Hello Pejman Shayanfard

There are two cases that I can think of where you could set the partial dericative of stress with respect to the temperature, i.e., DDSDDT, equal to zero:

1. when the coefficient of thermal expansion of the material could be considered almost zero and the material doesn't produce or absorb any latent heat or

2. the respective partial derivatives of the material model equations seem to be negligible when considering various sets of representative values.

Regards,

Anargyros