13th International Conference on Fracture June 16–21, 2013, Beijing, China The 3D in-situ laminography observation, particularly adapted to the observation of sheet-like objects, carried out on a sample with a circular punched hole has allowed us to characterize, for the first time, the damage evolution from a cut-edge in-situ and in 3D during mechanical tension and bending loading. The growth of needle voids was especially along flow lines from fracture zone surface but also in the bulk along the martensite alignments. The initial void growth direction is parallel to the burnish plan and normal to the loading direction. We observe that the coalescence of needle voids from the fracture zone with the burnish zone occurs via narrow coalescence zones. These cracks are inclined by 45° compared to the L-direction. Several cracks are formed, especially in the fracture zone, but the one located close to the geometrical defect grows faster. This is consistent with the increased level of stress triaxiality that is known to favor ductile damage growth. References [1]: A. Dalloz, J. Besson, A.-F. Gourgues-Lorenzon, T. Sturel, A. Pineau, Effect of shear cutting on ductility of a dual phase steel, Engineering Fracture Mechanics, 76 (2009) 1411 – 1424. [2]: Daniel J. Thomas, Effect of Mechanical Cut-Edges on the Fatigue and Formability Performance of Advanced High-Strength Steels, Failure Analysis and Prevention, 12 (2012) 518-531. [3]: X. Wu, H. Bahmanpour, K. Schmid, Characterization of mechanically sheared edges of dual phase steels, Materials Processing Technology, 212 (2012) 1209 – 1224. [4]: H. So, D. Fasmann, H. Hoffmann, R. Golle, M. Schaper, An investigation of the blanking process of the quenchable boron alloyed steel 22MnB5 before and after hot stamping process, Materials Processing Technology, 212 (2012) 437-449. [5]: C. Landron, O. Bouaziz, E. Maire, J. Adrien, Characterization and modeling of void nucleation by interface decohesion in dual phase steels, Scripta Materialia, 63 (2010) 973–976. [6]: C. Landron, E. Maire, O. Bouaziz, J. Adrien, L. Lecarme, A. Bareggi, Validation of void growth models using X-ray microtomography characterization of damage in dual phase steels, Acta Materialia, 59 (2011) 7564–7573. [7]: X. Sun and K.S. Choi and A. Soulami and W.N. Liu and M.A. Khaleel, On key factors influencing ductile fractures of dual phase (DP) steels, Materials Science and Engineering, 526 (2009) 140 – 149. [8]: M. Ben Bettaieb, X. Lemoine, O. Bouaziz, A. M. Habraken and L. Duchane, Numerical modeling of damage evolution of DP steels on the basis of X-ray tomography measurements, Mechanics of Materials, 43 (2011) 139 – 156. [9]: B.S. Levy and C.J. Van Tyne, Review of the Shearing Process for Sheet Steels and Its Effect on Sheared-Edge Stretching, Material and Engineering Performance, (2011) 1-9. [10]: B.S. Levy and C.J. Van Tyne, Effect of a Strain-Hardening Rate at Uniform Elongation on Sheared Edge Stretching, Materials Engineering and Performance, (2012) 1-8. [11]: M. Azuma, S. Goutianos, N. Hansen, G. Winther and X. Huang, Effect of hardness of martensite and ferrite on void formation in dual phase steel, Materials Science and Technology, 28 (2012) 1092-1100. [12]: T.F. Morgeneyer, L. Helfen, I. Sinclair, H. Proudhon, F. Xu and T. Baumbach, Ductile crack initiation and propagation assessed via in situ synchrotron radiation-computed laminography, Scripta Materialia, 65 (2011),1010–1013. [13]: L. Helfen, T. Baumbach, P. Mikulik, D. Kiel, P. Pernot, P. Cloetens, J. Baruchel,Highresolution three-dimensional imaging of flat objects by synchrotron-radiation computed laminography, Applied Physics Letters, 86 (2005) 071915. [14]: L. Helfen, A. Myagotin, P. Mikulík, P. Pernot, A. Voropaev, M. Elyyan, M. Di Michiel, J. Baruchel, and T. Baumbach, On the implementation of computed laminography using synchrotron radiation,Review of Scientific Instruments, 82 (2011) 063702. -8-
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