Fracture Toughness Measurements and Acoustic Emission Activity in Brittle Rocks

Nasseri, M. H. B.; Mohanty, B.; Young, R. P.

doi:10.1007/s00024-006-0064-8

Cited by 106 publications

(25 citation statements)

References 37 publications

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“…The geometry of the microstructure is not the sole parameter controlling the roughness. Other experiments performed using sandstone reported a roughness exponent close to ζ = 0.75 ± 0.03 [21] disagreing with the observation of [17,18]. However, in this work [21] a fracture process zone measured by acoustic emission ahead of the fracture front was actually present while in the latter experiments [17,18] such zone was not existing.…”

Section: Roughness Of the Fracture Wallssupporting

confidence: 80%

Influence of wall roughness on the geometrical, mechanical and transport properties of single fractures

Auradou¹

2009

J. Phys. D: Appl. Phys.

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This article reviews the main features of the transport properties of single fractures. A particular attention paid to fractures in geological materials which often display a roughness covering a broad range of length scales. Because of the small distance separating the fracture walls, the surface roughness is a key parameter influencing the structure of the void space. Studies devoted to the characterization of the surface roughness are presented as well as works aimed at characterizing the void space geometry. The correlation of the free space is found to be crucially function of the failure mechanism (brittle, quasi brittle or plastic...) but also of possible shear displacements during the failure. The influence of the surface roughness on the mechanical behavior of fractures under a normal load and a shear stress is also described. Finally, experimental, numerical and theoretical works devoted to the study of the influence of the fracture void geometry on the permeability and on the hydrodynamic dispersion of a dissolved species are discussed.

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Section: Roughness Of the Fracture Wallssupporting

confidence: 80%

Influence of wall roughness on the geometrical, mechanical and transport properties of single fractures

Auradou¹

2009

J. Phys. D: Appl. Phys.

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“…This is evidenced by many field observations of dykes, veins, and joints and field and laboratory experiments on man-made hydraulic fractures in petroleum engineering. Layering in solid materials in general is known to have strong effects on fracture propagation (e.g., Daniel and Ishai, 1994;Broberg, 1999;Brooks and Choudhury, 2002;Nasseri et al, 2006;Zhang et al, 2007;Tvergaard and Hutchinson, 2008). In the following section we explore hydrofracture emplacement in mechanically layered rocks in detail.…”

Section: Hydrofracture Tip Stressesmentioning

confidence: 99%

Effects of mechanical layering on hydrofracture emplacement and fluid transport in reservoirs

2013

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Fractures generated by internal fluid pressure, for example, dykes, mineral veins, many joints and man-made hydraulic fractures, are referred to as hydrofractures. Together with shear fractures, they contribute significantly to the permeability of fluid reservoirs such as those of petroleum, geothermal water, and groundwater. Analytical and numerical models show that-in homogeneous host rocks-any significant overpressure in hydrofractures theoretically generates very high crack tip tensile stresses. Consequently, overpressured hydrofractures should propagate and help to form interconnected fracture systems that would then contribute to the permeability of fluid reservoirs. Field observations, however, show that in heterogeneous and anisotropic, e.g., layered, rocks many hydrofractures become arrested or offset at layer contacts and do not form vertically interconnected networks. The most important factors that contribute to hydrofracture arrest are discontinuities (including contacts), stiffness changes between layers, and stress barriers, where the local stress field is unfavorable to hydrofracture propagation. A necessary condition for a hydrofracture to propagate to the surface is that the stress field along its potential path is everywhere favorable to extension-fracture formation so that the probability of hydrofracture arrest is minimized. Mechanical layering and the resulting heterogeneous stress field largely control whether evolving hydrofractures become confined to single layers (stratabound fractures) or not (non-stratabound fractures) and, therefore, if a vertically interconnected fracture system forms. Non-stratabound hydrofractures may propagate through many layers and generate interconnected fracture systems. Such systems commonly reach the percolation threshold and largely control the overall permeability of the fluid reservoirs within which they develop.

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“…The size of the FPZ and pre-critical stable crack growth are the key factors affecting the fracture toughness. Nasseri et al (2006) measured the fracture toughness and acoustic emission activity in brittle rocks. They found that the variation of fracture toughness is caused by the pre-existing microcrack density and its orientation with respect to the fracture propagation direction.…”

Section: List Of Symbolsmentioning

confidence: 99%

Evaluation of Mode I Fracture Toughness Assisted by the Numerical Determination of K-Resistance

et al. 2014

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The fracture toughness of a rock often varies depending on the specimen shape and the loading type used to measure it. To investigate the mode I fracture toughness using semi-circular bend (SCB) specimens, we experimentally studied the fracture toughness using SCB and chevron bend (CB) specimens, the latter being one of the specimens used extensively as an International Society for Rock Mechanics (ISRM) suggested method, for comparison. The mode I fracture toughness measured using SCB specimens is lower than both the level I and level II fracture toughness values measured using CB specimens. A numerical study based on discontinuum mechanics was conducted using a two-dimensional distinct element method (DEM) for evaluating crack propagation in the SCB specimen during loading. The numerical results indicate subcritical crack growth as well as sudden crack propagation when the load reaches the maximum. A Kresistance curve is drawn using the crack extension and the load at the point of evaluation. The fracture toughness evaluated by the K-resistance curve is in agreement with the level II fracture toughness measured using CB specimens. Therefore, the SCB specimen yields an improved value for fracture toughness when the increase of K-resistance with stable crack propagation is considered.Keywords Fracture toughness Á SCB specimen Á Fracture process zone Á DEM Á K-resistance curve List of Symbols

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Fracture Toughness Measurements and Acoustic Emission Activity in Brittle Rocks

Cited by 106 publications

References 37 publications

Influence of wall roughness on the geometrical, mechanical and transport properties of single fractures

Influence of wall roughness on the geometrical, mechanical and transport properties of single fractures

Effects of mechanical layering on hydrofracture emplacement and fluid transport in reservoirs

Evaluation of Mode I Fracture Toughness Assisted by the Numerical Determination of K-Resistance

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