UMAT or USDFLD

[p282h]

Hi:

I am trying to study phase transformations in LENS process (laser deposition). I have used HETVAL subroutine and it works fine and calculates phase fractions. But the flux(1)=internal heat generated = conductivity matrix+specific heat matrix.

Q = [k]T*+[c]T (HETVAL subroutine)

Conductivity(i)= ki*Vi+ki-1*Vi-1+ki-2*Vi-2.....
Sp. heat= ci*Vi+ci-1*Vi-1+ci-2*Vi-2.....

V=vol fraction of phases (i=1,n)

My material properties are dependant on temperature and field variables (FV1:i-phase, FV2:i-1 phase). For Ex:

Conductivity Temp FV1 FV2
25 300 0 1
30 500 1 0

Sp heat Temp FV1 FV2
250 300 0 1
500 500 1 0

When phase transformation occurs: the conductivity and specific heat values adjust accordingly.

I would like to know if USDFLD can solve this problem by calculating k and cp. If yes, then are these commands correct:
k=STATEV(1)
cp=STATEV(2)
FV1=STATEV(3)
FV2=STATEV(4)

if temp.le.301 then

(C Vi, Vi-1 are the volume fractions which are dependant purely on current temperature)

STATEV(1)= Vi*FV1+Vi-1*FV2
STATEV(2)= Vi*FV1+Vi-1*FV2

end if


Note: I want the subroutine to calculate and update new thermal conductivity and specific heat values as a result of phase transformations, so that it can be used by HETVAL to calculate internal heat generated as a result of the phase change.

Or, is UMAT the only way to work with such problem, although i see UMAT is used for stresses.


Will appreciate your help.

Thanks,

 

[sticksjoerd]

I believe UMATHT is the sub-routine best suited for calculating k and cp.

Let us know how it went (share the code if you can...) -- the simulation you want to do is very interesting indeed

 

[ozenozdemir]

I could suggest you to use just one field variable for k and Sp, each. Exclude temperature while defining the material property and set the field variable terms equal to the corresponding property (FVk = conductivity value, FVSp = SP value), such as:

Conductivity Temp FVk
300, , 300
500, , 500
Sp heat Temp FVSp
250 , , 250
500 , , 500

and then write the subroutine code so that you calculate the k and Sp terms as a function of temperature and phase transformations. After all you set the field(1) value to the calculated one and send it to the ABAQUS:

... codes to determine k....
field(1)=k (and/or Sp)

If you need help during FORTRAN code, you can ask