On a viscoplastic model for rocks with mechanism-dependent characteristic times

Fossum, A.F.; Brannon, Rebecca M.

doi:10.1007/s11440-006-0010-z

Cited by 50 publications

(22 citation statements)

References 12 publications

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“…On the other hand, the kinematic hardening corresponds to a translation of the elastic domain. The use of this formulation is motivated by the observation of nonlinear behavior during indentation unloading (see Section 2) and its use in a model for rock material can be found e.g., in 37 . The kinematic hardening variable (i.e.…”

Section: Inelastic Flow Hardening and Damagementioning

confidence: 99%

Experimental and numerical study of Kuru granite under confined compression and indentation

Tkalich

Fourmeau

Kane

et al. 2016

International Journal of Rock Mechanics and Mining Sciences

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Section: Inelastic Flow Hardening and Damagementioning

confidence: 99%

Experimental and numerical study of Kuru granite under confined compression and indentation

Tkalich

Fourmeau

Kane

et al. 2016

International Journal of Rock Mechanics and Mining Sciences

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“…There have recently been several successful applications of this model for predicting fracture of ceramics under static and dynamic loading (Fossum and Brannon 2006). The M-C criterion is a special case of the Sandia GeoModel (Fossum and Brannon 2005).…”

Section: Introductionmentioning

confidence: 99%

Application of extended Mohr–Coulomb criterion to ductile fracture

2009

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The Mohr-Coulomb (M-C) fracture criterion is revisited with an objective of describing ductile fracture of isotropic crack-free solids. This criterion has been extensively used in rock and soil mechanics as it correctly accounts for the effects of hydrostatic pressure as well as the Lode angle parameter. It turns out that these two parameters, which are critical for characterizing fracture of geo-materials, also control fracture of ductile metals Xue 2007;Barsoum 2006;Wilkins et al. 1980). The local form of the M-C criterion is transformed/extended to the spherical coordinate system, where the axes are the equivalent strain to fractureε f , the stress triaxiality η, and the normalized Lode angle parameterθ . For a proportional loading, the fracture surface is shown to be an asymmetric function ofθ . A detailed parametric study is performed to demonstrate the effect of model parameters on the fracture locus. It was found that the M-C fracture locus predicts almost exactly the exponential decay of the material ductility with stress triaxiality, which is in accord with theoretical analysis of Rice and Tracey (1969) and the empirical equation of Hancock and Mackenzie (1976), Johnson and Cook

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“…Other concerns are that Eqs. (4.25) and (4.26) have not been well validated in tension, and the current (2008) implementation does not consistently incorporate a "z-tensor" of the type discussed by Brannon [14] that is required in incremental plasticity with elastic-plastic coupling.…”

Section: Shear and Bulk Modulimentioning

confidence: 99%

Survey of four damage models for concrete.

Leelavanichkul

Brannon

2009

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Four conventional damage plasticity models for concrete, the Karagozian and Case model (K&C), the Riedel-Hiermaier-Thoma model (RHT), the Brannon-Fossum model (BF1), and the Continuous Surface Cap Model (CSCM) are compared. The K&C and RHT models have been used in commercial finite element programs many years, whereas the BF1 and CSCM models are relatively new. All four models are essentially isotropic plasticity models for which "plasticity" is regarded as any form of inelasticity. All of the models support nonlinear elasticity, but with different formulations. All four models employ three shear strength surfaces. The "yield surface" bounds an evolving set of elastically obtainable stress states. The "limit surface" bounds stress states that can be reached by any means (elastic or plastic). To model softening, it is recognized that some stress states might be reached once, but, because of irreversible damage, might not be achievable again. In other words, softening is the process of collapse of the limit surface, ultimately down to a final "residual surface" for fully failed material. The four models being compared differ in their softening evolution equations, as well as in their equations used to degrade the elastic stiffness. For all four models, the strength surfaces are cast in stress space. For all four models, it is recognized that scale effects are important for softening, but the models differ significantly in their approaches. The K&C documentation, for example, mentions that a particular material parameter 3 affecting the damage evolution rate must be set by the user according to the mesh size to preserve energy to failure. Similarly, the BF1 model presumes that all material parameters are set to values appropriate to the scale of the element, and automated assignment of scale-appropriate values is available only through an enhanced implementation of BF1 (called BFS) that regards scale effects to be coupled to statistical variability of material properties. The RHT model appears to similarly support optional uncertainty and automated settings for scale-dependent material parameters. The K&C, RHT, and CSCM models support rate dependence by allowing the strength to be a function of strain rate, whereas the BF1 model uses Duvaut-Lion viscoplasticity theory to give a smoother prediction of transient effects. During softening, all four models require a certain amount of strain to develop before allowing significant damage accumulation. For the K&C, RHT, and CSCM models, the strain-to-failure is tied to fracture energy release, whereas a similar effect is achieved indirectly in the BF1 model by a time-based criterion that is tied to crack propagation speed.4

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On a viscoplastic model for rocks with mechanism-dependent characteristic times

Cited by 50 publications

References 12 publications

Experimental and numerical study of Kuru granite under confined compression and indentation

Experimental and numerical study of Kuru granite under confined compression and indentation

Application of extended Mohr–Coulomb criterion to ductile fracture

Survey of four damage models for concrete.

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