Two-Scale Analysis of Microscopic Damage Mechanisms at Early Stage of Fracture Process of Ferritic Ductile Iron by Means of Computational Modelling and Experimental Methodologies

Abstract

In this work, a two-scale analysis to study the early stage of fracture process of ferritic ductile iron is presented. The methodology combines numerical analysis and exhaustive experimental observations in both macro and micro scales. The multi-scale problem is modeled using the pre-critical regime of the Failure–Oriented Multi-Scale Variational Formulation (FOMF), which is implemented via a FE2 approach. Finite element analysis in the micro-scale is customized to account for plastic deformation and matrix-nodule debonding. Experiments in the micro-scale are used for microstructural characterization of the material mechanical properties and the assessment of the micro-scale plasticity/damage mechanisms; experiments in the macro-scale provide the data to calibrate and validate the methodology. The multi-scale model is found effective for capturing the sequence of events and extent of the plasticity/damage mechanisms in the micro-scale as well as to infer, via inverse analyses, the parameters of the matrix-nodule debonding law (fracture energy and peak tensile stress), which cannot be estimated through experiments. Results allow to draw conclusions related to the applicability of the FOMF and the RVE sizing for non-linear damage analysis. Additionally, it allows to develop new insights for the better understanding of ductile iron damage micromechanisms at early stage of damage.