Virtual Crack Extension Method
Similar to the J-integral method, the virtual crack extension method is used for computing the energy release rate and stress intensity factors. These two methods complement each other. The advantage with the virtual crack extension method is that it contains less assumptions. It can be used, for example, in the presence of body loads and thermal strains.
The virtual crack extension evaluation does, however rely on a significantly more complicated setup of the model, so for cases when the J-integral method is applicable, that should be the first choice.
Using the Virtual Crack Extension Method
The first step is to add a Virtual Crack Extension Method subnode under the Crack node used to model the crack. You can only have one Virtual Crack Extension subnode under each Crack node.
In most cases, the default settings in Virtual Crack Extension are sufficient. You may want to adjust the size of the sensitivity region. Its significance is discussed in Virtual Crack Extension Theory. If the crack geometry is such that there may be more than one crack front, you also need make a selection in the Crack Front section.
Then, click the Automated Model Setup icon () on the Sensitivity section toolbar and select the Create Deformed Geometry and Study (). This will initiate the following actions:
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A Deformed Geometry node with subnodes is added in the component. See Deformed Geometry Features for more information.
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A Control Variable Field node is added under Definitions, having the crack front as selection.
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A new study named Virtual Crack Extension Study is added. It contains a Sensitivity study step with an appropriate objective function.
When the study has been run, the predefined evaluation group Fracture Mechanics Results will contain the values of the energy release rate and stress intensity factors.