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When subjected to fatigue loading microstructurally short cracks grow ina zigzag shape in a single shear mechanism due to nucleation, gliding and annihilationof dislocations. Such crack shapes are computationally time consuming due to the scaleof refinement needed in a numerical model. Therefore an investigation of to what extenta zigzag geometry could be simplified, keeping acceptable accuracy as regardsgeometry dependent parameters, was performed. It was found that using a modelcorrectly describing the zigzag section closest to the crack tip only, ignoring all zigzagsections between this last one and the initial crack tip, very good agreement wasobtained, both when calculating the nucleation stress for dislocations and the resolvedshear stress in front of the crack.