We are planning to begin on this very soon - good timing! I will link to this issue when we begin

We currently assume a single material interaction. But we already have a particle property that defines the "type", either for different layers in a composite, different grains in a polycrystal, or different materials entirely. A new interaction list will be needed to map the various types to different interaction models

Just to clarify so there is included the ability to define different types of materials in a single simulation, but we can't define the interaction between them?

If so what is the current standard interaction? Is it just averaging the bond stiffness of the two types? or is it more like type1 exerts a force to type 2 using the stiffness of type 1, but type 2 rebound with type 2 stiffness? Wouldn't that cause an imbalance of force?

Apologies if I have completely misunderstood your meaning.

What I said was a bit confusing - we have some things ready, but not enough to do a useful simulation with multiple materials

Ah, I get you. You have the types ready, but haven't added the interactions list for the forces. Sorry for the misunderstanding. Looking forward to when that is ready.

Also as a side note, I was looking into stress calculations in PD and came a cross and article titled "Peridynamic stress is the static first Piola–Kirchhoff Virial stress". Do you have stress calculations integrated into the code, as I don't know if it is possible to calculate this in post.

Also as a side note, I was looking into stress calculations in PD and came a cross and article titled "Peridynamic stress is the static first Piola–Kirchhoff Virial stress". Do you have stress calculations integrated into the code, as I don't know if it is possible to calculate this in post.

We don't currently, but @pabloseleson mentioned that it should be pretty straightforward. We'll probably want to move the stress discussion to a new issue to keep track of everything more easily

Yes, we can compute stress in PD. We will look into this.