Article records
https://feeds.library.caltech.edu/people/Andrade-J-E/article.rss
A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenTue, 16 Apr 2024 13:17:14 +0000A novel and general form of effective stress in a partially saturated porous material: The influence of microstructure
https://resolver.caltech.edu/CaltechAUTHORS:20110323-164417570
Authors: {'items': [{'id': 'Vlahinić-I', 'name': {'family': 'Vlahinić', 'given': 'Ivan'}}, {'id': 'Jennings-H-M', 'name': {'family': 'Jennings', 'given': 'Hamlin M.'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}, {'id': 'Thomas-J-J', 'name': {'family': 'Thomas', 'given': 'Jeffrey J.'}}]}
Year: 2011
DOI: 10.1016/j.mechmat.2010.09.007
A recently published constitutive model for drying of a partially saturated porous material is extended to take into account finite air (gas) pressure as well as finite external load, variables that are absent during simple drying under atmospheric conditions. We further use the result to derive a general form of effective stress in a partially saturated material. The proposed framework overcomes a primary shortcoming of the classic Bishop effective stress expression and offers a novel way to incorporate important morphological features. In addition, we show how existing micromechanical homogenization techniques aided by basic descriptions of material morphology may be used to inform the study of elastic deformations in the partially saturated media. We further show that for two very specific schemes, and thus for two particular morphologies of porous materials, the proposed effective stress framework remarkably reduces to a volumetric average pressure form which is commonly encountered in literature. In this work, we also provide an extensive discussion and critique of the classic Bishop effective stress approach.https://authors.library.caltech.edu/records/f7rzv-cdt02Multiscale modeling and characterization of granular matter: From grain kinematics to continuum mechanics
https://resolver.caltech.edu/CaltechAUTHORS:20110307-093950071
Authors: {'items': [{'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'J. E.'}}, {'id': 'Avila-C-F', 'name': {'family': 'Avila', 'given': 'C. F.'}}, {'id': 'Hall-Stephen-A', 'name': {'family': 'Hall', 'given': 'S. A.'}, 'orcid': '0000-0002-5232-4942'}, {'id': 'Lenoir-N', 'name': {'family': 'Lenoir', 'given': 'N.'}}, {'id': 'Viggiani-G', 'name': {'family': 'Viggiani', 'given': 'G.'}}]}
Year: 2011
DOI: 10.1016/j.jmps.2010.10.009
Granular sands are characterized and modeled here by explicitly exploiting the discrete-continuum duality of granular matter. Grain-scale kinematics, obtained by shearing a sample under triaxial compression, are coupled with a recently proposed multiscale computational framework to model the behavior of the material without resorting to phenomenological evolution (hardening) laws. By doing this, complex material behavior is captured by extracting the evolution of key properties directly from the grain-scale mechanics and injecting it into a continuum description (e.g., elastoplasticity). The effectiveness of the method is showcased by two examples: one linking discrete element computations with finite elements and another example linking a triaxial compression experiment using computed tomography and digital image correlation with finite element computation. In both cases, dilatancy and friction are used as the fundamental plastic variables and are obtained directly from the grain kinematics. In the case of the result linked to the experiment, the onset and evolution of a persistent shear band is modeled, showing—for the first time—three-dimensional multiscale results in the post-bifurcation regime with real materials and good quantitative agreement with experiments.https://authors.library.caltech.edu/records/13dfw-rmk42Connecting microstructural attributes and permeability from 3D tomographic images of in situ shear-enhanced compaction bands using multiscale computations
https://resolver.caltech.edu/CaltechAUTHORS:20110608-072339539
Authors: {'items': [{'id': 'Sun-W', 'name': {'family': 'Sun', 'given': 'WaiChing'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}, {'id': 'Rudnicki-J-W', 'name': {'family': 'Rudnicki', 'given': 'John W.'}}, {'id': 'Eichhubl-P', 'name': {'family': 'Eichhubl', 'given': 'Peter'}}]}
Year: 2011
DOI: 10.1029/2011GL047683
Tomographic images taken inside and outside a compaction band in a field specimen of Aztec sandstone are analyzed by using numerical methods such as graph theory, level sets, and hybrid lattice Boltzmann/finite element techniques. The results reveal approximately an order of magnitude permeability reduction within the compaction band. This is less than the several orders of magnitude reduction measured from hydraulic experiments on compaction bands formed in laboratory experiments and about one order of magnitude less than inferences from two-dimensional images of Aztec sandstone. Geometrical analysis concludes that the elimination of connected pore space and increased tortuosities due to the porosity decrease are the major factors contributing to the permeability reduction. In addition, the multiscale flow simulations also indicate that permeability is fairly isotropic inside and outside the compaction band.https://authors.library.caltech.edu/records/t1jky-6r519A nanoscale numerical model of calcium silicate hydrate
https://resolver.caltech.edu/CaltechAUTHORS:20110906-152521681
Authors: {'items': [{'id': 'Fonseca-P-C', 'name': {'family': 'Fonseca', 'given': 'P. C.'}}, {'id': 'Jennings-H-M', 'name': {'family': 'Jennings', 'given': 'H. M.'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'J. E.'}}]}
Year: 2011
DOI: 10.1016/j.mechmat.2011.05.004
This manuscript presents a numerical model of the low-density and high-density calcium–silicate–hydrate (C–S–H) gel phases in cement paste. Generated using an autocatalytic growth algorithm, C–S–H is introduced as an assemblage of discrete granular particles at nanoscale with realistic particle-level properties, such as elastic modulus, friction, and cohesion. Using the discrete element method, nanoindentation simulations are performed on each phase, demonstrating that its mechanical contact properties compare well to the results from nanoindentation experiments in the literature. By creating an additional
loosely packed phase of C–S–H and maintaining constant particle-level material properties, the results further show that the indentation modulus, as a function of the volumetric packing fraction of the C–S–H gel phase, compares well to a linear self-consistent scaling
relation while the hardness most closely fits a nonlinear self-consistent scaling relation.https://authors.library.caltech.edu/records/v5020-bkh02AES for multiscale localization modeling in granular media
https://resolver.caltech.edu/CaltechAUTHORS:20110803-080949323
Authors: {'items': [{'id': 'Chen-Q', 'name': {'family': 'Chen', 'given': 'Qiushi'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}, {'id': 'Samaniego-S', 'name': {'family': 'Samaniego', 'given': 'Esteban'}}]}
Year: 2011
DOI: 10.1016/j.cma.2011.04.022
This work presents a multiscale strong discontinuity approach to tackle key challenges in modeling localization behavior in granular media: accommodation of discontinuities in the kinematic fields, and direct linkage to the underlying grain-scale information. Assumed enhanced strain (AES) concepts are borrowed to enhance elements for post-localization analysis, but are reformulated within a recently-proposed hierarchical multiscale computational framework. Unlike classical AES methods, where material properties are usually constants or assumed to evolve with some arbitrary phenomenological laws, this framework provides a bridge to extract evolutions of key material parameters, such as friction and dilatancy, based on grain scale computational or experimental data. More importantly, the phenomenological softening modulus typically used in AES methods is no longer required. Numerical examples of plane strain compression tests are presented to illustrate the applicability of this method and to analyze its numerical performance.https://authors.library.caltech.edu/records/rz84g-3zp80Numerical simulation of the instability line based on laws of physics
https://resolver.caltech.edu/CaltechAUTHORS:20120213-121821478
Authors: {'items': [{'id': 'Ramos-A-M', 'name': {'family': 'Ramos', 'given': 'Alfonso M.'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}, {'id': 'Lizcano-A', 'name': {'family': 'Lizcano', 'given': 'Arcesio'}}]}
Year: 2011
This work presents a numerical study of the instability line that relies on balance laws of physics rather than phenomenology. The instability line defines the onset of static liquefaction for loose sandy materials in the p-q space of effective stresses under undrained loading conditions. The onset of static liquefaction is predicted by means of a recently developed criterion and specialized to an elastoplastic constitutive model. The performance of this criterion is compared with laboratory tests showing satisfactory results. For a given void ratio and different mean pressures, it is found that the mobilized friction angle at the onset of static liquefaction is not constant. Therefore, the instability line is not an intrinsic property of the sand, but depends on the current state of the material. This work re-interprets the hypothesis given by VaidandChern, which has been amply used to analyze liquefaction phenomena.https://authors.library.caltech.edu/records/6k05e-5wa15Multiscale method for characterization of porous microstructures and their impact on macroscopic effective permeability
https://resolver.caltech.edu/CaltechAUTHORS:20120113-131031067
Authors: {'items': [{'id': 'Sun-W-C', 'name': {'family': 'Sun', 'given': 'W. C.'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'J. E.'}}, {'id': 'Rudnicki-J-W', 'name': {'family': 'Rudnicki', 'given': 'J. W.'}}]}
Year: 2011
DOI: 10.1002/nme.3220
Recent technology advancements on X-ray computed tomography (X-ray CT) offer a nondestructive approach to extract complex three-dimensional geometries with details as small as a few microns in size. This new technology opens the door to study the interplay between microscopic properties (e.g. porosity) and macroscopic fluid transport properties (e.g. permeability). To take full advantage of X-ray CT, we introduce a multiscale framework that relates macroscopic fluid transport behavior not only to porosity but also to other important microstructural attributes, such as occluded/connected porosity and geometrical tortuosity, which are extracted using new computational techniques from digital images of porous materials. In particular, we introduce level set methods, and concepts from graph theory, to determine the geometrical tortuosity and connected porosity, while using a lattice Boltzmann/finite element scheme to obtain homogenized effective permeability at specimen-scale. We showcase the applicability and efficiency of this multiscale framework by two examples, one using a synthetic array and another using a sample of natural sandstone with complex pore structure.https://authors.library.caltech.edu/records/y8nxm-9b115Granular element method (GEM): linking inter-particle forces with macroscopic loading
