Adaptive FEM-SPIM Coupling for Phase-Field Modeling of Fracture

This article proposes an adaptive coupling strategy between the standard FEM and smoothed point interpolation methods (SPIMs) for the solution of phase-field fracture problems, where the SPIM discretization is used to model the fracture propagation regions. Adaptive strategies are an important tool for problems that demand highly refined meshes in localized regions, such as in phase-field problems. In the proposed strategy, the problem is initially discretized with a coarse FEM mesh, that is automatically replaced and refined by an SPIM discretization when and where fracture occurs. Five different benchmark tests are presented to illustrate the robustness of the proposed strategy. Brittle and quasi-brittle problems are simulated and evaluated in terms of phase-field contour plots and load-displacement paths, showing good agreement with literature results and with results obtained with previously refined FEM models. The numerical simulations consider different criteria for the identification of the regions where the discretization replacement and refinement must occur, different sizes of the substitution regions, and different SPIM strategies. The proposed strategy relies on three properties of the meshfree strategy: (i) the reduced connectivity that ease the adaptive refinement, (ii) the presence of the Kronecker-delta property, that makes the coupling with the FEM mesh straightforward, and (iii) the presence of nonpolynomial approximation functions, that provide a better approximation of the phase-field profile. As illustrated by the simulations, this new strategy results in computational times that are comparable with the ones of a previously refined FEM mesh, without requiring an a priori knowledge of the replacement regions.