13th International Conference on Fracture June 16–21, 2013, Beijing, China -7- fluid transport simulation, thereby enabling a one-way coupling between the local mechanical degradation of the material and its local permeability. Figure 4. Principle of XFEM enrichment by level set function 5. Application to rock-type materials The concepts presented previously are now illustrated using two RVEs generated with the tools described in Section 3 and in [4]. The first RVE used for fluid transport homogenisation is produced starting from an initial distribution of elongated inclusions that are subsequently morphed into grains separated by joints. Considering the aspect ratio of the grains, if different permeability properties of the constituents are selected, the resulting average permeability should be anisotropic, as will be illustrated in Section 5.1. The second RVE contains grains without any preferential orientation. The evolving macroscopic permeability resulting from the local plasticity-induced permeability evolution in the joints is analysed in Section 5.2. 5.1. Averaged anisotropic permeability properties As a first illustration of the proposed level set based homogenisation of heterogeneous materials, the permeability of a anisotropic grain-based material is considered. An anisotropic RVE is generated with a 69% volume fraction of grains (Fig. 5). A grain permeability 0IJ 2:3 10K AL² is used, while the joints are assumed 10 times more permeable (06N2:O3 10K @L²). Since the inclusions are parallel and elongated along the vertical direction, the macroscopic averaged vertical permeability should be higher than for the transverse directions. This is indeed the case as the obtained permeability properties read 0PQJO24 R 3 10K AL@ and 0TNJ2UN:O R 2,3 10K AL@ This is further illustrated in Fig. 5 where the fluid flow is illustrated for a unit pressure gradient along the horizontal and vertical directions. As can be seen the preferential orientation of the inclusions clearly favors the fluid flow along the vertical direction, leading to a higher vertical permeability. 5.2. Plasticity-induced permeability evolution in a triaxial test The coupling between the local mechanical degradation and the fluid transport properties is
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