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Measurements of Geometrically Necessary Dislocation Densities on Individual Slip Systems

Jeffrey Kysar's picture

We have recently published a paper on measurements of the density of geometrically necessary dislocations (GND) associated with wedge indentation of a single face-centered cubic crystal. The deformation field is two-dimensional and there are three effective in-plane slip systems that contribute to the plastic slip. We determine the lower bound on the total GND density with a three micrometer spatial resolution. We also show that in certain regions of the domain, the lower bound on total GND density corresponds to the exact total GND density. Therefore, in those regions we can determine the apportionment of the total GND density onto the individual slip systems. Among other things, this gives direct insight into the types of dislocation structures that are formed as a consequence of the wedge indentation.

The title, abstract and URL are below: 

J.W. Kysar, Y. Saito, M.S. Oztop, D. Lee and W.T. Huh, Experimental lower bounds on geometrically necessary dislocation density, International Journal of Plasticity, 26, 1097-1123, 2010.

Abstract: A single nickel crystal is indented with a wedge indenter such that a two-dimensional deformation state with three effective plane strain slip systems is induced. The in-plane lattice rotation of the crystal lattice is measured with a three micrometer spatial resolution using Orientation Imaging Microscopy (OIM). All non-zero components of the Nye dislocation density tensor are calculated from the lattice rotation field. A rigorous analytical expression is derived for the lower bound of the total Geometrically Necessary Dislocation (GND) density. Existence and uniqueness of the lower bound are demonstrated, and the apportionment of the total GND density onto the effective individual slip systems is determined. The lower bound solution reduces to the exact solution under circumstances in which only one or two of the effective slip systems are known to have been activated. The results give insight into the active slip systems as well as the dislocation structures formed in the nickel crystal as a result of the wedge indentation.


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