“…In order to consider the effect of internal friction on a system, Ferrero and Gazzola [8] studied the following linear damped wave equation u tt + ∆ 2 u + δu t + h (x, y, u) = f (x, y, t) , (x, y, t) ∈ Ω × (0, T ) , (5) with the initial boundary data conditions (2) and (3), where h (•, •, s) is a Lipschitz function and increasing with respect to s ∈ R. They proved the existence and uniqueness of global solutions, but did not give any non-global results due to the linear source term. It is worth mentioning the work on an extensible beam model similar to the model equation in this paper, the so-called polyharmonic Kirchhoff equation was considered in [1], to show the global nonexistence and a priori estimates for the life span of solution.…”