# The meaning of specific internal energy and dissipated inelastic specific energy in VUMAT

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What is the meaning of specific internal energy and dissipated inelastic specific energy in VUMAT? Can I ignore calculating specific internal energy and dissipated inelastic specific energy in VUMAT?
Currently, I’m coding a damaged plasticity model in VUMAT, and it works well for 1 element without calculating specific internal energy and dissipated inelastic specific energy. However, for many elements, the results are not reasonable, so this means the specific internal energy and dissipated inelastic specific energy affect my results?
Thanks so much for your time!

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## Updating Internal and Dissipated Inelastic Energies in VUMAT

When writing a VUMAT, the following quantities must be defined:

» Stress at the end of an increment

» SDVs (if there is any) at the end of an increment

But internal and dissipated energies at the end of the increment may be defined.

If you have any problem with the VUMAT results (stresses, strains, etc.) it can not be due to updating energies. You should investigate stress updating terms.

Now, let me ask you a question. What about the UMAT subroutine? I mean, do you think we should check the stresses for this same issue in the UMAT subroutine? What are the differences between the UMAT and VUMAT subroutines, especially in the stress terms calculations? If you check out the “Writing UMAT subroutine” section in the Abaqus Free course, you will have your answers. Trust me, it’ll make it worth your while.

## Specific Internal Energy and Dissipated Inelastic Specific Energy

The internal energy (IE) is the sum of the recoverable elastic strain energy, EE; the dissipated inelastic energy (dissipated through inelastic processes such as plasticity), PE; the energy dissipated through viscoelasticity or creep, CDE; and the artificial strain energy (includes energy stored in hourglass resistances and transverse shear in shell and beam elements), AE:

IE = EE + PE + CDE + AE

Specific here means per unit of mass.

See Also:

Training Package: Introduction to UMAT and VUMAT Subroutines

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