  In this paper, a micro-mechanical model is introduce to characterize the
stress softening phenomenon in double network hydrogels. Damage in polymer
matrices under deformation, which appears as the rupture of cross-linking, is
assumed to result in stress softening. The evolution of a polymer matrix is
described with the network evolution method by Dargazany and Itskov [Dargazany
and Itskov, International Journal of Solids and Structures, 2009, 46, 2967].
The model includes a number of physically-motivated material parameters and
obtains good agreement against different sets of experimental data of uniaxial
cyclic tension tests.
