Abaqus xfem crack initiation

For more information, see Modeling discontinuities as an enriched feature using the extended finite element method. From the main menu bar in the Interaction module , select Special Crack Create. Enter the name of the crack, and click Continue to close the dialog box. From the model in the viewport, select the entities representing the crack domain. You can select cells from a three-dimensional part instance or faces from a two-dimensional part instance.

If you have an orphan mesh or an instance containing both orphan mesh and native mesh elements, you can select elements to represent the crack domain. You should select the entities that contain an existing crack along with any entities into which a crack might propagate.

Without going into too many details, essentially we can have a crack propagating in between an element, effectively splitting it into two parts. As this is a very discontinuous and difficult problem to obtain a converged solution, we need to modify the solution controls. Press continue when the warning message is displayed. If we superimpose the crack location and propagation path on the full THR implant we get the image below.

Even though we are using steel instead of CoCr, the crack location is not to dissimilar to the the experimental crack investigation by Ryniewicz et al. In their specimen, there is also an additional smaller fracture near the failed region. XFEM is a nice tool, but generally we're more interested if there will be a crack forming in a specific region and perhaps more important IF the crack will propagate.

For that purpose the more traditional approach of modeling cracks using J- integrals or stress intensity factors K may be sufficient A brief overview by Christine shown here. So when would XFEM be more important? First, when we have no idea where the crack tip will be located.

A second would be to match FE model predictions to real physical specimens. If the fracture behavior is accurate, this could replace physical testing. You could cycle through several designs and optimize the final product. Get notified! Reasonably good agreement is obtained.

Subroutine for a user-defined damage initiation criterion with two different failure mechanisms. Problem description A plate with a circular hole is studied. Results and discussion Figure 3 shows plots of the prescribed displacement versus the corresponding reaction force with different mesh discretizations when the XFEM -based cohesive segments method is used.

References Tada , H. Paris , and G. Louis, Missouri, , Figures Figure 1. Model geometry of the plate with a hole specimen. Figure 2. A separate part representing the crack without properties or mesh can be instanced into the assembly and moved to the correct position. By choosing this part as crack location, the crack is defined.

The crack does not need to be along the element edges. In fact, the XFEM method works best if the crack crosses through the element. Frictionless small-sliding contact can be defined for the contact between both sides of the crack.

To aid in obtaining a converged solution, the solution controls can be modified. Press continue when a warning message is displayed. In the time incrementation tab, discontinuous analysis can be checked. This allows Abaqus to do more iterations before checking whether the solution is going anywhere.

If large cut-backs are required, increasing the number of attempts is useful. This is the signed distance function to describe the crack surface using the level set method. If PHILSM is requested, Abaqus automatically creates an isosurface view cut based on this output, which shows the location of the crack. If it is not requested, the crack will not be visible and results shown will be counterintuitive.

It gives the status of the enriched elements, it is 0. Of course the normal outputs such as stress and strain are available as well. With the isosurface view cut based on PHILSM on default the results of this simulation nicely show the crack developing in time. By applying translucency, the internal part of the crack is also visible. Topics: Modelling crack propagation.