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[Solved] Energy balance in Abaqus Explicit (ETOTAL)  


Melly
Posts: 19
(@melly)
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Joined: 1 month ago

Dr. Jorgen,

In reference to Abaqus manual, the sum of all the energy components (ETOTAL) should be constant with an error of less than 1%. 

This is not the case in my VUMAT subroutine as the ETOTAL increases exponentially in the negative direction with the number of increments. 

For comparison purposes, I decided to write a subroutine of one of the Abaqus inbuilt hyperelastic models (Mooney-Rivlin). The stress/strain curves and the contour plots are comparable. The only difference is the ETOTAL with the inbuilt one having a constant value and my subroutine an increasing negative value

Could there be something wrong with my model? what does it mean to have negative ETOTAL value?

Thank you very much

Warm regards, 

Melly

 

3 Replies
Melly
Posts: 19
(@melly)
Active Member
Joined: 1 month ago

I found out the origin of the problem. 

According to the energy balance equation, The external work (ALLWK) should be equal to the internal energy (ALLIE) for the ETOTAL to be a constant. 

For my case, I did not include the internal energy in the subroutine resulting in negative ETOTAL. 

This is because I did not find the expression for the internal energy of AB viscoplastic model. 

I will appreciate any hints on calculating the internal energy. 

Thank you very much, 

Melly

Jorgen
Posts: 3835
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(@jorgen)
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Joined: 2 months ago

Hello Melly, I did a quick search on this forum and found this old answer. Which is similar to your response.

You can calculate the internal energy from the strain energy in the hyperelastic "springs".

-Jorgen

1 Reply
Melly
(@melly)
Joined: 1 month ago

Active Member
Posts: 19

@jorgen

Thank you very much. 

Melly

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