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Experimental Examination of the Effect of Cavity in Shear Failure of Ductile Materials

Ali Ghahremaninezhad (University of Miami), K Ravi-Chandar (University of Texas at Austin)

Crack initiation and growth: methods, applications, and challenges

Wed 9:00 - 10:30

Barus-Holley 161

It has now become evident that Gurson-Tvergaard-Needleman (GTN) type models are not capable of capturing fracture in dominant shear deformation scenarios, which arise commonly in the form of shear localizations in polycrystalline metallic materials. Ad-hoc phenomenological modifications by means of an artificial augmentation of void growth in shear have been introduced to extend the applicability of these models to low stress triaxiality regimes. However, the mechanics and physics of deformation and failure in dominant shear loading at the microstructure of ductile polycrystalline alloys are not well understood. In this paper, we report in-situ multiscale examination of deformation processes and failure mechanisms in Al 6061-T6, a material with a dispersion of second phase particles in the microstructure, and porous nodular cast iron under dominant shear loading using Arcan shaped specimens. The strains at the macroscale were measured using digital image correlation and correlated to that at the grain level calculated based on the change in the grain size. The interaction between matrix and cavities in each material was examined in a scanning electron microscope and the effects of grain size, cavity size and interdistance in deformation and failure of each polycrystalline material were evaluated. Large strains in the range of 2-2.5 in Al 6061-T6 and 1.3 in nodular cast iron were measured before failure initiation. It was observed that in Al 6061-T6 the nucleated cavities at the broken particles get filled by matrix flow and does not appear to affect the deformation at the grain level; on the contrary, in nodular cast iron deformation became highly localized in the intervoid ligaments. The results were compared with the recent studies indicating a decrease in failure strain in low stress triaxiality regimes.