Constraint effects on fracture toughness of ductile cast iron in the ductile regime

To assess the effect of constraint loss on fracture toughness of ductile cast iron (DCI), GJS-400-15, in the ductile regime at 0 degrees C, the fracture toughness was characterised with two different types of fracture toughness specimens, compact tension (C(T)) and single edge tension (SE(T)) specimens. The constraint state in the specimens was quantified using finite element analysis. Overall, the constraint dependence of fracture toughness for DCI is comparable to typical ferritic structural steels. For the obtained J-R curves, the fracture toughness increases as the crack grows, and the crack growth is stable on macroscopic scale up to J = 290 kJ/m2. Independent of the constraint state in the stable crack growth regime, the global failure mechanism is ductile fracture, including occasional local brittle areas.