Imaginary part of a orthotropic material in subroutine UMAT

Hi everyone,

I want to model a complex stiffness matrix of a orthotropic material in a UMAT subroutine. I want to define the real part and imaginary part of the different Young's and shear modulus and create the C matrix.

Is it correct to use the UMAT subroutine or is there any other subroutine more appropriate?

And if it is possible to use the UMAT subroutine is enough to define the C matrix or it is necessary to define the constitutive equation?

Any help will be greatly appreciated. Thank you.

Jaione