Numerical analysis of microstructure influence on mechanical properties and failure behaviour of compacted graphite iron

Compacted graphite iron (CGI), also known as vermicular graphite iron, is increasingly used in the automotive sector thanks to its excellent mechanical properties and good thermal conductivity. Its fracture behaviour at the microscale remains poorly understood, particularly regarding the influence of graphite inclusions. This is due to a random distribution of graphite particles and the different properties of these particles and the matrix. To investigate CGI’s performance and fracture behaviour under uniaxial tensile load, four different types of 2D models are developed in this study. The cohesive zone model (CZM), Johnson-Cook (JC) damage model, and ductile damage model are utilised for the matrix or graphite phases to capture the microstructure-related fracture evolution in CGI. The research sequence is as follows: first, models with single inclusions are developed to mitigate the influence of other particles on adjacent inclusions. Next, models with two inclusions are introduced to investigate the effect of graphite morphology and inter-particle spacing on the fracture behaviour of CGI. After that, models with real and simplified morphologies derived from SEM images are used to predict the crack paths and their mechanical properties. Finally, models with randomly distributed inclusions, based on microstructural characteristics of CGI, are generated to statistically analyse the effect of graphite particles on fracture behaviour. It was found that crack-initiation strain had a complex dependency on the shape, orientation, size, and distribution of graphite inclusions. The developed models contribute to the understanding of the CGI’s fracture behaviour.