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ABAQUS UMAT

Question about implicit creep subroutine in Abaqus

The implicit implementation of creep in abaqus requires dh/d(\delta \epsilon_c ) as Jacobian in Newton-Raphson's iteration. The derivative can be expanded as shown in the figure attached. The term dh/dq, the one underlined by a green stroke, is expected to be provided by users through specifying DECRA, whereas the term dq/d(\delta \epsilon), underlined by a red one, is confusing me. It seems that that term is computed by Abaqus but I have no idea how it is done. The same question applies to the last derivative on the right hand side.

Problem about the Jacobian matrix (DDSDDE) in UMAT

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Hi all friends,

I have a basic question. Why the Jacobian matrix (DDSDDE) in UMAT is defined as:

∂Δσ/∂Δε

rather than:

 ∂σ/∂ε

And what's the difference between them

 

Thank you all for your help,

Tianhao Yan

Calculating material jacobian matrix for ABAQUS UMAT subroutine

Hello everyone, 

 

I found that there is no comprehensive topic about how to calculate material jacobian matrix for UMAT while it's one of the most complicated and important parts of writing a subroutine and a lot of the researchers deal with it. 

I think it would be great if experts share their sources and experiences here for all. I personally, try to provide the basics and essential materials as well. 

Here is an essential available PDF on Imechanica:

Parallel computing for non-local damage model in abaqus

Hello all,I am simulating epoxy damage using a non-local damage model through abaqus user subroutine UMAT.Based on the idea of Prof. Bazant's non-local treatment, the non-local damage at a particular integration point is obtained by averaging the local damage values of all the integration points within a characteristic length (Lc) of that point.

Material Jacobian in UMAT

Normal
0

21

false
false
false

DE
X-NONE
X-NONE

Hidroxid's picture

Assigning crystal plasticity material constants for one crystal with more than one element (default of Dr Huangs model)

Hi!

 

I am just a beginner in Abaqus UMAT and I have started working with Dr Huang's crystal plasticity UMAT in Abaqus.

When I am assigning one material constants for one element crystal it works but when I try to assign it to more than one element for one crystal (for example group of elements with same grain orientation) it give me error code 144.

Can anybody explain me the reason?

 

 

Thanks in advance,

Kind regards,

Omid

 

UMAT subroutine for 3d solid elements

Dear All,
I am okay in ABAQUS although trying subroutines for the first time.
I am trying to modify some codes available online, but the primary UMAT which I am posting here, is not working.
It shows no error in .log file but the job monitor says "Problem during compilation - D:\Abaqus Work Directory\Trial_user_subroutine\try\Umat_mine.for"

Please help me this, its very urgent.
Thanking you all,
P.S. The code is attached in .txt format
Here is the code

Abaqus query on UMAT: NaN issues

Hello, I have a written a UMAT for a hyperfoam type material in Abaqus. To validate it I am comparing my UMAT results with that from a *HYPERFOAM material definition. I am facing a particular problem: 

Numerical approximation of tangent moduli

 

In this study, we presented a numerically robust procedure to evaluate 4th order tangent moduli which are vital for acheiving quadratic convergence of global Newton-Raphson scheme.

In this study, the proposed method is verified for hyperelastic models alone. However, the same can be extended to other constitutive models.

The paper can be found at

Numerically approximated Cauchy integral (NACI) for implementation of constitutive models

10.1016/j.finel.2014.05.016

System error 3 when running a user subroutine in Abaqus

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I am trying to run a UMAT in Abaqus but the program aborts with the following error message: 

 ***ERROR: System error 3  std_ElemWorkspaceManager::DeAllocate: An offset overwrite was detected for Workspace idEW_MaterialStiffness (ID = 13), offset = 16.

I have searched the yahoo Abaqus usergroup and the net and it seems like a couple of people had the same problem and posted online but there are no replies, solutions or comments.

I would highlhy appreciate any help on this.

priyank_upadhyaya's picture

Abaqus UMAT, DDSDDE calculation for hyperelastic material

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Abaqus UMATs

I have funding for software development to provide a UMAT interface in the parallel versions of the code from Smith I.M. and Griffiths D.V. "Programming the Finite Element Method", 4th Edition, Wiley, 2004.

I would be interested to hear about any open source UMATs available for download. I'd also like to hear from anyone who might like to use their closed source UMATs in a parallel environment.

The funding has been awarded by the UK National HPC Service HECToR to encourage the greater use of HECToR for Structural Engineering.

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