Multiscale Modeling for Assessment of Sub-Surface Damage in Iron-Titanium Carbide Metal Matrix Composites

This study is concerned with investigating the effect of laser assisted machining on sub-surface damage during turning of iron-titanium carbide metal matrix composite (MMC) manufactured through laser direct deposition. A high-fidelity 3D multi-scale computational model is presented to predict the macroscopic and micromechanical response of the metal matrix composites undergoing laser assisted turning. Implementation of the multi-scale model has been realized through a hierarchical multi-scale modeling methodology where the results of interfacial mechanics for Fe-TiC composites determined from MD calculations have been used to parameterize the cohesive zone model in the finite element simulations. The 3D nose turning simulation model is capable of predicting the mechanics of cutting of composites, tool-particle interaction, cutting forces and sub-surface damage, hence providing a holistic framework for investigation of machinability of metal matrix composites. With the help of the simulation model, it has been discovered that the particles plough through the matrix material due to their increased concentration ahead of the cutting tool. This contributes to the dynamic loading of the machined workpiece in addition to loading from the secondary cutting edge of the tool. These two mechanisms collectively contribute towards sub-surface damage in the machined metal matrix composites. Damage analysis of Fe-TiC MMC revealed three-different types of damage mechanisms, namely particle pullout/fracture, interfacial debonding leading to void nucleation in matrix and coalescence of voids in the matrix. Localized heating of the Fe-TiC workpiece via a CO2 laser ahead of the cutting tool has been shown to be effective in reducing sub-surface debonding by approximately 20%. An experimental evaluation of the machinability of MMCs revealed a reduction in specific cutting energy by approximately 19%, a 20% improvement in tool life when using carbide tool at an optimum material removal temperature of 300 °C as compared to conventional machining after full annealing of the MMC