https://resolver.caltech.edu/CaltechAUTHORS:20120210-132453393
Authors: {'items': [{'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}, {'id': 'Avila-C-F', 'name': {'family': 'Avila', 'given': 'Carlos F.'}}]}
Year: 2012
DOI: 10.1007/s10035-011-0298-8
We present a new method capable of inferring, for the first time, inter-particle contact forces in irregularly-shaped natural granular materials (e.g., sands), using basic Newtonian mechanics and balance of linear momentum at the particle level. The method furnishes a relationship between inter-particle forces and corresponding average particle stresses, which can be inferred, for instance, from measurements of average particle strains emanating from advanced experimental techniques (e.g., 3D X-ray diffraction). Inter-particle forces are the missing link in understanding how forces are transmitted in complex granular structures and the key to developing physics-based constitutive models. We present two numerical examples to verify the method and showcase its promise.https://authors.library.caltech.edu/records/rja4r-xtd46Characterization of random fields and their impact on the mechanics of geosystems at multiple scales
https://resolver.caltech.edu/CaltechAUTHORS:20120217-111405018
Authors: {'items': [{'id': 'Chen-Q', 'name': {'family': 'Chen', 'given': 'Qiushi'}}, {'id': 'Seifried-A', 'name': {'family': 'Seifried', 'given': 'Andrew'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}, {'id': 'Baker-J-W', 'name': {'family': 'Baker', 'given': 'Jack W.'}}]}
Year: 2012
DOI: 10.1002/nag.999
The behavior of particulate media, such as sands, is encoded at the granular-scale and hence methods for upscaling such behavior across relevant scales of interest—from granular-scale (~1 mm) to field-scale (>1m)—are needed to attain a more accurate prediction of soil behavior. Multi-scale analysis is especially important under extreme conditions, such as strain localization, penetration, or liquefaction, where the classical constitutive description may no longer apply. In this paper, internally consistent probabilistic models for undrained shear strength and Young's modulus are developed at multiple scales, and incorporated into a simulation framework where refinement of the material description to finer scales is pursued only as necessary. This probabilistic simulation approach is then coupled with the finite element method. Numerical examples are presented to show how the performance of the geosystem is influenced by taking into account multi-scale random fields.https://authors.library.caltech.edu/records/fxv0f-dnd62On the rheology of dilative granular media: Bridging solid-and
fluid-like behavior
https://resolver.caltech.edu/CaltechAUTHORS:20120521-075840860
Authors: {'items': [{'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}, {'id': 'Chen-Qiushi', 'name': {'family': 'Chen', 'given': 'Qiushi'}}, {'id': 'Le-Phong-H', 'name': {'family': 'Le', 'given': 'Phong H.'}}, {'id': 'Avila-C-F', 'name': {'family': 'Avila', 'given': 'Carlos F.'}}, {'id': 'Evans-T-M', 'name': {'family': 'Evans', 'given': 'T. Matthew'}, 'orcid': '0000-0001-5442-1300'}]}
Year: 2012
DOI: 10.1016/j.jmps.2012.02.011
A new rate-dependent plasticity model for dilative granular media is presented, aiming to bridge the seemingly disparate solid- and fluid-like behavioral regimes. Up to date, solid-like behavior is typically tackled with rate-independent plasticity models emanating from Mohr–Coulomb and Critical State plasticity theory. On the other hand, the fluid-like behavior of granular media is typically treated using constitutive theories amenable to viscous flow, e.g., Bingham fluid. In our proposed model, the material strength is composed of a dilation part and a rate-dependent residual strength. The dilatancy strength plays a key role during solid-like behavior but vanishes in the fluid-like regime. The residual strength, which in a classical plasticity model is considered constant and rate-independent, is postulated to evolve with strain rate. The main appeal of the model is its simplicity and its ability to reconcile the classic plasticity and rheology camps. The applicability and capability of the model are demonstrated by numerical simulation of granular flow problems, as well as a classical shear banding problem, where the performance of the continuum model is compared to discrete particle simulations and physical experiment. These results shed much-needed light onto the mechanics and physics of granular media at various shear rates.https://authors.library.caltech.edu/records/ejqk6-d6096Modelling diffuse instabilities in sands under drained conditions
https://resolver.caltech.edu/CaltechAUTHORS:20120711-124900547
Authors: {'items': [{'id': 'Ramos-A-M', 'name': {'family': 'Ramos', 'given': 'A. M.'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'J. E.'}}, {'id': 'Lizcano-A', 'name': {'family': 'Lizcano', 'given': 'A.'}}]}
Year: 2012
DOI: 10.1680/geot.10.P.109
This paper presents a criterion for detecting diffuse
(homogeneous) instabilities in granular soils sheared under
fully drained conditions. The criterion is based on
bifurcation theory and applied to elasto-plasticity by
allowing multiple incremental solutions in elasto-plastic
soils, physically losing controllability of stress boundary
conditions. Drained diffuse instabilities are poorly understood,
and are induced by kinematic modes different
from those observed in shear bands and liquefaction
instabilities. Unlike shear bands, diffuse instabilities occur
under fairly homogenous deformation modes and,
unlike liquefaction, drained instabilities are not generated
by the excess pore pressures. Recent experiments under
drained constant shear report sudden homogeneous instabilities
in samples of relatively dense and loose sands.
The criterion presented in this paper is used in conjunction
with an elasto-plasticity model for sands to predict
and explain these reported drained instabilities. From a
practical standpoint, these developments serve to expand
the repertoire of potential instabilities that occur well
before failure, and which have been reported in case
studies of puzzling slope instability failures under fully
drained conditions.https://authors.library.caltech.edu/records/v05rv-bb468Transient creep effects and the lubricating power of water in materials ranging from paper to concrete and Kevlar
https://resolver.caltech.edu/CaltechAUTHORS:20120625-095958802
Authors: {'items': [{'id': 'Vlahinić-I', 'name': {'family': 'Vlahinić', 'given': 'Ivan'}}, {'id': 'Thomas-J-J', 'name': {'family': 'Thomas', 'given': 'Jeffrey J.'}}, {'id': 'Jennings-H', 'name': {'family': 'Jennings', 'given': 'Hamlin M.'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}]}
Year: 2012
DOI: 10.1016/j.jmps.2012.03.003
A diverse class of viscous materials, which includes familiar materials such concrete, wood, and Kevlar, exhibit surprising, counterintutive properties under internal moisture content fluctuations. In test after test over the past 50 years, the viscosity of these materials is observed to decrease, often dramatically, during wetting and drying. The key characteristics of the observed viscous softening are: the decrease in viscosity is temporary, and depending on the specimen size can be greatly delayed with respect to the associated change in weight; the decrease in viscosity is absent under steady state flow.
Based on recent research on the properties of water and other polar fluids confined by hydrophilic surfaces, we provide a physical explanation and propose a constitutive law. The resulting model accurately captures the interplay between the pore fluid movement and macroscopic constitutive properties in totality. The model is verified against published data for the creep of paper sheets exposed to cyclic moisture conditions. Experimental data of different materials under similar boundary conditions are compared using a new metric, the creep rate factor. The results further reinforce the idea that nanoscale movement of water enhances the internal 'lubrication' of the studied materials, interpreted as loosening of the hydrogen bonds.https://authors.library.caltech.edu/records/mtq4z-hz790Granular element method for computational particle mechanics
https://resolver.caltech.edu/CaltechAUTHORS:20121018-111644740
Authors: {'items': [{'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}, {'id': 'Lim-K-W', 'name': {'family': 'Lim', 'given': 'Keng-Wit'}}, {'id': 'Avila-C-F', 'name': {'family': 'Avila', 'given': 'Carlos F.'}}, {'id': 'Vlahinić-I', 'name': {'family': 'Vlahinić', 'given': 'Ivan'}}]}
Year: 2012
DOI: 10.1016/j.cma.2012.06.012
This paper presents a method within the family of the discrete element method (DEM) capable of accurately capturing grain shape by using Non-Uniform Rational Basis-Splines (NURBS). The new method, called GEM, bypasses one of the current bottlenecks in computational discrete mechanics of granular materials by allowing discrete elements to take realistic and complex granular shapes encountered in engineering and science (e.g., sand grains). More than a new method, this paper presents a new concept for DEM: using NURBS to seamlessly transition from advanced visualization tools (e.g., X-ray CT) to physics-based computational models where particle shape is realistically modeled. It is expected that, with the rapid advancement of computational power, combining high-fidelity characterization with physics-based computations will lead to more predictive modeling approaches. The granular element method may help transition from characterization to modeling and could lead to more realistic predictions at the grain scale.https://authors.library.caltech.edu/records/g7et0-5sp56Design and implementation of a particle image velocimetry method for analysis of running gear–soil interaction
https://resolver.caltech.edu/CaltechAUTHORS:20140116-100622121
Authors: {'items': [{'id': 'Senatore-C', 'name': {'family': 'Senatore', 'given': 'Carmine'}}, {'id': 'Wulfmeier-M', 'name': {'family': 'Wulfmeier', 'given': 'Markus'}}, {'id': 'Vlahinić-I', 'name': {'family': 'Vlahinić', 'given': 'Ivan'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'Jose'}}, {'id': 'Iagnemma-K', 'name': {'family': 'Iagnemma', 'given': 'Karl'}}]}
Year: 2013
DOI: 10.1016/j.jterra.2013.09.004
Experimental analysis of running gear–soil interaction traditionally focuses on the measurement of forces and torques developed by the running gear. This type of measurement provides useful information about running gear performance but it does not allow for explicit investigation of soil failure behavior. This paper describes a methodology based on particle image velocimetry for analyzing soil motion from a sequence of images. A procedure for systematically identifying experimental and processing settings is presented. Soil motion is analyzed for a rigid wheel traveling on a Mars regolith simulant while operating against a glass wall, thereby imposing plain strain boundary conditions. An off-the-shelf high speed camera is used to collect images of the soil flow. Experimental results show that it is possible to accurately compute soil deformation characteristics without the need of markers. Measured soil velocity fields are used to calculate strain fields.https://authors.library.caltech.edu/records/zvdhy-f3j75Criterion for flow liquefaction instability
