J-integral

[ruham]

Dear all,

I`m trying to calculate the j-integral with 3D-Elements and I keep getting the error message "The following contour integral objects contains regions that cannot be mapped into layers of node sets". I`ve made circular mesh around the crack tip with quadratic wedge elements in the crack front and quadratic hexahedral elements in the remainder of the j-integral region. Has anyone experienced the same problem and solved it?

 

[Mustaine3]

Do you have regular mesh layer along the crack front?

In the Example Problems Manuals are examples how it should look like.

 

[ruham]

Thanks for the reply Mustaine3,

I have circular partitions around the crack tip so the mesh is circular. just like in the example problems manual. With wedge elements adjacent to the crack tip and brick elements around the wedge elements. I can't see any difference to the mesh in the example problems manual. The crack tip and the q vectors are correct too and there is a seam crack inside.
I also tried to write the model to an input file to import the orphan mesh and define the crack on the mesh. When I defined a circular line of element edges to form the crack tip I had the error message that "the line must be a closed loop". So I guess there must be a gap between the elements somewhere. Maybe its because of a bad quality of the geometry?

 

[Mustaine3]

I've ment that you also need regular layers of elements in axial direction (along the crack line), not only radial (the contours).

 

[ruham]

Yes I do have regular mesh along the crack line. It looks just like the circular crack in the Example Problems Manual. I attached a picture of the mesh.

 

[ruham]

An there is the mesh along the crack line

 

[ruham]

Finally I found out that the error message occurs when a "penny-shaped" crack is modelled on a geometry. Again, I wrote the model to an input file and imported the orphan mesh to define the crack on the mesh. The problem that arises here is that, if the orphan mesh includes collapsed hexahedral elements at the crack tip, it´s not possible to select a closed circle of element edges as the crack line. I guess it's because every element edge at the desired crack line consists of 2 collapsed element edges.
That means if an orphan mesh is being imported in order to define a crack the imported crack front must not contain collapsed nodes. The collapsed nodes which account for the singularity must be generated at the orphan mesh.