Virtual Crack Extension

Add a node to compute the energy release rate and stress intensity factors at a crack tip using the virtual crack extension method.

This is an alternative to using a J-Integral. The J-integral is easier to use, but the virtual crack extension method is more versatile.

The node is only available with some COMSOL products (see https://www.comsol.com/products/specifications/).

Here you select the boundaries that constitute the crack surface to be used in the computation. The default is the same boundaries that are selected in the parent node. In most cases, you do not have to change the selection.

Select the edges (3D) or point (2D) that define the tip of the crack for which the energy release rate is to be computed.

Enter the , Rs, of the sensitivity region. This is the region that is deformed by the associated Deformed Geometry feature during the sensitivity analysis. The default radius is an expression of the form solid.<crack_tag>.crackSize*0.5. The variable crackSize is estimated from the crack geometry.

In order to separate the stress intensity factors for the different crack modes, the displacements on the crack surfaces are analyzed. In order to get a good value, this analysis should be performed in a region where the theoretical solution for the fields around a crack tip is valid. Ideally, this is close to the crack tip. It is, however, not possible to get an accurate numerical evaluation very close to the crack tip, due to the singularity of the fields.

The default is that the region used for the evaluation starts at a distance of 20% of the crack length from the tip, and extends to half the crack length. You can modify these values by entering a , b, and an , c.

In this section, you can specify if the special virtual crack extension study should also contain a parametric sweep. Select — or .

If is selected, then specify the — or . Then, add parameters, their ranges, and their units on the table. The interpretation of the settings are the same as for the Parametric Sweep study step.

Physics tab with node selected in the model tree: