Incorporating dual BCC/FCC Zerilli-Armstrong and blue brittleness constitutive material models into Oxley’s machining shear zone theory

Abstract

This work presents an extension of Oxley's shear zone theory by substituting the original velocity-modified power form by the widely used constitutive material model developed by Zerilli and Armstrong (ZA). Used are variations of ZA constitutive laws capable of accounting for operating strains, strain rates, and temperatures as well as the appropriate crystal structure such as body-centered cubic (BCC) and face-centered cubic (FCC). This latter feature is useful in cutting simulations of metal alloys with complex phase diagrams (e.g., carbon steels) having temperature-dependent crystal structures. Loss of ductility encountered at elevated temperatures, dubbed Blue Brittleness (BB), adds another challenge to the simulations.For validation purposes, cutting and thrust forces of single-phase Aluminum 6061-T6 (FCC crystal structure) were investigated. Additionally, and in order to illustrate the utility of the methodology for dual phase materials, AISI 1045 steel was utilized as a metal with temperature-dependent crystal structure that evolve from BCC to FCC as temperatures increase due to increasingly aggressive cutting parameters. The simulations utilized publicly available cutting force values from orthogonal machining tests conducted at different cutting speeds and feeds. For both 6061-T6 Aluminum and AISI 1045 steel, the methodology of extending Oxley’s thick shear zone analysis by incorporating the widely used Zerilli-Armstrong constitutive laws (dual BCC/FCC) was shown to produce accurate estimates of forces and chip thickness over a wide range of cutting conditions.