It has been recently reported that metal matrix composites provide significantly enhanced properties — like higher strength, stiffness and weight savings — in comparison to conventional monolithic materials. One particular type of metal matrix composites: i.e. the Particulate-reinforced metal matrix composites (PRMMCs), have been massively applied in industries, such as aerospace, electronics and automotive credit to their superior properties. Unfortunately, the hard and brittle reinforcements make PRMMCs difficult to machine. Technically, such poor machinability can be attributed to the intricate interactions among the matrix, particles and cutting edge. Consequently, extensive studies aiming at improving the machining performance have been undertaken. Nonetheless, a great deal of the resultant literature concentrates on the effects of cutting parameters on cutting forces and machined surface integrity, which cannot provide adequate understanding of material removal mechanisms. As a result, counteractive measures aimed at revealing the material removal process in the machining of PRMMCs have been proposed where two finite element modeling approaches have been demonstrated.
Generally, existing literature fails to capture a good description of the particles inter-granularities, e.g., particle clusters, together with the ideal PRMMC’s microstructure and the impact of the two on the machining process. On this account, a recent publication by researchers from The University of New South Wales in Australia: Dr. Qi Wu, Dr. Weixing Xu and led by Scientia Professor Liangchi Zhang developed an accurate microstructure-based finite element model to investigate the chip formation mechanisms and subsurface damage in the machining of PRMMCs. Their work is currently published in the research journal, Journal of Materials Processing Technology.
In their study, the morphology and distribution of the particles, the debonding of the particle-matrix interface and the fracture of particles and the matrix were comprehensively integrated during modelling. Technically, their approach was in two steps: Particle characterization and modelling and Material behavior modelling. Lastly, numerical analysis undertaken was verified by relevant cutting experiments.
The authors were able to confirm that the established model could accurately predict the machining process, including chip morphology, subsurface deformation and cutting forces. Additionally, the researchers found out that the depth of cut significantly influenced the machined surface integrity and cutting forces. Moreover, particle fracture was seen to occur mainly along the primary shear zone in the cutting path. The team also reported that the high strain and stress concentration induced by the extrusion of the cutting edge or large particles on the machined surface could potentially cause particle fracture beneath the cutting path.
In summary, the study presented the development of a microstructure-based finite element model combining the equivalent homogeneous material and multi-phase modelling in order to more accurately describe the microstructure, deformation and failure behaviors of PRMMCs. Overall, the capability of the model was confirmed by the corresponding experiments. In a statement to Advances in Engineering, Scientia Professor Liangchi Zhang highlighted that the newly established model provided an accurate prediction of chip morphology, machined surface integrity and cutting forces.
Qi Wu, Weixing Xu, Liangchi Zhang. Machining of particulate-reinforced metal matrix composites: An investigation into the chip formation and subsurface damage. Journal of Materials Processing Technology, volume 274 (2019) 116315