The Effect of Compacted Graphite Iron Microstructure on Fracture and Machining

Abstract

<p>The graphite structure in compacted graphite iron (CGI) is more coral-like and interconnected only within each eutectic cell. The irregular surface of the graphite-matrix interface has blunt edges which results in the intimate adhesion of the graphite particles to the metal matrix producing more resistance to crack initiation and more vermicular paths arrest crack propagation. Furthermore, the coral-like graphite particles, which are characterized with round edges, also do not promote crack propagation and serve as crack arrestors once cracks are initiated. This unique morphology of graphite in CGI, thereafter, pays off in a higher tensile strength and modulus of elasticity while possessing reasonable thermal conductivity.</p> <p>This work is divided into two phases. The first phase establishes a foundation of a microstructure modeling technique which will be then applied to model CGI in machining. Modeling is being done to shift the approach away from trial and error as is currently being done to a more physics based approach. As machining is conceptually a controlled fracture process, this stage comprehensively studies and models the initiation and propagation of fracture in compacted graphite iron.</p> <p>The second phase serves as an application of the previously built model to capture the more complex scenario involving machining of CGI at different cutting speeds and feeds. The finite element modeling of CGI in machining provides an as of yet unavailable procedure on which future optimization techniques can be performed. The study of chip formation, cutting insert wear, and force measurements are performed in parallel with the modeling process and are employed as means to validate the FE model. Validation of both work phases has been completed to support the model developed in this thesis that captures the critical aspects of machining CGI under different operating scenarios.</p>