Earth Systems Science Computational Centre Publications - UQ eSpace

Convective instability of 3-D fluid-saturated geological fault zones heated from below

2007-08-13T00:00:00Z

We conduct a theoretical analysis to investigate the convective instability of 3-D fluid-saturated geological fault zones when they are heated uniformly from below. In particular, we have derived exact analytical solutions for the critical Rayleigh numbers of different convective flow structures. Using these critical Rayleigh numbers, three interesting convective flow structures have been identified in a geological fault zone system. It has been recognized that the critical Rayleigh numbers of the system have a minimum value only for the fault zone of infinite length, in which the corresponding convective flow structure is a 2-D slender-circle flow. However, if the length of the fault zone is finite, the convective flow in the system must be 3-D. Even if the length of the fault zone is infinite, since the minimum critical Rayleigh number for the 2-D slender-circle flow structure is so close to that for the 3-D convective flow structure, the system may have almost the same chance to pick up the 3-D convective flow structures. Also, because the convection modes are so close for the 3-D convective flow structures, the convective flow may evolve into the 3-D finger-like structures, especially for the case of the fault thickness to height ratio approaching zero. This understanding demonstrates the beautiful aspects of the present analytical solution for the convective instability of 3-D geological fault zones, because the present analytical solution is valid for any value of the ratio of the fault height to thickness. Using the present analytical solution, the conditions, under which different convective flow structures may take place, can be easily determined.

Correlation length evolution in cellular automata with long-range stress transfer

2007-08-24T00:00:00Z

Correlation length evolution in cellular automata wtih long-range stress transfer

2008-06-06T00:00:00Z

Coulomb stress changes due to Queensland earthquakes and the implications for seismic risk assessment

Weatherley, D K — 2007-08-23T00:00:00Z

Cracks of higher modes in Cosserat continua

2007-08-27T00:00:00Z

Rotational degrees of freedom in Cosserat continua give rise to higher fracture modes. Three new fracture modes correspond to the cracks that are surfaces of discontinuities in the corresponding components of independent Cosserat rotations. We develop a generalisation of J- integral that includes these additional degrees of freedom. The obtained path-independent integrals are used to develop a criterion of crack propagation for a special type of failure in layered materials with sliding layers. This fracture propagates as a progressive bending failure of layers – a “bending crack that is, a crack that can be represented as a distribution of discontinuities in the layer bending. This situation is analysed using a 2D Cosserat continuum model. Semi-infinite bending crack normal to layering is considered. The moment stress concentrates along the line that is a continuation of the crack and has a singularity of the power − 1/4. A model of process zone is proposed for the case when the breakage of layers in the process of bending crack propagation is caused by a crack (microcrack in our description) growing across the layer adjacent to the crack tip. This growth is unstable (in the moment-controlled loading), which results in a typical descending branch of moment stress – rotation discontinuity relationship and hence in emergence of a Barenblatt-type process zone at the tip of the bending crack.

Critical Point Systems, self-organised critically, and earthquake forecasting

2008-06-06T00:00:00Z

Damage in step-overs may enable large cascading earthquakes

Finzi, Y. og Langer, S. — 2012-08-27T08:47:37Z

Seismic hazard analysis relies on the ability to predict whether an earthquake will terminate at a fault tip or propagate onto adjacent faults, cascading into a larger, more devastating event. While ruptures are expected to arrest at fault discontinuities larger than 4–5 km, scientists are often puzzled by much larger rupture jumps. Here we show that material properties between faults significantly affect the ability to arrest propagating ruptures. Earthquake simulations accounting for fault step-over zones weakened by accumulated damage provide new insights into rupture propagation. Revealing that lowered rigidity and material interfaces promote rupture propagation, our models show for the first time that step-overs as wide as 10 km may not constitute effective earthquake barriers. Our results call for re-evaluation of seismic hazard analyses that predict rupture length and earthquake magnitude based on historic records and fault segmentation models.

