Free-Material Optimization in a Peridynamic World

Abstract

We study free-material optimization for nonlinear bond-based nonlocal diffusion and its localization as the interaction horizon $δ$ vanishes. Bond conductivities are subject to pointwise bounds and a global material budget constraint. After normalization, the asymptotic behavior of these problems is governed by the fraction $θ_δ$ of potentially active bonds that can be assigned the maximal conductivity. We identify three distinct limiting regimes. If $θ_δ\to0$, the normalized optimal values converge to those of the classical vanishing-material optimal design problem, equivalently formulated as a Lipschitz-constrained state problem or a measure-valued flux problem. For $θ_δ\toθ\in(0,1)$, we obtain a directional local free-material problem governed by the upper tail of the directional $p$-strain over position-direction space. Thus the state variable localizes, while the limiting constitutive law retains an internal directional variable inherited from the bonds. If $θ_δ\toθ\geq1$, the limit is the isotropic local $p$-Dirichlet problem. A convex minimax argument eliminates the normalized conductivity variable exactly, after which the analysis combines convex duality, nonlocal compactness, and $Γ$-convergence for convex integrands. We prove a unified $Γ$-convergence result for the reduced state energies whenever $θ_δ\toθ\in[0,+\infty)$, yielding convergence of normalized optimal values and compactness and identification of optimal states throughout the full parameter range. At the vanishing-material endpoint, we additionally recover optimal measure-valued local fluxes from optimal nonlocal two-point fluxes.