PSI - Issue 68

Minghua Cao et al. / Procedia Structural Integrity 68 (2025) 828–834 M. Cao et al. / Structural Integrity Procedia 00 (2025) 000–000

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Fig. 6. Distributions of shear strain (LE12) and shear stress (S12) in matrix at 20 °C after cooling down for graphite with T-CTE: (a) Ver_VV; (b) Nod; (c) Ver_VH.

4. Conclusion In this study, the thermal expansion mechanism in micro-structured CGI was investigated with a set of three dimensional numerical models. The models considered the morphology of a graphite inclusion embedded within a cubic domain of the metallic matrix, assuming perfect bonding between the phases. Both phases were modelled using elastoplastic constitutive behaviour. Pure thermal loading, cycling from 20°C to 500°C and back to 20°C, was applied to the unit cell under PBCs. The coefficient of thermal expansion of the metallic matrix is significantly higher than those of the graphite particle, resulting in greater thermal deformation in the matrix than in the inclusion. This thermal expansion mismatch between the two phases is the primary cause of damage in the graphite inclusion. Under the PBC conditions, the damage initiated from the free top surface. A higher volume of nodular graphite inclusions had a more pronounced effect on the overall damage within the unit cell. Although the volume fraction of graphite inclusions is significantly lower than that of the metallic matrix, the behaviour of the graphite inclusions still influences the overall behaviour of the matrix. Additionally, compared to the constant CTE (C-CTE), the lower temperature-dependent CTE (T-CTE) for the graphite domain resulted in a greater thermal expansion mismatch between the graphite and the matrix. This mismatch led to higher damage in the graphite but induced lower stress in the metallic matrix. References Andriollo, T, Thorborg, J., Hattel, J., 2015. The influence of the graphite mechanical properties on the constitutive response of a ferritic ductile cast iron--a micromechanical FE analysis, COMPLAS XIII: proceedings of the XIII International Conference on Computational Plasticity: fundamentals and applications, Barcelona, Spain. Andriollo, T, Thorborg, J., Tiedje, N., Hattel, J., 2015. Modeling of damage in ductile cast iron - The effect of including plasticity in the graphite nodules. IOP Conference Series: Materials Science and Engineering 84, 12027. Andriollo, T., Thorborg, J., Hattel, J., 2016. Modeling the elastic behavior of ductile cast iron including anisotropy in the graphite nodules. International Journal of Solids and Structures 100–101, 523–535. Andriollo, T., Zhang, Y., Fæster, S., Thorborg, J., Hattel, J., 2019. Impact of micro-scale residual stress on in-situ tensile testing of ductile cast iron: Digital volume correlation vs. model with fully resolved microstructure vs. periodic unit cell. Journal of the Mechanics and Physics of Solids 125, 714–735. Cao, M., Baxevanakis, K., Silberschmidt, V., 2023. Effect of graphite morphology on the thermomechanical performance of compacted graphite iron. Metals 13. Dawson, S., 2008. Compacted graphite iron - a material solution for modern diesel engine cylinder blocks and heads, 68th WFC - World Foundry Congress, Chennai, India.