A damage model for wire drawing

Abstract

Wire drawing parameters such as area reduction and die angle have an important effect on damage generation. One of the most common defects appearing under certain critical configurations are the so-called “chevron cracks”. These defects are difficult to identify since they are typically located at the wire core. To address this, great efforts have been made in the last two decades to develop numerical models capable of predicting damage evolution and failure. Continuum Damage Mechanics (CDM) models present the advantage of being coupled with the constitutive behaviour of the material. Among these models, Lemaitre’s approach is one of the most widely used. In its original formulation, the model did not distinguish between tension and compression stresses in terms of damage accumulation. An additional parameter was then included to consider the crack closure effect under compressive stresses. However, this formulation is not valid for wire drawing, since it overestimates damage under these conditions. For this reason, a new damage model following Lemaitre’s approach has been derived by redefining the crack closure effect under compressive stresses. In this way, under high hydrostatic compressive stresses, such as in the case of wire drawing, the model yields more realistic results in terms of damage accumulation. The model has been implemented in ABAQUS through user subroutines UMAT (for implicit cases) and VUMAT (for explicit cases). Single-pass wire drawing simulations have been performed to compare the original model with the new formulation.