Micromechanics of strain stiffening in stochastic network materials

Many biological and man-made materials have a random fiber network as primary structural component and belong to the broad class of network materials. A subset of these materials exhibits hyperelastic behavior characterized by strong strain stiffening. In this work we evaluate the origins of strain stiffening and discuss the relative contributions of geometric and constitutive nonlinearities, and of the bending and stretching deformation modes of fibers. The deformation is strongly controlled by instability modes which emerge recurrently during deformation. We observe that the formation of stress paths is a consequence of the interplay between the bending and axial modes. The effect of the network architecture is also discussed.