Localization of deformation and failure around elliptical perforations based on a polar continuum

Papanastasiou, Panos

doi:10.1007/s004660000183

Cited by 14 publications

(8 citation statements)

References 17 publications

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“…As mentioned earlier the Cosserat model switches to the localized branch smoothly, without the need to perturb the primary solution with an imperfection. Similar computations and extensive analysis can be found in (Papanastasiou andVardoulakis, 1992, 1994;Papamichos, 2010). The predicted failure mode is depicted in Figure 3 where the contours of the plastic strain have been drawn in the vicinity of the hole after localization of deformation has taken place.…”

Section: Failure In Thick Walled Cylinder Testsupporting

confidence: 61%

“…According to Figure 1 we distinguish among the primary branch (I) and the secondary branch (II), which intersects (I) at the bifurcation point. We found that the Cosserat model follows smoothly the branch (III) without the need to disturb the solution with the eigenvector of the zero eigenvalue (Papanastasiou andVardoulakis, 1992, 1994). The studies mentioned above were restricted in the primary path and to the location of the bifurcation point (Vardoulakis and Papanastasiou, 1988;Papanastasiou and Vardoulakis, 1989;Papanastasiou and Durban, 1995;Papamichos and van den Hoek, 1995).…”

Section: Introductionmentioning

confidence: 82%

“…The material parameters are those of the Castlegate sandstone which were used in the above computations. More computations and details can be found in Papanastasiou (2000). It is demonstrated that it is essential to carry out advanced localization analysis in order to reach correct results upon which a new perforation shape design can be based.…”

Section: Stability Analysis Of Elliptical Shape Perforationsmentioning

confidence: 99%

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Computational post failure analysis with Cosserat continuum

Papanastasiou¹

2010

European Journal of Environmental and Civil Engineering

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We present computational analysis of geomechanics problems in the post failure regime based on a Cosserat material modelThe introduction of internal length (related to grain size) in the Cosserat model improves the computational stability and allows for robust progressive localization modelling. The model is capable of predicting advanced deformation modes such as surface buckling and localization of deformation in shear bands that may cause failure in a structure. The obtained results show clearly a progressive failure mechanism and the computed modes are in a good qualitative agreement with laboratory and field observations. As illustration we present results of two applications from petroleum engineering: the modelling of failure in thick walled cylinder test and the stability of elliptical shape perforations.

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Section: Failure In Thick Walled Cylinder Testsupporting

confidence: 61%

Section: Introductionmentioning

confidence: 82%

Section: Stability Analysis Of Elliptical Shape Perforationsmentioning

confidence: 99%

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Computational post failure analysis with Cosserat continuum

Papanastasiou¹

2010

European Journal of Environmental and Civil Engineering

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“…Hole size effects have also been analyzed and the results were compared with experimental data [12]. The failure of elliptical holes has also been analyzed numerically with Cosserat elastoplasticity [13] and has been shown that elliptical holes are stronger as long as their axes ratio is higher than the far-field stress anisotropy ratio.…”

Section: Introductionmentioning

confidence: 99%

Borehole failure analysis in a sandstone under anisotropic stresses

Papamichos

2009

Num Anal Meth Geomechanics

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SUMMARYBorehole failure under anisotropic stresses in a sandstone is analyzed numerically for various borehole sizes using a nonlinear elastic-plastic constitutive model for a Cosserat continuum. Borehole failure is identified as macroscopic failure of the borehole through the development of shear bands and breakouts. The results compare well both qualitatively and quantitatively with experimental results from polyaxial tests on Red Wildmoor sandstone. They show that the hole size effect of the borehole failure strength is independent of the far-field stress anisotropy and follows a 2 5 power law of the hole size. A similar scale effect equation with a 4 5 power law is proposed for the scale effect of the maximum plastic shear strain at failure. This equation can be useful for better predicting hole-size-dependent failure with standard codes based on classical continua. The effect of stress anisotropy on the borehole failure stress is found to be independent of the hole size. The failure stress decreases linearly to 40% as the stress anisotropy increases. However, the maximum plastic shear strain at failure is stress anisotropy independent and therefore the critical plastic shear strain for failure is only hole-size dependent.

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“…For bedded salt rocks consisting of several different rock types the volume fractions of the materials can be determined from the dissoluble material ratios obtained from borehole cores through the formations. It is noted that the introduction of h in the form of Equation (27) gives the components of the generalized stress and strain vectors the same dimensions, as in References [23,24]. So far, a new three-dimensional Cosserat-like medium constitutive model, in which the influence of bending is taken into account, is proposed for bilaminated layered salt rocks.…”

Section: Three-dimensional Cosserat-like Constitutive Relationshipmentioning

confidence: 97%

A new Cosserat‐like constitutive model for bedded salt rocks

Yang

Daemen

et al. 2009

Num Anal Meth Geomechanics

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SUMMARYSalt rocks are commonly used as geologic host rocks for storage of gas and crude oil, and are being considered for the disposal of radioactive waste. Different from the salt rock domes in many countries, the salt rock formations in China are usually laminar with many alternating layers, i.e. rock salt, anhydrite, and/or mudstone. Considering the unique stratigraphic characteristics of these salt rocks, a new Cosseratlike medium constitutive model is proposed in order to facilitate efficient modeling of the mechanical behavior of these formations. In this model, a new representative volume element, containing two different layers, is employed to simulate the compatibility of the meso-displacement between two different layers and also the bending effect. A new method for the deformation and failure analysis of bedded salt rocks is derived therefrom. Having the macro-average stresses, the conventional stresses in the different layers can be obtained in sequence. The conventional stresses can then be utilized in a routine way for the strength and failure analysis. For the initial numerical modeling, the new Cosserat-like medium is reduced to a transversely isotropic one. The simplified constitutive model for layered media is then implemented into FLAC3D codes. A test sample validates that the results by using the numerical model are in good agreement with that by using the built-in model, and the mesh size for the new model is reduced greatly. Finally, an application for the stability of oil storage caverns in deep thinly bedded salt rocks is carried out. The effects on convergence of storage caverns and on the failure of surrounding rock due to the presence of the mudstone interlayers (hard phase) are discussed in detail.

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Localization of deformation and failure around elliptical perforations based on a polar continuum

Cited by 14 publications

References 17 publications

Computational post failure analysis with Cosserat continuum

Computational post failure analysis with Cosserat continuum

Borehole failure analysis in a sandstone under anisotropic stresses

A new Cosserat‐like constitutive model for bedded salt rocks

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