Fracture of a Crosslinked Polymer

Hello everyone,
I am trying to study the fracture behavoir of en epoxy system inthe atomistic scale. I have made an initial configuration of the system, equilibrated using NVT and then NPT for a fair amout of ns and then I crosslinked it. Now I would like to strech it so I can monitor its fracture behavour. I have already created a “pre cracked” area so that the crack propagation starts from there but I have a question.
I am using Dreiding ff which is not a reactive force field. When the crack propagates using this ff the bonds will never break so I thought to use fix bond/break command. But as I thought it deeper is not that the bondi inside the chains of the polymer break but the pair interactions between the molecules that do not exist as the crack propagates. Fron the other hand the pair interactions have cutoff radius and they turn to zero when the radius exceeds a specific value.
Do you have any idea how can I model this in LAMMPS ?

Thank you in advance!

What do you mean by this?

And this?

Can you elaborate some more?

Dear Axel,
Thank you for your imediate response.

When the fracture propagates macroscopicaly what we observe is the separation of the materials in two pieces. So if we scale down to the atomistic level when a microcrack propagates is not that the material changes its chemical form (it is still an epoxy) but it is separated in two parts by breaking the bonds between molecules (the chains of the epoxy in this particular situation). If I am wrong please let me know.

The pair interactions for example the LJ potential has a cutoff distance so as to turn zero then the atoms get further that distance

Thank you again!

What you describe is a hypothesis and without making a study myself of the specific material that you are researching, I cannot tell you whether that hypothesis is true or not. So I am still confused what you are asking here.

LAMMPS will do what you define in the input as commands and what those commands do is described in the documentation. If you have questions about details of how those work, you are in the right place and should ask them. But if you want to know which are commands that will provide a meaningful model for your specific research topic, then you are not. Instead you need to study the relevant published literature and see how others have modeled the same kind of system and what kind of conclusions they have been able to derive from it.

Thank you very much for your imediate responce! I will folow your advice!