Hello,

I have a problem in which a steel nail is 'embedded' in a wood piece. The head of the nail is in contact with a steel bracket. As I apply cyclic load on the vertical wood 'wall', the bracket moves up and pulls the nails of the horizontal wood part, which gets pulled out of the wood (see Image). However, as the bracket unloads (and consequently so does the nail) the cohesive interaction that I defined between the nail and the wood simply unload to zero as well. This causes the nails to follow the bracket back into original position. I wanted the nail to retain the maximum displacement imposed by the contact with the bracket before the bracket starts to unload.

Looking at the ABAQUS documentation, it says the when using cohesive behavior, it will always unload to the initial position (see image of the cohesive material model used in ABAQUS). How can I overcome this? It can be either using contact pairs or any other strategy in ABAQUS (except cohesive elements, which I've tried and could not manage to work in my model).

I've already tried to use a custom defined FRIC subroutine in a tangential interaction behavior (doesn't work). I've thought about writing a custom UMAT subroutine, but ABAQUS does not allow a user-defined routine for cohesive response of contact pairs. I've tried to run an analysis with the ABAQUS default cohesive response, then get the nail deformations at peak and try to apply these as boundary conditions at the correct steps of the analysis. I also tried to use the option where ABAQUS maintains the initial position of an object during a step. However, these last two approaches seems to cause numerical instabilities in ABAQUS due to activating and deactivating boundary conditions in between steps.