Abaqus VUMAT doesn't given identical results for orthotropic linear elastic material 1

[tyzhang]

Dear Community,

Hi! I am trying to verify Abaqus VUMAT with simple examples so I wrote a VUMAT for orthotropic material and compare the result with Abaqus built-in material model (Elastic -> Engineering constants). The material constants are given in 1.png and 2.png. All other settings from part to mesh is identical. The stress distribution of built-in material model is in 3.png and the stress distribution of VUMAT is in 4.png. The discrepancy is not ignorable. The VUMAT code is also attached as a .txt file.

Is there anything that I miss in my code? I will appreciate your help. Thanks!

The Fortran code is based on code from

https://github.com/rutger-kok/composite_cdm_tan,

which is a VUMAT for continuum damage model for composite material, written in a nice and readable style.

 

[tyzhang]

A previous question on this forum is cited here,

https://www.eng-tips.com/viewthread.cfm?qid=475510#post

 

[FEA way]

That’s a simplified version of VUMAT subroutine composite_cdm.for available on Rutger Kok’s github repository, right ? He mentions there that the code may not work properly for multi-element models. I guess that it relates to the CDM part but it would be better to start from single element tests anyway. Also, there is a chance that you accidentally removed some part of the code that should stay there.

 

[tyzhang]

Yes! I have added reference to his repo and thx for mentioning that. Actually, I have already done one element test for my code for orthotropic elastic material. The results had discrepancy too but it's negligible so I didn't pay attention on it. Although Rutger mentions that his VUMAT may not work for multi-elements case, I believe that he is referring to the damage model part. The code should work fine during elastic stage, when no damage happens. Besides, the VUMAT in this thread just implements elastic material.

By the way, I believe there is one place in Rutger's code that doesn't work as it should do. I will contact him about the issue and maybe some update is needed.

Another question about VUMAT: do we have to implement inertia forces? I have viewed several VUMAT code but none of them considers that.

Thanks again for your comment.

 

[FEA way]

No, that’s on the side of the element formulation (VUEL subroutine if user-defined elements are used).

 

[tyzhang]

Got it. Indeed it doesn't make sense to incorporate that in VUMAT since it defines constitutive relation.