The behavior of interfaces in seismic faults, and tribological systems in general, is governed by the interaction of discrete microconstituents trapped between contacting surfaces, often referred to as the gouge or the third-body. This is an amorphous wear particle agglomeration undergoing significant deformation, while the surrounding regions experience comparatively moderate strain. Understanding the dynamics of such systems, and in particular the evolution of the third body, can rely on particle-based numerical models such as the Discrete Element Method (DEM). The predicted behavior of the gouge can be sensitive to the boundary conditions, and therefore to the system size. However, the important computational costs prevent handling arbitrarily large domain sizes, which calls for cheaper Discrete-Continuum coupled methods. To accurately capture the behavior of continuum (long-range boundary) and discrete regions (gouge), we employed a hybrid modeling strategy combining the Finite Element Method (FEM) for continuum regions and the Discrete Element Method (DEM) [1,2].

To accommodate the evolving nature of the third body and prevent limitations imposed by the size of the discrete region, we will introduce in this presentation an adaptive coupling. This approach allows FEM regions to transition dynamically into DEM regions when a sufficient deformation criterion is met. Such a condition is evaluated within the third body near the coupling region. The adaptive framework supports large-scale simulations, and it will be demonstrated to support amorphous and ordered (crystalline) material setups for a gouge. Finally, the adaptive coupling is used to model the evolution of a third body comprising elliptical rigid bodies, which will be shown to impact the gouge evolution in certain conditions. Our findings underscore the importance of coupling techniques in modeling the complex, multiscale nature of frictional interfaces and contribute to a deeper understanding of the role of granularity in dynamic friction and third-body evolution.

[1] Xiao, S. P. and T. Belytschko (2004). “A bridging domain method for coupling continua with molecular dynamics”. Computer Methods in Applied Mechanics and Engineering. doi: 10.1016/j.cma.2003.12.053 [2] Voisin-Leprince, M., J. Garcia-Suarez, G. Anciaux, and J.-F. Molinari (2022). “Finite element method–discrete element method bridging coupling for the modeling of gouge”. International Journal for Numerical Methods in Engineering. doi: 10.1002/nme.7171