Electronic Journal of Differential Equations, Vol. 2025 (2025), No. 39, pp. 1–14. ISSN: 1072-6691. URL: https://ejde.math.txstate.edu, https://ejde.math.unt.edu DOI: 10.58997/ejde.2025.39 BLOW-UP SOLUTIONS FOR DAMPED RAO-NAKRA BEAMS WITH SOURCE TERMS MIRELSON M. FREITAS, MAURO L. SANTOS, CARLOS A. RAPOSO, ANDERSON A. RAMOS, JORGE FERREIRA Abstract. This article concerns the blow-up of solutions for a damped Rao-Nakra beam equa- tion with nonlinear source terms at arbitrary initial energy levels. We estimate the lower and upper bounds of the lifespan of the blow-up solution and the blow-up rate by considering both linear and nonlinear weak damping terms. 1. Introduction In this article, we study the Rao-Nakra beam model with nonlinear source terms and nonlinear damping ρ1h1utt − E1h1uxx − k(−u+ v + αwx) + g1(ut) = f1(u, v, w), in (0, 1)× R+, ρ3h3vtt − E3h3vxx + k(−u+ v + αwx) + g2(vt) = f2(u, v, w), in (0, 1)× R+, ρhwtt + EIwxxxx − kα(−u+ v + αwx)x + g3(wt) = f3(u, v, w), in (0, 1)× R+, (1.1) with initial conditions u(x, 0) = u0(x), ut(x, 0) = u1(x), in (0, 1), v(x, 0) = v0(x), vt(x, 0) = v1(x), in (0, 1), w(x, 0) = w0(x), wt(x, 0) = w1(x), in (0, 1), (1.2) and Dirichlet boundary conditions u(0, t) = u(1, t) = 0, in R+, v(0, t) = v(1, t) = 0, in R+, w(0, t) = w(1, t) = 0, in R+. (1.3) Rao-Nakra sandwich beam was derived from the following general three-layer laminated beam model developed in 1999 by Liu-Trogdon-Yong [16], ρ1h1utt − E1h1uxx − τ = 0, (1.4) ρ3h3vtt − E3h3vxx + τ = 0, (1.5) ρhwtt + EIwxxxx −G1h1(wx + ϕ1)x −G3h3(wx + ϕ3)x − h2τx = 0, (1.6) ρ1I1ϕ1,tt − E1I1ϕ1,xx − h1 2 τ +G1h1(wx + ϕ1) = 0, (1.7) ρ3I3ϕ3,tt − E3I3ϕ3,xx − h3 2 τ +G3h3(wx + ϕ3) = 0. (1.8) The parameters hi, ρi, Ei, Gi, Ii > 0 are the thickness, density, Young’s modulus, shear modulus, and moments of inertia of the i-th layer for i = 1, 2, 3, from the bottom to the top, respectively. In addition, ρh = ρ1h1 + ρ2h2 + ρ3h3 and EI = E1I1 + E3I3. 2020 Mathematics Subject Classification. 35B40, 35B41, 37B55, 37L30. Key words and phrases. Rao-Nakra beam; nonlinear damping; source term; blow-up. ©2025. This work is licensed under a CC BY 4.0 license. Submitted November 5, 2024. Published April 10, 2025. 1 2 M. M. FREITAS, M. L. SANTOS, C. A . RAPOSO, A. A. RAMOS, J. FERREIRA EJDE-2025/39 The Rao-Nakra system [22] ρ1h1utt − E1h1uxx − k(−u+ v + αwx) = 0, in (0, L)× R+, ρ3h3vtt − E3h3vxx + k(−u+ v + αwx) = 0, in (0, L)× R+, ρhwtt + EIwxxxx − αk(−u+ v + αwx)x = 0, in (0, L)× R+, is obtained from (1.4)-(1.8) when we consider the core material to be linearly elastic, i.e., τ = 2G2γ with the shear strain γ = 1 2h2 (−u+ v + αwx) and α = h2 + 1 2 (h1 + h3), where k := G2 h2 , G2 = E2 2(1+ν) is the shear modulus, and −1 < ν < 1 2 is the Poisson ratio. In [13], it was studied the Rao-Nakra system with internal damping, ρ1h1utt − E1h1uxx − k(−u+ v + αwx) + a0ut = 0, in (0, 1)× R+, (1.9) ρ3h3vtt − E3h3vxx + k(−u+ v + αwx) + a1vt = 0, in (0, 1)× R+, (1.10) ρhwtt + EIwxxxx − αk(−u+ v + αwx)x + a3wt = 0, in (0, 1)× R+, (1.11) and was proved that the polynomial stability occurs when there is only one viscous damping acting either on the beam equation or one of the wave equations. Now, we present a brief review of the literature. the Rao-Nakra with both internal damping and Kelvin-Voigt damping was considered in [14], and the polynomial stability when two of the three equations are directly damped was obtained. Méndez et al. [17] proved the lack of exponential stability when the Kelvin-Voigt damping terms act on the first and third equations in the Rao- Nakra sandwich beam model. Then, the system was proved to have polynomial decay. Exact controllability results for the multilayer Rao-Nakra plate system with locally distributed control in a neighborhood of a portion of the boundary were obtained in [7, 8]. Boundary controllability for the Rao-Nakra beam equation has been studied in [9, 10, 19, 20, 21]. Rao-Nakra sandwich beam equation with internal damping and time delay was analyzed in [23]. Exponential stabilization and observability inequality for Rao-Nakra sandwich beam with time-varying weight and time-varying delay was proved in [3]. By using semigroup theory, they obtained well-posedness, and exponential stability. In [24], well-posedness and exponential stability were proved for the Rao-Nakra sandwich beam with Cattaneo’s law for heat conduction. Exponential and general energy decay rates for a Rao-Nakra sandwich beam equation with time-varying weights and frictional damping terms acting complementarily in the domain were obtained in [1],. Blow-up solutions have been investigated in several works. For wave equations with nonlinear damping and source terms see [18]. For systems of nonlinear wave equations with damping and source terms, see [2]. For a viscoelastic Kirchhoff-type equation with logarithmic nonlinearity and strong damping, see [4]. For Kirchhoff type equation with variable-exponent nonlinearity, see [15, 25]. For the Timoshenko beam with nonlinear damping and source terms, see [26] and its references. By the way, blow-up results for the Rao-Nakra beam were not analyzed previously. In this manuscript, we consider (1.9)-(1.11) in a general context, and we investigate the competition between a nonlinear stabilization mechanism and a nonlinear source term. We estimate the lower and upper bound of the lifespan of the blow-up solution and the blow-up rate by considering both linear and nonlinear weak damping terms. This manuscript is organized as follows. Section 2 introduces notation and preliminary results. Section 3 presents the main results: the blow-up of solutions at high initial energy for both linear and nonlinear weak damping. We establish some technical lemmas in Section 4 to prove the main results. Finally, in Section 5, we prove the finite time blow-up of solutions by using the so-called concavity method. 2. Preliminaries The following notation will be used for the rest of this article: ∥u∥p = ∥u∥Lp(0,L), ⟨u, v⟩ = ⟨u, v⟩L2(0,1). EJDE-2025/39 BLOW-UP SOLUTIONS FOR DAMPED RAO-NAKRA BEAMS 3 Similarly, for z = (u, v, w) and z̃ = (ũ, ṽ, w̃) we will use ∥z∥p := ( ∥u∥pp + ∥v∥pp + ∥w∥pp )1/p , ⟨z, z̃⟩ := ⟨u, ũ⟩+ ⟨v, ṽ⟩+ ⟨w, w̃⟩. Let us consider the Hilbert spaces H = L2(0, 1)× L2(0, 1)×H1(0, 1), V = H1 0 (0, 1)×H1 0 (0, 1)×H2(0, 1) ∩H1 0 (0, 1). with inner products ⟨z, z̃⟩V = E1h1⟨ux, ũx⟩+ E3h3⟨vx, ṽx⟩+ EI⟨wxx, w̃xx⟩+ κ⟨−u+ v + αwx,−ũ+ ṽ + αw̃x⟩, (2.1) and ⟨U, Ũ⟩H = ⟨z, z̃⟩V + ⟨z1, z̃1⟩, (2.2) for z = (u, v, w), z̃ = (ũ, ṽ, w̃), z1 = (u1, v1, w1), z̃1 = (ũ1, ṽ1, w̃1), and U = (z, z1), Ũ = (z̃, z̃1). The corresponding norms are ∥z∥2V = E1h1∥ux∥22 + E3h3∥vx∥22 + EI∥wxx∥22 + κ∥ − u+ v + αwx∥22, (2.3) and ∥U∥2H = ∥z∥2V + ∥z1∥22. (2.4) Assumption 2.1. (i) Damping: g1, g2, g3 : R → R are continuous, monotone increasing functions with g1(0) = g2(0) = g3(0) = 0. In addition, the following growth conditions: there exist positive constants α and β such that for all s ∈ R, α|s|m+1 ⩽ g1(s)s ⩽ β|s|m+1, m ⩾ 1, α|s|r+1 ⩽ g2(s)s ⩽ β|s|r+1, r ⩾ 1, α|s|l+1 ⩽ g3(s)s ⩽ β|s|l+1, l ⩾ 1. (2.5) (ii) Sources: fj ∈ C2(R) and there is a positive constant C such that |∇fj(z)| ⩽ C ( |u|p−1 + |v|p−1 + |w|p−1 + 1 ) , j = 1, 2, 3 and p ⩾ 1. (2.6) There exists a positive function F ∈ C2(R2) such that ∇F = F = (f1, f2, f3). (2.7) There exists α0 > 0 such that F (z) ⩾ α0 ( |u|p+1 + |v|p+1 + |w|p+1 ) . (2.8) Furthermore, F is homogeneous of order p+ 1, that is F (λz) = λp+1F (z), ∀λ > 0, z ∈ R3. (2.9) (iii) Coefficients: ρ1h1 = ρ2h2 = ρh = 1. Remark 2.2. It is easy to see that f1, f2 and f3 are also homogeneous functions of degree p and there exists a positive constant C such that fj(z) ⩽ C(|u|p + |v|p + |w|p), j = 1, 2, 3. (2.10) We also recall the definition of weak solution of problem (1.1)-(1.3). Let W = (Lm+1((0, 1)× (0, T ))× Lr+1((0, 1)× (0, T ))× Ll+1((0, 1)× (0, T ))). Definition 2.3. A vector-valued function z = (u, v, w) is called a weak solution of (1.1)-(1.3) on [0, T ] if: (i) z ∈ C([0, T ];V ), (z(0), z′(0)) = (z0, z1) ∈ H; (ii) zt ∈ C([0, T ]; (L2(0, 1)) 3 ) ∩W ; 4 M. M. FREITAS, M. L. SANTOS, C. A . RAPOSO, A. A. RAMOS, J. FERREIRA EJDE-2025/39 (iii) z = (u, v, w) satisfies ⟨z′(t), θ(t)⟩ − ⟨z1, θ(0)⟩+ ∫ t 0 (−⟨z′(τ), θt(τ)⟩+ ⟨z(τ), θ(τ)⟩)dτ + ∫ t 0 ⟨G (z′(τ)), θ(τ)⟩dτ = ∫ t 0 ⟨F (z(τ)), θ(τ)⟩dτ , for all t ∈ [0, T ] and test functions θ in Θ = {θ = (θ1, θ2, θ3) ∈ C([0, T ];V ), θt ∈ L1(0, T ; (L2(0, 1)) 3 )}, where G (z) = (g1(u), g2(v), g3(w)), F (z) = (f1(u, v, w), f2(u, v, w), f3(u, v, w)). Moreover, we know that if z is a weak solution of problem (1.1)-(1.3) on [0, T∞) where T∞ is maximal existence time, then we have the energy identity E(t) = E(0)− ∫ t 0 ⟨G (z′(τ)), z′(τ)⟩dτ , ∀t ∈ [0, T∞), (2.11) where E(t) = 1 2 ( ∥z′(t)∥22 + ∥z(t)∥2V ) − ∫ 1 0 F (z(x, t))dx. (2.12) By using a standard continuation procedure for ODE’s to conclude that, if T∞ < ∞, then lim t→T∞ ( ∥z′(t)∥22 + ∥z(t)∥2V ) = ∞. Combining this with (2.11) and (2.12), we obtain lim t→T∞ ∫ 1 0 F (z(x, t))dx = ∞. 3. Main results 3.1. Blow-up at high initial energy with linear weak damping. In this subsection, we consider problem (1.1)-(1.3) with g1(s) = g2(s) = g3(s) = λs where λ > 0. Theorem 3.1. Suppose that Assumption 2.1 holds and that the initial data (z0, z1) ∈ H satisfies ∥z1∥22 − 2⟨z0, z1⟩+ α∗E(0) < 0, (3.1) where α∗ = 2(p+ 1) (p− 1)S2 2 , Sp = inf z∈V \{0} ∥z∥V ∥z∥p . Suppose further that E(0) > 0 and z0 ∈ N−. Then the weak solution of (1.1)-(1.3) blows up in finite time. Furthermore, we have the following upper bound of the lifespan: T∞ ⩽ 4 p− 1 ζ + √ ζ + β∗∥z0∥22 β∗ , (3.2) where ζ = 2λ p− 1 ∥z0∥22 − (z0, z1)2, β∗ = (p− 1)S2 2 p+ 1 [ ∥z0∥22 − 2(p+ 1) (p− 1)S2 2 E(0) ] . Next, we give a lower bound for the lifespan and a blow-up rate. Theorem 3.2. Under the assumptions in Theorem 3.1. We have the following lower bound T∞ ⩾ ∫ ∞ K(0) dz E(0) + z + 2p+1C2S−2p p (E(0) + z) p , (3.3) where K(t) = ∫ 1 0 F (z(x, t))dx. Next, we introduce another way for obtaining a lower bound of the lifespan. EJDE-2025/39 BLOW-UP SOLUTIONS FOR DAMPED RAO-NAKRA BEAMS 5 Theorem 3.3. Under the assumptions in Theorem 3.1. We have the lower bound T∞ ⩾ 1 p− 1 ln(1 + 2−p−1C−2S2p p E1−p(0)). (3.4) For the blow-up rate, we have ∥z(t)∥p+1 V ≳ ∥z(t)∥p+1 p+1 ≳ K(t) ⩾ X−1(T∞ − t), ∀t ∈ [0, T∞), (3.5) where X−1 is an inverse function of the function X(s) = ∫ ∞ s dz E(0) + z + 2p+1C2S−2p p (E(0) + z) p , ∀s ∈ [0,∞). 3.2. Blow-up at high initial energy with nonlinear weak damping. Theorem 3.4. Suppose that max{m, r, l} < p and (z0, z1) ∈ H satisfies ⟨z0, z1⟩ > ME(0) > 0, then the weak solution blows up in finite time, where M = q q + 1 (α β )q/q[ϵ0(p+ 1)2α0 β(1− θ) ]−1/q , where ϵ0 is a root of the equation q q + 1 (α β )− q+1 q [ (p+ 1) 2 α0ϵ0 β(1− θ) ]−1/q = (p+ 1)(1− ϵ0) α(ϵ0) , such that ϵ1 = (α β ) q q+1 [ϵ0(p+ 1) 2 α0 β(1− θ) ] ] 1 q+1 < 1 where α(ϵ) = 2 √ [ (p+ 1)(1− ϵ) 2 + 1][κ(ϵ)− (p+ 1) 2 θα0ϵ 2(1− θ) ], κ(ϵ) = [ (p+ 1)(1− ϵ) 2 − 1]S2 2 , q = max{m, r, l}, q = min{m, r, l}, θ = max{θ1, θ2, θ3} = p− q p− 1 , θ = min{θ1, θ2, θ3} = p− q p− 1 . 4. Technical lemmas to prove the theorems above, we need the following lemmas. Lemma 4.1 ([6]). Let δ > 0, T > 0 and let h be a Lipschitzian function over [0, T ). Assume that h(0) ⩾ 0 and h′(t) + δh(t) > 0 for a.e. t ∈ (0, T ). Then h(t) > 0 for all t ∈ (0, T ). Lemma 4.2. Suppose that λ > 0. Let z0 = (u0, v0, w0) ∈ N− = {z ∈ V : I(z) = ∥z∥2V − (p+ 1) ∫ 1 0 F (z(x))dx < 0}, (4.1) and z1 = (u1, v1, w1) ∈ (L2(0, 1))3 such that ⟨z0, z1⟩ ⩾ 0. (4.2) Then the map t 7→ ∥z(t)∥22 is strictly increasing as long as z(t) ∈ N−. 