Damage modelling in nodular cast iron

Abstract
The damage mechanism of two types of ductile cast iron have been studied by precise microscopical observations and careful chemical, morphological and mechanical characterizations. Two modes of damage are observed as a function of graphite morphology : the void growth at the pole of the graphite or the void growth by internal cracking. These two types of damage are considered by micro mechanical method. The plastic deformation of the matrix is taken into account and the damage processes are modeled : replacing the nodule by a void or anisotropic inclusion for void growth at interface case, introducing two population of inclusions (nodule and penny-shape crack) for internal cracking case. These results show that graphite nodules in cast iron serve essentially as void nucleation sites and that as soon as debonding occurs, the nodules can be replaced by voids (cast iron A). The predicted local of flow stress in the case of internal cracking is higher than in the case of the voids one. This seems to be confirmed by the experimental result of cast iron B (contents more internal cracks than cast iron A). A comparison between analytical and numerical results is presented.