Dating and geochemical tracing of paleoseismic events

2007-08-23T00:00:00Z

Debris-flow deposits in an alluvial-plain succession: The Upper Triassic Callide Coal Measures of Queensland, Australia

Jorgensen, Peter J. og Fielding, Christopher R. — 2008-06-10T00:00:00Z

The Carnian-Rhaetian Callide Coal Measures are preserved in a small (22.5 km by 8 km), partially fault-bounded basin remnant in east-central Queensland, Australia. The <150 m thick coal-measure succession is interpreted to have accumulated during a phase of mild crustal extension that formed a series of discrete, intermontane basins in eastern Australia. The succession fines upward from a conglomerate-rich lower part into a finer-grained and coal-bearing upper section (including coal seams <34 m thick), and is interpreted as the deposits of an alluvial-plain environment. Anomalous, matrix-rich diamictites, breccias, and conglomerates have been recognized within the succession at several localities, in many cases interbedded with coals. These are interpreted as the product of debris flows. Two debris-flow lithofacies are recognized: (1) mixtures of fine carbonaceous material, clay, silt, sand, gravel, and volcaniclastic debris, and (2) breccias consisting principally of coal clasts in a coaly matrix with minor clastic and volcaniclastic debris. Facies 1 is found in sharp-based, simple or composite bodies (<15 m thick) that are elongate to lobate in plan (with some multi-lobate), and as much as at least 1500 m long and 600 m wide. Facies 2 is less common and occurs in sharp-based units as much as 1.5 m thick, at least 200 m in length, and 60 m in width. Both facies are characterized by abundant fine matrix and a very poorly sorted clast population, and show little internal organization or sedimentary structure other than variably developed imbrication of coarse clasts. Parts of some bodies show an erosional base (with up to several meters of coal removed), although a flat, apparently non-erosional contact is more common. The distribution of debris flows in the Callide Coal Measures shows a coincidence with mapped faults and interpreted structural lineaments. The debris flows may have been triggered by fault movements, which formed rupture topography on the flat alluvial plain, and caused destabilization of water-saturated clastic and organic sediments. Some debris-flow bodies may have been mounded, such that subsequent peat formation was restricted until those bodies were buried. The preservation of debris-flow units at different stratigraphic levels along mapped structures suggests multiple paleoseismic events or multiple debris-flow events along those structures. The mixing of volcaniclastic debris into debris-flow facies suggests that seismic events were coincident with (or perhaps caused by) nearby, explosive volcanic activity. The close relationship between debris-flow deposits and thick coal bodies on the inferred downthrown sides of faults at Callide further suggests that periodic, tectonic subsidence may have facilitated thick coal accumulation.

Deformation mechanism of the eastern Tibetan plateau: Insights from numerical models

2012-04-30T20:55:45Z

DEM Simulation of Rock Fragmentation and Size Distribution Under Different Loading Conditions

Wang, Y og Alonso-Marroquin, Fernando — 2009-05-20T00:00:00Z

Depositional environments for strata cored in CRP-3 (Cape Roberts Project), Victoria Land Basin, Antarctica: palaeoglaciological and palaeoclimatological inferences

2007-08-14T00:00:00Z

Cape Roberts Project drill core 3 (CRP-3) was obtained from Roberts ridge, a sea-floor high located at 77°S, 12 km offshore from Cape Roberts in western McMurdo Sound, Antarctica. The recovered core is about 939 m long and comprises strata dated as being early Oligocene (possibly latest Eocene) in age, resting unconformably on ∼ 116 m of basement rocks consisting of Palaeozoic Beacon Supergroup sediments. The core includes ten facies commonly occuring in five major associations that are repeated in particular sequences throughout the core and which are interpreted as representing different depositional environments through time. Depositional systems inferred to be represented in the succession include: outer shelf, inner shelf, nearshore to shoreface each under iceberg influence, deltaic and/or grounding-line fan, and ice proximal-ice marginal-subglacial (mass flow/rainout diamictite/subglacial till) singly or in combination. The record is taken to represent the initial talus/alluvial fan setting of a glaciated rift margin adjacent to the block-uplifted Transantarctic Mountains. Development of a deltaic succession upcore was probably associated with the formation of palaeo-Mackay valley with temperate glaciers in its headwaters. At that stage glaciation was intense enough to support glaciers ending in the sea elsewhere along the coast, but a local glacier was fluctuating down to the sea by the time the youngest part of CRP-3 was being deposited. Changes in palaeoenvironmental interpretations in this youngest part of the core are used to estimate relative glacial proximity to the drillsite through time. These inferred glacial fluctuations are compared with the global δ18O and Mg/Ca curves to evaluate the potential of glacial fluctuations on Antarctica for influencing these records of global change. Although the comparisons are tentative at present, the records do have similarities, but there are also some differences that require further evaluation.

Development of a Virtual Earth Simulator for Earthquake Micro-physics: LSMearth

Place, D. G. og Mora, P. R. og Abe, S. — 2008-06-06T00:00:00Z

Discrete and continuous models for dry masonry columns

Muhlhaus, HB og Sulem, J og Unterreiner, P — 2007-08-13T00:00:00Z

The dynamic response of dry masonry columns can be approximated with finite-difference equations. Continuum models follow by replacing the difference quotients of the discrete model by corresponding differential expressions. The mathematically simplest of these models is a one-dimensional Cosserat theory. Within the presented homogenization context, the Cosserat theory is obtained by making ad hoc assumptions regarding the relative importance of certain terms in the differential expansions. The quality of approximation of the various theories is tested by comparison of the dispersion relations for bending waves with the dispersion relation of the discrete theory. All theories coincide with differences of less than 1% for wave-length-block-height (L/h) ratios bigger than 2 pi. The theory based on systematic differential approximation remains accurate up to L/h = 3 and then diverges rapidly. The Cosserat model becomes increasingly inaccurate for L/h < 2 pi. However, in contrast to the systematic approximation, the wave speed remains finite. In conclusion, considering its relative simplicity, the Cosserat model appears to be the natural starting point for the development of continuum models for blocky structures.

Discussion of Gorter & Glikson: Talundilly, Western Queensland, Australia: geophysical and petrological evidence for a 84 km-large structure and an Early Cretaceous impact cluster

Heidecker, E. J. — 2012-12-16T00:43:24Z

Distribution of climatic indicators in the Permian succession of the Bowen Basin, Australia

Jones, A. og Fielding, C. R. — 2008-06-06T00:00:00Z

3D mesh generation in geocomputing

Xing, Huilin og Yu, Wenhui og Zhang, Ji — 2010-04-26T00:00:00Z

Dorothy Hill, A.C., C.B.E.

Campbell, K. S. W. og Jell, J. S. — 2008-06-10T00:00:00Z

Double diffusion-driven convective instability of three-dimensional fluid-saturated geological fault zones heated from below

2007-08-13T00:00:00Z

We conduct a theoretical analysis to investigate the double diffusion-driven convective instability of three-dimensional fluid-saturated geological fault zones when they are heated uniformly from below. The fault zone is assumed to be more permeable than its surrounding rocks. In particular, we have derived exact analytical solutions to the total critical Rayleigh numbers of the double diffusion-driven convective flow. Using the corresponding total critical Rayleigh numbers, the double diffusion-driven convective instability of a fluid-saturated three-dimensional geological fault zone system has been investigated. The related theoretical analysis demonstrates that: (1) The relative higher concentration of the chemical species at the top of the three-dimensional geological fault zone system can destabilize the convective flow of the system, while the relative lower concentration of the chemical species at the top of the three-dimensional geological fault zone system can stabilize the convective flow of the system. (2) The double diffusion-driven convective flow modes of the three-dimensional geological fault zone system are very close each other and therefore, the system may have the similar chance to pick up different double diffusion-driven convective flow modes, especially in the case of the fault thickness to height ratio approaching 0. (3) The significant influence of the chemical species diffusion on the convective instability of the three-dimensional geological fault zone system implies that the seawater intrusion into the surface of the Earth is a potential mechanism to trigger the convective flow in the shallow three-dimensional geological fault zone system.

