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UMAT Multi-element Issues

Hello All:


I have written a UMAT code to predict the viscoelastic behaviour within a shape adaptive structure. I have followed similar steps used in Abaqus subroutine manual, I have applied this UMAT to a single quad element and it works as predicted. But when I apply it multiple elements model it breaks down. 

Is there any special command i need to put in UMAT subroutine to account multi element analysis? I will appreciate all related comments, 




brunda's picture

No there is no special command. The UMAT should be automatically called for all the integration points of all the elements.


What kind of error does it give? Does the analysis fail right at the begining or does it work for few elements?

You should start by printing the element number (NOEL) and have write statements throughout your UMAT. That is the only way you can debug the UMAT. Sometimes the error is thrown only when multiple elements are used. 

Good luck




Thanks Brunda:

 Interestly enough Abaqus runs the code to the end for all the steps in the model with no error but the predictions are incorrect for the multiple elements but yet they are correct in single element. Note sure where to begin the debug especially when the code runs smoothly to the end???

I will try and prin the NOEL but not sure how that will help me yet. 


Thanks again

brunda's picture

Well in that case, the best thing to do would be to take say 4 element sample and run the simulation and do the hand calculations for all the stresses etc... it would tell you whether all the UMAT code is correct.


It does seem a bit strange though.. But unfortunately you have to start from first line to debug.. check all the equations...and compare them with hand calculations..



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