Author Topic: eliminate homogeneous deformation  (Read 196 times)

zhen

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eliminate homogeneous deformation
« on: April 04, 2018, 03:31:08 PM »
Hi,

I have a question regarding how the elimination of homogeneous deformation is done in the atomic strain and displacement modifiers. If I understood correctly, the modifier will first rescale the deformed simulation cell to its original (i.e. the reference) simulation cell geometry before calculating the deformation tensor or atomic displacement. But, will the modifier rescale the calculated strain or displacement to match the current cell size? Otherwise, it seems the modifier would underestimate the strain or displacement if the current simulation cell has been expanded, e.g. tensile simulations.

I appreciate any explanation on this.
 
regards,
Zhen

Alexander Stukowski

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Re: eliminate homogeneous deformation
« Reply #1 on: April 04, 2018, 04:10:31 PM »
Dear Zhen,

Yes, I think you understood correctly. If this option is active, then the deformed cell including all particles is rescaled to match the shape of the reference cell. After that, the atomic strain is calculated.

And no, the macroscopic strain corresponding to this rescaling is not added to the computed per-particles strains. This would not make any sense in my eyes. The whole point of this option is to exclude any strain coming from the cell deformation. If you want that macroscopic strain to be included in the atomic strain tensors, then you should turn the option off.

-Alex

zhen

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Re: eliminate homogeneous deformation
« Reply #2 on: April 04, 2018, 04:24:06 PM »
Dear Alex,

Thank you for your quick response. I think I've understood more about this option. So basically activation of this option will consider only the non-affine part of the deformation, and thus the calculated results are non-affine strain and non-affine displacement. Right?

Regards,
Zhen

Alexander Stukowski

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Re: eliminate homogeneous deformation
« Reply #3 on: April 04, 2018, 10:46:10 PM »
Yes, correct. With this option active, the calculated atomic strain/displacement values will no longer include the affine deformation described by the simulation cell.

You may want to take a look at the updated doc page for the Atomic Strain modifier in Ovito 3.0.0 (development version) for a more detailed description:

http://ovito.org/manual_testing/particles.modifiers.atomic_strain.html

Here, the Eliminate homogeneous cell deformation option has been replaced with a new option, which allows controlling the affine cell transformation in a more refined way, similar to the Displacement Vectors modifier in Ovito 2.9.0.

zhen

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Re: eliminate homogeneous deformation
« Reply #4 on: April 05, 2018, 10:04:54 AM »
Thanks a lot. Now things become much clear to me.

Zhen