A stocky tubular tension-torsion specimen geometry was optimized to characterize the effect of the stress state (stress triaxiality and Lode angle parameter) on metals ductility, at low stress triaxialities. Biaxial tests (proportional and non-proportional) were performed on 36NiCrMo16 steel and 2024-T351 aluminum alloy. Strain fields were measured by stereo-correlation of digital images during the tests. Loading paths to fracture (evolution of the equivalent plastic strain, the stress triaxiality and the Lode angle parameter at the critical point) were determined. The evolution of aluminum ductility with respect to the stress triaxiality measured from tension-torsion tests differed substantially from that obtained by Bao and Wierzbicki in 2004. Indeed, the latter suggested a minimal ductility under shear, while the tension-torsion technique revealed a maximal ductility under shear. Non-proportional loading paths were shown to have an influence on ductility, by means of tests consisting in a pre-compression, pre-tension or pre-torsion, followed by a proportional loading sequence under combined tension-torsion. SEM observations of metallographic sections from biaxial interrupted tests, a real-time monitoring of the surface strain and damage during in-situ torsion tests in the SEM, and a crack propagation test coupled with in-situ X-ray synchrotron laminography brought evidences of localization phenomena at different scales, and of the growth of some cavities, even under pure shear, by contrast with the total collapse predicted by unit cell models. This growth may be due to the significant axial elongation measured under pure torsion (Swift effect). Shear localization was identified as the main coalescence mechanism, which justifies the choice of the Hosford-Coulomb fracture initiation criterion. Used in conjunction with a non-linear damage indicator, it accounts for the measured ductilities, even under possibly non-proportional loadings.
Authors
- Bibliographic Reference
- Jessica Papasidero. Etude expérimentale et numérique de la rupture ductile sous chargement multiaxial. Mécanique [physics.med-ph]. Ecole Polytechnique X, 2014. Français. ⟨NNT : ⟩. ⟨pastel-00945367⟩
- HAL Collection
- ['Ecole Polytechnique', 'Institut Mines Télécom', 'PASTEL - ParisTech', 'ParisTech', 'CNRS - Centre national de la recherche scientifique', 'Laboratoire de Mécanique des Solides (LMS)', 'Polytechnique', 'Département de mécanique']
- HAL Identifier
- 945367
- Institution
- École polytechnique
- Laboratory
- Laboratoire de mécanique des solides
- Published in
- France
Table of Contents
- Introduction ......................................................................................................... 13 10
- I. Determination of the Effect of Stress State on the Onset of Ductile Fracture through Tension-Torsion Experiments ............................................................... 35 10
- II. Bao-Wierzbicki revisited Ductile Fracture of Al2024-T351 under Proportional and Non-proportional Loading ....................................................... 63 10
- III. Ductile damage mechanisms and strain localization in 2024-T351 aluminum alloy and 36NiCrMo16 steel at low stress triaxiality ........................ 91 11
- IV. Crack initiation and propagation in aluminum 2024-T351 via in-situ synchrotron radiation computed laminography ................................................ 123 12
- Conclusions and Perspectives ........................................................................... 137 12
- References ......................................................................................................... 143 12
- Introduction 14
- I. Determination of the Effect of Stress State on the 36
- Onset of Ductile Fracture through Tension-Torsion 36
- Experiments 36
- .0053 and 11327. MPa 6.1 60
- II. Bao-Wierzbicki revisited Ductile Fracture of 64
- Al2024-T351 under Proportional and Non- 64
- III. Ductile damage mechanisms and strain 92
- 36NiCrMo16 steel at low stress triaxiality 92
- IV. Crack initiation and propagation in aluminum 124
- 2024-T351 via in-situ synchrotron radiation 124
- Conclusions and Perspectives 138
- References 144