“…Linear and nonlinear internal frictional dampings have been considered in the papers of Soufyane [24,25], Shi and Feng [21], Soufyane and Wehbe [26], Xu and Yung [32,33], Muñoz Rivera and Racke [15], Raposo et al [18,19] and Alabau-Boussouira [1]. The problems were of the form ρ 1 ϕ tt − k(ϕ x + ψ) x + f (ϕ t ) = 0, 0 < x < l,…”