[Solved] Energy balance in Abaqus Explicit (ETOTAL)
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
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,
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".