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Polycrystalline modeling of fcc materials under changes in strain path

Speaker:Irene Beyerlein
Theoretical Division, Los Alamos National Laboratory
Los Alamos, NM 87545, USAAbstractStudies show that when the load path is changed, the stress-strain behavior of a polycrystalline metal highly depends on the texture (the distribution of crystallographic orientations of the crystals) and microstructures that developed during the pre-straining. Particularly when the pre-strains are large, texture and microstructural evolution within individual crystals become heterogeneous, potentially inducing noticeable changes in the macroscopic flow response when the direction of loading is changed. At Los Alamos, we are developing a constitutive model for fcc materials under strain path changes, including reversals of the applied load (leading to a drop in yield stress, the so-called Bauschinger effect) and straining in directions normal to the pre-strain (leading to an increase in yield stress, a cross-effect). The model accounts for both texture evolution and several microscale mechanisms responsible for the possible directional anisotropy in the single crystals. These mechanisms include the formation of dislocation microstructures preferentially on slip planes, localized destruction of such microstructures generated by channeling dislocations activated in subsequent strain paths, and the release of polar dislocations when slip is locally reversed. We apply this model to predict the response under Bauschinger tests, in which the direction of axial loading is reversed. As a more complex example, we also apply our model to predict the subsequent flow stress in pure copper processed by equal channel angular extrusion (ECAE), a process which imposes severe plastic shear strains.

Location: Kaprielian Hall (KAP) - 203

Audiences: Everyone Is Invited

Contact: Evangeline Reyes