https://resolver.caltech.edu/CaltechAUTHORS:20131018-153344168
Authors: {'items': [{'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}, {'id': 'Ramos-A-M', 'name': {'family': 'Ramos', 'given': 'Alfonso M.'}}, {'id': 'Lizcano-A', 'name': {'family': 'Lizcano', 'given': 'Arcesio'}}]}
Year: 2013
DOI: 10.1007/s11440-013-0223-x
This study describes a general liquefaction flow instability criterion for elastoplastic soils based on the concept of loss of uniqueness. We apply the criterion to the general case of axisymmetric loading and invoke the concepts of effective stresses and loss of controllability to arrive at a general criterion for the onset of liquefaction flow. The criterion is used in conjunction with an elastoplastic model for sands to generate numerical simulations. The numerical results are compared with experimental evidence to give the following insights into predicting liquefaction. (1) The onset of liquefaction flow is a state of instability occurring under both monotonic and cyclic tests, and coincides with loss of controllability. (2) The criterion proposed herein clearly and naturally differentiates between liquefaction flow (instability) and cyclic mobility. (3) Flow liquefaction not only depends on the potential of the material to generate positive excess pore pressures, but more importantly, it also depends on the current state of the material, which is rarely predicted by phenomenology.https://authors.library.caltech.edu/records/f2dx9-6wh24A contact dynamics approach to the Granular Element Method
https://resolver.caltech.edu/CaltechAUTHORS:20140320-104636713
Authors: {'items': [{'id': 'Lim-K-W', 'name': {'family': 'Lim', 'given': 'Keng-Wit'}}, {'id': 'Krabbenhoft-K', 'name': {'family': 'Krabbenhoft', 'given': 'Kristian'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}]}
Year: 2014
DOI: 10.1016/j.cma.2013.10.004
We present a contact dynamics (CD) approach to the Granular Element Method (GEM) Andrade et al. (2012) [1], abbreviated here as CD–GEM. By combining particle shape flexibility through Non-Uniform Rational Basis Splines, properties of implicit time-integration discretization (e.g., larger time steps) and non-penetrating constraints, as well as a reduction to a static formulation in the limit of an infinite time step, CD–GEM targets system properties and deformation regimes in which the classical discrete element method either performs poorly or simply fails; namely, in granular systems comprising of rigid or highly stiff angular particles and subjected to quasi-static or intense dynamic flow conditions. The integration of CD and GEM is made possible while significantly simplifying implementation and maintaining comparable performance with existing CD approaches.https://authors.library.caltech.edu/records/1khtd-61k80Towards a more accurate characterization of granular media: extracting quantitative descriptors from tomographic images
https://resolver.caltech.edu/CaltechAUTHORS:20160224-161057713
Authors: {'items': [{'id': 'Vlahinić-I', 'name': {'family': 'Vlahinić', 'given': 'Ivan'}}, {'id': 'Andò-E', 'name': {'family': 'Andò', 'given': 'Edward'}}, {'id': 'Viggiani-G', 'name': {'family': 'Viggiani', 'given': 'Gioacchino'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}]}
Year: 2014
DOI: 10.1007/s10035-013-0460-6
Imaging, epitomized by computed tomography, continues to provide unprecedented 3D access to granular microstructures at ever-greater resolutions. The non-destructive technique has enabled deep insight into the morphology and behavior of granular materials, in situ and as a function of macroscopic states, e.g., loads. However, a significant bottleneck in this paradigm is that it ultimately yields qualitative 'pictures' of microstructure. Hence, a major challenge is to extract quantitative descriptors of grain-scale processes, e.g., morphological description of particles, kinematics, and spatial interactions. Existing methods, including watershed and burn algorithms, are plagued with limitations related to image resolution and with the inability to sharply identify grain-to-grain contact regions, which is crucial for studying force transmission and strength in granular materials. In this work, we propose a method to overcome these drawbacks. Specifically, a novel way to extract grain topology in particulate materials via level sets is introduced. It is shown that the proposed method can sharply resolve the topology of grain surfaces near to and far from grain-to-grain contact regions with sub-voxel resolution, and is capable of grain extraction directly in three dimensions. The proposed method still relies on traditional techniques for input, but ultimately leads to much improved grain characterization. We validate the approach using three dimensional CT images of highly rounded (Caicos ooid) and highly angular (Hostun sand) natural materials, with excellent results.https://authors.library.caltech.edu/records/mvyjp-j6390Extracting inter-particle forces in opaque granular materials:
Beyond photoelasticity
https://resolver.caltech.edu/CaltechAUTHORS:20140313-103152302
Authors: {'items': [{'id': 'Hurley-R', 'name': {'family': 'Hurley', 'given': 'Ryan'}}, {'id': 'Marteau-E', 'name': {'family': 'Marteau', 'given': 'Eloïse'}}, {'id': 'Ravichandran-G', 'name': {'family': 'Ravichandran', 'given': 'Guruswami'}, 'orcid': '0000-0002-2912-0001'}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}]}
Year: 2014
DOI: 10.1016/j.jmps.2013.09.013
This paper presents the first example of inter-particle force inference in real granular materials using an improved version of the methodology known as the Granular Element Method (GEM). GEM combines experimental imaging techniques with equations governing particle behavior to allow force inference in cohesionless materials with grains of arbitrary shape, texture, and opacity. This novel capability serves as a useful tool for experimentally characterizing granular materials, and provides a new means for investigating force networks. In addition to an experimental example, this paper presents a precise mathematical formulation of the inverse problem involving the governing equations and illustrates solution strategies.https://authors.library.caltech.edu/records/k7a5s-c7x07Granular element method for three-dimensional discrete element calculations
https://resolver.caltech.edu/CaltechAUTHORS:20140131-082001153
Authors: {'items': [{'id': 'Lim-K-W', 'name': {'family': 'Lim', 'given': 'Keng-Wit'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}]}
Year: 2014
DOI: 10.1002/nag.2203
This paper endows the recently-proposed granular element method (GEM) with the ability to perform 3D discrete element calculations. By using non-uniform rational B-Splines to accurately represent complex grain geometries, we proposed an alternative approach to clustering-based and polyhedra-based discrete element methods whereby the need for complicated and ad hoc approaches to construct 3D grain geometries is entirely bypassed. We demonstrate the ability of GEM in capturing arbitrary-shaped 3D grains with great ease, flexibility, and without excessive geometric information. Furthermore, the applicability of GEM is enhanced by its tight integration with existing non-uniform rational B-Splines modeling tools and ability to provide a seamless transition from binary images of real grain shapes (e.g., from 3D X-ray CT) to modeling and discrete mechanics computations.https://authors.library.caltech.edu/records/crf35-csp28On the contact treatment of non-convex particles in the granular element method
https://resolver.caltech.edu/CaltechAUTHORS:20170616-104550749
Authors: {'items': [{'id': 'Lim-Keng-Wit', 'name': {'family': 'Lim', 'given': 'Keng-Wit'}}, {'id': 'Krabbenhoft-K', 'name': {'family': 'Krabbenhoft', 'given': 'Kristian'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}]}
Year: 2014
DOI: 10.1007/s40571-014-0019-2
We present a new contact algorithm that endows the granular element method [1] with the ability to model non-convex particles using non-uniform rational basis splines. This significant extension allows for the representation of particle morphological features, namely, sphericity and angularity, to their fullest extent, with local contact rolling resistance and interlocking emanating directly from grain geometry. Both particle elasticity and friction at the contact level are treated implicitly and simultaneously, and the contact algorithm is cast into a mathematical programming-based contact dynamics framework. The framework provides the advantages of implicit time integrators (for e.g., stability and larger time steps) and ability to handle both rigid and highly stiff particles. By allowing for particle non-convexity, modeling flexibility is significantly enhanced, to a level that is comparable with isogeometric methods. As such, the transition from image data to particle shapes is greatly streamlined. More importantly, increased macroscopic strength in granular packings comprising of non-convex particles is fully captured. All the above capabilities are achieved under a very modest implementation effort.https://authors.library.caltech.edu/records/xf04f-pn354Force chains as the link between particle and bulk friction angles in granular material
https://resolver.caltech.edu/CaltechAUTHORS:20150313-112024347
Authors: {'items': [{'id': 'Booth-A-M', 'name': {'family': 'Booth', 'given': 'Adam M.'}, 'orcid': '0000-0002-7339-0594'}, {'id': 'Hurley-R', 'name': {'family': 'Hurley', 'given': 'Ryan'}}, {'id': 'Lamb-M-P', 'name': {'family': 'Lamb', 'given': 'Michael P.'}, 'orcid': '0000-0002-5701-0504'}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}]}
Year: 2014
DOI: 10.1002/2014GL061981
From sediment transport in rivers to landslides, predictions of granular motion rely on a Mohr-Coulomb failure criterion parameterized by a friction angle. Measured friction angles are generally large for single grains, smaller for large numbers of grains, and no theory exists for intermediate numbers of grains. We propose that a continuum of friction angles exists between single-grain and bulk friction angles due to grain-to-grain force chains. Physical experiments, probabilistic modeling, and discrete element modeling demonstrate that friction angles decrease by up to 15° as the number of potentially mobile grains increases from 1 to ~20. Decreased stability occurs as longer force chains more effectively dislodge downslope "keystone" grains, implying that bulk friction angles are set by the statistics of single-grain friction angles. Both angles are distinct from and generally larger than grain contact-point friction, with implications for a variety of sediment transport processes involving small clusters of grains.https://authors.library.caltech.edu/records/2f4ra-hnw68Flow liquefaction instability prediction using finite elements
