Fractional-Order models for the static and dynamic analysis of nonlocal plates

This study presents the analytical formulation and the finite element solution of a fractional-order nonlocal plate under both Mindlin and Kirchhoff formulations. By employing consistent definitions for fractional-order kinematic relations, the governing equations and the associated boundary conditions are derived based on variational principles. Remarkably, the fractional-order nonlocal model gives rise to a self-adjoint and positive definite system that accepts a unique solution. Further, owing to the difficulty in obtaining analytical solutions to this fractional-order differ-integral problem, a 2D finite element model for the fractional-order governing equations is presented. Following a thorough validation against benchmark problems, the 2D fractional finite element model is used to study the static as well as the free dynamic response of fractional-order plates subject to various loading and boundary conditions. It is established that the fractional-order nonlocality leads to a reduction in the stiffness of the plate structure thereby increasing the displacements and reducing the natural frequency of vibration of the plates. Further, it is seen that the effect of nonlocality is stronger on the higher modes of vibration when compared to the fundamental mode. These effects of the fractional-order nonlocality are observed irrespective of the nature of the boundary conditions. More specifically, the fractional order model of nonlocal plates is free from boundary effects that lead to mathematical ill-posedness and inaccurate (paradoxical) predictions such as hardening and absence of nonlocal effects, typical of classical strain-driven integral approaches to nonlocal elasticity. This consistency in the predictions is a result of the well-posed nature of the fractional order governing equations that accept a unique solution. (C) 2020 Elsevier B.V. All rights reserved.