Restart an analysis after changing element properties

[compositeFEA]

Hello Ansys users,

My question is about the "Restart" technique, which allows to start an analysis from the last converged loadstep. I understand the concept and how to use it, but the problem comes up when I try to change the material number of an element prior to restart the analysis: at each *Do loop, the "Restart" command seems to "forget" the last modification of the material numbers. Here is a rough description of what I want to do:

/PREP7
 (...)      ! Parameters, geometry, materials...

/SOLU
 (...)      ! Boundary conditions, loadings
 NLGEOM,ON  ! Large displ.
 SOLVE      ! First solution

*DO,j,1,2
  /SOLU
    PARSAV
    ANTYPE,,REST    ! Restart the analysis from the last converged loadstep
    PARRES          ! Bring back the parameters
    MPCHG,2,j  ! Change the material # of element j to #2
    F,....     ! Change the loadings
    ALLS
    SOLVE      ! Solution with new loadings, new material #, starting from the last converged solution
  /POST1
    (...)      ! Verification of the rupture criteria, ....
  SAVE         ! Save the database
*ENDDO

With the previous code I expect to get 3 solutions:
1- The initial solution;
2- The 2nd solution with new loading and material of element 1 changed to #2;
3- The 3rd solution with new loading and material of elements 1 and 2 changed to #2.

Unfortunately, at step 3 the element 1 is back to its initial material number. I thought that adding a SAVE command at the end of the loop would rectify this, but it does not... So apparently there is something I don't understand regarding the combination of the RESTART technique and the modification of element properties.

Any advice would be appreciated. Thanks!

 

[compositeFEA]

Precision:

What I want to do is a cumulative load analysis with the verification of the failure criteria between each load step, combined with the alteration of the damaged elements (by changing their material #). Since it is a large displacement model, I don't want the SOLVE operation to perform the entire calculation at every load step. I would like to solve each load step according to the previous one, but with modified materials.

Perhaps it is impossible to change the material properties before restarting the analysis, since the "Restart" command resumes the DB of the converged solution, which was performed with the initial material. This is what I need to know!

 

[wootletootle1]

I would tend to do as much as possible from a single /SOLU
environment (ie remove the /SOLU command from the loop). Then
there will be no necessity to SAVE/RESTORE. You might have to
post-process the output in several successive steps (one for
each SOLVE command) though there is probably a way of avoiding
this if you are smart enough.

Regards,
Roger

 

[compositeFEA]

Roger, thank you for the input. I also found something on the ansys.net website:
-----------------
"ANSYS states that ekilled elements are not included in any restart runs. They must be killed agian in the restart.

Workaround:

Issue normal "rescontrol" command
Save extra DB files for all loadsteps.For eq. at loadstep 05 "Save,jobname05,db"
If restart at LS05 is needed rename file05.db to file.rdb
Keep jobname.R05
Keep jobname.ldhi
Resume the job with the normal "antype,,restart" command.
and the restart with killed elements is possible.
-----------------

I am going to check this out...