Role of weak flaws in nucleation of shear zones: an experimental and theoretical study

Mandal, Nibir; Misra, S.; Samanta, Susanta Kumar

doi:10.1016/j.jsg.2004.01.001

Cited by 26 publications

(21 citation statements)

References 24 publications

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“…Also, the strain-induced rotation and motion of individual or multiple clasts within a deforming matrix was investigated in analytical and numerical studies (Jiang, 2013;Mancktelow, 2011Mancktelow, , 2013Treagus, 2002;Treagus and Treagus, 2001). Numerical approaches were used to study localization induced by shear heating or inclusions (Kaus and Podladchikov, 2006;Mancktelow, 2002;Mandal et al, 2004;Mandal et al, 2003;Misra and Mandal, 2007;Regenauer-Lieb et al, 2006;Takeda and Griera, 2006).…”

Section: Stress Concentrationmentioning

confidence: 99%

“…For comparison, the stress increases around weak or strong spherical and ellipsoidal inclusions is about a factor of 2.3, inferred from experimental compression of inclusionbearing analogue materials (PMMA) and analytical calculations (Mandal et al, 2004;Misra and Mandal, 2007). Based on finite element modeling, stress enhancement around strong inclusion in a creeping matrix was estimated to range from 1.1-2.3 (Kenkmann and Dresen, 1998) to 3-8 (Dimanov et al, 2011), depending on the assumed rheology, viscosity contrast, shape of inclusions, and the degree of coupling.…”

Section: Stress Concentrationmentioning

confidence: 99%

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Strain localization during high temperature creep of marble: The effect of inclusions

et al. 2014

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The deformation of rocks in the Earth's middle and lower crust is often localized in ductile shear zones. To better understand the initiation and propagation of high-temperature shear zones induced by the presence of structural and material heterogeneities, we performed deformation experiments in the dislocation creep regime on Carrara marble samples containing weak (limestone) or strong (novaculite) second phase inclusions. The samples were mostly deformed in torsion at a bulk shear strain rate of ≈ 1.9x10 -4 s -1 to bulk shear strains γ between 0.02 and 2.9 using a Paterson-type gas deformation apparatus at 900°C temperature and 400 MPa confining pressure. At low strain, twisted specimens with weak inclusions show minor strain hardening that is replaced by strain weakening at γ > 0.1 -0.2.Peak shear stress at the imposed conditions is about 20 MPa, which is ≈8% lower than the strength of intact samples. Strain progressively localized within the matrix with increasing bulk strain, but decayed rapidly with increasing distance from the inclusion tip.Microstructural analysis shows twinning and recrystallization within this process zone, with a strong crystallographic preferred orientation, dominated by {r} and (c) slip in .Recrystallization-induced weakening starts at local shear strain of about 1 in the process zone, corresponding to a bulk shear strain of about 0.1. In contrast, torsion of a sample containing strong inclusions deformed at similar stress as inclusion-free samples but do not show localization. The experiments demonstrate that the presence of weak heterogeneities initiates localized creep at local stress concentrations around the inclusion tips. Recrystallizationinduced grain size reduction may only locally promote grain boundary diffusion creep. Accordingly, the bulk strength of the twisted aggregate is close to or slightly below the lower (isostress) strength bound, determined from the flow strength and volume fraction of matrix and inclusions.

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Section: Stress Concentrationmentioning

confidence: 99%

Section: Stress Concentrationmentioning

confidence: 99%

Strain localization during high temperature creep of marble: The effect of inclusions

et al. 2014

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“…Physical experiments were performed on Polymethylmethacrylate (PMMA), a kind of polymer material widely used for studying plastic deformation [ Bowden and Raha , 1970; Anand and Spitzig , 1982; Küntz et al , 1998; de Joussineau et al , 2003; Mandal et al , 2004; Wong et al , 2004]. PMMA deforms elastically up to a strain of 8–9%, and then yields plastically at a stress of 120 MPa.…”

