Effective toughness estimation by FFT based phase field fracture: application to composites and polycrystals

TL;DR

This paper introduces a FFT-based phase field fracture method to estimate the effective toughness of heterogeneous materials, accounting for microstructural effects, anisotropy, and crack path deviations, with applications to composites and polycrystals.

Contribution

It presents a novel FFT-based approach for estimating effective toughness that incorporates heterogeneity, anisotropy, and crack path effects in microstructured materials.

Findings

Heterogeneity and anisotropy increase effective toughness.

Crack passage through tougher phases enhances toughness.

High heterogeneity or anisotropy leads to toughening saturation.

Abstract

An estimate of the effective toughness of heterogeneous materials is proposed based on the Phase Field Fracture model implemented in an FFT homogenization solver. The estimate is based on the simulation of the deformation of representative volume elements of the microstructure, controlled by a constant energy dissipation rate using an arc-length type control. The definition of the toughness corresponds to the total energy dissipated after the total fracture of the RVE -- which can be accurately obtained thanks to the dissipation control -- divided by the RVE transverse area (length in 2D). The proposed estimate accounts for both the effect of heterogeneity in toughness and elastic response on the overall fracture energy and allows as well to account for phases with anisotropic elastic and fracture response (fracture by cleavage). To improve toughness predictions, crack-tip enrichment is used to model initial cracks. The method is applied to obtain the effective toughness of composites and elastic polycrystals in a series of examples. In the two types of materials, it is found that both heterogeneity in elastic response and fracture energy contribute to increase the effective toughness. Microscopically, it is found that toughening mechanisms are related to the passage of the crack through tougher phases and deviation of the crack path. It is also found that the latter is the controlling mechanism for cases with marked heterogeneity and high anisotropy, eventually provoking toughening saturation for sufficiently high values of heterogeneity or anisotropy.