Problem with fatigu...
 
Notifications
Clear all

Problem with fatigue analysis and MAT ADD EROSION

10 Posts
3 Users
0 Likes
1,391 Views
Negative Volume
Posts: 641
Admin
(@negativevolume)
CEO
Joined: 6 years ago

Hi @javat33489

I believe your implementation is fine as long as your units are correct. But I'd like to question whether removing elements is the correct approach here. It seems like putting a band-aid on a bullet wound. 

Most of my Dyna experience is in dynamic impacts, with some implicit here and there. I've never looked at fatigue analysis, nor anything to do with drilling. But I'll try to help regardless of my lack in specific knowledge. 

Have you tried changing the material model of the drill to something more simple? Say *Mat_Elastic with some basic parameters that somewhat represent the material, just so you can see if the problem persists? If it does, then you know it's not the material model. 

At that point, I'd look into the mesh. Have you tried reducing the mesh size or changing the ELFORM of the tetrahedrals? Maybe try ELFORM 13 if you are using 10?

If that doesn't work, then look into the contact perhaps? Maybe there's something funny happening as the drill passes through the plate. 

These are my thoughts. 

Reply
1 Reply
javat33489
(@javat33489)
Joined: 2 years ago

Paid Intern
Posts: 25

@negativevolume 

Thanks for your reply sir.

>>I believe your implementation is fine as long as your units are correct. But I'd like to question whether removing elements is the correct approach here. It seems like putting a band-aid on a bullet wound.

Yes, the units are fine. Everything works well. The problem is that I cannot do a full analysis due to the increase in voltage in some elements. It is possible to remove elements incorrectly; this is one of the options to avoid increasing voltage. But I have another idea but I don’t know how to implement it. The idea is this: how to make it so that when calculating the fatiuge, I could indicate the voltage above which it would not be taken into account (without deleting). Then I would be able to convey stress analysis without singular elements in the fatiga. Do you know how to set this up?

>>Have you tried changing the material model of the drill to something more simple? Say *Mat_Elastic with some basic parameters that somewhat represent the material, just so you can see if the problem persists? If it does, then you know it's not the material model.

Yes sir, I tried MAT_ELASTIC. This material model does not suit me because it requires plastic in the material and it is needed for drilling.

>>At that point, I'd look into the mesh. Have you tried reducing the mesh size or changing the ELFORM of the tetrahedrals? Maybe try ELFORM 13 if you are using 10?

Sir I am 99% sure that grinding the mesh will fix this problem. But I need the ability to avoid singular elements because this is a test model and it is very small. Real models are very large and take up a lot of resources.
I need the ability to limit voltage readings for Fatouge analysis.

Sir I can send you my model. Maybe you can solve the problem?

Reply




javat33489
Posts: 25
Topic starter
(@javat33489)
Paid Intern
Joined: 2 years ago
I am doing fatigue calculations and I need to exclude from recording in the file the stresses of elements exceeding the specified values, for example, over 500 MPa. I use the material PLASTIC KINEMATIC.
I could do this with:
1. FAILTOL graphs in CONTROL_TERMINATION, but this does not exist in the latest version of LS-Dyna.
2. I could use the CONTROL_LIMITS card and the FAILTOL column there, but this is not in the latest version of LS-Dyna.
3. I could use the DATABASE_BINARY_HISTORY map and specify OUTPUT ALL ELEMS WITH STRESS > 500.0 MPa there, but this is not in the latest version of LS-Dyna.
4. I could use the DATABASE_BINARY_STATE_HISTORY map and specify LIMITS_STRESS 500.0 there, but this is not in the latest version of LS-Dyna.
 
Tell me please. How can this be done in the latest version of LS-Dyna? What maps and settings?
Reply




Page 2 / 2




Share: