Metrikine A.V. and Vesnitsky A.I. 
Instability of vibrations of a mass moving uniformly over periodically and randomlyinhomogeneous elastic systems 

Summary. Vibrations of a mass are studied moving uniformly along an infinite string on a weakly inhomogeneous viscoelastic foundation. Periodical and quasiperiodical types of the inhomogeneity are considered. It is shown that the mass vibrations can be unstable. The conditions of instability are analytically derived. The instability zone occurs at lower mass velocities as the period (characteristic period) of the inhomogeneity decreases. The larger the mass, the wider the instability zones. The stabilization effect of the foundation viscosity increases when the mass velocity grows. 