6 M. M. FREITAS, M. L. SANTOS, C. A . RAPOSO, A. A. RAMOS, J. FERREIRA EJDE-2025/39 Proof. Let Ψ(t) = ∥z(t)∥22 and G(t) = Ψ′(t) = 2⟨z′(t), z(t)⟩. By multiplying the first equation and the second equation in (1.1) by u, v and w, respectively, and adding the two equations together, we have ⟨z′′(t), z(t)⟩+ λ⟨z′(t), z(t)⟩ = (p+ 1) ∫ 1 0 F (z(x, t))dx− ∥z(t)∥2V = −I(z(t)). (4.3) By using (4.3) and direct calculations, we obtain G′(t) = 2∥z′(t)∥22 + 2⟨z′′(t), z(t)⟩ = 2∥z′(t)∥22 + 2[−∥z(t)∥2V + (p+ 1) ∫ 1 0 F (z(x, t))dx− λ 2 G(t)], which yields (with z(t) ∈ N−) that G′(t) + λG(t) = 2∥z′(t)∥22 + 2 [ (p+ 1) ∫ 1 0 F (z(x, t))dx− ∥z(t)∥2V ] > 0. Therefore, by Lemma 4.1, we have Ψ′(t) = G(t) > 0. Thus, Ψ(t) is strictly increasing. The proof is complete. □ We now prove the invariance set of N− for E(0) > 0. Lemma 4.3. Suppose that (3.1) holds. Then the solution z of problem (1.1)-(1.3) with E(0) > 0 belong to N−, provided z0 ∈ N−. Proof. We proceed by contradiction, by the continuity of I(z(·)) in t, we suppose that there exists a first time t0 ∈ (0, T∞) such that I(z(t0)) = 0 and I(z(t)) < 0 for t ∈ [0, t0). By the Cauchy- Schwarz inequality and Lemma 4.2, we have Ψ(t) = ∥z(t)∥22 > ∥z0∥22 ⩾ 2⟨z0, z1⟩ − ∥z1∥22 > α∗E(0), ∀t ∈ (0, t0). From the continuity of z(t) with respect to t, we have Ψ(t0) = ∥z(t0)∥22 > α∗E(0). By the definition of total energy functional E and Lemma 4.2, we obtain E(0) ⩾ 1 2 ∥z′(t0)∥22 + ( 1 2 − 1 p+ 1 )∥z(t0)∥2V + I(z(t0)) p+ 1 ⩾ (p− 1)S2 2 2(p+ 1) ∥z(t0)∥22 which yields that ∥z(t0)∥22 ⩽ 2(p+ 1) (p− 1)S2 2 E(0). This implies that α∗E(0) < Ψ(t0) = ∥z(t0)∥22 ⩽ 2(p+ 1) (p− 1)S2 2 E(0) = α∗E(0), which contradicts with E(0) > 0. The proof is complete. □ 5. Proofs In this section, we prove the finite time blow-up of solutions by using the so-called concavity method, which was first introduced by Levine [11, 12]. Proof of Theorem 3.1. Arguing by contradiction, we suppose that the solution z is a global so- lution. By Lemmas 4.2 and 4.3, we know that z(t) ∈ N− and Ψ(t) = ∥z(t)∥22 > ∥z0∥22 ⩾ 2⟨z0, z1⟩ − ∥z1∥22 > α∗E(0) for all t ∈ [0,∞). Next, for T0 > 0, β0 > 0, τ0 > 0 specified later, we may consider the function η : [0, T0] −→ [0,∞) defined by η(t) = ∥z(t)∥22 + λ ∫ t 0 ∥z(s)∥22ds+ λ(T0 − t)∥z0∥22 + β0(t+ τ0) 2, ∀t ∈ [0, T0]. (5.1) EJDE-2025/39 BLOW-UP SOLUTIONS FOR DAMPED RAO-NAKRA BEAMS 7 By direct calculation, we obtain η′(t) = 2⟨z′(t), z(t)⟩+ λ∥z(t)∥22 − λ∥z0∥20 + 2β0(t+ τ0) = 2⟨z′(t), z(t)⟩+ 2λ ∫ t 0 ⟨z′(s), z(s)⟩ds+ 2β0(t+ τ0). (5.2) Moreover, by using (4.3), we can easily obtain η′′(t) = 2∥z′(t)∥22 + 2⟨z′′(t), z(t)⟩+ 2λ⟨z′(t), z(t)⟩+ 2β0 = 2∥z′(t)∥22 + 2β0 − 2I(z(t)). (5.3) Notice that η(t) ⩾ β0τ 2 0 > 0 for all t ∈ [0, T0] and η′(0) = 2⟨z1, z0⟩+ 2β0τ0 > 0. By using Cauchy-Schwarz inequality, we can easily obtain (η′(t)) 2 4 = (⟨z′(t), z(t)⟩+ λ ∫ t 0 ⟨z′(s), z(s)⟩ds+ β0(t+ τ0)) 2 ⩽ [∥z(t)∥22 + λ ∫ t 0 ∥z(s)∥22ds+ β0(t+ τ0) 2 ](∥z′(t)∥22 + λ ∫ t 0 ∥z′(s)∥22ds+ β0) ⩽ η(t)(∥z′(t)∥22 + λ ∫ t 0 ∥z′(s)∥22ds+ β0). (5.4) From (5.1)-(5.3) and (5.4), we obtain the estimate η′′(t)η(t)− (p+ 3)(η′(t)) 2 4 ⩾ η(t)ξ(t), ∀t ∈ [0, T0], (5.5) where ξ(t) = −(p+ 1)∥z′(t)∥22 − λ(p+ 3) ∫ t 0 ∥z′(s)∥22ds− 2I(z(t))− (p+ 1)β0. (5.6) On the other hand, from (2.11) and (2.12), we deduce that E(0) = 1 2 ∥z′(t)∥2 + p− 1 2(p+ 1) ∥z(t)∥2V + I(z(t)) p+ 1 + λ ∫ t 0 ∥z′(s)∥22ds, or equivalently − (p+ 1)∥z′(t)∥2 − λ(p+ 3) ∫ t 0 ∥z′(s)∥22ds− 2I(z(t)) = (p− 1)∥z(t)∥2V + λ(p− 1) ∫ t 0 ∥z′(s)∥22ds− 2(p+ 1)E(0). Therefore, from (5.6), we have ξ(t) = (p− 1)∥z(t)∥2V − 2(p+ 1)E(0) + (p− 1)λ ∫ t 0 ∥z′(s)∥22ds− (p+ 1)β0 ⩾ (p− 1)S2 2∥z0∥22 − 2(p+ 1)E(0)− (p+ 1)β0. (5.7) Choose β0 ∈ (0, β∗] where β∗ = (p− 1)S2 2 p+ 1 ∥z0∥22 − 2E(0) = (p− 1)S2 2 p+ 1 [∥z0∥22 − 2(p+ 1) (p− 1)S2 2 E(0)] > 0, then (5.7) leads to ξ(t) > 0 for all t ∈ [0, T0]. Therefore, (5.5) yields that η(t) ⩾ η(0) [ 1− (p− 1)η′(0)t 4η(0) ]− 4 p−1 , ∀t ∈ [0, T0]. (5.8) We choose τ0 ∈ (τ∗,∞) where τ∗ = { { 0 if ζ = 2λ p−1∥z0∥ 2 2 − (z0, z1)2 ⩽ 0, ζ β∗ if ζ > 0, 8 M. M. FREITAS, M. L. SANTOS, C. A . RAPOSO, A. A. RAMOS, J. FERREIRA EJDE-2025/39 and T0 ∈ [ 2 p−1 β0τ 2 0+∥z0∥2 2 β0τ0−ζ ,∞), then we have T∗ = 4η(0) (p− 1)η′(0) = 2(∥z0∥22 + λT0∥z0∥22 + β0τ 2 0 ) (p− 1)((z0, z1)2 + β0τ0) ∈ [0, T0]. Therefore, (5.8) gives us limt→T∗ η(t) = ∞. This is a contradiction with the fact that the solution is global and it shows that the solution blows up at finite time. To derive the upper bound for T∞, we know that T∞ ⩽ 2 p− 1 β0τ 2 0 + ∥z0∥22 β0τ0 − ζ = 2 p− 1 f(β0, τ0), ∀(β0, τ0) ∈ (0, β∗]× (τ∗,∞). By direct calculation, we have fτ0(β0, τ0) = β0(β0τ 2 0 − 2ζτ0 − ∥z0∥22) (β0τ0 − ζ) 2 = 0 ⇐⇒ τ±0 = ζ ± √ ζ2 + β0∥z0∥22 β0 . Therefore, for any (β0, τ0) ∈ (0, β∗]× (τ∗,∞), we have f(β0, τ0) ⩾ f(β0, τ + 0 ) = 2τ+0 = 2 ζ + √ ζ + β0∥z0∥22 β0 ⩾ 2 ζ + √ ζ + β∗∥z0∥22 β∗ . This fact implies T∞ ⩽ 4 p− 1 ζ + √ ζ + β∗∥z0∥22 β∗ . The proof is complete. □ Proof of Theorem 3.2. First, we know that ∀t ∈ [0, T∞), E(t) = 1 2 (∥z′(t)∥22 + ∥z(t)∥2V ) = E(t) + ∫ 1 0 F (z(x, t))dx ⩽ E(0) + ∫ 1 0 F (z(x, t))dx. To obtain the lower bound of the blow-up time T∞, we define the auxiliary functional K(t) = ∫ 1 0 F (z(x, t))dx, ∀t ∈ [0, T∞). It is clear that limt→T∞ K(t) = ∞. By direct calculation and using Cauchy inequality, we find K ′(t) = ∫ 1 0 F (z(x, t))z′(x, t)dx ⩽ ∫ 1 0 |F (z(x, t))z′(x, t)|dx ⩽ 1 2 ∥z′(t)∥22 + 1 2 ∫ 1 0 |F (z(x, t))|2dx ⩽ 1 2 ∥z′(t)∥22 + 2C2∥z(t)∥2pp ⩽ E(0) +K(t) + 2C2S−2p p ∥z(t)∥2pV ⩽ E(0) +K(t) + 2p+1C2S−2p p (E(0) +K(t))p. This fact implies, for any t1, t2 ∈ [0, T∞) with t1 < t2, that t2 − t1 ⩾ ∫ K(t2) K(t1) dz E(0) + z + 2p+1C2S−2p p (E(0) + z) p . (5.9) In (5.9), let t2 → T∞ and t1 = 0, we obtain T∞ ⩾ ∫ ∞ K(0) dz E(0) + z + 2p+1C2S−2p p (E(0) + z) p . On other hand, in (5.9), let t2 → T∞ and t1 = t ∈ [0, T∞), we obtain T∞ − t ⩾ ∫ ∞ K(t) dz E(0) + z + 2p+1C2S−2p p (E(0) + z) p = X(K(t)). (5.10) EJDE-2025/39 BLOW-UP SOLUTIONS FOR DAMPED RAO-NAKRA BEAMS 9 We note that the function X is continuous and strictly decreasing on (0,∞). Therefore the inverse function X−1 : X(0,∞) −→ (0,∞) is also continuous and strictly decreasing. Then (5.10) leads to ∥z(t)∥p+1 V ≳ ∥z(t)∥p+1 p+1 ≳ K(t) ⩾ X−1(T∞ − t), ∀t ∈ [0, T∞). The proof is complete. □ Proof of Theorem 3.3. We put E(t) = 1 2 (∥z ′(t)∥22 + ∥z(t)∥2V ) for all t ∈ [0, T∞). It is clear that E(t) > 0 for all t ∈ [0, T∞) and limt→T∞ E(t) = ∞. By direct calculation, we obtain E′(t) = −λ∥z′(t)∥22 + ⟨F (z(t)), z′(t)⟩ ⩽ 1 2 ∥z′(t)∥22 + 1 2 ∥F (z(t))∥22 ⩽ 1 2 ∥z′(t)∥22 + 2C2∥z(t)∥2pp ⩽ 1 2 ∥z′(t)∥22 + 2C2S−2p p ∥z(t)∥2pV ⩽ E(t) + 2p+1C2S−2p p Ep(t). (5.11) We put Σ(t) = −E1−p(t) p−1 . By direct calculation, we have Σ′(t) = E′(t)E−p(t) ⩽ (E(t) + 2p+1C2S−2p p Ep(t))E−p(t) = 2p+1C2S−2p p + E1−p(t) = 2p+1C2S−2p p − (p− 1)Σ(t). (5.12) We deduce from (5.12) that exp[(p− 1)t]Σ(t)− Σ(0) ⩾ 2p+1C2S−2p p p− 1 {exp[(p− 1)t]− 1}, or equivalently t ⩾ 1 p− 1 ln( 2p+1C2S−2p p + E1−p(0) 2p+1C2S−2p p + E1−p(t) ). (5.13) By letting t → T∞ in (5.13), we conclude that the estimate (3.4) holds. The proof is complete. □ Proof of Theorem 3.4. Assume that z is a global solution to (1.1)-(1.3). Without loss of generality, we may assume that E(t) ⩾ 0 for all t ∈ [0,∞) (See [5, Theorem 2.8]). We put Γ(t) = ⟨z′(t), z(t)⟩ for all t ∈ [0,∞). By direct calculation, we have Γ′(t) = ∥z′(t)∥22 + ⟨z′′(t), z(t)⟩ = ∥z′(t)∥22 − ∥z(t)∥2V + (p+ 1) ∫ 1 0 F (z(x, t))dx− ⟨G (z′(t)), z(t)⟩ = [ (p+ 1)(1− ϵ) 2 + 1]∥z′(t)∥22 + [ (p+ 1)(1− ϵ) 2 − 1]∥z(t)∥2V + ϵ(p+ 1) ∫ 