Designing against failures resulting from static and time-varying loading in thick-walled components made of ductile cast iron

Ductile cast iron (DCI) is a pivotal material in Europe’s foundry industry due to its strength, flexibility, and versatility. Widely employed in sectors such as automotive manufacturing, construction, energy production, and wastewater systems, DCI is exploited to produce complex and large components. Despite its advantages, the production of thick-walled DCI components faces significant challenges, including variability in mechanical properties influenced by chemical composition, cooling rates, and melt treatment, as well as the presence of casting defects such as micro-shrinkage porosity and degenerated graphite, mainly induced by the long solidification times. Current European standards (UNI EN 1563) only partially address DCI’s mechanical properties, limiting the standardization to relatively small wall thickness, thus leaving critical gaps in classification and performance guidelines of thick-walled components. This lack of standardization complicates efforts to optimize material use for lightweight, sustainable designs, highlighting the need for a robust scientific foundation to support such developments. This thesis investigates the macro- and micro-mechanical behaviour of thick-walled DCI castings under various loading conditions. A method for casting quality assessment is proposed, based on the Voce hardening model and the concept of Defects-Driven Plasticity. The study extends to the uniaxial fatigue response, analysing the interaction between micro-shrinkage porosity and geometrical notches using probabilistic approaches, the concept of Highly Stressed Volume and local fatigue criteria. Furthermore, multiaxial fatigue is explored through volumetric Strain Energy Density approaches, with particular emphasis on meanstresses and out-of-phase loadings. Simplified frameworks are presented for industrial application, alongside detailed formulations for complex analyses. Insights and observations are finally offered on the impact of the solidification rate and its potential integration into the primary framework of this study.