Distance map based micromechanical analysis of the impact of matrix heterogeneities on the yield stress of nodular cast iron

A method to construct 3D representative volume element (RVE) models of the nodular cast iron microstructure that accounts for the presence of heterogeneities in the matrix is proposed. The main advantage is the possibility to generate a wide spectrum of realistic distributions of the matrix heterogeneities in a simple and fast way. The method takes advantage of the fact that the spatial distribution of some of the matrix heterogeneities is intrinsically connected to the distribution of the graphite nodules, due to the nature of the solidification process. Accordingly, the graphite morphology is reconstructed first via X-ray computed tomography and subsequently used to estimate the distribution of the pearlite and of the Si micro-segregation – considered as case studies – by means of dedicated distance functions. The obtained 3D models are used to show that the spatial variation in the matrix plastic properties associated with the Si micro-segregation is not expected to influence the material yielding behavior significantly. In addition, it is shown that when the matrix pearlite content increases for a fixed overall C concentration, the corresponding decrease in the nodules’ volume fraction can account for as much as 1/3 of the obtained increment in the material macroscopic proof stress.