An efficient A-FEM for arbitrary cracking in solids

In this paper a new augmented finite element method (A-FEM) that can account for multiple, intra-elemental discontinuities in heterogeneous solids has been derived. It does not need the extra DoFs as in the extended finite element method (X-FEM), or the additional nodes as in the phantom node method (PNM). The new A-FEM employs four internal nodes to facilitate the calculation of subdomain stiffness and the crack displacements due to an intra-elemental discontinuity. It is shown that through a novel efficient solving algorithm the displacement DoFs associated with the internal nodes can be solved analytically as functions of the regular nodal DoFs for any piece-wise linear cohesive laws, which leads to a fully-condensed elemental equilibrium equation that is mathematically exact. The new formulation permits repeated elemental augmentation to include multiple interactive cracks within a single element, enabling a unified treatment of the evolution from a weak discontinuity, to a strong discontinuity, and to multiple intra-element discontinuities, all within a single element that employs standard DoFs only. The new A-FEM's capability in high-fidelity simulation of interactive cohesive cracks in homogeneous and heterogeneous solids has been demonstrated through several numerical examples. It has been demonstrated that the new A-FEM achieved more than two orders of magnitude improvement in numerical accuracy, efficiency, and robustness, compared to the X-FEM.