Griffith crack with pressure elements

[Jfrisch]

Dear FEAP users,

I want to redo some calculations of a Griffith crack for testing issues. The mesh is a simple horizontal crack at the edge of the mesh and the author wrote, that his boundary condition is an imposed pressure on the faces of the crack (one calculation with perpendicular stresses and one calculation with shear stresses). I've tried to rebuild this kind of situation but failed so far. I've found the pressure elements, but they didn't work (no convergence).

An especially difficult task in modeling crcks is, that you can't distinguish the faces of the crack by their coordinates, so the usual options like csurf or ebou aren't - at least to my knowledge - applicable. Are these pressure elements the way to go to impose a pressure (and especially a shear stress) on a face of a crack or is there another way to deal with this kind of boundary condition?

Thanks in advance.

[Prof. R.L. Taylor]

I was able to create a small mesh that used the pressure element.  The CSURf probably will not work as it will not find the correct nodes.  It may be necessary to write a user element to do the tangential loading (probably the pressure element can be used as a basis). 

To do the mesh I started with 4-blocks using loops and transformation, used 4 different materials (Icrack), used TIE MATE to merge the parts.  Did an outmesh to create Icrack1  which I used to make all parts the same material. This outmesh was renamed Icrack2 which I added the pressure loads and its mesh.

[Prof. R.L. Taylor]

I also tried with csurf and it seems to work fine also -- all in one mesh but still with 4 MATEs.

[Jfrisch]

Dear Prof. Taylor, many thanks for your help. We've tried and figures out how to get csur working. We still need to exclude the node at the cracktip itself, but everything looks fine, converges and is set up the way we want it too. Also the shear stresses are applicable with csurf without any problems so far. So many thanks again: you helped a lot!