  An elasto-plasticity model with coupled hardening variables of strain type is
presented. In the theoretical framework of generalized associativity, the
formulation of this model is based on the introduction of two hardening
variables with a coupled evolution. Even if the corresponding hardening rules
are linear, the stress-strain hardening evolution is non-linear. The numerical
implementation by a standard return mapping algorithm is discussed and some
numerical simulations of cyclic behaviour in the univariate case are presented.