Drilling-constrained 3D gravity interpretation

2008-06-10T00:00:00Z

In interpretation of gravity surveys, it is essential to exploit all the information available from drill holes in order to reduce the ambiguity. Accordingly, a new modelling and inversion methodology has been developed to expedite joint geological/geophysical interpretation of gravity data. The key features of the approach are the enforcement of drill constraints (pierce points) and the imposition of density bounds on geological formations and basement. 3D density models are constructed from close-packed vertical rectangular prisms with internal contacts. Prism tops honour topography, so that terrain effects are modelled, not 'corrected'. Detailed local models can be embedded in regional models to permit fitting of full free-air data, not residual gravity. The geological sense of models is preserved during inversion: the shape and density of homogeneous geological units are adjusted iteratively, subject to the drilling and density constraints. The methodology is illustrated using data from an advanced exploration project in South Australia. Integrated interpretation of a drilled area has been undertaken in four stages. The first stage entailed construction of a 'regional' density model, satisfying gridded gravity data on a coarse mesh over a large area centred on the drill grid. Next, a local density model was created on a fine mesh for the drill grid area, based on drill intercepts and density logs. Thirdly, the detailed density model was inserted into the regional model. Finally, constrained inversion was performed, to adjust the local starting model until a fit to the free-air gravity data was achieved.

3D Simulations of Block Caving Flow Using ESyS-Particle

William Rodney Hancock og Weatherley, Dion K. — 2009-05-20T00:00:00Z

Dynamic compexity in cellular automata with long-range stress transfer

2008-06-06T00:00:00Z

Dynamic rupture in a 3-D particle-based simulation of a rough planar fault

Abe, S og Latham, S og Mora, P — 2007-08-15T00:00:00Z

An appreciation of the physical mechanisms which cause observed seismicity complexity is fundamental to the understanding of the temporal behaviour of faults and single slip events. Numerical simulation of fault slip can provide insights into fault processes by allowing exploration of parameter spaces which influence microscopic and macroscopic physics of processes which may lead towards an answer to those questions. Particle-based models such as the Lattice Solid Model have been used previously for the simulation of stick-slip dynamics of faults, although mainly in two dimensions. Recent increases in the power of computers and the ability to use the power of parallel computer systems have made it possible to extend particle-based fault simulations to three dimensions. In this paper a particle-based numerical model of a rough planar fault embedded between two elastic blocks in three dimensions is presented. A very simple friction law without any rate dependency and no spatial heterogeneity in the intrinsic coefficient of friction is used in the model. To simulate earthquake dynamics the model is sheared in a direction parallel to the fault plane with a constant velocity at the driving edges. Spontaneous slip occurs on the fault when the shear stress is large enough to overcome the frictional forces on the fault. Slip events with a wide range of event sizes are observed. Investigation of the temporal evolution and spatial distribution of slip during each event shows a high degree of variability between the events. In some of the larger events highly complex slip patterns are observed.

