Damage Prediction Using Several Types of Macro-scale Damage Models in Different Cold Wire Production Lines

International audienceThe 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 tension, notched bar tension, plane strain tension, and torsion for pure shear deformation. Both constitutive and damage model 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 seems to be the best basis for damage prediction in patented high carbon steel, a very ductile material

Comparison of reduction ability between multi-stage cold drawing and rolling of stainless steel wire – Experimental and numerical investigations of damage

International audienceThe present paper deals with the comparison between two multi-stage cold forming processes on an austenitic stainless steel, wire drawing and wire rolling, in terms of reduction ability. In the first step, experimental tests are carried out and reveal that, starting from an identical initial wire, higher reduction can be obtained with the drawing process. In the second step, numerical simulations are employed to investigate ductile damage in these two processes, using the phenomenological fracture criterion proposed recently by Bai and Wierzbicki (2008) and the coupled Lemaitre model in the framework of continuum damage mechanics (CDM). For the applications to forming processes, the models' parameters are identified first based on different mechanical tests at different loading configurations. Applications to wire drawing and rolling processes show the validity of these two models in fracture prediction both quantitatively and qualitatively. These two damage models are capable of predicting accurately the instant of fracture and also confirm the experimental comparative results between the reduction abilities of the two processes. Between the two studied forming processes, the results suggest the use of the drawing process instead of the rolling process to reduce wire section with minimum damage. It also shows that numerical simulations with the two developed damage models could be an effective tool to investigate ductile damage in other forming configurations or processes