Plain and notch fatigue strength of thick-walled ductile cast iron EN-GJS-600-3: A double-notch critical distance approach to defect sensitivity

•Inverse search based on two notched geometries to derive the critical length.•Defects analyses based on CT scans to investigate fatigue damage in ductile cast iron.•Fatigue strength ahead of notch tip controlled by graphite nodule.•Better notch fatigue strength predictions than classical critical distance theory.