Modeling ductile damage for complex loading paths

Abstract : The present PhD thesis aims at a better understanding and modeling of ductile damage mechanisms during cold forming processes, with wire drawing, rolling and cold pilgering as examples. In addition, special attention is paid to implemented damage models parameters identification methodology. All three approaches of ductile damage were investigated: uncoupled phenomenological fracture criteria; coupled phenomenological models; micromechanical model. These models have been implemented in Forge®, which required adaptation of algorithms to its mixed velocity-pressure formulation and to its finite element (P1+/P1). Parallel to the numerical work, various mechanical tests on three different materials (high carbon steel, stainless steel and zirconium alloy) were carried out for work hardening, and damage models parameters identification. In situ X-ray micro-tomography tensile tests have also been exploited for the identification of ductile damage mechanisms (nucleation, growth and coalescence) as well as the identification of micromechanical model. Finally, we carried out comparative studies of these models on our three abovementioned forming processes and materials. Regarding wire drawing and rolling of stainless steel, good agreement between numerical simulations and experimental results was found. For high carbon perlitic steel ultimate wire drawing, the GTN micro-mechanical model has given the best result, both qualitatively and quantitatively. Moreover, the comparison of the different models on different processes (wire rolling on high carbon steel, cold pilgering on zirconium alloy) highlights on the one hand the important role of the third deviatoric stress invariant in damage localization for shear-dominated forming processes. It shows on the other hand that the identification process itself should be based on microstructure measurements to provide accurate results in forming application.
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Trong Son Cao. Modeling ductile damage for complex loading paths. Other. Ecole Nationale Supérieure des Mines de Paris, 2013. English. ⟨NNT : 2013ENMP0038⟩. ⟨pastel-00957315⟩

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