In this study, fracture toughness (J-integral) values in cracked welded nodular iron were determined experimentally, and stress-strain analyses were done by the finite element method, for different crack sizes and locations with various strength levels. As a result, the effect of yield strength mismatch on the constraint around crack tip was discussed by means of stress triaxiality (ST) and plastic strain. It was found that ST values increase with crack length. Different regions in the weldment affect the extent of plastic deformation in the material. (C) 2004 Elsevier B.V. All rights reserved.