Yes they are significant. Although the picture size got reduced, in my posted example, at the end of thermal step there is a 6% difference (34.6 vs 36.8 MPa), by the end of the mechanical step there is a 9% difference (368 vs 339 MPa), tried with other models too. It doesnt seem like a difference because of rounding or similar numerical issue, rather like a problem with the constitutive equation or simply because ABAQUS does not use this formulation, even if the documentation says so.

Im waiting for approval for the Yahoo mailing list.

The code:

[FONT=courier new]C********************************************************************

C*****************************************************************

C UMAT for elastic orthotropic material behaviour with thermal residual

C stress

C*****************************************************************

C********************************************************************

C

SUBROUTINE UMAT(STRESS,STATEV,DDSDDE,SSE,SPD,SCD,

1 RPL,DDSDDT,DRPLDE,DRPLDT,

2 STRAN,DSTRAN,TIME,DTIME,TEMP,DTEMP,PREDEF,DPRED,CMNAME,

3 NDI,NSHR,NTENS,NSTATV,PROPS,NPROPS,COORDS,DROT,PNEWDT,

4 CELENT,DFGRD0,DFGRD1,NOEL,NPT,LAYER,KSPT,JSTEP,KINC)

C

INCLUDE ABA_PARAM.INC

C

CHARACTER*80 CMNAME

C

DIMENSION STRESS(NTENS),STATEV(NSTATV),

1 DDSDDE(NTENS,NTENS),DDSDDT(NTENS),DRPLDE(NTENS),

2 STRAN(NTENS),DSTRAN(NTENS),TIME(2),PREDEF(1),DPRED(1),

3 PROPS(NPROPS),COORDS(3),DROT(3,3),DFGRD0(3,3),DFGRD1(3,3),

4 JSTEP(4), Q(6,6), DTHERM(6)

C

C********************************************************************

C Initialisation

C********************************************************************

C

E1 = PROPS(1)

E2 = PROPS(2)

E3 = PROPS(3)

NU12 = PROPS(4)

NU13 = PROPS(5)

NU23 = PROPS(6)

G12 = PROPS(7)

G13 = PROPS(8)

G23 = PROPS(9)

ALPHA11 = PROPS(10)

ALPHA22 = PROPS(11)

ALPHA33 = PROPS(12)

C

NU21 = (E2/E1)*NU12

NU32 = (E3/E2)*NU23

NU31 = (E3/E1)*NU13

C

C********************************************************************

C Calculate Q matrix

C********************************************************************

C

QQ = 1.0D0/(1.0D0-

1 NU12*NU21-NU23*NU32-NU31*NU13-2.0D0*NU21*NU32*NU13)

C

Q(1,1) = E1*(1.0D0-NU23*NU32)*QQ

Q(2,2) = E2*(1.0D0-NU13*NU31)*QQ

Q(3,3) = E3*(1.0D0-NU12*NU21)*QQ

Q(4,4) = G12

Q(5,5) = G13

Q(6,6) = G23

Q(1,2) = E1*(NU21+NU31*NU23)*QQ

Q(1,3) = E1*(NU31+NU21*NU32)*QQ

Q(2,3) = E2*(NU32+NU12*NU31)*QQ

Q(1,4) = 0.0D0

Q(1,5) = 0.0D0

Q(1,6) = 0.0D0

Q(2,4) = 0.0D0

Q(2,5) = 0.0D0

Q(2,6) = 0.0D0

Q(3,4) = 0.0D0

Q(3,5) = 0.0D0

Q(3,6) = 0.0D0

Q(4,5) = 0.0D0

Q(4,6) = 0.0D0

Q(5,6) = 0.0D0

C

C********************************************************************

C Calculate thermal strain

C********************************************************************

C

DTHERM(1) = ALPHA11*DTEMP

DTHERM(2) = ALPHA22*DTEMP

DTHERM(3) = ALPHA33*DTEMP

DTHERM(4) = 0.0D0

DTHERM(5) = 0.0D0

DTHERM(6) = 0.0D0

C

C********************************************************************

C Calculate stress matrix

C********************************************************************

C

DO K1=1,NTENS

DO K2=1,NTENS

STRESS(K2) = STRESS(K2)+Q(K2,K1)*(DSTRAN(K2)-DTHERM(K2))

END DO

END DO

C

C********************************************************************

C Calculate stiffness matrix

C********************************************************************

C

DO K1=1,NTENS

DO K2=1,NTENS

DDSDDE(K2,K1) = 0.0D0

END DO

END DO

C

DO K1=1,NTENS

DO K2=1,NTENS

DDSDDE(K2,K1) = Q(K2,K1)

END DO

END DO

C

RETURN

END [/FONT]