Fatigue in metals is determined by size and shape of defects or non-metallic inclusions. Fatigue strength predictions can be made using micromechanical simulations with the shakedown theorem. In these simulations a good geometrical representation of defects is mandatory since they cause high local stresses. An advanced method based on micrographs is presented to study the influence of inclusions and defects on fatigue strength and development of cyclic plasticity in ductile cast iron (DCI). In DCI, the graphite nodules influence the development of cyclic plasticity in the high cycle fatigue regime, eventually leading to microstructural damage and fatigue crack growth. A modelling technique to reconstruct graphite nodule geometries out of low-resolution micrographs is presented. The static shakedown theorem is applied to the micromechanical models to calculate the lower bound of the fatigue strength. The influence of graphite morphologies on the fatigue strength is analyzed based on a number of micrographs. The results are compared to experimentally determined SN-curves with varying graphite morphologies, and the fatigue damage mechanisms are analyzed with SEM and EBSD. Results show a significant influence of both size and shape of graphite nodules on the development of cyclic plasticity and microcrack formation.