  For a preloaded impact oscillator under superharmonic excitation of order 2,
the Hertzian non linearity constitutes the precursor of vibroimpacts
established over a wide frequency range. The theoretical study is performed by
using the shooting method with an arc length continuation. Experimental results
obtained from a devoted test rig agree with theoretical ones. Particularly, the
threeshold level of the excitation necessary to induce vibroimpacts is
confirmed.
