Ductile damage prediction in different cold forming processes

The purpose of the present paper is to show how and to what extent the introduction of refined, shear sensitive models improves on previous ones, based on triaxiality only, for the phenomenological description of ductile damage in bulk cold metal forming processes. Wire-drawing and wire rolling are taken as examples. A set of mechanical tests has been conducted: round bar, notched bar and plane strain tensions as well as torsion for pure shear deformation. Both constitutive and damage models parameters have been carefully identified, with back-computation of the laboratory tests for validation. Application of the models to the cold forming processes, described here, shows the superiority of the shear-enhanced models for locating maximum damage in flat wire rolling, where a significant amount of shear is present (``blacksmith's cross'' deformation pattern). On the contrary, it proves unnecessary for low-shear processes such as wire-drawing. The cavity-growth Gurson-Tvergaard-Needleman model, with a modified formulation for nucleation, seems to be the best basis for damage prediction in patented high carbon steel