Hello,
My work is related to creep in ceramics. Often I find the relation between the creep strain rate and stress as:
creep_strain_rate = constant x stress x other_factors (1)
"stress" is a general term here. Sometimes this relation (1) is applied along the principal stress direction; stress then refers to principal stress. In other cases stress is used to represent the effective stress which is expressed as following (not sure if this is complete/correct definition):
effective_stress = effective_triaxial_stress - 3 x shear_modulus x p (where p represents scalar creep increment)
effective_triaxial_stress = - square_root ( 1.5 x double_contraction_of_deviatoric_triaxial_stress)
I am confused about which definition of "stress" should be used in (1). I would also appreciate if someone could direct me to the relevant literature.
Thanks,
Gyan