how to use MPCHG

[babaye]

Hi,
Thank you Alex for your assistance. I have another question:
In /SOLU I need to do a change in material (MAT1 to MAT2) of some elements and to leave the others such as they are. With MPCHG, ANSYS carries out this change well but does not hold account of this change at the time of the calculation of the constraints for example (It carries out its calculation by considering that all the elements are MAT1). Why ANSYS do that???

/SOLU
……….
……….
*DO,i,1,n ! n : number of steps
*DO,j,1,m ! m: number of elements
*if, x,EQ,y,THEN
MPCHG,2,j
*ENDIF
*ENDDO
loads
TIME,i*dt
*ENDDO
….

 

[meshparts]

Hi,

The are some points you should check:

1. MPCHG command works just in /prep7, so make shure you are in prep7 when you change material.

2. Element j must be selected .

3. From ansys help on 'mpchg': "Between load steps in SOLUTION, material properties cannot be changed from linear to nonlinear, or from one nonlinear option to another."

If all the things above are respected, I don't see why it should not work.

Alex
Alex

 

[babaye]

hi Alex!
i know that but look: if I do this :
!!!!!thermal analysis
/PREP7
.....
MAT,1
TYPE,1
......
/SOLU
loads : heat flow
....
results : temperature
.....
FINISH
!!!!!structural analysis
/PREP7
ETCHG,TTS
...
ALLS,ALL,ELEM
MPCHG,2,ALL
....
FINISH
/SOLU
LDREAD,TEMP,,,TIMEXX,1,FILE,RTH
....
TIME,TIMEXX
....
SOLVE
FINISH
After calculation I find that ANSYS changes material from 1 to 2 (I can see it with ELIST) but it do the calculation of constraints with the material 1 which I declared in the thermal analysis. Perhaps ETCHG is at the origin of the problem? Or LDREAD.
Thank you very much Alex for your help and for all those which can be able to help me.
Barha

 

[meshparts]

Most likely is the LDREAD command, because the material information should be contained in the result file. Try to change the material after the ldread command.

Regards,
Alex

 

[babaye]

Hi Alex,
I removed LDREAD (I bring back the temperatures at nodes from the thermal analysis and I apply them to the nodes in structural analysis with BF,..), this is less precise but it is correct and it is right to see the effect of LDREAD. Result: the problem always persists. Thus it is ETCHG which is at the origin of the problem.
To remove ETCHG I must create a new structural model which is a copy of the thermal model (the same characteristics), but the problem is that instead of redefining the nodes from 1, 2,3.. ANSYS Continuous the numbering of the first model.
For example the nodes of the second model (structural) start from 320 to 638. And I do not know how reinitialise numbering.
I hope that I was well explained