Section: Experimental Approachmentioning

confidence: 99%

“…Some workers have employed viscoelastic or elastic‐plastic models to demonstrate the effects of inherent geometrical or mechanical imperfections in strain localization, giving rise to shear bands [cf. Tvergaard et al , 1981; Grujic and Mancktelow , 1998; Mandal et al , 2004]. Recently, Mancktelow [2002] has presented finite element models for the development of conjugate shear zones in viscoelastic inclusion matrix systems, where the inclusions were mechanically weaker than matrix.…”

Section: Introductionmentioning

confidence: 99%

Localization of plastic zones in rocks around rigid inclusions: Insights from experimental and theoretical models

Misra¹,

Mandal²

2007

J. Geophys. Res.

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[1] Employing analogue and numerical experiments, we investigated the process of plastic creep in the vicinity of stiff inclusions and its role in the formation of shear zones. Analogue experiments were performed on Polymethylmethacrylate (PMMA) models in pure shear (_ e % 10 À4 s À1 ), which produced shear zones at a bulk strain >0.05. The geometrical dispositions of the shear zones do not conform to the stress concentration map derived from the plane theory of elasticity. At the initial stage (e b < 0.03), PMMA models began to deform plastically in four discrete strain localizations, tracking the stress concentration map. These incipient plastic locations develop a new stress field, diverting the zone of plastic yield in the form of multiple shear zones. Finite element models were run to demonstrate the formation of shear zones in this mode. The pattern of shear zones varied with the inclusion geometry. Inclusions of low aspect ratio (<1.5) gave rise to multiple sets of shear zones in their neighborhood. The multiplicity of shear zones tends to progressively decrease toward a single set of conjugate zones when the inclusions have relatively high aspect ratio (>2) and are oriented at an angle (>20°) to the bulk compression direction. Inclusions with a large aspect ratio (>4) developed a single dominant shear zone. The experimental findings can be compared to inclusion-controlled shear zones from naturally deformed rocks.Citation: Misra, S., and N. Mandal (2007), Localization of plastic zones in rocks around rigid inclusions: Insights from experimental and theoretical models,

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“…Experimental (Bons and Jessell, 1999;Bauer et al, 2000;Mandal et al, 2004) and fi eld (Gapais et al, 1987;Burg, 1999;Burg et al, 2005;Fusseis et al, 2006) observations indicate that such an interconnected geometry might be intimately related to the mode of deformation localization and initiation of ductile shear zones. In addition, shear zone network development has implications for crustal weakening during deformation (Tullis and Yund, 1980) and fl uid fl ow in midlower crustal levels (Selverstone et al, 1991;Streit and Cox, 1998).…”

Section: Introduction Anastomosing Shear Zone Networkmentioning

confidence: 99%

Using network analyses within geographic information system technologies to quantify geometries of shear zone networks

Bhattacharyya

Czeck

2008

Geosphere

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Shear zones often exhibit anastomosing network geometries. Previous work hasshown that the detailed geometries of shear zone networks may partially control strain localization, fl uid fl ow, rheology, and deformation mechanisms. However, there are currently no reliable tools to quantify network geometries such as the distribution of individual small shear zones and the connectedness of the network. Geographic information systems (GIS) provide a potential method for quantifying network geometries. GISbased networking analyses have been used to quantify many different types of other networks, and here they are applied to shear zones. Many parameters within GIS-based networking analyses are useful for quantifying shear zone network geometries, including the connectivity parameters gamma and alpha, sinuosity, and vertex distribution patterns. Sets of these parameters are useful to quantitatively distinguish geometrical patterns of shear zone networks over a variety of conditions. Further quantifi cation of shear zone network geometries may allow us to link those geometries to shear zone mechanisms, strain accumulation, and rheology.

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Role of weak flaws in nucleation of shear zones: an experimental and theoretical study

Cited by 26 publications

References 24 publications

Strain localization during high temperature creep of marble: The effect of inclusions

Strain localization during high temperature creep of marble: The effect of inclusions

Localization of plastic zones in rocks around rigid inclusions: Insights from experimental and theoretical models

Using network analyses within geographic information system technologies to quantify geometries of shear zone networks

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