Microstructural CZE-based computational model for predicting tensile fracture behaviour of CGI

Compacted graphite iron (CGI), also known as vermicular graphite iron, is a double-phase engineering material, extensively used in engine cylinders and brake disks, thanks to its good combination of mechanical properties and thermal conductivity. Despite its wide use and considerable past research, the fracture behaviour of CGI at the microscale is not yet fully understood, especially the effect of graphite inclusions. Due to the complex shapes of graphite inclusions randomly embedded in the metallic matrix, development of realistic 3D models is time-consuming and computationally expensive. Hence, a novel 2D computational framework capable of predicting crack initiation and growth in CGI is necessary. In this work, a 2D CZE-based model is developed to predict crack initiation and propagation under different boundary conditions. Scanning electron microscopy was used to characterise the microstructure of CGI, with the resulting scans analysed using image-processing software. The metallic matrix and graphite particles were assumed isotropic and ductile. Cohesive elements were implemented into the models using a Python script and assigned to the ferritic matrix, graphite inclusions, and the graphite-ferrite interface. It was found that employing periodic boundary conditions increased the stiffness of CGI and accelerated interface debonding but prevented crack propagation to the matrix. The developed models will contribute to the understanding of CGI's fracture behaviour.