https://resolver.caltech.edu/CaltechAUTHORS:20150302-150334720
Authors: {'items': [{'id': 'Mohammadnejad-T', 'name': {'family': 'Mohammadnejad', 'given': 'Toktam'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}]}
Year: 2015
DOI: 10.1007/s11440-014-0342-z
In this paper, a mathematical criterion based on bifurcation theory is developed to predict the onset of liquefaction instability in fully saturated porous media under static and dynamic loading conditions. The proposed liquefaction criterion is general and can be applied to any elastoplastic constitutive model. Since the liquefaction criterion is only as accurate as the underlying constitutive model utilized, the modified Manzari–Dafalias model is chosen for its accuracy, relative simplicity and elegance. Moreover, a fully implicit return mapping algorithm is developed for the numerical implementation of the Manzari–Dafalias model, and a consistent tangent operator is derived to obtain optimal convergence with finite elements. The accuracy of the implementation is benchmarked against laboratory experiments under monotonic and cyclic loading conditions, and a qualitative boundary value problem. The framework is expected to serve as a tool to enable prediction of liquefaction occurrence in the field under general static and dynamic conditions. Further, the methodology can help advance our understanding of the phenomenon in the field as it can clearly differentiate between unstable behavior, such as flow liquefaction, and material failure, such as cyclic mobility.https://authors.library.caltech.edu/records/2npmj-vxq41Strength of Granular Materials in Transient and Steady State Rapid Shear
https://resolver.caltech.edu/CaltechAUTHORS:20160825-101053582
Authors: {'items': [{'id': 'Hurley-R-C', 'name': {'family': 'Hurley', 'given': 'Ryan C.'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}]}
Year: 2015
DOI: 10.1016/j.proeng.2015.04.032
This paper discusses relationships between the frictional strength of a flowing granular material and quantities including porosity and grain-scale energy dissipation. The goal of the paper is to foster an understanding of frictional strength that will facilitate the development of constitutive laws incorporating important physical processes. This is accomplished in several steps. First, a friction relationship is derived for a steady state simple shear flow using an energy balance approach. The relationship shows that friction is explicitly related to porosity, grain connectivity, and grain-scale dissipation rates. Next, the friction relationship is extended to describe transient changes in frictional behavior. The relationship shows that, in addition to the processes important for steady flows, the rate of dilatation and changes in internal energy play a role in the frictional strength of a granular material away from steady state. Finally, numerical simulations are performed to illustrate the accuracy of the friction relationships and illuminate important scaling behavior. The discussion of numerical simulations focuses on the rate-dependence of frictional strength and the partition of macroscopic energy dissipation into its grain-scale components. New interpretations of existing constitutive laws and ideas for new constitutive laws are discussed.https://authors.library.caltech.edu/records/mgtj2-43b85Friction in inertial granular flows: competition between dilation and grain-scale dissipation rates
https://resolver.caltech.edu/CaltechAUTHORS:20150603-094642638
Authors: {'items': [{'id': 'Hurley-R-C', 'name': {'family': 'Hurley', 'given': 'Ryan C.'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}]}
Year: 2015
DOI: 10.1007/s10035-015-0564-2
Friction plays an important role in the behavior of flowing granular media. The effective friction coefficient is a description of shear strength in both slow and rapid flows of these materials. In this paper, we study the steady state effective friction coefficient μ in a granular material in two steps. First, we develop a new relationship between the steady state effective friction coefficient, the shear rate, the solid fraction, and grain-scale dissipation processes in a simple shear flow. This relationship elucidates the rate- and porosity-dependent nature of effective friction in granular flows. Second, we use numerical simulations to study how the various quantities in the relationship change with shear rate and material properties. We explore how the relationship illuminates the grain-scale dissipation processes responsible for macroscopic friction. We examine how the competing processes of shearing dilation and grain-scale dissipation rates give rise to rate-dependence. We also compare our findings with previous investigations of effective friction in simple shear.https://authors.library.caltech.edu/records/yc8mt-4qe34Dynamic Inter-Particle Force Inference in Granular Materials: Method and Application
https://resolver.caltech.edu/CaltechAUTHORS:20160316-092646662
Authors: {'items': [{'id': 'Hurley-R-C', 'name': {'family': 'Hurley', 'given': 'R. C.'}}, {'id': 'Lim-K-W', 'name': {'family': 'Lim', 'given': 'K. W.'}}, {'id': 'Ravichandran-G', 'name': {'family': 'Ravichandran', 'given': 'G.'}, 'orcid': '0000-0002-2912-0001'}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'J. E.'}}]}
Year: 2016
DOI: 10.1007/s11340-015-0063-8
Inter-particle force transmission in granular media plays an important role in the macroscopic static and dynamic behavior of these materials. This paper presents a method for inferring inter-particle forces in opaque granular materials during dynamic experiments. By linking experimental measurements of particle kinematics and volume-averaged strains to forces, the method provides a new tool for quantitatively studying force transmission and its relation to macroscopic behavior. We provide an experimental validation of the method, comparing inter-particle forces measured in a simple impact test on two-dimensional rubber grains to a finite-element simulation. We also provide an application of the method, using it to study inter-particle forces during impact of an intruder on a granular bed. We discuss the current challenges for applying the method to both model materials and real geologic materials.https://authors.library.caltech.edu/records/4ha7k-6wb82Multiscale characterization and modeling of granular materials through a computational mechanics avatar: a case study with experiment
https://resolver.caltech.edu/CaltechAUTHORS:20160422-133622266
Authors: {'items': [{'id': 'Lim-Keng-Wit', 'name': {'family': 'Lim', 'given': 'Keng-Wit'}}, {'id': 'Kawamoto-Reid', 'name': {'family': 'Kawamoto', 'given': 'Reid'}, 'orcid': '0000-0002-4936-5321'}, {'id': 'Andò-E', 'name': {'family': 'Andò', 'given': 'Edward'}}, {'id': 'Viggiani-G', 'name': {'family': 'Viggiani', 'given': 'Gioacchino'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}]}
Year: 2016
DOI: 10.1007/s11440-015-0405-9
Through a first-generation computational mechanics avatar that directly links advanced X-ray computed tomographic experimental techniques to a discrete computational model, we present a case study where we made the first attempt to characterize and model the grain-scale response inside the shear band of a real specimen of Caicos ooids subjected to triaxial compression. The avatar has enabled, for the first time, the transition from faithful representation of grain morphologies in X-ray tomograms of granular media to a morphologically accurate discrete computational model. Grain-scale information is extracted and upscaled into a continuum finite element model through a hierarchical multiscale scheme, and the onset and evolution of a persistent shear band is modeled, showing excellent quantitative agreement with experiment in terms of both grain-scale and continuum responses in the post-bifurcation regime. More importantly, consistency in results across characterization, discrete analysis and continuum response from multiscale calculations are found, achieving the first and long sought-after quantitative breakthrough in grain-scale analysis of real granular materials.https://authors.library.caltech.edu/records/txeb5-j8x96Level set discrete element method for three-dimensional computations with triaxial case study
https://resolver.caltech.edu/CaltechAUTHORS:20160620-112549350
Authors: {'items': [{'id': 'Kawamoto-Reid', 'name': {'family': 'Kawamoto', 'given': 'Reid'}, 'orcid': '0000-0002-4936-5321'}, {'id': 'Andò-E', 'name': {'family': 'Andò', 'given': 'Edward'}}, {'id': 'Viggiani-G', 'name': {'family': 'Viggiani', 'given': 'Gioacchino'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}]}
Year: 2016
DOI: 10.1016/j.jmps.2016.02.021
In this paper, we outline the level set discrete element method (LS-DEM) which is a discrete element method variant able to simulate systems of particles with arbitrary shape using level set functions as a geometric basis. This unique formulation allows seamless interfacing with level set-based characterization methods as well as computational ease in contact calculations. We then apply LS-DEM to simulate two virtual triaxial specimens generated from XRCT images of experiments and demonstrate LS-DEM's ability to quantitatively capture and predict stress–strain and volume–strain behavior observed in the experiments.https://authors.library.caltech.edu/records/snpgb-dj395Effects of grain morphology on critical state: a computational analysis
https://resolver.caltech.edu/CaltechAUTHORS:20160915-100335066
Authors: {'items': [{'id': 'Jerves-A-X', 'name': {'family': 'Jerves', 'given': 'Alex X.'}}, {'id': 'Kawamoto-Reid-Y', 'name': {'family': 'Kawamoto', 'given': 'Reid Y.'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}]}
Year: 2016
DOI: 10.1007/s11440-015-0422-8
We introduce a new DEM scheme (LS-DEM) that takes advantage of level sets to enable the inclusion of real grain shapes into a classical discrete element method. Then, LS-DEM is validated and calibrated with respect to real experimental results. Finally, we exploit part of LS-DEM potentiality by using it to study the dependency of critical state (CS) parameters such as critical state line (CSL) slope λ, CSL intercept Γ, and CS friction angle Φ_(CS) on the grain's morphology, i.e., sphericity, roundness, and regularity. This study is carried out in three steps. First, LS-DEM is used to capture and simulate the shape of five different two-dimensional cross sections of real grains, which have been previously classified according to the aforementioned morphological features. Second, the same LS-DEM simulations are carried out for idealized/simplified grains, which are morphologically equivalent to their real counterparts. Third, the results of real and idealized grains are compared, so the effect of "imperfections" on real particles is isolated. Finally, trends for the CS parameters (CSP) dependency on sphericity, roundness, and regularity are obtained as well as analyzed. The main observations and remarks connecting particle's morphology, particle's idealization, and CSP are summarized in a table that is attempted to help in keeping a general picture of the analysis, results, and corresponding implications.https://authors.library.caltech.edu/records/39wez-kjy74A micro-mechanical study of peak strength and critical state
https://resolver.caltech.edu/CaltechAUTHORS:20160523-075406122
Authors: {'items': [{'id': 'Jerves-A-X', 'name': {'family': 'Jerves', 'given': 'Alex X.'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}]}
Year: 2016
DOI: 10.1002/nag.2478
We present a micro-mechanical analysis of macroscopic peak strength, critical state, and residual strength in two-dimensional non-cohesive granular media. Typical continuum constitutive quantities such as frictional strength and dilation angle are explicitly related to their corresponding grain-scale counterparts (e.g., inter-particle contact forces, fabric, particle displacements, and velocities), providing an across-the-scale basis for a better understanding and modeling of granular materials. These multi-scale relations are derived in three steps. First, explicit relations between macroscopic stress and strain rate with the corresponding grain-scale mechanics are established. Second, these relations are used in conjunction with the non-associative Mohr–Coulomb criterion to explicitly connect internal friction and dilation angles to the micro-mechanics. Third, the mentioned explicit connections are applied to investigate, understand, and derive micro-mechanical conditions for peak strength, critical state, and residual strength.https://authors.library.caltech.edu/records/szhh1-e6292Quantifying interparticle forces and heterogeneity in 3D granular materials
https://resolver.caltech.edu/CaltechAUTHORS:20160719-231519023
Authors: {'items': [{'id': 'Hurley-R-C', 'name': {'family': 'Hurley', 'given': 'R. C.'}}, {'id': 'Hall-Stephen-A', 'name': {'family': 'Hall', 'given': 'S. A.'}, 'orcid': '0000-0002-5232-4942'}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'J. E.'}}, {'id': 'Wright-J', 'name': {'family': 'Wright', 'given': 'J.'}}]}
Year: 2016
DOI: 10.1103/PhysRevLett.117.098005
Extensive theoretical, numerical, and experimental research has examined interparticle forces in granular materials. Interparticle forces are intimately linked to mechanical properties and are known to self-organize into heterogeneous structures, or force chains, under external load. Despite progress in understanding the statistics and spatial distribution of interparticle forces in recent decades, a systematic method for measuring forces in opaque, 3D, frictional, stiff granular media has yet to emerge. In this Letter, we present results from an experiment that combines 3D X-ray diffraction, X-ray tomography, and a numerical force inference technique to quantify interparticle forces and their heterogeneity in a granular material composed of quartz grains undergoing a 1D compression cycle. Forces exhibit an exponential decay above the mean and partition into strong and weak networks. We find a surprising inverse relationship between macroscopic load and the heterogeneity of interparticle forces, despite the clear emergence of two force chains that span the system.https://authors.library.caltech.edu/records/pzr9p-tqj17Mechanics of origin of flow liquefaction instability under proportional strain triaxial compression
https://resolver.caltech.edu/CaltechAUTHORS:20161013-140948216
Authors: {'items': [{'id': 'Mital-U', 'name': {'family': 'Mital', 'given': 'Utkarsh'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}]}
Year: 2016
DOI: 10.1007/s11440-015-0430-8
We define a flow liquefaction potential for determining flow liquefaction susceptibility during proportional strain triaxial compression . The flow liquefaction potential is a function of inconsistency between the natural dilative tendency of the soil and the imposed dilatancy during proportional strain triaxial compression. It helps us analyze why given the right conditions, a loose soil that contracts during drained triaxial compression and liquefies under undrained triaxial compression may be stable under proportional strain triaxial compression. Conversely, we also use the flow liquefaction potential to analyze why a dense soil that dilates during drained triaxial compression and is stable under undrained triaxial compression may liquefy under proportional strain triaxial compression. The undrained loose case is a special case of proportional strain triaxial compression under which a soil can liquefy. The central objective of this paper was to investigate the origins of flow liquefaction instability. Hence, we also analyze stress evolution during proportional strain triaxial compression and discuss the mechanics of the test leading up to flow liquefaction instability. We arrive at a necessary precursor for instability, which can serve as a warning sign for flow liquefaction instability, while the soil is still stable. The precursor is not a condition of sufficiency and should also not be confused with the onset of instability itself. The same loading must be applied continuously to induce flow liquefaction instability. The current progress is encouraging and facilitates a deeper understanding of origin of flow liquefaction instabilities.https://authors.library.caltech.edu/records/3nxpv-ygp70Numerical modeling of hydraulic fracture propagation, closure and reopening using XFEM with application to in-situ stress estimation
https://resolver.caltech.edu/CaltechAUTHORS:20161111-083143784
Authors: {'items': [{'id': 'Mohammadnejad-T', 'name': {'family': 'Mohammadnejad', 'given': 'T.'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'J. E.'}}]}
Year: 2016
DOI: 10.1002/nag.2512
In this paper, a fully coupled model is developed for numerical modeling of hydraulic fracturing in partially saturated weak porous formations using the extended finite element method, which provides an effective means to simulate the coupled hydro-mechanical processes occurring during hydraulic fracturing. The developed model is for short fractures where plane strain assumptions are valid. The propagation of the hydraulic fracture is governed by the cohesive crack model, which accounts for crack closure and reopening. The developed model allows for fluid flow within the open part of the crack and crack face contact resulting from fracture closure. To prevent the unphysical crack face interpenetration during the closing mode, the crack face contact or self-contact condition is enforced using the penalty method. Along the open part of the crack, the leakage flux through the crack faces is obtained directly as a part of the solution without introducing any simplifying assumption. If the crack undergoes the closing mode, zero leakage flux condition is imposed along the contact zone. An application of the developed model is shown in numerical modeling of pump-in/shut-in test. It is illustrated that the developed model is able to capture the salient features bottomhole pressure/time records exhibit and can extract the confining stress perpendicular to the direction of the hydraulic fracture propagation from the fracture closure pressure.https://authors.library.caltech.edu/records/0bvvd-wpv30Strength criterion for cross-anisotropic sand under general stress conditions
https://resolver.caltech.edu/CaltechAUTHORS:20161109-073532052
Authors: {'items': [{'id': 'Lü-Xilin', 'name': {'family': 'Lü', 'given': 'Xilin'}, 'orcid': '0000-0003-1045-6047'}, {'id': 'Huang-Maosong', 'name': {'family': 'Huang', 'given': 'Maosong'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}]}
Year: 2016
DOI: 10.1007/s11440-016-0479-z
By incorporating the fabric effect and Lode's angle dependence into the Mohr–Coulomb failure criterion, a strength criterion for cross-anisotropic sand under general stress conditions was proposed. The obtained criterion has only three material parameters which can be specified by conventional triaxial tests. The formula to calculate the friction angle under any loading direction and intermediate principal stress ratio condition was deduced, and the influence of the degree of the cross-anisotropy was quantified. The friction angles of sand in triaxial, true triaxial, and hollow cylinder torsional shear tests were obtained, and a parametric analysis was used to detect the varying characteristics. The friction angle becomes smaller when the major principal stress changes from perpendicular to parallel to the bedding plane. The loading direction and intermediate principal stress ratio are unrelated in true triaxial tests, and their influences on the friction angle can be well captured by the proposed criterion. In hollow cylinder torsional shear tests with the same internal and external pressures, the loading direction and intermediate principal stress ratio are related. This property results in a lower friction angle in the hollow cylinder torsional shear test than that in the true triaxial test under the same intermediate principal stress ratio condition. By comparing the calculated friction angle with the experimental results under various loading conditions (e.g., triaxial, true triaxial, and hollow cylinder torsional shear test), the proposed criterion was verified to be able to characterize the shear strength of cross-anisotropic sand under general stress conditions.https://authors.library.caltech.edu/records/tb1dm-m0b65Continuum modeling of rate-dependent granular flows in SPH
https://resolver.caltech.edu/CaltechAUTHORS:20161109-145544827
Authors: {'items': [{'id': 'Hurley-R-C', 'name': {'family': 'Hurley', 'given': 'Ryan C.'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}]}
Year: 2017
DOI: 10.1007/s40571-016-0132-5
We discuss a constitutive law for modeling rate-dependent granular flows that has been implemented in smoothed particle hydrodynamics (SPH). We model granular materials using a viscoplastic constitutive law that produces a Drucker–Prager-like yield condition in the limit of vanishing flow. A friction law for non-steady flows, incorporating rate-dependence and dilation, is derived and implemented within the constitutive law. We compare our SPH simulations with experimental data, demonstrating that they can capture both steady and non-steady dynamic flow behavior, notably including transient column collapse profiles. This technique may therefore be attractive for modeling the time-dependent evolution of natural and industrial flows.https://authors.library.caltech.edu/records/bj8ks-14q90From computed tomography to mechanics of granular materials via level set bridge
https://resolver.caltech.edu/CaltechAUTHORS:20161109-074756861
Authors: {'items': [{'id': 'Vlahinić-I', 'name': {'family': 'Vlahinić', 'given': 'Ivan'}}, {'id': 'Kawamoto-Reid', 'name': {'family': 'Kawamoto', 'given': 'Reid'}, 'orcid': '0000-0002-4936-5321'}, {'id': 'Andò-E', 'name': {'family': 'Andò', 'given': 'Edward'}}, {'id': 'Viggiani-G', 'name': {'family': 'Viggiani', 'given': 'Gioacchino'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}]}
