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.
D.C. Pham thank you for the suggestion. I'll try that and let you know what happens.
D.C. Pham, would you mind clarifying how can I use two contact algorithms at the same time? Do you mean separating my cyclic load into different steps and then in each step activating/deactivating different contact algorithms? Because I don't know how to layout my contact interactions in order to have one of them acting only when the pair in is contact, and another one when the pair is not in contact.
Thanks.
Hello D.C. Pham , thank you for your suggestion. However, it did not solve the problem. What I need is that as the bracket pushes (or pull, depending on the perspective) the nails, it follows the triangular shape of the cohesive behavior. However, once The bracket starts to recede (and granted that the cohesive response has exceeded the peak capacity), the nail remains in place, while the bracket can recede and, eventually, re-contact the nail (on its way up again).
Your suggestions did work as you described: basically, once the peak capacity of the cohesive response is reached, the tangential response specified kicks in. However, this occurs no matter if the bracket is still pushing the nail up, which is not the desired behavior. I want the cohesive behavior (the triangular response) to remain as long as the bracket is pushing the nail up and only retain the nail position when the bracket recedes. Implementing your solution causes high stress to develop on the nails, causing necking and, eventually premature failure (as the bracket is pushing the nail up with the new tangential behavior and not the degrading stiffness of the cohesive response intended).
Thank you for your suggestions, though. I am still struggling to find a solution to this problem. If you have any other ideas or know of a better place/person I can contact to help me, it would be greatly appreciated.
- Badges
- Science topic