Dynamics of slab tear faults: Insights from numerical modelling

2010-04-18T00:00:00Z

Tear resistance at the edge of a slab is an important parameter controlling the evolution of subduction zones. However, compared with other subduction parameters such as plate strength, plate viscosity, plate thickness and trench width, the dynamics of tearing are poorly understood. Here we obtain a first-order understanding of the dynamics and morphology of subduction zones to resistance during tear propagation, by developing and using a novel computational modelling technique for subducting slabs, with side boundaries described by visco-plastic weak zones, developing into tear faults. Our 3D model is based upon a visco-plastic slab that sinks into the less dense mantle, generating poloidal and toroidal flows. The asthenospheric mantle field is static and only develops flow due to the subducting slab. We use the finite element code eScript/Finley and the level set method to describe the lithosphere to solve this fluid dynamics problem. Our results show the importance of tear resistance for the speed of trench migration and for shaping the final geometry of subduction systems. We show that slab tearing along a weak layer can result in a relatively straight slab hinge shape, while increasing the strength in the weak layer results in the curvature of the hinge increasing substantially. High tear resistance at the slab edges may hinder rollback to the extent that the slab becomes stretched and recumbently folded at the base of the domain. Tear resistance also controls whether the subducting lithosphere can experience accelerating rollback velocities or a constant rollback velocity. © 2009 Elsevier B.V. All rights reserved.

Earthquake forecasting: retrospective studies in Australia - The Newcastle and Burra earthquakes - and numberical simulation of the physical process

2008-06-06T00:00:00Z

Earthquake processes: Physical modelling, numerical simulation and data analysis - Part I

2007-10-17T00:00:00Z

Earthquake Processes: Physical Modelling, Numerical Simulation and Data Analysis Part II

2007-08-22T00:00:00Z

Earthquakes : Simulations, Sources and Tsunamis

2009-04-08T00:00:00Z

Earthquake trend around Sumatra indicated by a New Implementation of LURR Method

2009-04-08T00:00:00Z

The current implementation of LURR (Load/Unload Response Ratio) theory has shown promise in intermediate to short-term earthquake forecasting through past practice, but has also met difficulties at the same time. In this paper a new implementation of LURR method is presented to address one of the problems. The major change in the new implementation is that LURR values will result from a calculated maximum faulting orientation (MFO) instead of any focal mechanism selected by users. After comparison with the world stress map, the calculated MFO has been found to be in good agreement with the observation from the regional tectonic stress regime. The MFO pattern in the Indonesia region has a special feature which may be related to the unique subduction complexity. The MFO pattern in the Sumatra region in general is different from that in the Java region after the 2004 M 9.0 Sumatra Andaman Islands earthquake. This phenomenon may be supported by the evidence of the recent observation that a section in the southern part of the Sumatran arc is locked. Furthermore, the MFO pattern before the 2004 main shock is different from that after the event. Retrospective examination of the Indonesia region by means of this implementation can produce significant LURR anomaly not only prior to the 2004 main shock but also before the 2006 M 7.7 South Java earthquake. Therefore future great earthquakes might favorably be forecasted if the LURR anomaly detected by MFO method could be considered a precursor.

Earthquake trend around Sumatra region indicated by a new LURR implementation

2008-02-19T00:00:00Z

Earth Systems simulations on SGI Altix systems using Python

2007-08-23T00:00:00Z

Effect of material anisotropy on the onset of convective flow in three-dimensional fluid-saturated faults

2007-08-13T00:00:00Z

In order to investigate the effect of material anisotropy on convective instability of three-dimensional fluid-saturated faults, an exact analytical solution for the critical Rayleigh number of three-dimensional convective flow has been obtained. Using this critical Rayleigh number, effects of different permeability ratios and thermal conductivity ratios on convective instability of a vertically oriented three-dimensional fault have been examined in detail. It has been recognized that (1) if the fault material is isotropic in the horizontal direction, the horizontal to vertical permeability ratio has a significant effect on the critical Rayleigh number of the three-dimensional fault system, but the horizontal to vertical thermal conductivity ratio has little influence on the convective instability of the system, and (2) if the fault material is isotropic in the fault plane, the thermal conductivity ratio of the fault normal to plane has a considerable effect on the critical Rayleigh number of the three-dimensional fault system, but the effect of the permeability ratio of the fault normal to plane on the critical Rayleigh number of three-dimensional convective flow is negligible.

