Can somebody assist me with modelling the crack propagation with XFEM (Abaqus) in connection with contact problems?

Hello,

I want to arrange a crack propagation in a screw thread. Therefor I use two dimensional axissymmetric elements in Abaqus 6.12-3 (it is the first version, that allows XFEM in axissymmetric models). The boundaries of the screw thread are on the one hand the symmetry axis, on the other hand the contact to a nut thread that is hold in vertical direction. Thus, there are two nonlinear problems: 1.) the contact problem and 2.) the XFEM crack growth.

1.) Arranging the analysis of the contact problem without crack growth works thoroughly.

2.) The XFEM crack propagation itself also works, when there is no contact (the screw thread is hold at the bottom). But it just works with problems (after a few little propagation steps, the analysis stops with the error:"ERROR: TOO MANY ATTEMPTS MADE FOR THIS INCREMENT"). The problem is that the tolerance f is exceeded. I think, this problem can be solved by increasing the number of possible attempts. But I do not know, where to change it.

3.) The connection of the XFEM crack growth with the contact is not possible. The analysis stops with the warning:"WARNING: DISPLACEMENT INCREMENT FOR CONTACT IS TOO BIG.". There is of course a certain expansion of the first carrying pitch of screw thread, but this condition I cannot change.

Has someone an idea, what I can do? How can I increase the number of attempts of an not working increment in CAE?I read, that the standart number is 5, but that is much to less. The minimum increment size is less enough (1e-12).

Greets,  

Thomas