Abstract
High silicon alloyed nodular cast iron consists of a purely ferritic matrix and graphite nodules, mainly. Varying wall thicknesses and manufacturing conditions result in different graphite morphologies throughout a structural component. From an experimental point of view, axial fatigue and tensile tests were carried out on specimens with differently degraded graphite. From a numerical point of view, the microstructure has been modelled using a finite element (FE) approach with representative volume elements (RVE). The RVE models were built according to micrographs of fatigue specimens. The generated RVEs determine effective material properties through elasto-plastic homogenization and were subsequently analysed using a shakedown approach. In shakedown theory, the material re-enters the elastic regime after a few cycles of initial plastic deformation. This work uses the shakedown theorem to derive a lower bound estimation of the endurance limit from a non-incremental simulation. Here, the material has to be modelled elastic-perfectly plastic. The major challenge in modelling nodular cast iron is to determine suitable material parameters for the graphite and ferrite phase, revealed by parameter studies on the static and cyclic model. By using reasonable material parameters, fundamental effects, observed in the fatigue tests, were reproduced on the model level.
Highlights
Ductile cast iron is a material that meets a wide range of engineering applications due to its ductility, fatigue and corrosion properties
The experiments reveal that defect-based approaches might be unsuitable for estimating the fatigue limit of high silicon alloyed nodular cast iron, as bigger nodules had a higher fatigue limit
The fatigue limit does not correlate with the nodularity
Summary
Ductile cast iron is a material that meets a wide range of engineering applications due to its ductility, fatigue and corrosion properties. Rare for these materials, which restricts its use in structural applications and leads to conservative design. Some of these applications feature a varying wall thickness, which yields different graphite morphologies throughout the component. The graphite morphology influences the endurance limit of nodular cast irons [2, 3]. Löblich obtained small improvements of the endurance limit of silicon alloyed DCI compared to conventional GJS-500-7. This data is statistically secured poorly and large deviations occurred during testing. When the graphite is considered as a defect the MATEC Web of Conferences 165, 14014 (2018)
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