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Crack penetration in cohesive zone models
I am conducting some cohesive crack simulations within the framework of XFEM. The cohesive model is an initially rigid traction-separation law for mode I. In order to deal with negative values of the normal sepration/jump, I use a penalty stiffness K.
The example is pretty simple: an un-notched three point bending test where a crack is initiated at the bottom edge of the beam and grow vertically upwards to the upper edge. During the simulation, some negative jumps are observed. The convergence is very much dependent on the penalty stiffness K used. Even for some cases, no convergence obtained at all. I tried K from 10^3 to 10^10.
Could you please share your experiences in dealing with crack penetration in crack grow simulation?