## Partitioning and element shapes option for my geometry

## Partitioning and element shapes option for my geometry

(OP)

Hello

I am working to do a compression test on a geometry as shown here (https://www.dropbox.com/s/vedla116tmutovt/Aul.PNG?... (https://www.dropbox.com/s/c6snoqflkx7wew2/Aul2.PNG...). I use tet shape element so Abaqus comes up with 200,000 elements which is a lot. What is the best way to partition such a structure and what element shapes do you recommend? The geometry length is 15 micron and It has pores in nano size about 250 nm. The problem is the mesh for nanosize pores to get the best accuracy.

Thanks

I am working to do a compression test on a geometry as shown here (https://www.dropbox.com/s/vedla116tmutovt/Aul.PNG?... (https://www.dropbox.com/s/c6snoqflkx7wew2/Aul2.PNG...). I use tet shape element so Abaqus comes up with 200,000 elements which is a lot. What is the best way to partition such a structure and what element shapes do you recommend? The geometry length is 15 micron and It has pores in nano size about 250 nm. The problem is the mesh for nanosize pores to get the best accuracy.

Thanks

## RE: Partitioning and element shapes option for my geometry

## RE: Partitioning and element shapes option for my geometry

Thanks

## RE: Partitioning and element shapes option for my geometry

## RE: Partitioning and element shapes option for my geometry

This error indicates convergence problems. Often caused by errors in BCs, loads, material data and so on. Mesh is usually not a reason. But check if there are any distorted elements in your model.

## RE: Partitioning and element shapes option for my geometry

Here is the stp file (https://www.dropbox.com/s/pm4sxnbk0d5xkzf/Assem2.S...)

regarding the error, in ODB, I opened Create Display Group and used WarmElemDistorted to see the distorted elements. Please see the figures: (https://www.dropbox.com/s/rgrfddyh12q0mxg/Capture1...) and (https://www.dropbox.com/s/u174ils0346xicm/Capture3... can I get rid of those? I used all tet here.

I may also use stabilizer in step to see if I can get convergence.

## RE: Partitioning and element shapes option for my geometry

The holes will be problematic but you can create some cubic volumes containing them and then mesh using free technique.

With tet meshing there are pretty much always some slightly distorted elements. In your case they don't look bad and it's not likely that they cause errors. But you can try also Verify Mesh tool in the Mesh module. The most important thing - read all Warning messages and see if they suggest any problems. Then check all your analysis settings.

## RE: Partitioning and element shapes option for my geometry

Do you know if I can run a quasi static problem like compression test with Explicit? I have heard some say explicit might converge! Currently I use static general but if there is a way,I wanna switch.

## RE: Partitioning and element shapes option for my geometry

One more thing regarding partitioning - for holes you can try using planes rotated about cylinder's axis.

## RE: Partitioning and element shapes option for my geometry

What do you mean by planes rotated about cylinder's axis?

Thanks

## RE: Partitioning and element shapes option for my geometry

Displacement control is often chosen to help solver reach convergence. You can use it but it should work woth force control too.

Your model is utilizing symmetry, right ? Bottom looks like it was cut in half with a plane. If you rotate this plane about cylinder’s axis you will get new datum planes for partitioning.

## RE: Partitioning and element shapes option for my geometry

## RE: Partitioning and element shapes option for my geometry

Gray part is your symmetrical model and blue dotted lines on the right side of it show how it looks like when you mirror it. Because if you want to use planar symmetry in FEA you must do it in such way that mirroring your symmetrical model will give you full part.

For planar symmetry you don't need any special elements. Just a symmetry boundary condition on the surface that was cut (to fix displacement normal to that surface). Only axial symmetry requires the use of special axisymmetric finite elements but this is not the case here.

## RE: Partitioning and element shapes option for my geometry

I tried running in Explicit mode, so I used Explicit static, Explicit elements, added density, and used all tet shape elements.I defined displacement control mode for the punch to apply in the model, so I used 750 nm displacement for the punch on top of the geometry but It also asks me to define a table and did like 0 0 and 1 750nm. But I got an error:

The analysis may need a larger number of increments (more than 20,000,000) and It might be affected by round-off errors.For accuracy, running double precision executable is reacquired. ???

## RE: Partitioning and element shapes option for my geometry

Is your whole model dimensioned in nm ? If yes then be careful with other units as you must keep consistency.

Finally, reduce the step time as much as possible because it makes the analysis longer. Turning double precision on (in the job options or directly in command window) will eliminate that error but also make the analysis much longer.