Enriched finite element methods (e-FEMs) have become a popular choice for modeling problems containing material discontinuities (e.g., multi-phase materials and fracture). The main advantage as compared to the standard finite element method (FEM) remains the versatility in the choice of discretizations, since e-FEMs resolve discontinuities by completely decoupling them from the finite element mesh. However, modeling complex kinematics such as branching and merging of discrete cracks remains challenging. This article extends previous research on the Discontinuity-Enriched Finite Element Method (DE-FEM) for simulating quasi-static crack propagation in brittle materials. In DE-FEM enrichments are added to nodes created directly along discontinuities. Most notably, we demonstrate DE-FEM can resolve complex kinematics, namely the modeling of multiple cracks propagating and merging—and with a straightforward computer implementation. We validate the formulation with experimental results carried out on a compact tension specimen. Other numerical examples show the capability of DE-FEM in capturing crack paths similar to those observed in the literature.

Fundamentals of Enriched Finite Element Methods provides an overview of the different enriched finite element methods, detailed instruction on their use, and their real-world applications, recommending in what situations they are best implemented. It starts with a concise background on the theory required to understand the underlying principles behind the methods before outlining detailed instruction on implementation of the techniques in standard displacement-based finite element codes. The strengths and weaknesses of each are discussed, as are computer implementation details, including a standalone generalized finite element package, written in Python. The applications of the methods to a range of scenarios, including multiphase, fracture, multiscale, and immersed boundary (fictitious domain) problems are covered, and readers can find ready-to-use code, simulation videos, and other useful resources on the companion website of the book.

This paper presents a methodology for the analysis of three-dimensional static fractures in fiber-reinforced materials. Fibers are discretely modeled using a modification of the embedded reinforcement method with bond Slip (mERS) that allows its combination with a generalized finite element method (GFEM) for three-dimensional fractures. Since the GFEM mesh does not need to fit fracture surfaces or fibers, the GFEM–mERS can handle fibers bridging across crack faces at arbitrary angles. The method is verified against three-dimensional FEM solutions using conformal discretizations for crack surfaces and fiber boundaries. The comparison of the method against experimental data and convergence studies of the h- and p-version of the method is also presented.

Crack propagation in polycrystalline specimens is studied by means of a generalized finite element method with linear elastic isotropic grains and cohesive grain boundaries. The corresponding mode-I intergranular cracks are characterized using a grain boundary brittleness criterion that depends on cohesive law parameters and average grain boundary length. It is shown that load–displacement curves for specimens with the same microstructure and for various cohesive law parameters can be obtained from a master load–displacement curve by means of simple linear elastic fracture mechanics scaling relations. This property is a consequence of the independence of intergranular crack paths from cohesive law parameters. Perfect scaling is obtained for cases characterized by the same grain boundary brittleness number, irrespective of its value, whereas scaling is approximated for cases with different but relatively large values of the grain boundary brittleness number. The former case corresponds to grain boundary traction profiles that are identical apart from a scale factor; in the latter case, a large grain boundary brittleness number implies similar, apart from a scale factor, traction profiles. By exploiting this property, it is demonstrated that computationally expensive simulations can be avoided above a certain grain boundary brittleness threshold value.