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Abaqus Umat for Shell elements

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Posts: 3
Topic starter
(@arugo1989)
New Member
Joined: 12 years ago

Hi everyone,

Im pretty new to implementation of Umats but i have coded some materials for a 3D case using solid elements, which have worked out fine. Now Im trying to do the same thing using shell elements (S4 and S4R) and I have some questionmarks here...

- What are the compeonets in the stress/stain tensor (STRESS and DSTRAIN) (S11,S22,S12,S33 ???) ?

- What is the size of the Jacobian?

- Do I need to convert my 3D implementaion to plane stress?, and if that is needed do I have to provide the out of plane strain (how is that done in this case)?

I would be very thankfull for some valuable hints 🙂

Mangan

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Posts: 3998
(@jorgen)
Member
Joined: 5 years ago

1) Stress and dstrain are: [11, 22, 12]
2) Jacobian is 3x3
3) Yes, you will (likely) have to re-implement your code. Yes, you will need to return the out of plane strain (for a VUMAT).

-Jorgen

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4 Replies
Posts: 3
Topic starter
(@arugo1989)
New Member
Joined: 12 years ago

Hi, Thanks for the reply!!!

One more question related to the last one above, In the Abaqus Manual I found

In the case of shell or plane stress elements, NDIR=3 and NSHR=1, you must definne strainInc(*,3) the thickness strain incement

So now Im a bit confued... (since I thought that strainInc(*,3) = strainInc_12), can someone help me with this???

all the best
Mangan

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Posts: 3998
(@jorgen)
Member
Joined: 5 years ago

Abaqus UMAT() and VUMAT() subroutines are completely different. A VUMAT() should return strainInc(*,3) which is the through thickness strain. See the User Subroutines manual for all the details.

Best of luck,
Jorgen

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Posts: 83
(@zhaiys)
Trusted Member
Joined: 17 years ago

To elaborate: ABAQUS needs the strain in the thickness direction to calculate a stable time step. Your job is to calculate it so that the plane stress constraint is enforced.

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