ANALYSIS OF THE METAL CUTTING PROCESS IN TERMS OF YIELD SURFACE TOPOLOGY.

In order to describe the deformation in the workpiece in metal cutting, a plastic yield surface was constructed which exhibited observed metal deformation behavior and metal cutting process characteristics. A von Mises type yield surface was used which was generalized to include strain softening and progression to a plane stress state. The metal cutting process was represented on the yield surface as a trajectory which moved from the strain hardening to the strain weakening region. The shear zone geometric characteristics were included by extending the yield surface to a plane stress state. When the change in shear zone stress state was represented by a continuous trajectory on the yield surface, the possibility of different regions of the shear zone being in different strain hardening conditions resulted in a reversal of strain increment direction across the shear zone. This strain direction reversal can explain the nonuniform deformation structure observed on metal cutting chips.