Good day.
what does it mean by mentioning "Nodal rotations" in solid element Elform3?
for progressive crush of a tube can I chose this Elform3?
Elform types -1,-2,1,2 make Negative volume despite using *Control_Hourglass6.
Hi @mass,
Below is a good overview of solid element formulations and the differences between them. There is actually a comparison between different solid formulations for a tube crush simulation.
https://awg.lstc.com/tiki-download_file.php?fileId=474
I will start by saying that I've never used solid elform=3, so I would suggest reading through the LS-Dyna theory manual if you are really interested in using that. From my knowledge, which may be incorrect, the nodal rotations are referring to how the rotation of the physical nodes that define the element affects the strain/displacement relationship. The benefits of this formulation are for when you have a shell and solid element sharing nodes. This formulation can help reduce shear locking during this case.
Again, take this with a grain of salt. If you don't have shells and solids sharing nodes then I wouldn't worry about using this.
Thank you for your information @negativevolume .
I should say that I don't have solid and shell element together. All are solid. However I doubt that it may be better to have rings in shell and tubes in solid according to the picture of structure put below. It 3/4 to see better.
Structure will be crushed up to 70% axially.
All Elforms -1,-2,1,2 type bring about Negative Volume error. But Elform3.
Is it still proper elform for my problem in your opinion? In the pdf have come it is good for small starins. So what is the better choice?!
and it is result of them:
See the differences.
You can see some element penetration in right pic.
@mass Okay it looks like you’ve got some complicated interactions during the tube crush. This issue may be solved with a change in the contact. Aside from the penetration, the response of the elements in the right image looks better so I would try to avoid ELFORM 3. There is some strange buckling occurring at the bends.
Can you copy an image of the contact definition that you are using?
Yes @negativevolume , although with elform3 there is no Negative Volume, bending shape seems quite strange as you said.
I use "Automatics Surface to Surface" for upper plate with tube and also for tube with down plate.
For Tube with itself I defined "Automatic Single Surface" as can you below.
Are they wrong point?
@mass the contact I’m referring to would be the Single Surface one. Try changing Soft=2 and Depth=5. You can also look into adding some damping through VDC=40. If these don’t work then you can try to coat the outer surface with 2D null shells which wouldn’t have any inherent stiffness and would only be used for the contact. This can help when you have a contact with solid elements.
Thank you very much dear @negativevolume
Soft2 with Depth 5 worked very well.
Btw it seems that I didn't have element penetration from the beginning because when I use Section Mode ( see picture below) penetration is not shown.
Using "Soft2 with Depth 5" leads to solve till end without you (Negative Volume).
😊
However, now I believe that I should change the model to have fracture. It will be near to reality.
In future I will ask some question about how to model failure . specially at the connecting of rings with inner and outer tubes.
@mass Great to hear it worked! Yeah sure, feel free to create a new topic if you want help defining fracture in your model.
dear @negativevolume I created a new topic at:
https://feassistant.com/forums/ls-dyna/to-model-fracture/#post-911