Effect of rolling on dissipation in fault gouges

2007-08-15T00:00:00Z

Sliding and rolling are two outstanding deformation modes in granular media. The first one induces frictional dissipation whereas the latter one involves deformation with negligible resistance. Using numerical simulations on two-dimensional shear cells, we investigate the effect of the grain rotation on the energy dissipation and the strength of granular materials under quasistatic shear deformation. Rolling and sliding are quantified in terms of the so-called Cosserat rotations. The observed spontaneous formation of vorticity cells and clusters of rotating bearings may provide an explanation for the long standing heat flow paradox of earthquake dynamics.

Effects of a non-coaxial flow rule on shear bands in viscous-plastic materials

2011-10-13T00:00:00Z

Effects of geological inhomogeneity on high Rayleigh number steady state heat and mass transfer in fluid-saturated porous media heated from below

Zhao, CB og Muhlhaus, HB og Hobbs, BE — 2007-08-13T00:00:00Z

A parametric study is carried out to investigate how geological inhomogeneity affects the pore-fluid convective flow field, the temperature distribution, and the mass concentration distribution in a fluid-saturated porous medium. The related numerical results have demonstrated that (1) the effects of both medium permeability inhomogeneity and medium thermal conductivity inhomogeneity are significant on the pore-fluid convective flow and the species concentration distribution in the porous medium; (2) the effect of medium thermal conductivity inhomogeneity is dramatic on the temperature distribution in the porous medium, but the effect of medium permeability inhomogeneity on the temperature distribution may be considerable, depending on the Rayleigh number involved in the analysis; (3) if the coupling effect between pore-fluid flow and mass transport is weak, the effect of the Lewis number is negligible on the pore-fluid convective flow and temperature distribution, hut it is significant on the species concentration distribution in the medium.

Effects of hot intrusions on pore-fluid flow and heat transfer in fluid-saturated rocks

2007-08-13T00:00:00Z

We use the finite element method to solve coupled problems between pore-fluid flow and heat transfer in fluid-saturated porous rocks. In particular, we investigate the effects of both the hot pluton intrusion and topographically driven horizontal flow on the distributions of the pore-flow velocity and temperature in large-scale hydrothermal systems. Since general mineralization patterns are strongly dependent on distributions of both the pore-fluid velocity and temperature fields, the modern mineralization theory has been used to predict the general mineralization patterns in several realistic hydrothermal systems. The related numerical results have demonstrated that: (1) The existence of a hot intrusion can cause an increase in the maximum value of the pore-fluid velocity in the hydrothermal system. (2) The permeability of an intruded pluton is one of the sensitive parameters to control the pore-fluid flow, heat transfer and ore body formation in hydrothermal systems. (3) The maximum value of the pore-fluid velocity increases when the bottom temperature of the hydrothermal system is increased. (4) The topographically driven flow has significant effects on the pore-fluid flow, temperature distribution and precipitation pattern of minerals in hydrothermal systems. (5) The size of the computational domain may have some effects on the pore-fluid flow and heat transfer, indicating that the size of a hydrothermal system may affect the pore-fluid flow and heat transfer within the system. (C) 2003 Elsevier Science B.V. All rights reserved.

Effects of medium thermoelasticity on high Rayleigh number steady-state heat transfer and mineralization in deformable fluid-saturated porous media heated from below

Zhao, CB og Hobbs, BE og Muhlhaus, HB — 2007-08-13T00:00:00Z

In this paper, a solution method is presented to deal with fully coupled problems between medium deformation, pore-fluid flow and heat transfer in fluid-saturated porous media having supercritical Rayleigh numbers. To validate the present solution method, analytical solutions to a benchmark problem are derived for some special cases. After the solution method is validated, a numerical study is carried out to investigate the effects of medium thermoelasticity on high Rayleigh number steady-state heat transfer and mineralization in fluid-saturated media when they are heated from below. The related numerical results have demonstrated that: (1) medium thermoelasticity has a little influence on the overall pattern of convective pore-fluid flow, but it has a considerable effect on the localization of medium deformation, pore-fluid flow, heat transfer and mineralization in a porous medium, especially when the porous medium is comprised of soft rock masses; (2) convective pore-fluid flow plays a very important role in the localization of medium deformation, heat transfer and mineralization in a porous medium. (C) 1999 Elsevier Science S.A. All rights reserved.

