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