Year: 2017
DOI: 10.1007/s11440-016-0491-3
This paper details the 'level set bridge': a single platform for the characterization of various aspects of granular micro-mechanics, including grain morphology, grain kinematics, and inter-granular contact. This platform is studied and verified for accuracy using synthetic examples, in particular, its robustness with respect to the variables of image resolution and noise. The level set bridge is then applied to analysis of XRCT images of real 3D triaxial experiments of two types of granular materials. Contact statistics and kinematics are reported inside and outside of the failure band of one, and kinematics inside a failure band are reported in the other, from preload to critical state.https://authors.library.caltech.edu/records/4nd6w-mmn36A geometry-based algorithm for cloning real grains
https://resolver.caltech.edu/CaltechAUTHORS:20170428-083442608
Authors: {'items': [{'id': 'Jerves-A-X', 'name': {'family': 'Jerves', 'given': 'Alex X.'}}, {'id': 'Kawamoto-Reid-Y', 'name': {'family': 'Kawamoto', 'given': 'Reid Y.'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}]}
Year: 2017
DOI: 10.1007/s10035-017-0716-7
We introduce a computational algorithm to "clone" the grain morphologies of a sample of real grains that have been digitalized. This cloning algorithm allows us to generate an arbitrary number of cloned grains that satisfy the same distributions of morphological features displayed by their parents and can be included into a numerical Discrete Element Method simulation. This study is carried out in three steps. First, distributions of morphological parameters such as aspect ratio, roundness, principal geometric directions, and spherical radius, called the morphological DNA, are extracted from the parents. Second, the geometric stochastic cloning (GSC) algorithm, relying purely on statistical distributions of the aforementioned parameters, is explained, detailed, and used to generate a pool of clones from its parents' morphological DNA. Third, morphological DNA is extracted from the pool of clones and compared to the one obtained from a similar pool of parents, and the distribution of volume-surface ratio is used to perform quality control. Then, from these results, the error (mutation) in the GSC process is analyzed and used to discuss the algorithm's drawbacks, knobs (parameters) tuning, as well as potential improvements.https://authors.library.caltech.edu/records/18tsq-4qx60An experimental investigation of the micromechanics of Eglin sand
https://resolver.caltech.edu/CaltechAUTHORS:20170427-114851319
Authors: {'items': [{'id': 'Nardelli-V', 'name': {'family': 'Nardelli', 'given': 'V.'}}, {'id': 'Coop-M-R', 'name': {'family': 'Coop', 'given': 'M. R.'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'J. E.'}}, {'id': 'Paccagnella-F', 'name': {'family': 'Paccagnella', 'given': 'F.'}}]}
Year: 2017
DOI: 10.1016/j.powtec.2017.02.009
The mechanical behaviour of Eglin sand at the micro-scale was studied in this work. Laboratory experiments using unconventional apparatuses were carried out in order to study the contact behaviour of pairs of particles in both compression (normal loading) and shearing (tangential loading) and the strength of grains. Particle fractions were identified according to their colour by visual observation and both their chemical composition and surface morphologies were obtained. The tangential stiffnesses and inter-particle coefficients of frictions for the different fractions found in the sand sample were determined under the range of normal loadings applied (1–9 N). The results show some discrepancies between the theoretical models commonly found in literature to describe either the normal or the tangential loading response, which are able to predict the trend of the force-displacement curves but using elastic moduli that are lower than those found in literature, especially in the case of tangential loading. Also, the results of particle crushing tests show quite consistent results (excluding one particle group), probably related to the similar mineralogy of all fractions, which are mainly constituted by silica.https://authors.library.caltech.edu/records/7p88x-mn961Image-Based Modeling of Granular Porous Media
https://resolver.caltech.edu/CaltechAUTHORS:20170502-144505731
Authors: {'items': [{'id': 'Tahmasebi-P', 'name': {'family': 'Tahmasebi', 'given': 'Pejman'}, 'orcid': '0000-0001-5548-4805'}, {'id': 'Sahimi-M', 'name': {'family': 'Sahimi', 'given': 'Muhammad'}, 'orcid': '0000-0002-8009-542X'}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}]}
Year: 2017
DOI: 10.1002/2017GL073938
We propose a new method of modeling granular media that utilizes a single two- or three-dimensional image and is formulated based on a Markov process. The process is mapped onto one that minimizes the difference between the image and a stochastic realization of the granular medium and utilizes a novel approach to remove possible unphysical discontinuities in the realization. Quantitative comparison between the morphological properties of the realizations and representative examples indicates excellent agreement.https://authors.library.caltech.edu/records/fb1ma-5c056Flow Liquefaction Instability as a Mechanism for Lower End of Liquefaction Charts
https://resolver.caltech.edu/CaltechAUTHORS:20170907-161431788
Authors: {'items': [{'id': 'Mital-U', 'name': {'family': 'Mital', 'given': 'Utkarsh'}}, {'id': 'Mohammadnejad-T', 'name': {'family': 'Mohammadnejad', 'given': 'Toktam'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}]}
Year: 2017
DOI: 10.1061/(ASCE)GT.1943-5606.0001752
The state-of-the-practice uses the "simplified procedure" for evaluating liquefaction susceptibility of soils. Based on this procedure, liquefaction charts have been developed that correlate soil resistance to earthquake-induced stresses. These charts are based on case histories of past earthquakes and have proven to be useful while evaluating liquefaction susceptibility at a new site. However, these charts are inherently empirical, which makes extrapolation into regimes with insufficient data difficult. In addition, they do not inform an engineer about the effects of liquefaction. This work hypothesizes that the lower end of liquefaction charts corresponds to soils that are susceptible to unstable flow liquefaction. A numerical investigation is undertaken, the results of which support this hypothesis. This implies that if test data at a new site correspond to the lower end of liquefaction charts, then the site may be susceptible to flow liquefaction. This in turn could provide an engineer with some predictive power regarding the effects of liquefaction.https://authors.library.caltech.edu/records/987ed-hf363Extended Pile Driving Model to Predict the Penetration of the Insight/HP^3 Mole into the Martian Soil
https://resolver.caltech.edu/CaltechAUTHORS:20171026-125007789
Authors: {'items': [{'id': 'Poganski-J', 'name': {'family': 'Poganski', 'given': 'Joshua'}}, {'id': 'Kömle-N-I', 'name': {'family': 'Kömle', 'given': 'Norbert I.'}}, {'id': 'Kargl-G', 'name': {'family': 'Kargl', 'given': 'Günter'}}, {'id': 'Schweiger-H-F', 'name': {'family': 'Schweiger', 'given': 'Helmut F.'}}, {'id': 'Grott-M', 'name': {'family': 'Grott', 'given': 'Matthias'}}, {'id': 'Spohn-T', 'name': {'family': 'Spohn', 'given': 'Tilman'}}, {'id': 'Krömer-O', 'name': {'family': 'Krömer', 'given': 'Olaf'}}, {'id': 'Krause-C', 'name': {'family': 'Krause', 'given': 'Christian'}}, {'id': 'Wippermann-T', 'name': {'family': 'Wippermann', 'given': 'Torben'}}, {'id': 'Tsakyridis-G', 'name': {'family': 'Tsakyridis', 'given': 'Georgios'}}, {'id': 'Fittock-M', 'name': {'family': 'Fittock', 'given': 'Mark'}}, {'id': 'Lichtenheldt-R', 'name': {'family': 'Lichtenheldt', 'given': 'Roy'}}, {'id': 'Vrettos-C', 'name': {'family': 'Vrettos', 'given': 'Christos'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}]}
Year: 2017
DOI: 10.1007/s11214-016-0302-z
The NASA InSight mission will provide an opportunity for soil investigations using the penetration data of the heat flow probe built by the German Aerospace Center DLR. The Heat flow and Physical Properties Probe (HP^3) will penetrate 3 to 5 meter into the Martian subsurface to investigate the planetary heat flow. The measurement of the penetration rate during the insertion of the HP3 will be used to determine the physical properties of the soil at the landing site. For this purpose, numerical simulations of the penetration process were performed to get a better understanding of the soil properties influencing the penetration performance of HP^3. A pile driving model has been developed considering all masses of the hammering mechanism of HP^3. By cumulative application of individual stroke cycles it is now able to describe the penetration of the Mole into the Martian soil as a function of time, assuming that the soil parameters of the material through which it penetrates are known. We are using calibrated materials similar to those expected to be encountered by the InSight/HP^3 Mole when it will be operated on the surface of Mars after the landing of the InSight spacecraft. We consider various possible scenarios, among them a more or less homogeneous material down to a depth of 3–5 m as well as a layered ground, consisting of layers with different soil parameters. Finally we describe some experimental tests performed with the latest prototype of the InSight Mole at DLR Bremen and compare the measured penetration performance in sand with our modeling results. Furthermore, results from a 3D DEM simulation are presented to get a better understanding of the soil response.https://authors.library.caltech.edu/records/b1y5t-1s846A novel experimental device for investigating the multiscale behavior of granular materials under shear
https://resolver.caltech.edu/CaltechAUTHORS:20171009-102112518
Authors: {'items': [{'id': 'Marteau-E', 'name': {'family': 'Marteau', 'given': 'Eloïse'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}]}
Year: 2017
DOI: 10.1007/s10035-017-0766-x
In this paper, we report a set of experiments performed on a novel mechanical device that allows a specimen composed of a two-dimensional opaque granular assembly to be subjected to quasi-static shear conditions. A complete description of the grain-scale quantities that control the mechanical behavior of granular materials is extracted throughout the shear deformation. Geometrical arrangement, or fabric, is quantified by means of image processing, grain kinematics are obtained using Digital Image Correlation and contact forces are inferred using the Granular Element Method. Aiming to bridge the micro-macro divide, macroscopic average stresses for the granular assembly are calculated based on grain-scale fabric parameters and contact forces. The experimental procedure is detailed and validated using a simple uniaxial compression test. Macroscopic results of shear stress and volumetric strain exhibit typical features of the shear response of dense granular materials and indicate that critical state is achieved at large deformations. At the grain scale, attention is given to the evolution of fabric and contact forces as the granular assembly is sheared. The results show that shear deformation induces geometrical (fabric) and mechanical (force) anisotropy and that principal stresses and force orientation rotate simultaneously. At critical state, stress, force and fabric orientation reach the same value. By seamlessly connecting grain-scale information to continuum scale experiments, we shed light into the multiscale mechanical behavior of granular assemblies under shear loading.https://authors.library.caltech.edu/records/p2sth-d2k35Predicting the initiation of static liquefaction of cross-anisotropic sands under multiaxial stress conditions
