DEM crack propagation using a FEM-DEM bridging coupling

The behavior of seismic faults depends on the response of the discrete microconstituents trapped in the region between continuum masses, which is usually termed “gouge”. The gouge is a particle region composed of amorphous grains. Conversely, the regions surrounding the gouge can be conceptualized as continua. The study of such system dynamics (slip) requires the understanding of several scales, from particle size to meter scale and above, to properly account for loading conditions. Our final objective in this study is to assess to what extent we can understand friction by leveraging an analogy to fracture. Dynamic friction between sliding surfaces resembles a dynamic mode-II crack, but this equivalence is brought into question when granularity at the interface is considered. Based on the theory of linear-elastic fracture mechanics (LEFM), a stress concentration should be observed at the rupture front if indeed friction can be modeled with the toolkit of LEFM.

Simulating this system numerically remains a challenge, as, in order to capture proper physics, both the continuum and discrete aspects of the system must be harmoniously incorporated and coupled into a single model. An energy-based coupling strategy between the Finite Element Method (FEM), used to resolve the continuum portions, and the Discrete Element Method (DEM), to model the granularity of the interface, is used [2]. In this exploratory study, we begin by modeling a medium with strong inter-granular cohesion [1]. The use of the coupling ensures a large enough effective domain to control nicely the crack propagation.  The linear-elastic properties of both DEM and FEM portions are therefore matched to avoid wave reflections. Both mode-I and mode-II cracks are considered.