Built-in Contact Models

The contact models provided with PFC are listed in the table below, together with their typical usage. The five models with “linear” in their keyword are referred to as “Linear-Based Models”. The linear contact bond, linear parallel bond, flat joint, and smooth joint contact models may be used to create Bonded-Particle Models (BPMs—see “Bonded Materials and Interfaces”).

Table 1: Built-in Contact Models
Keyword Name Behavior Summary
null null No mechanical interaction.
linear linear Linear elastic, frictional and viscous behavior.
linearcbond linear contact bond Linear model and contact bonding for BPM.
linearpbond linear parallel bond Linear model and parallel bonding for BPM.
sofbond soft bond Linear softening bond model for BPM or granular applications.
rrlinear rolling resistance linear Linear model and rolling-resistance mechanism for granular applications.
arrlinear adhesive rolling resistance linear Linear model, rolling-resistance mechanism and adhesion to give a cohesive granular material.
flatjoint flat joint Finite-size, linear elastic and either bonded or frictional interface with partial damage for BPM.
smoothjoint smooth joint Provides a joint within a BPM.
hertz hertz Non-linear elastic, frictional and viscous behavior for granular applications including impact problems.
hysteretic hysteretic Similar to hertz model but for impact problems, directly specify normal restitution coefficient.
burger Burger’s Provides a creep mechanism for granular applications.

Linear-Based Models

The linear contact bond, linear parallel bond, rolling resistance linear, and adhesive rolling resistance linear contact models are denoted as liner-based models, because they provide the behavior of the linear model. The properties consist of a Linear Group and a Dashpot Group, and these properties are identical for all of the linear-based models. The linear contact bond model adds a bonded behavior defined by the properties in its Contact-Bonded Group. The linear parallel bond model adds a second interface to provide the bonded behavior defined by the properties in its Parallel-Bonded Group. The rolling resistance linear model adds a rolling-resistance behavior defined by the properties in its Rolling-Resistance Group. The adhesive rolling resistance linear model adds both rolling-resistance and adhesive behaviors defined by the properties in its Rolling-Resistance and Adhesive Groups.

Bonded Materials and Interfaces

The bonded-particle modeling methodology provides a rich variety of microstructural models in the form of bonded materials ([Potyondy2015f]; [Potyondy2004d]). A bonded material is defined as a packed assembly of rigid grains (balls and/or clumps) joined by deformable and breakable cement at grain-grain contacts. It is the type of contact model at the grain-grain contacts that identifies the material as being contact-bonded, parallel-bonded or flat-jointed. A smooth-jointed interface can be inserted into the bonded materials by identifying the contacts near the interface, and replacing their contact models with the smooth-joint model. Damage in a bonded material consists of bond-breakage events, with each breakage event denoted as a crack.

Bonded materials can be created by generating a packed grain assembly, and then operating on the grain-grain contacts by either bonding them or installing a flat-joint contact model. Tutorial examples are provided below to illustrate the steps necessary to create bonded materials. These examples are simplified versions of what is provided in the material-modeling support package. This package creates and defines a particular instance of each type of bonded material, and also provides crack monitoring as well as facilities to perform standard rock-mechanics tests upon the synthetic material.

The creation of a parallel-bonded material is illustrated in the tutorial example “Generating a Bonded Assembly.” The tutorial “Using the CMAT” discusses the issue of specifying the cmat.proximity and the bonding gap appropriately to bond contacts with a desired contact gap. The tutorial “Inclusions in a Matrix” creates a complex bonded material with spatial heterogeneity of contact properties. The “Creation of a Synthetic Rock Mass (SRM) Specimen” example describes the insertion of smooth-jointed interfaces into a parallel-bonded material. The “Fragmentation” example creates a parallel-bonded material and performs an unconfined compression test on the specimen until complete failure; this example also illustrates how bond breakage and fragments can be monitored during the simulation. The “Rock Testing” example compares the mechanical response of parallel-bonded and flat-jointed materials under unconfined compression and direct-tension tests.

The material-modeling support package is described here.

References

[Potyondy2015f]Potyondy, D.O. “The Bonded-Particle Model as a Tool for Rock Mechanics Research and Application: Current Trends and Future Directions,” Geosystem Engineering, 18(1), 1–28 (2015), DOI:10.1080/12269328.2014.998346.
[Potyondy2004d]Potyondy, D.O., and P.A. Cundall. “A Bonded-Particle Model for Rock,” Int. J. Rock Mech. & Min. Sci., 41(8), 1329–1364 (2004).