Deformation history of the particles

Hello, ESyS Developers and Users,

I need to do some modification to the existing contact model (in the RotFricinteraction file). I need to remember the deformation history of the particles. Every time when a contact will occur, I need to check the previous maximum deformation of the particle. By comparing with the maximum deformation of the particle with the current deformation, I will calculate the contact force.

How difficult will it be to implement within the current ESyS framework?

How can I add an additional variable in the ESyS?

I have found some documents on how to include a new class of body force. Is there any documentation on how to add new interaction of contact model?

I will be really glad to get some suggestions on the issue.