Regarding phase transformation subroutine

[anoop_1989]

Dear all,
I am trying to simulate welding residual stress by incorporating phase transformation effect. After going through the literature, in most of the cases, the phase transformation is incorporated through Abaqus subroutine HETVAL along with STATEV. But when I referred the subroutine format I got stuck with the FLUX to be defined in the HETVAL and the functions to be called in the STATEV.
1. How do we define the volume fraction in STATEV?
2. Which equation is to be used to define the volume fraction?

SUBROUTINE HETVAL(CMNAME,TEMP,TIME,DTIME,STATEV,FLUX,
1 PREDEF,DPRED)
C
INCLUDE 'ABA_PARAM.INC'
C
CHARACTER*80 CMNAME
C
DIMENSION TEMP(2),STATEV(*),PREDEF(*),TIME(2),FLUX(2),
1 DPRED(*)

user coding to define FLUX and update STATEV [highlight #EF2929] *How to define?[/highlight]

RETURN
END

SUBROUTINE USDFLD(FIELD,STATEV,PNEWDT,DIRECT,T,CELENT,
1 TIME,DTIME,CMNAME,ORNAME,NFIELD,NSTATV,NOEL,NPT,LAYER,
2 KSPT,KSTEP,KINC,NDI,NSHR,COORD,JMAC,JMATYP,MATLAYO,LACCFLA)
C
INCLUDE 'ABA_PARAM.INC'
C
CHARACTER*80 CMNAME,ORNAME
CHARACTER*3 FLGRAY(15)
DIMENSION FIELD(NFIELD),STATEV(NSTATV),DIRECT(3,3),
1 T(3,3),TIME(2)
DIMENSION ARRAY(15),JARRAY(15),JMAC(*),JMATYP(*),COORD(*)


user coding to define FIELD and, if necessary, STATEV and PNEWDT *How to define

RETURN
END