Abaqus Xfem Crack Propagation Examples

This example verifies and illustrates the use of the extended finite element method (XFEM) in Abaqus/Standard to predict crack initiation and propagation of a single-edge notch in a specimen along an arbitrary path by modeling the crack as an enriched feature. Both the XFEM-based cohesive segments method and the XFEM-based linear elastic fracture mechanics (LEFM) approach are used to analyze this problem. Both two- and three-dimensional models are studied. The specimen is subjected to loadings ranging from pure Mode I to pure Mode II to mixed-mode. In some cases distributed pressure loads are applied to the cracked element surfaces as the crack initiates and propagates in the specimen. The results presented are compared to the available analytical solutions and those obtained using cohesive elements. In addition, the same model is analyzed using the XFEM-based low-cycle fatigue criterion to assess the fatigue life when the model is subjected to sub-critical cyclic loading.

Under the pure Mode II or mixed-mode loading, the crack will no longer propagate along a straight path and will instead propagate along a path based on the maximum tangential stress criterion according to Erdogan and Sih (1963). The direction of crack propagation is given by

abaqus xfem crack propagation examples

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Analysis procedureYou can include an XFEM crack in a static analysis procedure. Alternatively, you can include an XFEM crack in an implicit dynamic analysis procedure to simulate the fracture and failure in a structure under high-speed impact loading. The XFEM-based crack propagation simulated in an implicit dynamic procedure can also be preceded or followed by a static procedure to model the damage and failure throughout the loading history.

I have an idea: In abaqus, I want to simulate crack propagation by XFEM, and meanwhile I also want to define the stress update algorithm by writing a UMAT.Anybody wants to share related experiences?

I had actually never heard about simulating crack propagation by XFEM performed in abaqus. I had previously heard about couple of rhspec done over the platform. But, had never heard about anything like this before. I would be really interested if you would go through the test and tell us briefly more about it.

is a very attractive and effective way to simulate initiation and propagation of a discrete crack along an arbitrary, solution-dependent path without the requirement of remeshing in the bulk materials;

You can choose to model an arbitrary stationary crack or a discrete crack propagation along an arbitrary, solution-dependent path. The former requires that the elements around the crack tips are enriched with asymptotic functions to catch the singularity and that the elements intersected by the crack interior are enriched with the jump function across the crack surfaces. The latter infers that crack propagation is modeled with either the cohesive segments method or the linear elastic fracture mechanics approach in conjunction with phantom nodes. However, the options are mutually exclusive and cannot be specified simultaneously in a model.

You must assign a name to an enriched feature, such as a crack. This name can be used in defining the initial location of the crack surfaces, in identifying a crack for contour integral output, and in activating or deactivating the crack propagation analysis.

At the end of cycle , Abaqus/Standard extends the crack length, , from the current cycle forward over an incremental number of cycles, to by fracturing at least one enriched element ahead of the crack tips. Given the material constants and , combined with the known element length and the likely crack propagation direction at the enriched elements ahead of the crack tips, the number of cycles necessary to fail each enriched element ahead of the crack tip can be calculated as , where j represents the enriched element ahead of the th crack tip. The analysis is set up to advance the crack by at least one enriched element after the loading cycle is stabilized. The element with the fewest cycles is identified to be fractured, and its is represented as the number of cycles to grow the crack equal to its element length, . The most critical element is completely fractured with a zero constraint and a zero stiffness at the end of the stabilized cycle. As the enriched element is fractured, the load is redistributed and a new relative fracture energy release rate must be calculated for the enriched elements ahead of the crack tips for the next cycle. This capability allows at least one enriched element ahead of the crack tips to be fractured completely after each stabilized cycle and precisely accounts for the number of cycles needed to cause fatigue crack growth over that length.

