of the associated Hamiltonian system. Several authors, including Vakakis [*et al.*]{} [@Vakakis-JSV03] or Mikhlin and Reshetnikova [@Mikhlin-JSV] used the concept of Nonlinear Normal Modes (NNM) and their stability to explain this result. The concept of nonlinear normal modes was first introduced by Rosenberg [@Rosenberg-Ndof] and has been the subject of many investigations in the past years. Several authors [@Vakakis-NNM; @Shaw-Pierre] demonstrated that the use of NNM in studying the dynamics of nonlinear (and in particular [*strongly*]{} nonlinear) systems has interesting applications both in free and forced responses. Beside this concept, the effect of localisation of the vibratory energy and motion confinement due to strong nonlinearity was also addressed in several investigations (see Bendiksen [@Bendiksen-Localization] for a good review on the subject). A main feature of such phenomena is that they are more energy-dependent than frequency-dependent and a direct consequence is that the energy sinks are efficient in a quite wide range of frequency which contrasts with typical linear tuned dampers.

In this paper, we focus on a two degrees-of-freedom system, involving a nonlinear absorber with an hysteretic characteristic. Hysteretic nonlinearity requires some particular modelling and the one which is used in this study is the Bouc-Wen differential model [@Bouc-Hyst; @Wen-Hyst]. 