Abstract
This paper investigates the fracture surface topography of two steel and aluminum alloys subject to bending-torsion fatigue loadings, as well as their susceptibility to fatigue performance and failure mechanisms. Using fracture surface topography data analysis, elements with different geometries were elaborated. A correlation between the fractal dimension, other selected parameters of surface topography such as areal Sx, and fatigue loading conditions was found. Distinctions in particular regions of cracks were also recognized through proving the correctness and universality of the total fracture surface method. The influence of fatigue loading parameters on the surface topography of fatigue fractures was demonstrated. For the analyzed cases, results show that the fractal dimension and standard surface topography parameters represent a correlation between them and loading conditions. As a single parameter, the appropriate loading ratio cannot be outright calculated with fractal dimension, but can be estimated with some approximation, taking into account additional assumptions.
Highlights
Many service failures occur from components being subjected to mixed-mode multiaxial fatigue loadings
This paper is a systematic study of the relationship between the fracture surface geometry and the loading histories for components subjected to proportional and nonproportional bending-torsion loading, as well as pure bending and pure torsion
The investigation was carried out via surface fractal dimension Df and areal surface parameters Sa, Sq, Sz evaluated at total fracture fatigue surface area
Summary
Many service failures occur from components being subjected to mixed-mode multiaxial fatigue loadings. We can find many papers reporting ways of presenting surfaces in a 3D system to describe the surfaces of additive manufactured metals [21], machining results [22] and fretting wear [23] In all of these studies, digital filtering is very important and has a great influence on the calculation of results for the surface parameters [24,25,26]. In the context of filters, for the fractal dimension, and especially the enclosing boxes method, filters should be applied on the primary surface This means that the surface should be prepared for analysis, so the microroughness λs must be removed along with the form or slope λc, using levelling operations. This analysis would help to interpret the connections between fracture surface topography and trying to determine the models between fractal dimension and fatigue loading conditions
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