Application of the distinct element method and the extended finite element method in modelling cracks and coalescence in brittle

M. Nazem, M. Sharafisafa
Computational Materials Science
Closed flaw, Coalescence, Crack propagation, Discrete element method, Extended finite element method, Filling material, Open flaw

In this paper we study the performance of the discrete element method (DEM) and the extended finite element method (XFEM) modelling the crack initiation, propagation and coalescence in fractured rock masses. Firstly, the crack propagation in a rock sample with single closed and open flaws and subjected to an uniaxial compression is simulated by the DEM and XFEM. The results obtained by the two methods are then compared with the experimental results reported by Park and Bobet (2009). Under an uniaxial compression load, two types of cracks are observed including the tensile or wing cracks, and the shear or secondary cracks. The results obtained by the DEM are in good agreement with the experimental results, viz., both wing and shear cracks are accurately modelled. The XFEM, on the other hand, can predict the tensile (wing) cracks, but fails to model the shear cracks. In second part of this study we consider the analysis of fracture propagation and coalescence in rock masses containing two open or closed flaws. The results predicted by the DEM and XFEM are then compared with experimental test results. Coalescence is produced by the linkage of two flaws and a combination of wing and secondary cracks. In the crack propagation and coalescence problem, the DEM is able to predict all cracks involved in rock fracturing, such as the wing and secondary cracks, as well as the crack linkage between two adjacent flaws and their subsequent coalescence. However, the XFEM results only represent the wing cracks, and the method fails to predict the shear cracks. Finally, the effect of filling materials in open flaws on the crack propagation is investigated. The results indicate that the initiation and propagation of cracks and their coalescence in a material containing open flaws significantly change when the flaws are filled with a weak material.

Keywords: Discrete element method, Extended finite element method, Crack propagation, Coalescence, Open flaw, Closed flaw, Filling material

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