Efficient implementation of complex particle shapes in the Lattice Solid Model

Abe, S. og Mora, P. R. — 2007-08-24T00:00:00Z

Efficient implementation of complex particle shapes in the lattice solid model

Abe, S. og Mora, P. R. — 2007-10-17T00:00:00Z

The lattice solid model is a particle based simulation model for the study of earthquake micro-physics and rock mechanics. It consists of particles interacting by various types of mechanisms such as elastic-brittle forces and friction. Results of laboratory experiments have shown that the grain shape has a major influence on the frictional properties of fault gouge. In order to enable realistic simulations it is thus important to include the capability to model non-spherical particles into the simulation software. To achieve this goal a new class of particles with variable shapes have been implemented in the lattice solid model. The shape of the particles is described by an arbitrary number of piecewise spherical patches. This leads to a good balance between the computational cost of the contact detection and calculation of interactions between particles and the range of particle shapes available.

Efficient solvers for incompressible fluid flows in geosciences

Amirbekyan, A. og Gross, L. — 2008-08-18T00:00:00Z

Saddle point problems involving large systems of linear equations arise in a wide variety of applications in computational science and engineering. A variety of solvers have been developed for these type of problems typically with specific applications in mind. In this paper we will focus on saddle point problems as they arise from incompressible ﬂuid ﬂow problems in applications in geosciences. They are characterized through a spatially variable viscosity when modeling temperature dependencies (e.g. in Earth mantel convection models) or moving material interfaces (e.g. in subduction zones simulation and numerical volcano models). In this paper we will give an overview on some of the iterative techniques that can be used and discuss suitable preconditioning techniques. We will discuss the implementation of the schemes using the python module Escript and compare the efficiency of these schemes when applied to convection models on a parallel computer.

Ejection landslide at northern terminus of beichuan rupture triggered by the 2008 Mw 7.9 Wenchuan earthquake

2010-11-07T00:00:00Z

Elasticity and strength of partially sintered ceramics

2011-10-14T00:00:00Z

A discrete element model for the elastic and fracture behavior of partially sintered ceramics is presented. It accounts for the granular character of the material when a large amount of porosity (typically >0.2–0.4) is left after sintering. The model uses elastic force-displacement laws to represent the bond formed between particles during sintering. Bond fracture in tension and shearing is accounted for in the model. Realistic numerical microstructures are generated using a sintering model on random particle packings. In particular, packings with fugitive pore formers are used to create partially sintered microstructures with large pores. The effective elastic response and the strength of these microstructures are calculated in tension and compression. The link between important microstructural features such as bond size or coordination number and macroscopic behavior is investigated. In particular, it is shown that porosity alone is not sufficient to account for the mechanical properties of a partially sintered material.

Elasticity, yielding and episodicity in simple models of mantle convection

2007-08-23T00:00:00Z

Elasticity, Yielding and episodicity in simple models of mantle convection

2007-08-23T00:00:00Z

Elasticity, yielding and episodicity in simple models of mantle convection

2007-08-15T00:00:00Z

We explore the implications of refinements in the mechanical description of planetary constituents on the convection modes predicted by finite-element simulations. The refinements consist in the inclusion of incremental elasticity, plasticity (yielding) and multiple simultaneous creep mechanisms in addition to the usual visco-plastic models employed in the context of unified plate-mantle models. The main emphasis of this paper rests on the constitutive and computational formulation of the model. We apply a consistent incremental formulation of the non-linear governing equations avoiding the computationally expensive iterations that are otherwise necessary to handle the onset of plastic yield. In connection with episodic convection simulations, we point out the strong dependency of the results on the choice of the initial temperature distribution. Our results also indicate that the inclusion of elasticity in the constitutive relationships lowers the mechanical energy associated with subduction events.

