Voronoi-Based DEM Simulation Approach for Sandstone Considering Grain Structure and Pore Size

Li, Jun; Konietzky, Heinz; Frühwirt, Thomas

doi:10.1007/s00603-017-1257-4

Cited by 56 publications

(17 citation statements)

References 29 publications

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“…12 Alternatively, a Voronoi or Voronoi-like diagram might be generated firstly and then the polygons assigned with different phase types to represent the rock grains. [19][20][21][22][23][24] Then the phase types of the polygons can be inherited by the mesh or particle inside it after refinement. Although the mineral composition ratio or porosity can be easily satisfied in the mesh-based or polygon-based stochastic approaches, the pattern for the distribution of different components is rarely captured.…”

Section: Introductionmentioning

confidence: 99%

Grain-scale failure mechanism of porous sandstone: An experimental and numerical FDEM study of the Brazilian Tensile Strength test using CT-Scan microstructure

Chen

Xiang

Latham

et al. 2020

International Journal of Rock Mechanics and Mining Sciences

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Many widely used numerical models of rock fracture based on mesoscale laboratory test characterisation of effective 'intact' strength parameters neglect microstructure effects. They therefore cannot explain grain boundary and pore effects on crack propagation and consequently are inadequate for models of rock destruction that exploit point and indentation stresses. Understanding deep drilling processes involving drill-bit buttons and/or water-jetting where rock loading is concentrated in domains with fewer mineral grains will therefore require models with microstructure. To investigate microscale failure mechanisms of granular rocks in diverse scenarios, we target a porous sandstone and introduce a novel workflow consisting of a computerized tomography (CT) based microstructure construction approach and a complementary mechanical numerical approach. The construction approach extracts the realistic rock microstructure and transforms the large voxel number CT-scan data into significantly fewer triangular elements. The finite-discrete element method (FDEM) with grain-based model (GBM) is adopted to solve the mechanics. The microscale failure mechanism of sandstone during the Brazilian test was thoroughly analysed using the numerical results together with the post failure CT-scan test data. The build-up of compressive and tensile stress chains, micro-crack nucleation, local relaxation, chain switching and final crack-path development exploiting pores was illustrated, revealing the micro-to-macro failure mechanism in time and space. Fracture paths in the specimens during Brazilian tensile test were dominated by the pores and the inter-grain boundaries. The tensile strength of the inter-grain joints was estimated to be at least 3.67 times the mesoscale specimen's intact tensile strength, while the pores account for 72.76% of the fracture path. The influence of the cementation distribution and microscale discontinuities was investigated with numerical cases.

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Section: Introductionmentioning

confidence: 99%

Grain-scale failure mechanism of porous sandstone: An experimental and numerical FDEM study of the Brazilian Tensile Strength test using CT-Scan microstructure

Chen

Xiang

Latham

et al. 2020

International Journal of Rock Mechanics and Mining Sciences

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“…However, a smaller numerical model is used in the semicircular bending test to reduce computation time in the subsequent simulations. Previous studies suggest that reducing model size has no significant influence on the results but significantly improves the computing efficiency (Hofmann, Babadagli, & Zimmermann, ; J. Li, et al, ; Liu et al, ; Peng et al, ). Considering that each mineral should comprise several particles to allow the breakage of intragranular contacts, particle radius is set as a uniform distribution between 0.09 and 0.18 mm.…”

Section: Resultsmentioning

confidence: 99%

An Extended Grain‐Based Model Accounting for Microstructures in Rock Deformation

2019

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Reliable prediction of the rock fracturing process is a challenging issue in exploitation of deep earth resources in which artificial creation of complex fracture networks is employed. The grain-based modeling (GBM) approach is a promising numerical technique for its unique capability to simulate the fracturing behavior of crystalline rocks. An extended grain-based model is developed to improve the traditional Voronoi GBM from two aspects. First, digital image processing technique is presented to incorporate actual rock microstructures into the numerical model. Second, the effect of initial microcracks is considered by integrating a statistical discrete fracture network model into GBM. By simulating semicircular bending tests on 16 extended GBMs and 3 Voronoi GBMs, the effects of rock microstructures and initial microcracks on microcracking behavior and mechanical properties are analyzed. Cracking patterns are classified into four types for the first time with respect to fracture toughness and crack initiation threshold.The results indicate that the use of a statistical structure or a purely deterministic GBM without consideration of initial microcracks cannot realistically describe grain-scale discontinuities, which likely leads to biased evaluations of the rock failure process.

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“…Initially, many of these contributions dealt with the effect of degradation and cracking evolution on the mechanical response of geomaterials. This was achieved using various techniques such as micromechanically-inspired models [1], discrete element modelling [2] or RVE computations [3]. Fluid transport properties and their link to cracking evolution were also scrutinized using micromechanically-inspired models [1] and multiscale techniques [4,5].…”

Section: Contextmentioning

confidence: 99%

“…The size function is thus the starting point of the optimization process and of the initial nodes generation. The minimum initial imposed size values h 0 depending on the three geometrical parameters iis, curv and iis are first computed as expressed in Equation (2). In the present context, a low sensitivity to curvature is used to avoid too large differences in the element sizes that can cause a conditioning problem of the stiffness matrix in FEM simulations.…”

Section: Size Function Definitionmentioning

confidence: 99%

Comparison of advanced discretization techniques for image-based modelling of heterogeneous porous rocks

et al. 2019

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This contribution presents an assessment of computational techniques enabling automated simulations of complex porous rocks microstructures based on 3D imaging techniques. A subset of a CT-scanned sandstone sample is used to compare the results obtained by two advanced discretization frameworks. Raw scan results are processed by a level set-based segmentation technique to produce smooth geometries prone to finite element discretizations. A recently developed technique is outlined for conforming mesh generation for complex porous geometries described implicitly by functions. This allows generating high quality tetrahedral meshes with selective refinement. Next to this, a technique that uses a kinematic enrichment by incompatible modes to represent the heterogeneous geometry is explained. Both techniques use the same implicit geometry as main input for the simulations. Mechanical simulations are conducted on a subset of a scanned sample of a sandstone under triaxial loading conditions for isotropic compressive loading and for loading conditions involving a stress deviator. The results are compared and discussed based on local stress distributions and on a Mohr-Coulomb criterion with tensile cut-off. The results show that both discretization strategies yield complementary tools and allow envisioning automated simulations based on raw CT scan data for porous rocks exhibiting complex pore space morphologies.

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Voronoi-Based DEM Simulation Approach for Sandstone Considering Grain Structure and Pore Size

Cited by 56 publications

References 29 publications

Grain-scale failure mechanism of porous sandstone: An experimental and numerical FDEM study of the Brazilian Tensile Strength test using CT-Scan microstructure

Grain-scale failure mechanism of porous sandstone: An experimental and numerical FDEM study of the Brazilian Tensile Strength test using CT-Scan microstructure

An Extended Grain‐Based Model Accounting for Microstructures in Rock Deformation

Comparison of advanced discretization techniques for image-based modelling of heterogeneous porous rocks

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