PSI - Issue 68

Xingling Luo et al. / Procedia Structural Integrity 68 (2025) 694–700

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Xingling Luo et al. / Structural Integrity Procedia 00 (2025) 000–000

1. Introduction The history of cast iron can be dated back to ancient times, as reported by Stefanescu et al. (2018). Prior to the introduction of microscopic studies, cast irons were divided into two types based on their colour: white and grey. Another type of cast iron was discovered in 1938 as reported by Adey et al. (2005): compacted graphite iron (CGI). It is known for its excellent mechanical properties and machinability related to its intermediate graphite morphology, between that of grey and spheroidal cast irons, gaining significant attention over the past 20 years (König, 2010). It prevailed in several automotive applications, including diesel cylinder heads and blocks (Dawson, 1999). The mechanical properties of CGI at room temperature are important for numerical analysis of their mechanical behaviour, and these parameters vary across different studies, summarised in Table 1. There are two main factors in the micromechanics of cast irons that influence their mechanical properties: (i) type, size, and distribution of graphite particles; (ii) type of matrix, e.g., ferrite/pearlite relation (Chi, 2013). Consequently, understanding the relation between the mechanical properties and the microstructure of CGI becomes significant.

Table 1. Summary of mechanical properties of CGI at room temperature.

Source

Phase/name

E (GPa)

Poisson’s ratio

Yield strength (MPa)

Density (kg/m 3 )

Pearlite Graphite Matrix Graphite Pearlite Graphite Ferrite Graphite

190

0.3 0.2

514 125

7850 2560 7100 6800 2270

Ljustina et al. (2014)

25

Niu et al. (2021)

CGI-GJV450

203

0.26 0.25 0.2

384.38 324 27.56

150 15.85

Palkanoglou et al. (2022)

Joshi et al.(2023) Yang et al. (2021)

CGI-GJV450

130 210 210 17 145 145 136 10

-

324 500 N/A N/A 315 370 409 85

- - -

0.3 0.2 0.3 0.2

7850 1820 7000 7000

Zhang et al. (2018)

CGI-70% pearlite CGI-100% pearlite CGI-70% Pearlite

0.26 0.26

Guesser et al. (2001) Dawson et al. (1999)

- - - -

- - - -

CGI-JV/300 CGI-JV/350 CGI-JV/400 CGI-JV/450 CGI-GJV/400

130-145 135-150 140-150

210-260 245-295 245-295

König et al. (2010)

Pan et al. (2018) Norman et al. (2017)

106 154

0.25

-

7079

0.3 7846 RVE and unit-cell models are both widely used in the field of computational mechanics to simulate the mechanical properties and fracture behaviours of heterogeneous materials. The main difference between these models is the number of inclusions, which are selected in each approach. Generally, RVE models of random microstructures must have the capability to statistically represent the macroscopic behaviour of the continuum and consist of at least 10 inclusions, selected from a larger structure or material (Collini and Pirondi, 2019; Vajragupta et al., 2012). The 3D periodic RVEs containing a realistic distribution of matrix and nodules were developed by Collini et al. (2020) to study the effect of the triaxiality on failure strain and ductility of mixed ferritic/pearlitic DCI structures. It was found that triaxiality has a strong effect on material ductility and the growth of the volume fraction of voids. Then, they considered a real spatial distribution of nodules and modelled the mixed matrix. A similar RVE modelling approach to predict the elastic, plastic, and fracture properties of composite materials was suggested by Higuchi et al. (2024). However, image-based RVE should consider real graphite morphology as well. Zhang et al. (2018) constructed a micro-scale damage cohesive finite-element model based on real graphite morphology to investigate the quantitative relationship between mechanical properties and microstructures. The unit cell approach is also a very important method, which focuses only on a single repeating element (Palkanoglou et al., 2022). The strength of this approach is in its capability to interpret the mechanical response of materials with complex microstructures. Andriollo et al. (2016) simulated the effect of the manufacturing process of a typical ferritic ductile iron grade on the development of local residual stresses around graphite particles with the unit-cell approach. Cao et al. (2023) generated a set of three dimensional finite-element models to explore the effect of graphite morphology on the thermomechanical performance 252