Author Topic: constuct surface mesh, trying to find void formation  (Read 119 times)

liammo29

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constuct surface mesh, trying to find void formation
« on: April 04, 2019, 10:07:21 PM »
Hi,

I am straining a cube of Al to 50% with the hope of seeing a void nucleate. I am trying to use construct surface mesh as my tool but when using the recommended probe radius I do not see any void formation. However, if I lower the probe radius value slightly, I am able to see some voids in the material during straining. Moreover, when tracking dislocations these voids appear at "logical times" when dislocations are aggregating. As a check, there are no voids for my probe radius in the elastic phase of straining.

My question is, is there any issue with reducing the probe radius slightly? The nearest neighbor spacing in aluminum is 2.86, I can see voids if I go down to 2.3. I see in the manual it says to not go lower than half the interatomic spacing. So is 2.3 ok?

Thanks!

Liam

Alexander Stukowski

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Re: constuct surface mesh, trying to find void formation
« Reply #1 on: April 05, 2019, 08:16:08 AM »
Hi Liam,

It is okay to lower the probe sphere parameter somewhat below the recommended value. However, be aware that the surface construction is not made to detect very small voids. With 'small' I mean a size on the order of one or two vacancies (note that vacancies can easily form during dislocation plasticity). If you lower the probe sphere radius, at some point the algorithm may start to detect holes in the material that are actually single vacancies or a pair of them. However, whether it detects them or not will depend on the details of the local atomic configuration, thermal displacements, elastic strains, etc. Sometimes you will be lucky, sometimes not. In other words, it's not really a good analysis tool in this size regime.

I would crosscheck whether the defects marked by the Construct Surface Mesh algorithm are indeed voids. Use, for example, the Polyhedral Template Matching function in combination with Select Type and Delete Selected modifiers to filter out all perfect FCC atoms. Then inspect the local defect configurations around the "void" identified by the Construct Surface Mesh modifier to see how big they actually are in terms of missing atoms.

-Alex