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

Abstract

[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,

The interactions between shear bands and rigid lamellar inclusions in a ductile metal matrix

“…Moreover, the results pertaining to low strain hardening (NZ0.1, figure 5b) show that the bands closest to the stiffener line are privileged, so that something resembling a 'thick' shear band parallel to the stiffener appears, a finding in qualitative agreement with the experimental results of Misra & Mandal (2007).…”

“…Therefore, the presence of defects is crucially important in the understanding of failure in ductile matrix composites, particularly when defects involve stress concentrations, as is the case of the lamellar suspensions experimentally investigated in metals (Ö ztürk et al 1991), plastics ) and rocks (Misra & Mandal 2007). In these composites, only an analytical solution can detail the structure of singularities related to the sharpness of both lamellae and shear bands, while numerical approaches can hardly have the necessary resolution.…”

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

“…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.…”

“…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).…”

Thermodynamic equilibrium at heterogeneous pressure

“…4 in Tajčmanová et al 2015). Studies of stress perturbations around inclusions involving also plastic deformation investigate the importance of non-homogeneous stress (and pressure) distribution on the formation of shear zones in polymineralic rocks (Misra and Mandal 2007). Whereas viscous stresses relax over time, elastic stresses will always be there as long as there is an applied load.…”