https://resolver.caltech.edu/CaltechAUTHORS:20171130-075335618
Authors: {'items': [{'id': 'Lü-Xilin', 'name': {'family': 'Lü', 'given': 'Xilin'}, 'orcid': '0000-0003-1045-6047'}, {'id': 'Huang-Maosong', 'name': {'family': 'Huang', 'given': 'Maosong'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}]}
Year: 2017
DOI: 10.1002/nag.2697
Experimental evidence has shown that the liquefaction instability of sands can be affected by its material density, stress state, and inherent anisotropy. In order to predict the initiation of the static liquefaction of inherent cross-anisotropic sands under multidimensional stress conditions, a rational constitutive model is needed. An elastoplasticity model able to capture the influences of intermediate principal stress ratio (b = (σ_2 – σ_3)/(σ_1 – σ_3)) and loading direction on stress–strain relationships and volumetric properties was proposed. The yield function was formulated to be controlled by Lode angle, loading direction, and material state; the stress–dilatancy was a material state-dependent function. After using the existing drained hollow cylinder tests to validate the proposed model, this model was used to simulate the existing undrained hollow cylinder tests. During this simulation, the second-order work criterion was used to determine the initiation of static liquefaction. The results showed that an increase in both the intermediate principal stress ratio and the loading angle induces a decrease in the second-order work. Static liquefaction is initiated more easily at a stress state with a large intermediate principal stress ratio and a large loading angle, and the mobilized friction angle at the instability points decreases with the intermediate principal stress ratio and the loading angle.https://authors.library.caltech.edu/records/v2ag5-yj065Modeling the static liquefaction of unsaturated sand containing gas bubbles
https://resolver.caltech.edu/CaltechAUTHORS:20180425-130259176
Authors: {'items': [{'id': 'Lü-Xilin', 'name': {'family': 'Lü', 'given': 'Xilin'}, 'orcid': '0000-0003-1045-6047'}, {'id': 'Huang-Maosong', 'name': {'family': 'Huang', 'given': 'Maosong'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}]}
Year: 2018
DOI: 10.1016/j.sandf.2017.11.008
As a modification of the deviatoric hardening plasticity model, a material state-dependent model was proposed to simulate the response of unsaturated sand containing gas bubbles under undrained triaxial conditions. Affected by the compressibility of gas, the stress paths under undrained conditions approach the drained response of sand when the initial degree of saturation is low. Upon an increase in the degree of saturation, the stress path gradually approaches the saturated undrained response. According to the prediction based on the second-order work criterion, static liquefaction occurs in loose sand, but not in dense sand. Increases in the degree of saturation and the initial gas pressure reduce the stress ratio at the instability points. The instability line obtained by connecting those instability points in the p-q space is nonlinear, and its slope depends on the initial void ratio, the initial degree of saturation, the initial gas pressure, and the confining stress. After comparing the experimental results in the literature with the theoretical prediction, the proposed model was shown to precisely predict the onset of the static liquefaction of unsaturated sand containing gas bubbles.https://authors.library.caltech.edu/records/3fg5z-4qw71All you need is shape: predicting shear banding in sand with LS-DEM
https://resolver.caltech.edu/CaltechAUTHORS:20171115-092059666
Authors: {'items': [{'id': 'Kawamoto-Reid', 'name': {'family': 'Kawamoto', 'given': 'Reid'}, 'orcid': '0000-0002-4936-5321'}, {'id': 'Andò-E', 'name': {'family': 'Andò', 'given': 'Edward'}}, {'id': 'Viggiani-G', 'name': {'family': 'Viggiani', 'given': 'Gioacchino'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}]}
Year: 2018
DOI: 10.1016/j.jmps.2017.10.003
This paper presents discrete element method (DEM) simulations with experimental comparisons at multiple length scales—underscoring the crucial role of particle shape. The simulations build on technological advances in the DEM furnished by level sets (LS-DEM), which enable the mathematical representation of the surface of arbitrarily-shaped particles such as grains of sand. We show that this ability to model shape enables unprecedented capture of the mechanics of granular materials across scales ranging from macroscopic behavior to local behavior to particle behavior. Specifically, the model is able to predict the onset and evolution of shear banding in sands, replicating the most advanced high-fidelity experiments in triaxial compression equipped with sequential X-ray tomography imaging. We present comparisons of the model and experiment at an unprecedented level of quantitative agreement—building a one-to-one model where every particle in the more than 53,000-particle array has its own avatar or numerical twin. Furthermore, the boundary conditions of the experiment are faithfully captured by modeling the membrane effect as well as the platen displacement and tilting. The results show a computational tool that can give insight into the physics and mechanics of granular materials undergoing shear deformation and failure, with computational times comparable to those of the experiment. One quantitative measure that is extracted from the LS-DEM simulations that is currently not available experimentally is the evolution of three dimensional force chains inside and outside of the shear band. We show that the rotations on the force chains are correlated to the rotations in stress principal directions.https://authors.library.caltech.edu/records/bq6nh-gb059Failures in sand in reduced gravity environments
https://resolver.caltech.edu/CaltechAUTHORS:20180530-103229436
Authors: {'items': [{'id': 'Marshall-J-P', 'name': {'family': 'Marshall', 'given': 'Jason P.'}, 'orcid': '0000-0001-6208-1801'}, {'id': 'Hurley-R-C', 'name': {'family': 'Hurley', 'given': 'Ryan C.'}}, {'id': 'Arthur-D', 'name': {'family': 'Arthur', 'given': 'Dan'}}, {'id': 'Vlahinic-I', 'name': {'family': 'Vlahinic', 'given': 'Ivan'}}, {'id': 'Senatore-C', 'name': {'family': 'Senatore', 'given': 'Carmine'}}, {'id': 'Iagnemma-K', 'name': {'family': 'Iagnemma', 'given': 'Karl'}}, {'id': 'Trease-B', 'name': {'family': 'Trease', 'given': 'Brian'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}]}
Year: 2018
DOI: 10.1016/j.jmps.2018.01.005
The strength of granular materials, specifically sand is important for understanding physical phenomena on other celestial bodies. However, relatively few experiments have been conducted to determine the dependence of strength properties on gravity. In this work, we experimentally investigated relative values of strength (the peak friction angle, the residual friction angle, the angle of repose, and the peak dilatancy angle) in Earth, Martian, Lunar, and near-zero gravity. The various angles were captured in a classical passive Earth pressure experiment conducted on board a reduced gravity flight and analyzed using digital image correlation. The data showed essentially no dependence of the peak friction angle on gravity, a decrease in the residual friction angle between Martian and Lunar gravity, no dependence of the angle of repose on gravity, and an increase in the dilation angle between Martian and Lunar gravity. Additionally, multiple flow surfaces were seen in near-zero gravity. These results highlight the importance of understanding strength and deformation mechanisms of granular materials at different levels of gravity.https://authors.library.caltech.edu/records/d0xda-xew22A model for decoding the life cycle of granular avalanches in a rotating drum
https://resolver.caltech.edu/CaltechAUTHORS:20171205-111425606
Authors: {'items': [{'id': 'Marteau-Eloïse', 'name': {'family': 'Marteau', 'given': 'Eloïse'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}]}
Year: 2018
DOI: 10.1007/s11440-017-0609-2
Granular materials can behave as harmless sand dunes or as devastating landslides. A granular avalanche marks the transition between these distinct solid-like and fluid-like states. The solid-like state is typically described using plasticity models from critical state theory. In the fluid regime, granular flow is commonly captured using a visco-plastic model. However, due to our limited understanding of the mechanism governing the solid–fluid-like transition, characterizing the material behavior throughout the life cycle of an avalanche remains an open challenge. Here, we employ laboratory experiments of transient avalanches spontaneously generated by a rotating drum. We report measurements of dilatancy and grain kinematics before, during, and after each avalanche. Those measurements are directly incorporated into a rate-dependent plasticity model that quantitatively predicts the granular flow measured in experiments. Furthermore, we find that dilatancy in the solid-like state controls the triggering of granular avalanches and therefore plays a key role in the solid–fluid-like transition. With the proposed approach, we demonstrate that the life cycle of a laboratory avalanche, from triggering to run out, can be fully explained. Our results represent an important step toward a unified understanding of the physical phenomena associated with transitional behavior in granular media.https://authors.library.caltech.edu/records/f6ktf-n7n04Geology and Physical Properties Investigations by the InSight Lander
https://resolver.caltech.edu/CaltechAUTHORS:20180713-152627927
Authors: {'items': [{'id': 'Golombek-M-P', 'name': {'family': 'Golombek', 'given': 'M.'}, 'orcid': '0000-0002-1928-2293'}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'J.'}}, {'id': 'Marshall-J-P', 'name': {'family': 'Marshall', 'given': 'J.'}, 'orcid': '0000-0001-6208-1801'}]}
Year: 2018
DOI: 10.1007/s11214-018-0512-7
