Zero-shear viscosity ($\mu ={\int }_0^{\infty }G(s)ds$)

For an integrable relaxation modulus, a small constant shear rate sustained from the remote past gives stress equal to that rate times the displayed integral, including any instantaneous solvent mass. For the linear Oldroyd-B model it is ${\mu }_0+G_0\tau$. A nondecaying elastic modulus would make this integral infinite rather than describe a fluid with finite steady viscosity.