Elmer Discussion Forum

Hi,

I'm very new to Elmer (have just installed it). As I browsed through the documentations I haven't seen anything related to material plasticity.

Is Elmer capable to handle elasto-plastic materials If not, is it possible to add the required material and solver routines to the Elmer system

Thanks,

Kazem

Hi Kazem

There is no material law with plasticity. It could of course be implemented but this would mean heavy modification of the existing elasticity solver, or writing a totally new one. As far as I know the current solvers do not have a simple place to plugin the plasticity model. If you know how to implement it we could certainly provide some assistance for a common good.

-Peter

Hallo Peter,

Does ELMER provide a solver for plasticity already ?
If not, is is planned to be implemented ?
If not planned: do you know a freeware 3D Fem Package that can handle it ?

kind regards,
David.

Calculix is an excellent open source solver for material plasticity. It uses the ABAQUS input deck format. I wrote a program to convert a Salome unv file into a calculix input file that converts groups to nsets and elsets. nsets and elsets allow you to easily apply boundary conditions and materials.
Calculix comes with its own pre/post processor, CGX
To post process in paraview you have to do this.
https://www.openaircraft.com/calculix-extras/

Hi

There has been some development. If you have material library in UMAT format of Abaqus it should not be overly complex to have it included as material law in ElasticSolver.

-Peter

Peter,

Good information to know, thanks. However, for material plasticity the element stiffness matrix needs to be updated every step is this something Elmer already does?

Kevin

Hi Kevin,

Elmer always recomputes the matrices by default. Some modules allow to take use of constant matrices. The philosophy has usually been that don't make any assumptions on how material parameters change with respect to time, space, or other field variables. This adds some computational cost but real-world cases have seldom constant parameters.

-Peter

Peter,

I do have an ABAQUS UMAT for classic plasticity material. I do not know how to include a UMAT in an Elmer solution. I do not see any reference to it in the standard documentation. Is there a tutorial, example, or some other documentation for using a UMAT?

Kevin

Hi,

The development of this feature (umat) has not yet come to an end and therefore its proper documentation is also missing. Anyhow, you could try to proceed in the following manner. First, you should check whether your implementation of the umat subroutine employs only subroutine arguments which Elmer supports at the moment. The arguments which can be supposed to be supported by Elmer are documented in the file ../fem/src/UMAT.F90:

https://github.com/ElmerCSC/elmerfem/bl ... c/UMAT.F90

This is also the file which you should modify in order to include your implementation of umat. The implementation shouldn't rely on utility subroutines that are available only within Abaqus.

After modifying the file ../fem/src/UMAT.F90 and recompiling the solver of Elmer the finite elasticity solver (the module ElasticSolve) should call the umat from this file provided the solver section includes the following commands

Solver ...
User Defined UMAT = Logical True
Use UMAT = Logical True

In addition, the material section should define the number of both state variables and material constants together with the values of material constants, for example

Material ...
Number of Material Constants = Integer 3
Number of State Variables = Integer 13
Material Constants(3) = 192.15 0.0 5.11
...

For some very simple examples that utilize the umat convention see also

https://github.com/ElmerCSC/elmerfem/tr ... otropic_2D
https://github.com/ElmerCSC/elmerfem/tr ... tVenant_2D

I'm almost certain that I forgot to mention something important in this quick answer.

Best regards,
Mika

Mika,

Thank you, I will look into it.

Kevin