In this paper, we consider the nonlinear viscoelastic equation | u t | ρ u tt − u − u tt + t 0 g(t − s) u(s)ds + | u| p u = 0 , in a bounded domain with initial conditions and Dirichlet boundary conditions. We prove an arbitrary decay result for a class of kernel function g without setting the function g itself to be of exponential (polynomial) type, which is a necessary condition for the exponential (polynomial) decay of the solution energy for the viscoelastic problem. The key ingredient in the proof is based on the idea of Pata (Q Appl Math 64:499-513, 2006)
IntroductionIt is well known that viscoelastic materials have memory effects. These properties are due to the mechanical response influenced by the history of the materials themselves. As these materials have a wide application in the natural sciences, their dynamics are of great importance and interest. From the mathematical point of view, their memory effects are modeled by an integro-differential equations. Hence, questions related to the behavior of the solutions for the PDE system have attracted considerable attention in recent years. Many authors have focused on this problem for the last two decades and several results concerning existence, decay and blow-up have been obtained, see and the reference therein.In [3], Cavalcanti et al. studied the following problemwhere Ω ⊂ R N , N ≥ 1, is a bounded domain with a smooth boundary ∂Ω, g ≥ 0,, and the function g: R + R + is a nonincreasing function. This type of equations usually arise in the theory of viscoelasticity when the material density varies according to the velocity. In that paper, they proved a global existence result of weak solutions for g ≥ 0 and a uniform decay result for g > 0. Precisely, they showed that the solutions goes to zero in an exponential rate for g > 0 and g is a positive bounded C 1 -function satisfyingandfor all t ≥ 0 and some positive constants ξ 1 and ξ 2 . Later, this result was extended by Messaoudi and Tatar [15] to a situation where a nonlinear source term is competing with the dissipation terms induced by both the viscoelasticity and the viscosity. Recently Messaoudi and Tatar [14] studied problem (1.1) for the case of g = 0, they improved the result in [3] by showing that the solution goes to zero with an exponential or polynomial rate, depending on the decay rate of the relaxation function g.The assumptions (1.2) and (1.3), on g, are frequently encountered in the linear case (r = 0), see [1,2,[4][5][6]13,22,23,[29][30][31]. Lately, these conditions have been weakened by some researchers. For instance, instead of (1.3) Furati and Tatar [8] required the functions e at g(t) and e at g'(t) to have sufficiently small L 1 -norm on (0, ∞) for some a > 0 and they can also have an exponential decay of solutions. In particular, they do not impose a rate of decreasingness for g. Later on Messaoudi and Tatar [21] improved this result further by removing the condition on g'. They established an exponential decay under the conditions g'(t) ≤ 0 and e at g(t) L 1 (0, ∞) ...