where J(t) is the creep-recovery compliance as a function of time; J0 is the instantaneous compliance of the Maxwell spring; J1 is the viscoelastic compliance that represents the retarded compliance related to the Kelvin–Voigt element; s is the mean retardation time
associated to the Kelvin–Voigt element; and gN is the Newtonian viscosity associated to the Maxwell dashpot.