Irazu: a Finite-Discrete Element simulation software

Geomechanica’s Irazu simulation software is a state-of-the-art simulation tool based on the hybrid finite-discrete element method (FEMDEM or FDEM), a numerical method which combines continuum mechanics principles with discrete element method (DEM) algorithms to simulate multiple interacting deformable bodies. In Irazu, each solid is discretized as a mesh consisting of nodes and triangular elements. An explicit time integration scheme is applied to solve the equations of motion for the discretized system and to update the nodal coordinates at each simulation time step.

Geomechanica has released Irazu simulation software as a standalone software and on the Cloud. Parties interested in purchasing Irazu licenses or Cloud subscriptions should contact info@geomechanica.com. Read more here.
Material deformation and fracturing

The progressive failure of intact rock material is modelled using a cohesive-zone approach, which aims at capturing the non-linear interdependence between stresses and strain that characterizes the zone ahead of a macro-crack tip known as the Fracture Process Zone (FPZ). When using cohesive-zone models, the failure of the material progresses based solely on the strength degradation of dedicated interface elements (known as crack elements) and therefore emerges as a natural outcome of the deformation process without employing any additional macroscopic failure criterion. Since the material strain is expected to be localized in the cohesive zone, the bulk material (i.e., the continuum, or unfractured, portion of the model) is treated as linear-elastic using constant-strain triangular elements. The bonding stresses transferred by the material are decreasing functions of the displacement discontinuity across the crack elements. Both Mode I and Mode II failure can be reproduced. In Irazu, the crack elements are interspersed throughout the material (i.e, across the edges of all triangular element pairs) from the very beginning of the simulation. Thus, cracks are allowed to nucleate and grow without any additional assumption or criterion other than the crack element constitutive response. Upon breakage of the cohesive surface, the crack element is removed from the simulation and therefore the model locally transitions from a continuous to a discontinuous statew. As the simulation progresses, finite displacements and rotations of discrete bodies are allowed and new contacts are automatically recognized.

Contact detection and interaction

An Irazu simulation can comprise a very large number of potentially interacting distinct elements. To correctly capture this behaviour, contacting couples (i.e., pairs of contacting discrete elements) must first be detected. Subsequently, the interaction forces resulting from such contacts can be defined. Contact interaction forces are calculated between all pairs of elements that overlap in space. Two types of forces are applied to the elements of each contacting pair: repulsive forces and frictional forces. The repulsive forces between the elements of each contacting pair (i.e., couples) are calculated using a penalty function method. The frictional forces between contacting couples are calculated using a Coulomb-type friction law. These frictional forces are used to simulate the shear strength of intact material and of pre-existing and newly-created fractures.


Further Reading:

  • Mahabadi OK, Lisjak A, Grasselli G and Munjiza A (2012). "Y-Geo: a new combined finite-discrete element numerical code for geomechanical applications". International Journal of Geomechanics. 12(6), 676-688. (DOI: 10.1061/(ASCE)GM.1943-5622.0000216)
  • The open-source FEMDEM code, Y-Geo, and its graphical user interface, Y-GUI, can be downloaded here. A video tutorial of these codes is also available on YouTube.
Note that Geomechanica Inc. does not maintain or support Y-Geo or Y-GUI codes.
Cohesive-zone approach for material failure modelling in FEM/DEM. (a) Conceptual model of a tensile crack in a heterogeneous rock material (modified after Labuz et al. (1987)). (b) Theoretical FPZ model of Hillerborg (Hillerborg et al., 1976). (c) Cross-section of FEM/DEM implementation of the FPZ using tetrahedral elastic elements and six-noded crack elements to represent the bulk material and the fracture, respectively. Triangles are shrunk for illustration purposes.