We show that for the simulation of crack propagation in quasi-brittle, two-dimensional solids, very good results can be obtained with an embedded strong discontinuity quadrilateral finite element ...that has incompatible modes. Even more importantly, we demonstrate that these results can be obtained without using a crack tracking algorithm. Therefore, the simulation of crack patterns with several cracks, including branching, becomes possible. The avoidance of a tracking algorithm is mainly enabled by the application of a novel, local (Gauss-point based) criterion for crack nucleation, which determines the time of embedding the localisation line as well as its position and orientation. We treat the crack evolution in terms of a thermodynamical framework, with softening variables describing internal dissipative mechanisms of material degradation. As presented by numerical examples, many elements in the mesh may develop a crack, but only some of them actually open and/or slide, dissipate fracture energy, and eventually form the crack pattern. The novel approach has been implemented for statics and dynamics, and the results of computed difficult examples (including Kalthoff’s test) illustrate its very satisfying performance. It effectively overcomes unfavourable restrictions of the standard embedded strong discontinuity formulations, namely the simulation of the propagation of a single crack only. Moreover, it is computationally fast and straightforward to implement. Our numerical solutions match the results of experimental tests and previously reported numerical results in terms of crack pattern, dissipated fracture energy, and load–displacement curve.
•A novel quadrilateral finite element Q6 with embedded strong discontinuity is presented.•A novel criterion for crack nucleation is described.•The proposed embedded discontinuity model is used for static and dynamic simulations of crack propagation.•Numerical examples are computed without using a crack tracking algorithm.
•Continuum and discrete damage models are applied in embedded strong discontinuity formulation.•Sensitivity of results on material parameters for mixed mode fracture is studied.•Locking of element ...with constant opening and sliding is assessed.
We derive a finite element formulation for modelling fracture in 2d quasi-brittle solids. The kinematics of isoparametric quadrilateral is enriched by strong discontinuity in displacements in order to capture the discrete crack opening and sliding. To describe both the bulk and crack-surface dissipative phenomena induced by the crack propagation, a combination of continuum and discrete damage models is used. The continuum damage model describes dissipation in the bulk, which mainly occurs ahead of the crack front. The discrete damage model includes two uncoupled rigid-damage cohesive laws to deal with fracture energy release due to crack propagation in modes I and II. The numerical solution strategy is based on a local-global operator-split procedure and incorporates a crack-tracking algorithm for enforcing continuity of the crack path. Numerical examples illustrate very satisfying performance of the derived formulation in terms of mesh independency and robustness. The sensitivity of results on material parameters for mixed mode fracture is also illustrated.
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