Setup peridynamic interaction

[georghammerl]

This is the initial draft for implementing peridynamic interaction within the particle-based SPH framework. The methodological work is by @armanshojaei

Peridynamic in a nutshell:
Peridynamics is a nonlocal continuum mechanics theory that replaces classical partial differential equations with integral equations, making it well-suited for modeling discontinuities like cracks. Unlike traditional continuum methods, it treats material points as interacting through bonds over a finite distance, similar to particles. This approach conceptually relates to particle methods like DEM (Discrete Element Method), but while DEM is purely particle-based for granular materials, peridynamics retains continuum properties while enabling fracture and damage simulation without special crack-tracking algorithms.

The main idea of the current implementation is as follows:

• A peridynamic body consists of several rigid bodies (assumption: each rigid body consists of a single rigidphase particle) which are tied together via peridynamic interaction forces
• A peridynamic body can fracture and even break into smaller pieces
• Breakage between interacting bonds occurs if a certain stretch is exceeded
• Peridynamic bodies interact with each other (and also with walls and other rigid bodies) in a DEM-like fashion

The code changes can be summarized as follows:

• Insert a new handler for peridynamic in the SPH framework in 4C_particle_interaction_sph.cpp
• Computation of peridynamic interaction force and care of the peridynamic bonded pairs is taken in 4C_particle_interaction_sph_peridynamic.hpp
• To distinguish between "normal" DEM-like particle contact scenario (=short range interaction) and the peridynamic interaction scenario (=long range interaction), an additional pair is introduced: 4C_particle_interaction_pd_neighbor_pairs.hpp which is capable of excluding the peridynamic pairs from the colliding pairs.
• In 4C_particle_interaction_sph_rigid_particle_contact.cpp, the condition for evaluation of collisions relies on the initialparticlespacing (in the standard SPH case) which needs further clarification in the peridynamic contact scenario (WIP)

Interested groups

@ppraegla