Metallographic analysis of the deformation microstructure of copper subjected to orthogonal cutting

Metallographic sections taken from commercially pure copper samples, which formed continuous chips during the orthogonal cutting process, were examined to determine the displacement gradients (or the shear angles), and the local strain gradients generated in the material ahead of the cutting tool tip. The local flow stress variations in the deformed material ahead of the cutting tool tip were estimated from the microhardness measurements. An empirical relationship was established between the equivalent stresses and strains in the deformed material ahead of the tool tip. The equivalent flow stress and the equivalent strain relationship obeyed a Voce type exponential equation. It was shown that a saturation flow stress (422 MPa) is reached at strain levels ε̄>3.0. Plastic deformation work expended for each strain increment and the corresponding local temperature increase were calculated from the empirical flow curve. The highest temperatures rise (857 °C) was estimated to occur immediately ahead of the tool tip, and in the secondary deformation zone adjacent to the tool rake face.