Author Topic: How to find atoms passing partial dislocation in FCC structure?  (Read 217 times)

DJing

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Hi everyone,

Is it possible to show atoms that experienced a partial (or full) dislocation distance at a certain strain in OVITO? Thank you very much.

Alexander Stukowski

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Re: How to find atoms passing partial dislocation in FCC structure?
« Reply #1 on: May 29, 2019, 07:46:53 AM »
Hi,

You should be able to use the Atomic Strain function of OVITO for that (set the cutoff radius to be halfway between the first and second neighbor distance). Due to dislocation slip, atoms right above and below the glide plane will exhibit high atomic shear strain values. You can use the Color Coding modifier to visualize those values or use the Expression selection modifier to select and highlight atoms whose shear strain value is above a threshold.

Note that this method is not exact, because atomic shears will be affected by elastic displacements of atoms, thermal vibrations and other noise. But since the atomic shear values due to plastic slip are typically much larger than these other effects, it should still work.

Crystal slip resulting from partial dislocations and full dislocations should lead to markedly different shear strain levels. So it should be possible to discriminate between the two types as well.

-Alex

DJing

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Re: How to find atoms passing partial dislocation in FCC structure?
« Reply #2 on: May 31, 2019, 05:28:49 PM »
Hi Alexander,

Thank you for your reply, but I have no idea about how to define a threshold distinguishing shear strain that was caused by partial and full dislocations? could you give me some suggestions? Thanks a lot.

Alexander Stukowski

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Re: How to find atoms passing partial dislocation in FCC structure?
« Reply #3 on: June 03, 2019, 01:33:32 PM »
Hi,

Given the magnitude of the (partial and full) Burgers vectors and the atomic plane distance of the crystal it should be possible to predict what the atomic strain values will be. But making this prediction is rather difficult and I don't have any numbers readily available. It's probably easier to use the Atomic Strain modifier and inspect the typical values found for atoms adjacent to the slip plane (or their distribution). You can then derive appropriate thresholds to discriminate between the two types of slip.

I have attached an example analysis from a simple shear strain simulation of an FCC crystal. The left picture shows the calculated atomic shear strain values, and the right hand side shows the results of the Common Neighbor Analysis for the deformed configuration. You can find slip traces of a full dislocation (yellow arrow) and partial dislocations (blue arrow). The latter slip traces are associated with a remaining stacking fault, visible in the second picture (red hcp-like atoms). The shear strain values of the atoms in the partial slip trace are around 0.2 while the values of atoms in the fully slipped crystal reach around 0.4.

-Alex