Propagation of fractures from an interface in a Brazilian test specimen

This study investigates the influence of microscale heterogeneity and microcracks on the failure behavior and mechanical response of a crystalline rock. The thin section analysis for obtaining the microcrack density is presented. Using micro X‐ray computed tomography (μCT) scanning of failed laboratory specimens, the influence of heterogeneity and, in particular, biotite grains on the brittle fracture of the specimens is discussed and various failure patterns are characterized. Three groups of numerical simulations are presented, which demonstrate the role of microcracks and the influence of μCT‐based and stochastically generated phase distributions. The mechanical response, stress distribution, and fracturing process obtained by the numerical simulations are also discussed. The simulation results illustrate that heterogeneity and microcracks should be considered to accurately predict the tensile strength and failure behavior of the sample.

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Section: Resultssupporting

confidence: 91%

“…If the loading had continued, the specimen could have completely detached into two or more pieces. This fracturing process corresponds well with experimental observations [Colback, 1966;Malan et al, 1994]. A number of final fracture patterns for selected simulations are presented in Figure 11.…”

Section: Stress Distribution and Fracturing Processsupporting

confidence: 85%

Influence of microscale heterogeneity and microstructure on the tensile behavior of crystalline rocks

2014

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“…Therefore, to overcome analytical limitations, numerical methods have been used to simulate the stress distribution and/or crack initiation and propagation of (transversely) isotropic rocks for the Brazilian test (see Li and Wong [2013] for a brief review). For example, these numerical efforts include the displacement continuity for investigating the influence of the loading contact on the initiation and propagation of fractures [e.g., Malan et al, 1994], the boundary element method for evaluating the effect of the initiated cracks on stress distribution within isotropic rock samples [e.g., Lanaro et al, 2009], the finite element method for 3-D stress analysis to show size/shape effects under the Brazilian test [e.g., Yu et al, 2006], and for analyzing failure process of heterogeneous isotropic rocks under static/dynamic loading [e.g., Zhu and Tang, 2006]. Recently, the numerical methods have been extended to utilize the extended finite element method for simulating crack propagation in the cracked Brazilian disc [e.g., Eftekhari et al, 2015], the discrete element method for the mechanical behavior of transversely isotropic rocks using embedded smooth joints (e.g., Park and Min [2015] in 2-D and Park et al [2016] in 3-D), and the hybrid finite element method-discrete element method for analyzing the influence of microscale heterogeneity and microcracks on the brittle fractures [e.g., Mahabadi, 2012] and for modeling the transition from continuum to discontinuum during fracturing process [e.g., An et al, 2016].…”

mentioning

confidence: 99%

Effects of spatial heterogeneity and material anisotropy on the fracture pattern and macroscopic effective toughness of Mancos Shale in Brazilian tests

Sun

Ingraham

et al. 2017

JGR Solid Earth

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For assessing energy‐related activities in the subsurface, it is important to investigate the impact of the spatial variability and anisotropy on the geomechanical behavior of shale. The Brazilian test, an indirect tensile‐splitting method, is performed in this work, and the evolution of strain field is obtained using digital image correlation. Experimental results show the significant impact of local heterogeneity and lamination on the crack pattern characteristics. For numerical simulations, a phase field method is used to simulate the brittle fracture behavior under various Brazilian test conditions. In this study, shale is assumed to consist of two constituents including the stiff and soft layers to which the same toughness but different elastic moduli are assigned. Microstructural heterogeneity is simplified to represent mesoscale (e.g., millimeter scale) features such as layer orientation, thickness, volume fraction, and defects. The effect of these structural attributes on the onset, propagation, and coalescence of cracks is explored. The simulation results show that spatial heterogeneity and material anisotropy highly affect crack patterns and effective fracture toughness, and the elastic contrast of two constituents significantly alters the effective toughness. However, the complex crack patterns observed in the experiments cannot completely be accounted for by either an isotropic or transversely isotropic effective medium approach. This implies that cracks developed in the layered system may coalesce in complicated ways depending on the local heterogeneity, and the interaction mechanisms between the cracks using two‐constituent systems may explain the wide range of effective toughness of shale reported in the literature.

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“…According to experiments conducted by Malan et al (1994) [20], a typical fracture propagation in BTS test includes primary tensile cracks along the loading diameter and secondary shear cracks from the loading sides parallel to the primary cracks. Thus hybrid finite-discrete element method obtains a valid failure pattern in BTS test.…”

Section: Fig7 -Comparison Of the Numerical And Experiential Resultsmentioning

confidence: 99%

Hybrid Continuum-Discontinuum Modelling of Rock Fracutre Process in Brazilian Tensile Strength Test

An¹,

Liu²,

Wang³

et al. 2017

CEJ

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A hybrid continuum-discontinuum method is introduced to model the rock failure process in Brazilian tensile strength (BTS) test. The key component of the hybrid continuum-discontinuum method, i.e. transition from continuum to discontinuum through fracture and fragmentation, is introduced in detail. A laboratory test is conducted first to capture the rock fracture pattern in the BTS test while the tensile strength is calculated according to the peak value of the loading forces. Then the proposed method is used to model the rock behaviour during BTS test. The stress propagation is modelled and compared with those modelled by finite element method in literatures. In addition, the crack initiation and propagation are captured and compared with the facture patter in laboratory test. Moreover, the force-loading displacement curve is obtained which represents a typical brittle material failure process. Furthermore, the stress distributions along the vertical direction are compared with the theoretical solution. It is concluded that the hybrid continuum-discontinuum method can model the stress propagation process and the entire rock failure process in BTS test. The proposed method is a valuable numerical tool for studying the rock behaviour involving the fracture and fragmentation processes.

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Propagation of fractures from an interface in a Brazilian test specimen

Abstract: The influence of an interface on the initiation and propagation of fractures was investigated using the Brazilian tensile test (diametral compression of a disc

Cited by 33 publications

References 9 publications

Influence of microscale heterogeneity and microstructure on the tensile behavior of crystalline rocks

Influence of microscale heterogeneity and microstructure on the tensile behavior of crystalline rocks

Effects of spatial heterogeneity and material anisotropy on the fracture pattern and macroscopic effective toughness of Mancos Shale in Brazilian tests

Hybrid Continuum-Discontinuum Modelling of Rock Fracutre Process in Brazilian Tensile Strength Test

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