A Finite Element Study of Large Strain Extrusion Machining Using Modified Zerilli-Armstrong Constitutive Relation

The objective of this work is to study the performance of modified Zerilli-Armstrong constitutive relation proposed in our previous study for the finite element modeling of a severe plastic deformation technique called large strain extrusion machining. The modified Zerilli-Armstrong constitutive relation is implemented in a finite element model of large strain extrusion machining of Inconel 718 to analyze the influence of process parameters, i.e., the chip compression ratio and tool-chip friction, on deformation, effective strain distribution, and hydrostatic pressure distribution along the extruded chip. The predicted strain values for different chip compression ratios were validated by comparison with those obtained through an analytical model. The finite element predictions also served as a guideline in designing the large strain extrusion-machining setup on which experiments were conducted to generate Inconel 718 foils with superior mechanical properties. The predicted limits of chip compression ratio were in close agreement with experimentally realizable values. Furthermore, the predicted strain distribution through the thickness of the chip was validated with the results of hardness measurement tests. Microstructural characterization of the Inconel 718 foils was carried out by using both optical and transmission-electron microscopic studies in order to reveal the presence of fine-grain structures. The validations showed the effectiveness of the modified Zerilli-Armstrong constitutive relation in modeling large strain extrusion machining-a variant of the conventional machining process.