Microstructural effect on fracture evolution in spheroidal graphite iron: Numerical analysis

Spheroidal graphite iron (SGI) has found extensive application across various engineering sectors thanks to its excellent combination of mechanical properties at elevated temperatures and durability. The morphology of graphite inclusions in SGI has a great effect on its mechanical properties in tension. Despite extensive research, the influence of its microstructure on the fracture behaviour has not been fully investigated. In contrast to previous studies of fracture behaviour, the present work attempts to investigate the relation between graphite morphology and fracture behaviour of SGI by using 2D images (slices) from X-ray tomography (X-CT). In this study, a novel approach based on microstructural simulations is proposed. SGI slices were obtained from X-CT and every fifth image was selected to ensure a balanced representation of the microstructure that neither completely alters the character of the distribution of graphite particles nor significantly changes the fraction of any specific graphite particle. The crack path generated in representative volume elements (RVEs) is used to investigate the effect of graphite particles and depict the crack thickness in 3D. The tensile properties and damage mechanism of finite-element methods are validated from experiments. It was found that large and irregular graphite particles accelerated the crack-initiation process. Besides, the spacing between graphite particles should be as large as possible to enhance the material’s fracture toughness. This research provides an effective way to find optimum arrangements of graphite particles or voids for the design of structural components with increased fracture toughness. The application of micromechanics modelling has the potential to provide new insights useful for the design and manufacture of metal-matrix composites.