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Possible reasons for variation in results using a VUMAT and inbuilt model

Possible reasons for variation in results using a VUMAT and inbuilt model

Possible reasons for variation in results using a VUMAT and inbuilt model

(OP)
Hi all,

I have a generic doubt. I have written a VUMAT for Johnson cook plasticity model, it works alright. But, the results are a bit off from the abaqus inbuilt model. Von Mises stress is off by around 100MPa while PEEQ is off by 50%. The VUMAT result is the lower one. I am using the equations used by ABAQUS (as given in the documentation). Can there be any general reason for the variation seen in the results?

RE: Possible reasons for variation in results using a VUMAT and inbuilt model

Highly unlikely that Abaqus is "incorrect". If you are using the exact same equations as Abaqus, then the results must agree - regardless of which material model you implement.

My recommendation is to run the code independent of Abaqus in a FORTRAN wrapper script that provides the VUMAT everything it expects and see if the results make sense against your calculations. Insert some sanity check blocks in the code.

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