  Non linear dynamic behaviour of a normally excited preloaded Hertzian contact
(including possible contact losses) is investigated using an experimental test
rig. It consists on a double sphere plane contact loaded by the weight of a
rigid moving mass. Contact vibrations are generated by a external Gaussian
white noise and exhibit vibroimpact responses when the input level is
sufficiently high. Spectral contents and statistics of the stationary
transmitted normal force are analysed. A single-degree-of-freedom non linear
oscillator including loss of contact and Hertzian non linearities is built for
modelling the experimental system. Theoretical responses are obtained by using
the stationary Fokker-Planck equation and also Monte Carlo simulations. When
contact loss occurrence is very occasional, numerical results shown a very good
agreement with experimental ones. When vibroimpacts occur, results remain in
reasonable agreement with experimental ones, that justify the modelling and the
numerical methods described in this paper. The contact loss non linearity
appears to be rather strong compared to the Hertzian non linearity. It actually
induces a large broadening of the spectral contents of the response. This
result is of great importance in noise generation for a lot of systems such as
mechanisms using contacts to transform motions and forces (gears,
ball-bearings, cam systems, to name a few). It is also of great importance for
tribologists preoccupied to prevent surface dammage.
