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Investigating the evolution of grain scale microstructure during large plastic deformation of polycrystalline aluminum
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http://hdl.handle.net/1860/114
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| Title: | Investigating the evolution of grain scale microstructure during large plastic deformation of polycrystalline aluminum |
| Authors: | Bhattacharyya, Abhishek |
| Keywords: | Polycrystalline deformation
Crystal plasticity
Orientation Imaging Microscopy
Taylor factor grains |
| Issue Date: | 24-Apr-2003 |
| Abstract: | Polycrystalline deformation and its modeling by currently used crystal plasticity
models has been investigated by means of experiments involving direct
measurement of deformation induced orientation changes. The experiments used a
polycrystalline aluminum sample with columnar grains, whose initial lattice
orientations were mapped using the Orientation Imaging Microscopy (OIM)
technique. The sample was then deformed under (i) simple compression by 40%
along the axis of the columnar grains and (ii) plane strain compression along the
normal direction with the columnar grains along the transverse direction of the
channel-die, in steps of 10% up to a total reduction of 40%. The lattice orientations
after deformation were studied by OIM and it was found that most of the grains had
significant in- grain misorientations in the form of deformation bands with two
morphologies - either elongated on the grain scale or nearly equiaxed. In many, but
not all cases, more than one similarly oriented deformation band was found in an
individual grain. The deformations were then simulated using (i) a classical Taylortype
model, and (ii) a finite element model of the polycrystalline aggregate imposing
equilibrium and compatibility between and within the constituent grains (in the weak
numerical sense). A comparison of the predictions with the experimental results
indicated that the Taylor-type model captured well the overall deformation texture of
the sample but failed to predict the orientation of individual grains in the sample and
also by its implicit assumptions could not predict any in-grain misorientation. The
finite element model predicted, reasonably well, grain rotations as well as the
magnitude of the in- grain misorientations in most, but not all, of the individual
grains, but failed completely to predict the morphology of the deformation bands
that developed within the grains. Based upon the principle of minimization of plastic
energy dissipation rate, it was revealed that the larger âhighâ Taylor factor grains
deformed in a way so as to minimize their internal plastic work whereas the
deformation of âlowâ Taylor factor grains were strongly influenced by their
neighboring âhighâ Taylor factor large grains. |
| URI: | http://dspace.library.drexel.edu/handle/1860/114 |
| Appears in Collections: | Drexel Theses and Dissertations
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