X-ray tomography, digital volume correlation and FE modelling: A synergistic combination to study the processing-structure-property relations in ductile iron

The mechanistic understanding of the processing-structure-property relations in ductile iron is still far from complete. One reason is that the impact on the mechanical properties of some of the microstructural features arising from the casting process can be hard or even impossible to investigate using experimental methods alone. The present work shows that a solution can be the synergistic combination of X-ray tomography, digital volume correlation (DVC) and finite element modelling, which are applied here to study the effect played by the Si micro-segregation and local residual stresses upon mechanical loading. First, miniaturized tensile and compact tension specimen are loaded incrementally while imaging with X-ray tomography. Then, the micro-scale displacement is reconstructed with DVC and used to prescribe the boundary conditions in high-fidelity 3D finite element models of the microstructure. Simulations are run considering or not the formation of the local residual stresses and build-up of micro-segregation during manufacturing. The numerical predictions are compared to the corresponding experimental data both at the macro-scale - applied load - and at the micro-scale - strain field reconstructed with DVC. This allows for a first assessment of the impact of the local residual stresses and Si micro-segregation on the mechanism of tensile deformation as well as of crack propagation of ductile iron.