Hello,

I am trying to formulate tangent stiffness matrix DDSDDE with a scalar damage variable in UMAT. Generally, I need to incorporate the damage variable in formulation of DDSDDE, for example 

DDSDDE(1,1) = (1-D)* (LAMBDA + 2*MU)

DDSDDE(1,2) = (1-D)* LAMBDA

where LAMBDA and MU are Lame constants

If I write DDSDDE as 

DDSDDE(1,1)=LAMBDA + 2*MU

DDSDDE(1,2) = LAMBDA

and then when updating stress I use

STRESS(1) = STRESS(1) + (1-D)*(DDSDDE(1,1)*DSTRAN(1)+DDSDDE(1,2)*DSTRAN(2))

This will not work, since in the ABAQUS solver, DDSDDE is required in numerical scheme and its formulation should be dependent on the damage variable, right? Thanks !