finally increase gradually. The multifractal study of 3D surface topographies reveals the singularity and nonlinear behavior of the friction system.