This paper is on the asymptotic behavior of the elastic string equation with localized degenerate Kelvin–Voigt damping
utt(x,t)badbreak−false[ux(x,t)+b(x)uxt(x,t)false]xgoodbreak=0,x∈(−1,1),tgoodbreak>0,\begin{equation} u_{tt}(x,t)-[u_{x}(x,t)+b(x) u_{xt}(x,t) ]_{x}=0,\; x\in (-1,1),\; t>0, \end{equation}where bfalse(xfalse)=0$b(x)=0$ on x∈false(−1,0false]$x\in (-1,0]$, and b(x)=xα>0$b(x)=x^\alpha >0$ on x∈false(0,1false)$x\in (0,1)$ for α∈false(0,1false)$\alpha \in (0,1)$. It is known that the optimal decay rate of solution is t−2$t^{-2}$ in the limit case α=0$\alpha =0$ and exponential for α≥1$\alpha \ge 1$. When α∈false(0,1false)$\alpha \in (0,1)$, the damping coefficient bfalse(xfalse)$b(x)$ is continuous, but its derivative has a singularity at the interface x=0$x=0$. In this case, the best known decay rate is t−3−α2(1−α)$t^{-\frac{3-\alpha }{2(1-\alpha )}}$, which fails to match the optimal one at α=0$\alpha =0$. In this paper, we obtain a sharper polynomial decay rate t−2−α1−α$t^{-\frac{2-\alpha }{1-\alpha }}$. More significantly, it is consistent with the optimal polynomial decay rate at α=0$\alpha =0$ and uniform boundedness of the resolvent operator on the imaginary axis at α=1$\alpha = 1$ (consequently, the exponential decay rate at α=1$\alpha =1$ as t→∞$t\rightarrow \infty$). This is a big step toward the goal of obtaining eventually the optimal decay rate.