Abstract
We investigate deformation and failure of Al 6061-T6 in plane strain conditions through in situ scanning electron microscopy. The global behavior of the specimen, as well as the local deformation of the matrix material, second phase particles, and preexisting voids, is observed with a combination of high temporal/low spatial resolution images and low temporal/high spatial resolution images. It is found that the matrix dominates the deformation response, with the second phase particles and voids imparting little influence on the deformation under the moderate triaxiality levels encountered in this experiment. The initiation or nucleation of cracks is observed to occur by plastic slip.
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Notes
The distinction between slip bands and shear bands is simple: slip bands are within one grain, and oriented along crystallographic planes; shear bands, on the other hand, span multiple grains, and their orientation is dictated by the macroscopic stress state. Grains within such a shear band will still exhibit discrete slip along favored crystallographic planes.
We identify low triaxiality to correspond to a state of nearly pure shear, moderate triaxiality to correspond to plane strain tension, and high triaxiality to correspond to tensile loading perpendicular to deep notches or cracks.
While etching would have revealed the initial grain structure, it might also influence the development of deformation on the polished surface. Grain boundaries become visible without etching due to the discrete nature of the deformation even from the onset of plastic deformation.
Two important experimental ingredients are missing; electron back scatter diffraction (EBSD) data that could provide crystallographic orientation information and atomic force microscopy or similar tool that can provide topographic information that could quantify the amount of slip; these are needed to make these observations quantitative and useful for model development.
The area growth is estimated by identifying a region surrounding the feature of interest and tracking its change with global deformation.
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Acknowledgements
This work was performed during the course of an investigation into ductile failure under two related research programs funded by the Office of Naval Research: MURI Project N00014-06-1-0505-A00001 and FNC Project N00014-08-1-0189. This support is gratefully acknowledged.
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Gross, A.J., Ravi-Chandar, K. On the deformation and failure of Al 6061-T6 in plane strain tension evaluated through in situ microscopy. Int J Fract 208, 27–52 (2017). https://doi.org/10.1007/s10704-017-0209-z
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DOI: https://doi.org/10.1007/s10704-017-0209-z