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Converting UMAT to VUMAT

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Dear All,

I would like to convert UMAT to VUMAT. I looked into the documentation and i found that they coded differently. UMAT is call at each integration point individually, whereas block of data at different integration points are inputted in VUMAT for processing. Moreover, i have defined local subroutines inside my UMAT to facilitate the constitutive definition. I am not sure that this would work in VUMAT.

Could you please give me some advices on converting UMAT to VUMAT


Fahad Almaskari

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while i search through the documentation, i found that

- VUMAT is written with a vector interface, which means that block of data are passed to the subroutine.

what does this means in terms of converting UMAT to VUMAT

- in vectorized code, branching inside the loops should be avioded

does this means i can not calls to local user- subroutines inside VUMAT

- the material jacobian does not need to be defined

i think i only need to update the stresses and state varaibles to their values at the end of time increment.

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You are partly right. The vector interface used by a VUMAT is simply a for loop through a number of integration points.

You can branch out of the for loop. It is nothing wrong doing that!

Converting from a UMAT to a VUMAT is easy, the other way is hard.


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Hi Fahad
I want to do a similar job for my master thesis. I should convert a umat material model to vumat material model. I know that it is an old post and you may have finished your job, but could you help me to find any reference or article or in a way instruction for changing a umat code in to vumat coding,

best regards