The Crack Node
The Crack node serves several purposes:
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In the case of an ideal crack on an interior boundary, the degrees of freedom are split so that the displacements on the two crack surfaces are independent.
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In the case that a crack is located in a symmetry plane, all constraints that may be applied (such as symmetry) are removed. It is then possible for the crack to open.
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If possible, a crack growth direction is computed. For some cases this is instead a user input.
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A number of variables, such as an estimate of the crack length are created.
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A mesh suggestion is generated.
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By using the J-Integral subnode under Crack, you can compute J-integrals and stress intensity factors.
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By using the Virtual Crack Extension subnode under Crack, you can compute energy release rates and stress intensity factors.
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By using the Crack Closure subnode under Crack, you can add contact conditions between the crack faces.
The selected boundaries can form branched cracks.
Mesh
At a crack tip, there will be an automatic mesh refinement. In the mesh sequence, you will find an extra Size node, with all crack tips selected. You may want to adjust the mesh size in that node.