Multiscale Nonlocal Elasticity: A Distributed Order Fractional Formulation

TL;DR

This paper introduces a multiscale nonlocal elasticity theory using distributed order fractional calculus to model complex media with multiscale and nonlocal effects, validated through theoretical and numerical comparisons.

Contribution

It develops a generalized distributed order fractional continuum model that captures multiscale nonlocal effects and establishes its equivalence with a discrete lattice model.

Findings

Excellent agreement between continuum and discrete models in displacement and energy predictions

Multiscale effects like displacement distortion and energy concentration are effectively modeled

The framework provides a physical interpretation of nonlocal effects in complex media

Abstract

This study presents a generalized multiscale nonlocal elasticity theory that leverages distributed order fractional calculus to accurately capture coexisting multiscale and nonlocal effects within a macroscopic continuum. The nonlocal multiscale behavior is captured via distributed order fractional constitutive relations derived from a nonlocal thermodynamic formulation. The governing equations of the inhomogeneous continuum are obtained via the Hamilton principle. As a generalization of the constant order fractional continuum theory, the distributed order theory can model complex media characterized by inhomogeneous nonlocality and multiscale effects. In order to understand the correspondence between microscopic effects and the properties of the continuum, an equivalent mass-spring lattice model is also developed by direct discretization of the distributed order elastic continuum. Detailed theoretical arguments are provided to show the equivalence between the discrete and the continuum distributed order models in terms of internal nonlocal forces, potential energy distribution, and boundary conditions. These theoretical arguments facilitate the physical interpretation of the role played by the distributed order framework within nonlocal elasticity theories. They also highlight the outstanding potential and opportunities offered by this methodology to account for multiscale nonlocal effects. The capabilities of the methodology are also illustrated via a numerical study that highlights the excellent agreement between the displacement profiles and the total potential energy predicted by the two models under various order distributions. Remarkably, multiscale effects such as displacement distortion, material softening, and energy concentration are well captured at continuum level by the distributed order theory.