A method for accurately predicting ductile fracture is desired to achieve efficient process optimization. The critical value of the Cockcroft & Latham equation as a typical model of uncoupled damage criteria is formulated taking into consideration the stress triaxiality and microstructural anisotropy. The medium-carbon steel S45C is used as a specimen material. Notched bar tensile test, taper anvil compression test, and torsion test are designed and conducted so as to represent different stress triaxiality states. These material tests are carried out while changing the direction of specimen relative to the rolling direction. Furthermore, tensile-compressive combined loading test is performed to confirm the applicability of the formulated critical value. The result shows that the proposed damage critical value has an advantage over the constant critical value in predicting the occurrence of fracture accurately.