Use the following option to deactivate the crack propagation capability automatically once all the pre-existing cracks (or if there are no pre-existing cracks, all the allowable newly nucleated cracks) have propagated through the boundary of the given enriched feature within the step definition:

Inconel 718 alloy is the most commonly used material of aero-engine turbine today. However, Inconel 718 alloy is known to suffer from the fatigue crack propagation during engine operation, which will lead to unstable fracture and seriously threatens the safety of the engine. In this paper, we research the fatigue crack propagation process of Inconel 718 alloy unilateral notched standard CT specimen at room temperature (298.15 K), 573.15 K, and 823.15 K under the type I cyclic fatigue load. The ABAQUS is used for numerical simulation. First, parametric models are established. Second, the extended finite-element method (XFEM) is used to in the calculation process for describing the crack state. Third, the stress intensity factor at the crack tip under different temperatures is calculated, and the extended finite-element crack length is solved to obtain the fatigue crack growth rate da/dN curve. The innovation is we use the XEFM method to predict the fatigue crack growth process of Inconel 718 alloy, and compare it with the test results to verify the reliability of the XEFM method under low stress intensity factor. We also provide some possible reasons for the error of XEFM results under high stress intensity factors, and the development of simulation methods should be emphasized.

Here in this training package, numerous methods of crack propagation modeling, such as the XFEM and H integral and so on, in concrete, steel, dams, bones, and other materials are examined through ten step-by-step tutorials. Every tutorial includes all needed files and a step-by-step English videos and is explained from A to Z. Package duration: +300 minutes

If you are a researcher, student, university professor, or Engineer in the company in the field of fracture mechanics, this training package in simulating crack growth in Abaqus software is the best selection.In this training package, everything you need to simulate crack growth is completely available from simple to advanced. It includes modeling crack growth in Abaqus to crack propagation methods and damage to various materials. Note that crack growth in some cases requires using special features of Abaqus software.

The extended finite element method [2-5] can approximate the discontinuous displacement field near cracks independently of the finite element mesh through the use of interpolation functions, which can describe the displacement field near cracks in the structure. Therefore, crack modelling for stress analyses in the field of fracture mechanics can be performed more easily by XFEM than by conventional FEM. Since information about the crack geometry is required in order to determine the interpolation functions in XFEM, the level set method, which expresses the geometry implicitly as the zero contour of the level set function, can be used to simplify the computation process in XFEM analysis. Since XFEM can model cracks of structures independently of the finite element models, the number of laborious and time consuming mesh division processes can be reduced. Therefore, XFEM can be used to perform crack propagation analyses, which is not possible in practice by the conventional FEM, which often requires remeshing procedures [5-7]. Thus, using extended finite element method to simulate fracture behaviours of structures can shorten the time to estimate safety of engineering structures and reduce experiment costs. Many researchers study the extended finite element method to simulate fracture behaviour. Modelling quasi-static crack growth in 2-D problems for isotropic and biomaterial media using XFEM is described in Sukumar and Prevost [8] in which the implementation of the crack growth using the XFEM within a general purpose finite element code is also described. The numerical applications are performed in Sukumar et al [9]. A 2-D numerical model of micro structural effects and quasistatic crack propagation in brittle materials using XFEM is presented in Sukumar et al [10]. The modelling of cracks with multiple branches, multiple holes and cracks emanating from holes is presented in Daux et al [11]. The implementation is based on using the same enrichment functions for the cracks (discontinuous and tip functions) and the enrichment scheme is developed based on the interaction of the discontinuous geometric features with the mesh. Whereas for holes, new enrichment function is introduced. Modelling 3-D planar cracks by XFEM was first introduced in Sukumar et al [12], who solved several planar crack mode-I problems and showed that the method compared well with analytical solutions.

Considering the fact that no one has ever studied the comparison between the three methods of theoretical, FEM and XFEM on crack growth simulations of a slantcracked plate, in this paper using the XFEM and finite element method (FEM), values of stress intensity factor, crack propagation direction, fatigue crack growth of a slant-cracked plate were calculated by Abaqus 6.10.1 software and the results were compared with the ones from the theoretical method. 2ff7e9595c