Fractal Analysis of Fracture Surfaces and Simulation of Fracture Process Using Fractal Dimension Maps in Stainless Steels Fatigued by Repeated Bending

摘要

The fractal dimension of the fracture surface (D ) was estimated in the different length scales of the fractal analysis, which were associated with the size of characteristic microstructures on the fracture surface, using thin plate specimens of stainless steels fatigued by repeated bending. The fracture surfaces were produced by ductile fatigue fracture in the 21Cr and SUS316 steels and by quasi-cleavage fracture in the SUS631 steel. The values of D evaluated on small regions of the fracture surface were displayed by the fractal dimension map (color-coded map, FDM) for the analysis of the fatigue fracture process. The fractal dimension represented not only the microstructural patterns on the fracture surface but also the damage caused by cyclic compressive loading during fatigue, irrespective of fracture mechanisms of steels. The fatigue fracture processes in the stainless steels were simulated using a set of the FDMs, in which the imaging conditions were appropriately chosen. The result of simulation using the FDMs was reasonably correlated to the fatigue crack shape detected by the heat tinting method in the 21Cr and SUS631 steels. The present fractal analysis is essentially applicable to the fracture surfaces of various types of fatigued specimens subjected to cyclic compressive loading.