1 0 F (z(x, t))dx− ⟨G (z′(t)), z(t)⟩ − (p+ 1)(1− ϵ)E(t) ⩾ [ (p+ 1)(1− ϵ) 2 + 1]∥z′(t)∥22 + [ (p+ 1)(1− ϵ) 2 − 1]∥z(t)∥2V + ϵ(p+ 1)α0∥z(t)∥p+1 p+1 − ⟨G (z′(t)), z(t)⟩ − (p+ 1)(1− ϵ)E(t). (5.14) For the fourth term on the right-hand side of (5.14), we have ⟨G (z′(t)), z(t)⟩ = ⟨g1(u′(t)), u(t)⟩+ ⟨g2(v′(t)), v(t)⟩+ ⟨g3(w′(t)), w(t)⟩. From Assumption 2.1, for any ϵ1 ∈ (0, 1), by using Hölder’s and Young’s inequalities, we obtain |⟨g1(u′(t)), u(t)⟩| ⩽ ∫ 1 0 |g1(u′(x, t))u(x, t)|dx 10 M. M. FREITAS, M. L. SANTOS, C. A . RAPOSO, A. A. RAMOS, J. FERREIRA EJDE-2025/39 ⩽ β ∫ 1 0 |u′(x, t)|m|u(x, t)|dx ⩽ βm+1α−mϵm+1 1 m+ 1 ∥u(t)∥m+1 m+1 + mαϵ −m+1 m 1 m+ 1 ∥u′(t)∥m+1 m+1. From the convexity of the function y 7→ xy y in y for x > 0 and y > 0, we obtain 1 m+ 1 ∥u(t)∥m+1 m+1 ⩽ θ1 2 ∥u(t)∥22 + 1− θ1 p+ 1 ∥u(t)∥p+1 p+1, where θ1 = p−m p−1 > 0. Then, we obtain |⟨g1(u′(t)), u(t)⟩| ⩽ βm+1α−mϵm+1 1 ( θ1 2 ∥u(t)∥22 + 1− θ1 p+ 1 ∥u(t)∥p+1 p+1) + mαϵ −m+1 m 1 m+ 1 ∥u′(t)∥m+1 m+1. Similarly, |⟨g2(v′(t)), v(t)⟩|t ⩽ βr+1α−rϵr+1 1 ( θ2 2 ∥v(t)∥22 + 1− θ2 p+ 1 ∥v(t)∥p+1 p+1) + rαϵ − r+1 r 1 r + 1 ∥v′(t)∥r+1 r+1, where θ2 = p−r p−1 > 0, and |⟨g3(w′(t)), w(t)⟩| ⩽ βl+1α−lϵl+1 1 ( θ3 2 ∥w(t)∥22 + 1− θ3 p+ 1 ∥w(t)∥p+1 p+1) + lαϵ − l+1 l 1 l + 1 ∥w′(t)∥l+1 l+1, where θ3 = p−l p−1 > 0. We put q = max{m, r, l}, q = min{m, r, l}, θ = max{θ1, θ2, θ3} = p− q p− 1 , θ = min{θ1, θ2, θ3} = p− q p− 1 , then q q + 1 ⩾ m m+ 1 , q q + 1 ⩾ r r + 1 , q q + 1 ⩾ l l + 1 , ϵ − q+1 q 1 ⩾ ϵ −m+1 m 1 , ϵ − q+1 q 1 ⩾ ϵ − r+1 r 1 , ϵ − q+1 q 1 ⩾ ϵ − l+1 l 1 . We denote Λ(t) = Γ(t)− ϵ − q+1 q 1 q q + 1 E(t). By using Assumption 2.1, we have E ′(t) = −⟨G (z′(t)), z′(t)⟩ ⩽ −α(∥u′(t)∥m+1 m+1 + ∥v′(t)∥r+1 r+1 + ∥w′(t)∥l+1 l+1). By direct calculation and using above estimates, we obtain Λ′(t) = Γ′(t)− ϵ − q+1 q 1 q q + 1 E ′(t) ⩾ [ (p+ 1)(1− ϵ) 2 + 1]∥z′(t)∥22 + [ (p+ 1)(1− ϵ) 2 − 1]∥z(t)∥2V + ϵ(p+ 1)α0∥z(t)∥p+1 p+1 − βm+1α−mϵm+1 1 ( θ1 2 ∥u(t)∥22 + 1− θ1 p+ 1 ∥u(t)∥p+1 p+1) − mαϵ −m+1 m 1 m+ 1 ∥u′(t)∥m+1 m+1 − βr+1α−rϵr+1 1 ( θ2 2 ∥v(t)∥22 + 1− θ2 p+ 1 ∥v(t)∥p+1 p+1) EJDE-2025/39 BLOW-UP SOLUTIONS FOR DAMPED RAO-NAKRA BEAMS 11 − rαϵ − r+1 r 1 r + 1 ∥v′(t)∥r+1 r+1 − βl+1α−lϵl+1 1 ( θ3 2 ∥w(t)∥22 + 1− θ3 p+ 1 ∥w(t)∥p+1 p+1) − lαϵ − l+1 l 1 l + 1 ∥w′(t)∥l+1 l+1 − (p+ 1)(1− ϵ)E(t) + ϵ − q+1 q 1 q q + 1 α(∥u′(t)∥m+1 m+1 + ∥v′(t)∥r+1 r+1 + ∥w′(t)∥l+1 l+1) ⩾ [ (p+ 1)(1− ϵ) 2 + 1]∥z′(t)∥22 + {[ (p+ 1)(1− ϵ) 2 − 1]S2 2 − βm+1α−mϵm+1 1 θ1 2 }∥u(t)∥22 + {[ (p+ 1)(1− ϵ) 2 − 1]S2 2 − βr+1α−rϵr+1 1 θ2 2 }∥v(t)∥22 + {[ (p+ 1)(1− ϵ) 2 − 1]S2 2 − βl+1α−lϵl+1 1 θ3 2 }∥w(t)∥22 + [ϵ(p+ 1)α0 − βm+1α−mϵm+1 1 (1− θ1) p+ 1 ]∥u(t)∥p+1 p+1 + [ϵ(p+ 1)α0 − βr+1α−rϵr+1 1 (1− θ2) p+ 1 ]∥v(t)∥p+1 p+1 + [ϵ(p+ 1)α0 − βl+1α−lϵl+1 1 (1− θ3) p+ 1 ]∥w(t)∥p+1 p+1 + α(ϵ − q+1 q 1 q q + 1 − ϵ −m+1 m 1 m m+ 1 )∥u′(t)∥m+1 m+1 + α(ϵ − q+1 q 1 q q + 1 − ϵ − r+1 r 1 r r + 1 )∥v′(t)∥r+1 r+1 + α(ϵ − q+1 q 1 q q + 1 − ϵ − l+1 l 1 l l + 1 )∥w′(t)∥l+1 l+1 − (p+ 1)(1− ϵ)E(t) ⩾ [ (p+ 1)(1− ϵ) 2 + 1]∥z′(t)∥22 + {[ (p+ 1)(1− ϵ) 2 − 1]S2 2 − ( β α ) q βϵ q+1 1 θ 2 }∥z(t)∥22 + [ϵ(p+ 1)α0 − βm+1α−mϵm+1 1 (1− θ1) p+ 1 ]∥u(t)∥p+1 p+1 + [ϵ(p+ 1)α0 − βr+1α−rϵr+1 1 (1− θ2) p+ 1 ]∥v(t)∥p+1 p+1 + [ϵ(p+ 1)α0 − βl+1α−lϵl+1 1 (1− θ3) p+ 1 ]∥w(t)∥p+1 p+1 − (p+ 1)(1− ϵ)E(t). (5.15) We choose ϵ1 > 0 such that ϵ(p+ 1)α0 − ( β α )q βϵ q+1 1 (1− θ) p+ 1 = 0 equivalently (α β )q ϵ(p+ 1) 2 α0 β(1− θ) = ϵ q+1 1 12 M. M. FREITAS, M. L. SANTOS, C. A . RAPOSO, A. A. RAMOS, J. FERREIRA EJDE-2025/39 equivalently ϵ1 = (α β ) q q+1 [ϵ(p+ 1) 2 α0 β(1− θ) ] 1 q+1 . We observe that if ϵ1 = [(α β )q ϵ(p+ 1) 2 α0 β(1− θ) ] 1 q+1 < 1, then ϵ(p+ 1)α0 − βm+1α−mϵm+1 1 (1− θ1) p+ 1 ⩾ ϵ(p+ 1)α0 − ( β α )q βϵ q+1 1 (1− θ) p+ 1 = 0, ϵ(p+ 1)α0 − βr+1α−rϵr+1 1 (1− θ2) p+ 1 ⩾ ϵ(p+ 1)α0 − ( β α )q βϵ q+1 1 (1− θ) p+ 1 = 0, ϵ(p+ 1)α0 − βl+1α−lϵl+1 1 (1− θ3) p+ 1 ⩾ ϵ(p+ 1)α0 − ( β α )q