Sandwich composites are widely used in design especially in transport because they combine bending rigidity and lightness. On the other hand, their attenuation properties are not always as good as expected, and it is necessary to overcome this limitation in order to improve the vibratory comfort and the durability of the structures in which they are integrated. Several strategies exist such as the introduction into the core of the sandwich of passive materials with viscoelastic properties for example to allow energy dissipation, or the use of electronic circuits for active control strategies. The approach presented in this paper is based in the introduction of vibro-impact zones to generate damping. The local interactions occurring during the impacts allow to dissipate the vibratory energy: it is about nonlinear phenomena which have the advantage to be effective over a wide range of frequencies, and to be few sensitive to environmental conditions such as temperature. A sandwich composite prototype has been designed for the purpose of the study, and small ceramic balls have been inserted in the sandwich core to generate impacts phenomena. Experiments have been performed to evaluate the damping performances obtained depending on the number of balls, on the amplitude on excitation and on the frequency band. Analytical and numerical models of the structure have also been developed to perform parametric studies and evaluate the impact of parameters such as the ball added mass or the positions of the masses for instance : numerical results have been confronted to experimental ones. It has thus been observed that good damping performances could be obtained on a large frequency band.