Elasticity, Yielding and Episodicity in Simple Models of Mantle Convection

2005-10-07T00:00:00Z

We explore the implications of refinements in the mechanical description of planetary constituents on the convection modes predicted by finite element simulations. The refinements consist in the inclusion of incremental elasticity, plasticity (yielding) and multiple simultaneous creep mechanisms in addition to the usual visco-plastic models employed in the context of unified plate-mantle models. The main emphasis of this paper rests on the constitutive and computational formulation of the model. We apply a consistent incremental formulation of the non-linear governing equations avoiding the computationally expensive iterations that are otherwise necessary to handle the onset of plastic yield. In connection with episodic convection simulations, we point out the strong dependency of the results on the choice of the initial temperature distribution. Our results also indicate that the inclusion of elasticity in the constitutive relationships lowers the mechanical energy associated with subduction events.

Elastodynamic simulation of fault system dynamics

Mora, P. R. og Weatherley, D. K. — 2007-08-24T00:00:00Z

Emergent anisotropy and flow alignment in viscous rock

Muhlhaus, H. B. og Moresi, L. og Cada, M. — 2007-08-15T00:00:00Z

A novel class of nonlinear, visco-elastic rheologies has recently been developed by MUHLHAUS et al. (2002a, b). The theory was originally developed for the simulation of large deformation processes including folding and kinking in multi-layered visco-elastic rock. The orientation of the layer surfaces or slip planes in the context of crystallographic slip is determined by the normal vector the so-called director of these surfaces. Here the model (MUHLHAUS et al., 2002a, b) is generalized to include thermal effects; it is shown that in 2-D steady states the director is given by the gradient of the flow potential. The model is applied to anisotropic simple shear where the directors are initially parallel to the shear direction. The relative effects of textural hardening and thermal softening are demonstrated. We then turn to natural convection and compare the time evolution and approximately steady states of isotropic and anisotropic convection for a Rayleigh number Ra=5.64x10(5) for aspect ratios of the experimental domain of 1 and 2, respectively. The isotropic case has a simple steady-state solution, whereas in the orthotropic convection model patterns evolve continuously in the core of the convection cell, which makes only a near-steady condition possible. This near-steady state condition shows well aligned boundary layers, and the number of convection cells which develop appears to be reduced in the orthotropic case. At the moderate Rayleigh numbers explored here we found only minor influences in the change from aspect ratio one to two in the model domain.

Emergent anisotropy and flow alignment in viscous rock

Muhlhaus, H. B. og Moresi, L. og Cada, M. — 2007-08-15T00:00:00Z

Energy and averages in the mechanics of granular materials

Muhlhaus, HB og Hornby, P — 2007-08-13T00:00:00Z

We derive a general thermo-mechanical theory for particulate materials consisting of granules of arbitrary whose material points possess three translational and three independent rotational degrees of freedom. Additional field variables are the translational and rotational granular temperatures, the kinetic energies shape and size. The kinematics of granulate is described within the framework of a polar continuum theory of the velocity and spin fluctuations respectively and the usual thermodynamic temperature. We distinguish between averages over particle categories (averages in mass/velocity and moment of inertia/spin space, respectively) and particle phases where the average extends over distinct subsets of particle categories (multi phase flows). The relationship between the thermal energy in the granular system and phonon energy in a molecular system is briefly discussed in the main body of the paper and discussed in detail in the Appendix A. (C) 2001 Elsevier Science B.V. All rights reserved.