Constitutive behavior study of copper alloy under cold and hot compression conditions towards LN2 assisted cutting

Abstract

New standards are being introduced to eliminate toxic elements in materials. For instance, copper alloys should no longer contain lead, although this makes them more challenging to machine. Additionally, for environmental reasons, it is crucial to eliminate cutting oils. To address these two challenges, cryogenic cooling during machining can be considered. However, it is first essential to understand the precise mechanical response of the material at low temperatures. This study conducts compression tests on copper across a wide temperature range, from cryogenic temperatures (liquid nitrogen, LN₂) to 700°C, and at strain rates from 0.01/s to 10/s. The microstructure of deformed test samples is also characterized by electron back-scattered diffraction (EBSD) to compare the different plastic deformation characteristics under low and high temperature. The stress-strain curves are fitted with Johnson-Cook (JC) model, which is then implemented into the finite element simulation of the compression process. The results indicate that the JC model with the fitted parameters is not precise enough in terms of modelling very low temperature dynamic response of copper alloy, thus is not proper for the simulation of cryogenic cooling assisted cutting. This is because different characteristics of strain hardening behavior is discovered under LN₂ atmosphere temperature and ordinary cutting temperature, which is further induced by a transition of plastic deformation mechanism with increased temperature. Therefore, a new constitutive law is proposed considering deformation mechanism at both traditional cutting temperature and cryogenic conditions. The results indicate that the new model has a better fitting of experimental curves than JC model. This study is helpful for the understanding of low temperature copper deformation behavior and new constitutive model exploitation oriented to cryogenic cooling assisted cutting.