Asymptotic stability of second-order evolution equations with intermittent delay

We consider second-order evolution equations in an abstract setting with intermittently delayed/not-delayed damping and give suf- ficient conditions ensuring asymptotic and exponential stability results. Our abstract framework is then applied to the wave equation, the elas- ticity system, and the Petrovsky system. For the Petrovsky system with clamped boundary conditions, we further prove an internal observability estimate that was not available in the literature.