What hardening equation does UMATHT subroutine use in Abaqus?

[Ander Azpi]

Hello,

I'm using UMATHT user subroutine in Abaqus (FEA) and I'm trying to see what hardening curve it applies. I introduce the hardening exponent, the yield stress and young modulus in the material module and there is some formulation. However, I'm unable to check the formulation used. Could anyone help?

The formulation regarding this is the following (where Sy is the yield stress, E is the young modulus and xn is the hardening exponent) :

! Get yield stress from the specified hardening curve
Sf=Sy*(1.d0+E*eqplas/Sy)**xn

! Determine if active yielding
if (Smises.gt.(1.d0+toler)*Sf) then

! Calculate the flow direction
Sh=(stress(1)+stress(2)+stress(3))/3.d0
flow(1:3)=(stress(1:3)-Sh)/Smises
flow(4:ntens)=stress(4:ntens)/Smises

! Solve for Smises and deqpl using Newton's method
Et=E*xn*(1.d0+E*eqplas/Sy)**(xn-1)
do kewton=1,newton
rhs=Smises-(3.d0*eg)*deqpl-Sf
deqpl=deqpl+rhs/((3.d0*eg)+Et)
Sf=Sy*(1.d0+E*(eqplas+deqpl)/Sy)**xn
Et=E*xn*(1.d0+E*(eqplas+deqpl)/Sy)**(xn-1)
if(abs(rhs).lt.toler*Sy) exit
end do
if (kewton.eq.newton) write(7,*)'WARNING: plasticity loop failed'

I also upload the UMATHT file, in case someone needs it (public access)

 

[FEA way]

UMATHT is a subroutine used to define thermal constitutive behavior. Your file contains also other subroutines, including UMAT for plasticity. But if you are using only UMATHT and a built-in model for plasticity then you should check the documentation for the theory behind it. Also, is there no sufficient information in the articles referenced in that file?