Local approach of damage and fracture toughness for nodular cast iron

The damage mechanisms of two types of ductile cast iron have been investigated. Tensile and tearing tests have been performed which provide information about the mechanical behaviour of the materials. In situ tensile tests performed inside a scanning electron microscope allowed the determination of the steps of physical damage evolution. From these observations two damage mechanisms can be defined. In one of the two cast irons, graphite nodules can be considered as voids and damage evolution is only related to void growth, whereas void nucleation has to be considered in the second one. The mechanical behaviour of these materials is modelled using the modified Gurson’s potential, and tearing test results can be predicted. The difference in fracture toughness of the two cast irons can be explained by the different sizes of the process zone in front of the crack.