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Welcome to the Micromechanics of Granular Media Group website!


News


Our paper (Shear bands as bottlenecks in force transmission) has been selected to be highlighted in Europhysics News volume 46/5-6.


 

Elizabeth and Frederick White Research Conference on

Mining Data for Detection and
Prediction of Failure in Geomaterials

The University of Melbourne, 2015 July 13-14

 


In a new paper in Europhysics Letters, patterns discovered from data on sand and discrete element simulations suggest that the early localization of bottlenecks in force transmission is the root cause of shear bands in dense cohesionless granular media. This mechanism was shown to initiate early in the loading history for initially (globally) homogeneous samples. The finding paves the way for early prediction of failure and highlights a potential to change the course of failure before it initiates. Tordesillas, Pucilowski, Tobin, Kuhn, Ando, Viggiani, Druckrey and Alshibli “Shear bands as bottlenecks in force transmission” (2015) Europhysics Letters.


A new method for predicting force chains without need for information on contact forces using Network Flow Theory for unbonded and bonded granular media is reported in a new paper in Physical Review E "Network flow model of force transmission in unbonded and bonded granular media" by Antoinette Tordesillas, Steven Tobin, Mehmet Cil, Khalid Alshibli and Robert P Behringer.


The percolating MFMC network that predicts most of the force chains (below) has a two-tier hierarchical architecture: local pathways (red) encapsulate intra-connections between particles in individual force chains and their confining weak contacts in 3-cycles; global pathways (blue dashed lines with dots at end) encapsulate inter-connections between distinct force chains. More new results will be coming soon on use of Network Flow to elucidate strength and failure processes at the mesoscale as well as major pathways for flow in the interstitial pore space. In this new work with PhD student Sebastian Pucilowski, we show a new capability for early prediction of failure for a range of natural and synthetic materials. The Abstract and supplementary file is here.


MGM's EPL paper on granular aging with Bob Behringer's group (Duke) has been selected for 2014 Editor's Choice.
David M. Walker, Antoinette Tordesillas, Jie Ren, Joshua A. Dijksman and Robert P. Behringer "Uncovering temporal transitions and self-organization during slow aging of dense granular media in the absence of shear bands" (2014) Europhysics Letters 107 18005
The Editorial Board members have nominated their personal highlights from those articles published in 2014. Those selected in Editor's Choice form a sampling of the journal's recent content that includes letters covering important new research, in topical areas, that the Board found particularly insightful and useful.


Join us for an upcoming workshop on the topic of Data Mining for Slope Stability Analysis (details soon!).


MGM research on the micromechanics of vortices in granular media (Tordesillas, Pucilowski, Walker, Peters, Walizer in International Journal for Numerical and Analytical Methods in Geomechanics, Volume 38, August 2014) has been featured in the Engineering Mechanics Institute of the American Society of Civil Engineers August newsletter. "The Vision of the Institute is to be a premier organization representing engineering mechanics by effectively serving the needs of the world-wide engineering community and promoting both research and application of scientific and mathematical principles to address a broad spectrum of existing and emerging engineering and societal problems."
Read more from the article by Andrew Bartolini (University of Notre Dame)

Bracing for shear: why sand gets stronger with age Recently established techniques from dynamical systems (used to study brain trauma), complex networks and structural mechanics are woven together in a study of a slowly drifting dynamics of granular systems in cyclic pure shear under constant volume. The experiments are unique in that uniform deformation is maintained throughout the test — free from any influence of shear bands. We uncovered a consistent pattern in which the prolonged cyclic shear slowly drove the system to the shear-jammed regime, where functional building blocks of force chains inhabit configurations that are more structurally stable to shear. The contact topology evolved towards a more densely connected structural configuration in which force chain columns are endowed with higher levels of triangular and rectangular truss-bracing. This results in an increase in the structural stability of force chains, consistent with the prevailing conjecture on the structural mechanism behind the observed increase in shear strength and shear stiffness in aging sand. (Walker, Tordesillas, Ren, Dijskman, Behringer in Europhysics Letters Volume 107, Number 1, July 2014). Read more


MGM welcomes Andrew Druckrey, PhD student in the Department of Civil and Environmental Engineering, The University of Tennessee, Knoxville as part of the East Asia and Pacific Summer Institutes (EAPSI) program, funded by the US National Science Foundation (NSF) and the Australian Academy of Science.

Duality of graphs sheds light on permeability. A new project with Masters student Scott Russell, aimed towards a characterization of the coupled evolution of the solid grain fabric and pore space, has uncovered a novel micromechanical measure of permeability using concepts of dual graphs.

A new project with Mehmet Cil and Prof Khalid Alshibli (University of Tennessee, Knoxville) examines the evolution of fracture in agglomerate models of silica sand.

A new paper with Dr. James Hilton reveals unique patterns of force chain evolution ahead of a single grain intruder.

Interested in an exciting maths project of relevance to the mining industry? Gilbert Riggs Foundation PhD scholarships are available for high achieving students to undertake research in micromechanics of granular failure with applications to mining. The scholarships also provide opportunities for students to gain joint PhD degrees (Univ, Melbourne and INPG-UJF) through these projects. For general information, contact A/Prof Antoinette Tordesillas

 

Our research focuses on developing mathematical models for granular materials. These materials are ubiquitous in everyday life: they range from cosmetic powders to vitamin pills, from jelly beans to M&Ms, from beach sand to the rings of Saturn, and from breakfast cereals to interstellar dust. Understanding the fundamental behaviour of these materials can determine the success or failure of a vast number of man-made and natural processes. In fact, this class of materials ranks second, behind water, on the scale of priorities of human activities and endeavours. Hence, even a fractional advance in our understanding of how granular media behave can have a profound impact on our economic and general well-being. This is particularly true for Australia with its primary industries being heavily reliant on granular media. Australia is a leading exporter of major commodities such as coal (~ $9.3 billion per annum), iron ore (~$3.8 billion per annum) and wheat (~$3.4 billion per annum).

The MGM research group is led by Dr. Antoinette Tordesillas. Our group currently collaborates with engineering research groups from both Australia and the USA. Our group's research objective is to use mathematics to help solve engineering problems encountered in particulate science and technologies. We are a multidisciplinary team with backgrounds in areas encompassing applied mathematics, software engineering, mechanical engineering, physics, mechanics, and materials science. Our research has been funded by the Australian Research Council, the US Army Research Office, the US Army Corps of Engineers - Engineering Research and Development Center, and the Australian Academy of Science.