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Experimental multiaxial Kitagawa diagrams are produced for cast A356 T6containing natural and artificial defects. Results are obtained for three differentloadings: tension, torsion and combined tension-torsion, for a load ratio R = -1. Theexperimental critical defect size determined is 400 +/- 100 mm in A356 T6 undermultiaxial loading. Below this value, the microstructure governs the fatigue limit mainlythrough the SDAS. We compared four theoretical approaches to simulate Kitagawadiagram for multiaxial loading: Murakami’s equation, a defect is equivalent to a crackusing Linear Elastic Fracture Mechanics, the Critical Distance Method (CDM)proposed by Susmel and Taylor and the Defect Stress Gradient (DSG) approachproposed here. It is shown that CDM and DSG methods give good results but needthree fatigue data for the identification.