Modeling mantle convection using an internal state variable model framework

In the current study we developed an internal state variable (ISV) model based on the Bammann inelasticity internal state variable model (BIISV) to include damage, recrystallization, and texture development, which we then implemented into a mantle convection code, TERRA2D, to incorporate higher fidelity material behavior into mantle convection simulations. With experimental stress strain data found in the literature model constants for the BIISV model were determined for a number of geologic materials. The BIISV model was shown to be far superior to the steady state power law model currently used by the geologic community to capture the deformation of geologic materials. Once implemented and verified in TERRA2D the BIISV model revealed locations of hardened material that behaved like diverters in the cold thermal boundary layer that the power law model could never produce. These hardened regions could be a plausible reason for the current subduction zones present on the earth. We then altered the BIISV model equation to include the effects of damage, recrystallization, and texture development in order to model possible weakening mechanisms in the cold thermal boundary layer of the mantle. Inclusion of damage and recrystallization allowed the cold thermal boundary layer to mobilize and plunge downward into the hotter region below. Texture development increased the intensity of rotational flow within the hotter zone as cold boundary material plunged downward which aided in destabilizing the cold upper thermal boundary layer. The inclusion of an internal state variable model with damage, recrystallization, and texture development represents a significant advancement in handling deformational physics for mantle phenomena in a comprehensive, unified, and automatic manner

Demystifying the dendralenes

We present herein an overview of our ongoing studies with dendralenes. The first synthetic routes to this fundamental family of compounds have revealed long-hidden secrets in hydrocarbon chemistry and set the scene for synthetic and materials chemistry applications.We thank the Australian Research Council for financial support

Geometric and Mechanical Modelling of Textiles

The quality of a composite material produced using a textile reinforcement depends largely on the way the textile deforms during processing. To ensure the production of high quality parts and minimise costs in designing such parts it is necessary to develop methods to predict the deformations of textiles. This thesis employs a multi scale modelling approach in predicting mechanical properties of textile fabrics. The three scales involved are the microscopic, mesoscopic and macroscopic. This thesis concentrates on the micro and mesoscopic scales leading to results applicable to the macroscopic scale. At the microscopic scale fibres are modelled as individual entities and the interactions between these entities are modelled. In compaction of yarns, the contact between fibres and bending resulting from these contacts governs the force response. A numerical model is developed to simulate this behaviour and results are validated against experimental studies found in the literature. The numerical model is extended to the mesoscopic scale where the shear of a plain woven fabric consisting of low filament count yarns is modelled. At the mesoscopic scale a large part of the work consists of characterising the geometry of textile fabrics. New and existing algorithms are combined together to form a consistent modelling approach. This work was performed in conjunction with the development of a software package named TexGen where these algorithms are implemented. The geometric models created by TexGen are then used to predict mechanical properties of textile unit cells using a finite element method which takes yarn properties as an input. Validation is performed for a series of woven fabrics subjected to compression and in-plane shear

Numerical Investigation of Strength-reducing Mechanisms of Mantle Rock During the Genesis Flood

This paper reports our efforts to model the effects of grain size, recrystallization, creep, and texture on overall rock strength within the Earth’s mantle during the Genesis Flood. Our study uses experimental rheological data obtained from the mineralogical literature for olivine, which is an important mantle mineral. We apply an Internal State Variable (ISV) constitutive model within the framework of the TERRA finite element code to capture the subscale structures and their associated dynamics, strength, and viscosity effects during the Flood episode. Our numerical investigations, in both 2D and 3D, that include the improved deformation model reveal even more clearly that the potential for mantle instability enabled an episode of catastrophic plate tectonics to occur. This mantle instability arises from the extreme weakening behavior resulting from the relationship between microstructural features (herein texture, recrystallization, and grain size) and thermomechanical properties (e.g., stress and viscosity) under the conditions of temperature, pressure, and strain rate within the mantle during the Genesis Flood. It is our conviction that such an episode played a major role in the global Flood described in Genesis 7-8

Simulation Analysis of Glacial Surging in the Des Moines Ice Lobe

We analyze the Des Moines Ice Lobe of the Laurentide Ice Sheet (a main portion of the glacier that fl owed into the United States) using fi nite element simulations to explore plausible surging scenarios that can reduce ice motion time scales from thousands of years to a couple of decades. We chose the Des Moines Ice Lobe of the Laurentide Ice Sheet, because of its relatively simple geometry. Previous studies considered idealized geometries of continental scale to investigate parameters related to the surging phenomena (cf., Horstemeyer & Gullett, 2003). These continental scale simulations of the Laurentide Ice Sheet provide boundary conditions for our local scale fi nite element simulations to allow us to examine effects of varying precipitation rates on the larger ice sheet. To further the work of Horstemeyer and Gullett, we performed three dimensional simulations, added a deformable basal till layer, and modifi ed the problem domain from a generic dome to a slab representing the front edge of the Des Moines Ice Lobe. These three dimensional simulation results illustrate clear surging lobing effects that have been observed in nature

New Material Model Reveals Inherent Tendency in Mantle Minerals for Runaway Mantle Dynamics

In this paper we apply a material model used for years in the engineering community to simulate deformation and failure of metal components to the problem of deformation of silicate minerals in the earth’s mantle. Known as the Bammann inelastic internal state variable (BIISV) model, this formulation utilizes not only the current state (e.g., temperature, density, stress) of each material parcel to compute the current deformation rate, but it also carries along features (internal state variables) that describe the parcel’s deformational history. This history information allows the model to represent more complex modes of material deformation than models which do not include such information. This study reveals for the first time that a type of solid-state plastic deformation known as dislocation glide may well be the crucial mechanism responsible for buoyancy-driven runaway in the mantle of a planet with a mass and gravity field like that of the earth. To explore the tendency for runaway behavior we applied a 2D Cartesian version of the finite element TERRA mantle dynamics program that includes the BIISV model. We obtain BIISV parameters appropriate for the earth’s mantle from experimental measurements of the material properties of the upper mantle rock lherzolite. We find that buoyancy anomalies of plausible size yield spectacular runaway behavior when the dislocation glide mechanism is enabled

Geometric and Mechanical Modelling of Textiles

The quality of a composite material produced using a textile reinforcement depends largely on the way the textile deforms during processing. To ensure the production of high quality parts and minimise costs in designing such parts it is necessary to develop methods to predict the deformations of textiles. This thesis employs a multi scale modelling approach in predicting mechanical properties of textile fabrics. The three scales involved are the microscopic, mesoscopic and macroscopic. This thesis concentrates on the micro and mesoscopic scales leading to results applicable to the macroscopic scale. At the microscopic scale fibres are modelled as individual entities and the interactions between these entities are modelled. In compaction of yarns, the contact between fibres and bending resulting from these contacts governs the force response. A numerical model is developed to simulate this behaviour and results are validated against experimental studies found in the literature. The numerical model is extended to the mesoscopic scale where the shear of a plain woven fabric consisting of low filament count yarns is modelled. At the mesoscopic scale a large part of the work consists of characterising the geometry of textile fabrics. New and existing algorithms are combined together to form a consistent modelling approach. This work was performed in conjunction with the development of a software package named TexGen where these algorithms are implemented. The geometric models created by TexGen are then used to predict mechanical properties of textile unit cells using a finite element method which takes yarn properties as an input. Validation is performed for a series of woven fabrics subjected to compression and in-plane shear