The impact of surface slope and calculation resolution on the fractal dimension for fractures of steels after bending-torsion fatigue

Abstract

The article presents the results of the fractal dimension measurements on the fatigue fracture surfaces of 10HNAP and S355J2 steels specimens after combined bending-torsion fatigue. For smooth and ring-notched specimens, three loading conditions were analyzed: (1) bending; (2) bending-torsion; and (3) torsion fatigue. Post-failure surface topography measurements were carried out on the entire fracture surfaces using an optical profilometer. The fractal dimension was computed with general slope and after removing them by leveling operation, as well as with two different resolutions. The analysis of the fractal dimension delineated by the enclosing boxes method (EBM) allowed to formulate guidelines that, in terms of further estimation of the method of failure, the optimum is extra-fine resolution without leveling.