Analyses of void growth and coalescence in cast iron by cell models

The fracture process of cast iron is initiated at the graphite nodules, followed by intensive void growth and coalescence. Two- and three-dimensional cell models are developed to study the influence of stress triaxiality and void arrangement on these microscopical damage processes in nodular cast iron The applicability of the Gurson model to this type of material is investigated and related to the cell model results. The calculations show that during a tensile loading graphite nodules hinder the transverse deformation of the matrix if the stress triaxiality for the loading is less than sigma(h)/sigma(e)=0.5. Otherwise the graphite nodules can simply be modelled by voids. The three-dimensional cell models turned out that the spatial arrangement of periodic arrays of voids has only weak influence on the deformation behaviour, whereas the plastic collapse behaviour is strongly affected. The simulation of tensile tests with notched bars demonstrates that the Gurson model can be used to characterize nodular cast iron if the triaxiality of the loading is not too low.