  Plasticity refers to thermodynamically irreversible deformation associated
with a change of configuration of materials. Friction is a phenomenological law
that describes the forces resisting sliding between two solids or across an
embedded dislocation. These two types of constitutive behaviors explain the
deformation of a wide range of engineered and natural materials. Yet, they are
typically described with distinct physical laws that cloud their inherent
connexion. Here, I introduce a multiplicative form of kinematic friction that
closely resembles the power-law flow of viscoplastic materials and that
regularizes the constitutive behavior at vanishing velocity, with important
implications for rupture dynamics. Using a tensor-valued state variable that
describes the degree of localization, I describe a constitutive framework
compatible with viscoplastic theories that captures the continuum between
distributed and localized deformation and for which the frictional response
emerges when the deformed region collapses from three to two dimensions.
