20.1.10 Controlling the singularity at the crack tip

If the geometry of the crack region defines a sharp crack, the strain field becomes singular at the crack tip, as described in Constructing a fracture mechanics mesh for small-strain analysis” in “Contour integral evaluation, Section 7.10.2 of the ABAQUS Analysis User's Manual. Including the singularity in your model for a small-strain analysis improves the accuracy of the contour integral and the stress and strain calculations.

To control the singularity at the crack tip:

  1. Display the Crack editor using one of the following methods:

  2. To include the strain singularity in your contour integral estimates, click the Singularity tab in the Crack editor, and do one of the following:

    • To create a strain singularity for an elastic fracture mechanics application:

      1. From the Second-order Mesh Options field, enter a value of 0.25 for the Midside node parameter to move the midside nodes to the points.

      2. From the Degenerate Element Control at Crack Tip/Line field, choose Collapsed element side, single node.

    • To create a strain singularity for a perfect plasticity fracture mechanics application:

      1. From the Second-order Mesh Options field, enter a value of 0.5 for the Midside node parameter to keep the midside nodes at the midside points.

      2. From the Degenerate element control at Crack Tip/Line field, choose Collapsed element side, duplicate nodes.

    • To create a combined and strain singularity for a power law hardening material:

      1. From the Second-order Mesh Options field, enter a value of 0.25 for the Midside node parameter.

      2. From the Degenerate element control at Crack Tip/Line field, choose Collapsed element side, duplicate nodes.

  3. Click OK to include the singularity in the contour integral estimation and to close the editor.

    Note:  In most cases you must assign second-order triangle or wedge elements to the crack front region to include the singularity in your contour integral estimates. If you assign first-order elements, ABAQUS ignores the value of the midside node setting in the Singularity tabbed page. However, if you assign first-order elements and choose Collapsed element side, duplicate nodes from the Degenerate Element Control at Crack Tip/Line field, you will create a strain singularity.