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 include the singularity in your contour integral estimates, click the Singularity tab in the Crack editor and choose the desired position of the midside node and degenerate element control. For detailed instructions, see “Controlling the singularity at the crack tip,” Section 20.1.10.
In addition, you must do the following in the Mesh module:
If the assembly or part is two-dimensional, you must model the crack front with a ring of triangles and assign quadrilateral elements to the remainder of the contour integral region.
If the assembly or part is three-dimensional, you must model the crack front with a ring of wedges and assign hexahedral elements to the remainder of the contour integral region.
Converts the elements in the crack front to collapsed quadrilateral or hexahedral elements.
If you modeled the crack front with a ring of second-order triangles or wedges, ABAQUS moves the midside nodes to the specified position along the element edges that radiate out from the crack tip or crack line. (If you modeled the crack front with a ring of first-order triangles or wedges, ABAQUS ignores the position that you specified for the midside nodes.)
An instance of an orphan mesh part is always a dependent instance. As a result, you cannot adjust the midside nodes of instances of orphan mesh parts in the assembly. For more information, see “What is the difference between editing an orphan mesh part, a meshed part, and a meshed part instance in the assembly?,” Section 41.2. You must display the original orphan mesh part and use the Edit Mesh toolset to adjust the position of the midsize nodes. For more information, see “Adjusting the position of midside nodes,” Section 41.5.5. In addition, you cannot create collapsed elements from triangular and wedge elements of an orphan mesh.