βϵ q+1 1 (1− θ) p+ 1 = 0, and (p+ 1) 2 θα0ϵ 2(1− θ) = ( β α )q βϵ q+1 1 θ 2 , ϵ − q+1 q 1 q q + 1 = q q + 1 (α β )−q/q[ϵ(p+ 1) 2 α0 β(1− θ) ]−1/q . Therefore, (5.15) gives us Λ′(t) = Γ′(t)− q q + 1 (α β )−q/q[ϵ(p+ 1) 2 α0 β(1− θ) ]−1/qE ′(t) ⩾ [ (p+ 1)(1− ϵ) 2 + 1]∥z′(t)∥22 + [κ(ϵ)− (p+ 1) 2 θα0ϵ 2(1− θ) ]∥z(t)∥22 − (p+ 1)(1− ϵ)E(t), (5.16) where κ(ϵ) = [ (p+ 1)(1− ϵ) 2 − 1]S2 2 . We note that κ(0) > 0. Then we can take ϵ > 0 small enough such that κ(ϵ)− (p+ 1) 2 θα0ϵ 2(1− θ) > 0. Using the Cauchy inequality, we have [ (p+ 1)(1− ϵ) 2 + 1]∥z′(t)∥22 + [κ(ϵ)− (p+ 1) 2 θα0ϵ 2(1− θ) ]∥z(t)∥22 ⩾ α(ϵ)Γ(t), where α(ϵ) = 2 √ [ (p+ 1)(1− ϵ) 2 + 1][κ(ϵ)− (p+ 1) 2 θα0ϵ 2(1− θ) ]. Therefore, (5.16) leads to Λ′(t) = Γ′(t)− q q + 1 (α β )−q/q[ϵ(p+ 1) 2 α0 β(1− θ) ]−1/qE ′(t) ⩾ α(ϵ)Γ(t)− (p+ 1)(1− ϵ)E(t) ⩾ α(ϵ)[Γ(t)− (p+ 1)(1− ϵ) α(ϵ) E(t)]. (5.17) It is easy to see that lim ϵ→1 [κ(ϵ)− (p+ 1) 2 θα0ϵ 2(1− θ) ] < 0. EJDE-2025/39 BLOW-UP SOLUTIONS FOR DAMPED RAO-NAKRA BEAMS 13 Hence, there exists ϵ∗ ∈ (0, 1) such that κ(ϵ)− (p+ 1) 2 θα0ϵ 2(1− θ) > 0, α(ϵ) > 0, ∀ϵ ∈ (0, ϵ∗), α(ϵ∗) = 0. Furthermore, lim ϵ→0 q q + 1 (α β )− q q [ϵ(p+ 1) 2 α0 β(1− θ) ]−1/q = ∞, lim ϵ→ϵ∗ q q + 1 (α β )− q q [ϵ(p+ 1) 2 α0 β(1− θ) ]−1/q > 0, and lim ϵ→0 (p+ 1)(1− ϵ) α(ϵ) > 0, lim ϵ→ϵ∗ (p+ 1)(1− ϵ) α(ϵ) = ∞. Then by continuity, there exists ϵ0 ∈ (0, ϵ∗) ⊂ (0, 1) such that q q + 1 (α β )−q/q[ϵ0(p+ 1) 2 α0 β(1− θ) ]−1/q = (p+ 1)(1− ϵ0) α(ϵ0) = γ∗ > 0. Choose ϵ = ϵ0, (5.17) implies Γ(t) ⩾ Λ(t) ⩾ exp(α(ϵ0)t), ∀t ∈ [0,∞). So, we have the estimate ∥z(t)∥22 ≳ ∫ t 0 Γ(s)ds ≳ exp(α(ϵ0)t), ∀t ∈ [0,∞). (5.18) By using H’́older’s inequality, we have ∥z(t)∥2 ≲ ∥u(t)∥2 + ∥v(t)∥2 + ∥w(t)∥2 ≲ ∫ t 0 ∥u′(s)∥2ds+ ∫ t 0 ∥v′(s)∥2ds+ ∫ t 0 ∥w′(s)∥2ds ≲ ∫ t 0 ∥u′(s)∥m+1ds+ ∫ t 0 ∥v′(s)∥r+1ds+ ∫ t 0 ∥w′(s)∥l+1ds ≲ t m m+1 (∫ t 0 ∥u′(s)∥m+1 m+1ds ) 1 m+1 + t r r+1 (∫ t 0 ∥v′(s)∥r+1 r+1ds ) 1 r+1 + t l l+1 (∫ t 0 ∥w′(s)∥l+1 l+1ds ) 1 l+1 ≲ t m m+1 + t r r+1 + t l l+1 , ∀t ∈ [0,∞), which contradicts (5.18). Therefore, the weak solution blows up in finite time. The proof is compete. □ References [1] A .M. Al-Mahdi,, M. Noor, M. M. Al-Gharabli, B. Feng, A. Soufyane; Stability analysis for a Rao-Nakra sandwich beam equation with time- varying weights and frictional dampings, AIMS Mathematics, 9(5) (2024), 12570–12587. [2] C. O. Alves, M. M. Cavalcanti, V. N. D. Cavalcanti, M. A. Rammaha, D. Toundykov; On existence, uniform decay rates and blow up for solutions of systems of nonlinear wave equations with damping and source terms, Discrete Contin. Dyn. Syst. - S., 2(3) (2009), 583–608. [3] B. Feng, C. A. Raposo, C. Nonato, A. Soufyane; Exponential stabilization and observability inequality for Rao-Nakra sandwich beam with time-varying weight and time-varying delay, Math. Control Relat. Fields., 13(2) (2023), 631–663. [4] J. Ferreira, E. Pişkin, N. Irkil, C.A., Raposo; Blow up results for a viscoelastic Kirchhoff-type equation with logarithmic nonlinearity and strong damping, Math. Morav., 25(2) (2021), 125–141. [5] M. M. Freitas, M. L. Santos, ,J. A. Langa; Some additional remarks on the nonexistence of global solutions to nonlinear wave equations, J. Differ. Equations, 264(4) (2018), 2970–3051. [6] F. Gazzola, M. Squassina; Global solutions and finite time blow up for damped semilinear wave equations, Ann. Inst. Henri Poincaré (C), Anal. Non Lineaire, 23(2) (2006), 185–207. [7] S. W. Hansen, O. Y. Imanuvilov; Exact controllability of a multilayer Rao-Nakra plate with free boundary conditions, Math. Control Relat. Fields, 1(2) (2011), 189–230. 14 M. M. FREITAS, M. L. SANTOS, C. A . RAPOSO, A. A. RAMOS, J. FERREIRA EJDE-2025/39 [8] S. W. Hansen, O. Y. Imanuvilov; Exact controllability of a multilayer Rao-Nakra Plate with clamped boundary conditions, ESAIM Control Optim. Calc. Var., 17(4) (2011), 1101–1132. [9] S. W. Hansen, R. Rajaram; Simultaneous boundary control of a Rao-Nakra sandwich beam, in: Proc. 44th IEEE Conference on Decision and Control and European Control Conference. (2005) 3146–3151. [10] S. W. Hansen, R. Rajaram; Riesz basis property and related results for a Rao-Nakra sandwich beam, Discrete Contin. Dyn. Syst., Conference Publications (2005), 365–375. [11] H. A. Levine; Instability and nonexistence of global solutions to nonlinear wave equations of the form Putt = −Au+ F (u), Trans. Am. Math. Soc., 192 (1974), 1–21. [12] H. A. Levine; Some additional remarks on the nonexistence of global solutions to nonlinear wave equations, SIAM J. Math. Anal., 5(1) (1974), 138–146. [13] V. Liu, B. Rao, Q. Zheng; Polynomial stability of the Rao-Nakra beam with a single internal viscous damping, J. Differential Equations, 269(7) (2020), 6125–6162. [14] Y. Li, Z. Liu, Y. Whang; Weak stability of a laminated beam, Math. Control Relat. Fields, 8(3-4) (2018), 789–808. [15] W. Liu, G. Li, L. Hong; General decay and blow-up of solutions for a system of viscoelastic equations of kirchhoff type with strong damping, J. Funct. Spaces, 2014 (2014), 1–21. Article ID 284809 [16] Z. Liu, S. A. Trogdon, J. Yong; Modeling and analysis of a laminated beam, Comput. Math. Model., 30(1-2) (1999), 149–167. [17] T. Q. Méndez, V. C. Zannini, B. Feng; Asymptotic behavior of the Rao-Nakra sandwich beam model with Kelvin-Voigt damping, Math. Mech. Solids., 29(1) (2024), 22–38. [18] S. A. Messaoudi, B. Said-Houari; Blow up of solutions of a class of wave equations with nonlinear damping and source terms, Math. Method. Appl. Sci., 27(14) (2004), 1687–1696. [19] A. Özkan Özer, S. W. Hansen; Uniform stabilization of a multilayer Rao-Nakra sandwich beam, Evol. Equ. Control Theory, 2(4) (2013), 695–710. [20] A. Özkan Özer, S.W. Hansen; Exact boundary controllability results for a multilayer Rao-Nakra sandwich beam, SIAM J. Control Optim., 52 (2014), 1314–1337. [21] R. Rajaram; Exact boundary controllability result for a Rao-Nakra sandwich beam, Syst. Control Lett., 56(7-8) (2007), 558–567. [22] Y. V. K. S Rao, B. C. Nakra; Vibrations of unsymmetrical sanwich beams and plates with viscoelastic cores, J. Sound Vibr., 3(34) (1974), 309–326. [23] C. A. Raposo; Rao-Nakra model with internal damping and time delay, Math. Morav., 25(2) (2021), 53–67. [24] C. A. Raposo, O. P. Vera Villagran, J. Ferreira, E. Pişkin; Rao-Nakra sandwich beam with second sound, Partial Differ. Equ. Appl. Math., 4 (2021), Article ID 100053 [25] M. Shahrouzi, F. Kargarfard; Blow-up of solutions for a Kirchhoff type equation with variable-exponent non- linearities, J. Appl. Anal., 27(1) (2021), 97–105. [26] H. Zhang, G. Zhang; Blow up of solutions for Timoshenko beam with nonlinear damping and source terms, J. Xinyang Norm. Univ. Nat. Sci. Ed., 30(1) (2017), 5–8. Mirelson M. Freitas Department of Mathematics, University of Braśılia, Braśılia 0910-900, Brazil Email address: m.m.freitas@mat.unb.br Mauro L. Santos Institute of Exact and Natural Sciences, Federal University of Pará, Belém - PA 66075-110, Brazil Email address: ls@ufpa.br Carlos A. Raposo (corresponding author) Faculty of Mathematics, Federal University of Pará, Salinópolis - PA 68721-000, Brazil Email address: carlosraposo@ufpa.br Anderson A. Ramos Faculty of Mathematics, Federal University of Pará, Salinópolis - PA 68721-000, Brazil Email address: ramos@ufpa.br Jorge Ferreira Department of Exact Sciences, Federal Fluminense University, Volta Redonda - RJ 27255-126, Brazil Email address: jorge ferreira@id.uff.br 1. Introduction 2. Preliminaries 3. Main results 3.1. Blow-up at high initial energy with linear weak damping 3.2. Blow-up at high initial energy with nonlinear weak damping 4. Technical lemmas 5. Proofs References