Abstract

When considering fatigue strength, local effects play a major role. Cast or additively manufactured components exhibit geometric deviations and porosity, which can significantly influence the fatigue strength in both directions. Corner radii can be larger or smaller than intended by the designer effecting an increase or decrease of the fatigue strength, while pores will reduce the lifetime depending on their size and location. Computed tomography (CT) enables to capture these deviations and evaluate their relevance for state-of-the-art fatigue approaches. Pores within structural components might act as a source of stress concentration and thus it is desired to include them in a structural simulation. As there is generally a high number of microstructural pores, including them all in a classical finite element (FE) simulation will require high effort in FE mesh generation and result in large simulation models with a high number of elements to resolve stress concentrations in the vicinity of each defect. Immersed boundary finite element methods are well suited for overcoming these meshing problems. As they do not require a geometry-conforming mesh, they can efficiently be applied to simulate local stress distributions directly on CT scans, which accurately represent complex material structures and internal discontinuities. It is shown that the immersed boundary FE method is suitable to calculate local stress concentrations for the use in fatigue predictions. For more sophisticated simulations, e.g. with non-linear material behavior, a workflow is presented on how to generate volumetric meshes directly from CT data including only critical pores where the linear elastic immersed boundary approach exceeds a certain stress. This method reduces the number of FE-elements and thereby the computation time for subsequent complex FE-simulations significantly. Comparison of the stress concentrations of the immersed boundary FE and a linear elastic classical FE are in good correspondence even with the reduced set of meshed pores.