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Urgent! Defining constrain between cohesive element and orphan mesh

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Posts: 2
Topic starter
(@distressa01)
New Member
Joined: 8 years ago

Hi every one,

I am doing a project and the deadline is just reaching I will be glad if you help me. I am modeling a poly crystalline material. I created my mesh using Neper and import cohesive element using the Phon library in python. I do my analysis with Abaqus, But I have problem defining the constraints because I do not have any surface (I have orphan mesh , with no part related to it). Also when I click on interaction/find contact pair and choose mesh in advanced part, It does not show any contact between them.

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Posts: 2
Topic starter
(@distressa01)
New Member
Joined: 8 years ago

is there any one who can help me?

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Posts: 15
(@araldimis01)
Active Member
Joined: 8 years ago

Hi, I am not familiar with Neper and Phon, but lets see how it can work. So correct me if Im wrong:
- you need to define contact to avoid elements overlapping when the (zero-thickness?) cohesives are in compression
- Phon creates the cohesive elements fine, but does not give information about the connected surfaces at the interface, i.e. the solid element number and its face number (S1-S4 for tetrahedrals)
- CAE is not capable of tracking those surfaces, because they are in the interior of an orphan mesh

But can you determine from the input-file which are the cohesive elements belonging to each grain-to-grain interface?
In that case you could create nodal surfaces using the nodes of those cohesive elements and not have to bother with identifying the attached solid elements and their faces.
Each cohesive element has a top and bottom face. Assuming C3D6, the first 3 nodes belong to the bottom face, the latter 3 to the top. Phon probably creates the top and bottom consistently.
With a text-editing script you could put all nodes belonging to the top side of an interface in one nodal surface (*Surface, type=node) and those of the bottom in another. Then define contact between both.

Or there might be simpler solutions. But it all depends on what information Phon gives about those interfaces.

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Posts: 15
(@araldimis01)
Active Member
Joined: 8 years ago

Another idea:
In the input-file, you could simply delete all the cohesive elements with a text editor. The solid elements will still be separated at the interfaces.
Then load it into the CAE as orphan mesh and start creating surfaces. Select regions to define the surface by angle and make sure to name the pairs appropriately for each interface. Play around with display groups to select them correctly.
Next, define contact between the pairs and use Interaction properties > Mechanical > Cohesive behaviour. This works more or less the same as cohesive elements and should impede overlapping in compression by definition.

Probably, this is a quicker way to work. Also, the nodal surfaces may be problematic when the cohesive elements have no thickness. The duplicate nodes do not know which side of the surface they are on and could prevent any normal debonding.

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