# SAMICORP's blog

## plane stress incompressible neo-Hookean hyperelasticity

Hello,

I was wondering how is it possible to implement incompressible neohookean material in abaqus?

With the incompressibility assumption c(3,3)=1/(- c(1,2)^2 + c11*c22), with c being the Cauchy-Green strain tensor. It also implies that S33=0 and it is possible to find the pressure directly. In addition, h=sqrt(c(3,3))*h0 with h and h0 being current and initial thickness, respectively.

my question is that how is it possible to implement the last condition in umat?

## initialization of initial condition in state variable in vumat

i am still struggling with  defining an initial condition in vumat. i have defined mine like this:

STATEV(1:nstatev)=stateOld(KM,1:nstatev)

if (steptime .eq. zero) then

STATEV(1) = 1.0d0

STATEV(2) = 1.0d0

STATEV(3) = 1.0d0

STATEV(4) = 0.0d0

STATEV(5) = 0.0d0

STATEV(6) = 0.0d0

STATEV(7) = 0.0d0

end if

BBAR_DE_N(1,1)= STATEV(1)

BBAR_DE_N(2,2)= STATEV(2)

BBAR_DE_N(3,3)= STATEV(3)