Abstract
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.
Highlights
Since its commercial introduction in 1948, ductile iron, known as nodular cast iron or spheroidal graphite iron (SGI), has constantly found new fields of application, ranging from the automotive sector to the wind power industry
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
A breakthrough in the experimental characterization of SGI has been achieved in the last 10-15 years with the introduction of techniques based on X-ray computed tomography (CT), which have been applied to visualize the microstructure evolution in 3D during both manufacturing
Summary
Since its commercial introduction in 1948, ductile iron, known as nodular cast iron or spheroidal graphite iron (SGI), has constantly found new fields of application, ranging from the automotive sector to the wind power industry Nowadays, this positive trend is challenged by the limitations in terms of reliability and range of applicability of the processing-microstructure-property relations available in the literature, which are rooted in the still incomplete understanding of the mechanisms controlling deformation and fracture at the microscale [1]. This positive trend is challenged by the limitations in terms of reliability and range of applicability of the processing-microstructure-property relations available in the literature, which are rooted in the still incomplete understanding of the mechanisms controlling deformation and fracture at the microscale [1] This is primarily a consequence of the complex material microstructure, composed of graphite nodules embedded in a matrix where multiple phases may coexist depending on chemistry and cooling conditions, which makes direct experimental investigations challenging.
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