Although not the prime focus of the InSight mission, the near-surface geology and physical properties investigations provide critical information for both placing the instruments (seismometer and heat flow probe with mole) on the surface and for understanding the nature of the shallow subsurface and its effect on recorded seismic waves. Two color cameras on the lander will obtain multiple stereo images of the surface and its interaction with the spacecraft. Images will be used to identify the geologic materials and features present, quantify their areal coverage, help determine the basic geologic evolution of the area, and provide ground truth for orbital remote sensing data. A radiometer will measure the hourly temperature of the surface in two spots, which will determine the thermal inertia of the surface materials present and their particle size and/or cohesion. Continuous measurements of wind speed and direction offer a unique opportunity to correlate dust devils and high winds with eolian changes imaged at the surface and to determine the threshold friction wind stress for grain motion on Mars. During the first two weeks after landing, these investigations will support the selection of instrument placement locations that are relatively smooth, flat, free of small rocks and load bearing. Soil mechanics parameters and elastic properties of near surface materials will be determined from mole penetration and thermal conductivity measurements from the surface to 3–5 m depth, the measurement of seismic waves during mole hammering, passive monitoring of seismic waves, and experiments with the arm and scoop of the lander (indentations, scraping and trenching). These investigations will determine and test the presence and mechanical properties of the expected 3–17 m thick fragmented regolith (and underlying fractured material) built up by impact and eolian processes on top of Hesperian lava flows and determine its seismic properties for the seismic investigation of Mars' interior.https://authors.library.caltech.edu/records/g013c-z0j30Closure to "Flow Liquefaction Instability as a Mechanism for Lower End of Liquefaction Charts" by Utkarsh Mital, Toktam Mohammadnejad, and José E. Andrade
https://resolver.caltech.edu/CaltechAUTHORS:20180801-130526379
Authors: {'items': [{'id': 'Mital-U-M', 'name': {'family': 'Mital', 'given': 'U. M.'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'J. E.'}}]}
Year: 2018
DOI: 10.1061/(ASCE)GT.1943-5606.0001932
[no abstract]https://authors.library.caltech.edu/records/tdkkh-2tb28A 3-D mechanics-based particle shape index for granular materials
https://resolver.caltech.edu/CaltechAUTHORS:20180718-090104243
Authors: {'items': [{'id': 'Kawamoto-Reid', 'name': {'family': 'Kawamoto', 'given': 'Reid'}, 'orcid': '0000-0002-4936-5321'}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José'}}, {'id': 'Matsushima-Takashi', 'name': {'family': 'Matsushima', 'given': 'Takashi'}}]}
Year: 2018
DOI: 10.1016/j.mechrescom.2018.07.002
Particle shape plays an important role in the mechanical properties of granular materials. This paper studies the effect it has on particle rotations and stress via a mechanics-based 3-D particle shape index, which is based on an earlier 2-D particle shape index. A level set discrete element method (LS-DEM) simulation, with experimental validation, of a specimen of a natural sand with varying particle shapes, subject to triaxial compression, is analyzed. We show that particles whose shapes allow for more moment transmission—as characterized by the particle shape index—experience less deviation in rotation and contribute more to the macroscopic shear stress, and provide possible micromechanical explanations of these trends. The results have implications in the construction of micromechanics-based granular models and higher-order continuum models.https://authors.library.caltech.edu/records/ypsg6-7qc83Granular object morphological generation with genetic algorithms for discrete element simulations
https://resolver.caltech.edu/CaltechAUTHORS:20181024-135818599
Authors: {'items': [{'id': 'de-Macedo-R-B', 'name': {'family': 'de Macedo', 'given': 'Robert Buarque'}}, {'id': 'Marshall-J-P', 'name': {'family': 'Marshall', 'given': 'Jason P.'}, 'orcid': '0000-0001-6208-1801'}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}]}
Year: 2018
DOI: 10.1007/s10035-018-0845-7
The Discrete Element Method is a popular method for modeling granular materials, however, it is typically limited to geometrically simple objects. A recent extension of this method, the Level Set Discrete Element Method (LS-DEM), overcomes this issue by allowing the use of any particle shape, including morphologically accurate computational grains generated from tomographic images. This method has the ability to provide insight into the physics of granular media that are challenging if granular shape morphology is not accurately represented. One challenge with fully utilizing LS-DEM is gathering the data necessary to reproduce the distinct shapes of grains. In this work, we develop a novel granular generation method that uses genetic algorithms to create new computational grains from a smaller set of input data. This method has the capability of building grains that match any well defined morphological property. We demonstrate the method by generating grains to match sphericity and principal curvature property distributions generated from an existing particle dataset captured with 3D X-Ray tomography.https://authors.library.caltech.edu/records/w1yy8-gkq02Neutron imaging: a new possibility for laboratory observation of hydraulic fractures in shale?
https://resolver.caltech.edu/CaltechAUTHORS:20190117-081917303
Authors: {'items': [{'id': 'Roshankhah-S', 'name': {'family': 'Roshankhah', 'given': 'S.'}, 'orcid': '0000-0002-1160-7882'}, {'id': 'Marshall-J-P', 'name': {'family': 'Marshall', 'given': 'J. P.'}, 'orcid': '0000-0001-6208-1801'}, {'id': 'Tengattini-A', 'name': {'family': 'Tengattini', 'given': 'A.'}}, {'id': 'Ando-E', 'name': {'family': 'Ando', 'given': 'E.'}}, {'id': 'Rubino-V', 'name': {'family': 'Rubino', 'given': 'V.'}, 'orcid': '0000-0002-4023-8668'}, {'id': 'Rosakis-A-J', 'name': {'family': 'Rosakis', 'given': 'A. J.'}, 'orcid': '0000-0003-0559-0794'}, {'id': 'Viggiani-G', 'name': {'family': 'Viggiani', 'given': 'G.'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'J. E.'}}]}
Year: 2018
DOI: 10.1680/jgele.18.00129
Hydraulic fracturing, the creation of fractures by high-pressure fluid injection into a solid medium, is of interest to enhance the permeability of rocks. This complex three-dimensional hydro-mechanical process, however, has only been studied in the laboratory by boundary measurements or acoustic techniques with low spatio-temporal resolutions until now. In this paper, direct, high spatial resolution, and near real-time visualisation results of hydraulic fracture generation and propagation in prismatic specimens of Marcellus shale rock under in situ conditions (70 MPa, plane strain) are presented. Poly-methyl methacrylate specimens are also tested under the same conditions to highlight the importance of rocks' internal structure on the response of the tested rock. The results reveal a complex interaction among the injected fluid, the pre-existing natural fractures in shale structure, and the hydraulically induced fracture highlighting the governing role of rock fabric even under high stresses. These measurements are possible due to the unique sensitivity of neutrons to water. Besides the intrinsic interest of the results presented, this exploratory investigation highlights the potential of neutron imaging in elucidating the evolution of fluid flow and fluid-driven fractures, as X-rays have done for the evolution of solid structure only. Further, understanding of the mechanics of fracking will lead to development of more accurate hydro-mechanical constitutive models thus enabling the design of field operations with higher efficiencies.https://authors.library.caltech.edu/records/4nhek-3gd70Capturing the inter-particle force distribution in granular material using LS-DEM
https://resolver.caltech.edu/CaltechAUTHORS:20190517-105032478
Authors: {'items': [{'id': 'Li-Liuchi', 'name': {'family': 'Li', 'given': 'Liuchi'}}, {'id': 'Marteau-E', 'name': {'family': 'Marteau', 'given': 'Eloïse'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}]}
Year: 2019
DOI: 10.1007/s10035-019-0893-7
Particle shape, as one of the most important physical ingredients of granular materials, can greatly alter the characteristic of inter-particle force distribution which is of vital importance in understanding the mechanical behavior of granular materials. However, currently both experimental and numerical studies remain limited in this regard. In this paper, we for the first time validate the ability of the level set discrete element method (LS-DEM) on capturing the inter-particle force distribution among particles of arbitrary shape. We first present the technical detail of LS-DEM; we then apply LS-DEM to simulate experiments of shearing granular materials composed of arbitrarily shaped particles. The proposed approach directly links experimentally measured material properties to model parameters such as contact stiffness without any calibration. Our results show that LS-DEM is able to not only capture the macro scale response such as stress and deformation, but also to reproduce the particle scale contact information such as the distribution of contact force magnitude, contact orientation and contact friction mobilization. Our work demonstrates the promising potential of LS-DEM on studying the mechanics and physics of natural granular material and on aiding design granular particle shape for novel macro-scale mechanical property.https://authors.library.caltech.edu/records/j5g3p-e5037Reduced Gravity Effects on the Strength of Granular Matter: DEM Simulations versus Experiments
https://resolver.caltech.edu/CaltechAUTHORS:20200409-071639201
Authors: {'items': [{'id': 'Karapiperis-Konstantinos', 'name': {'family': 'Karapiperis', 'given': 'Konstantinos'}, 'orcid': '0000-0002-6796-8900'}, {'id': 'Marshall-J-P', 'name': {'family': 'Marshall', 'given': 'Jason P.'}, 'orcid': '0000-0003-4504-9564'}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}]}
Year: 2020
DOI: 10.1061/(asce)gt.1943-5606.0002232
Quantifying the effect of reduced gravity on the behavior of granular matter is essential to understanding the evolution of planetary morphology and will likely affect the design of future extraterrestrial habitats. Yet despite recent research, the effect of reduced gravity/confining pressure on strength remains undetermined, with scarce results ranging from no effect to opposing trends. In this study, we employ high-fidelity discrete element simulations (DEM) of passive failure experiments to measure the influence of gravity on the peak and steady-state friction angle, and the angle of repose of sand. The results are compared against recently reported physical experiments, lending the latter support based on micromechanical information, that is unattainable experimentally. We find that the friction angles experience a small increase with decreasing gravity, while the angle of repose remains almost constant.https://authors.library.caltech.edu/records/p55ms-gep63Identifying spatial transitions in heterogenous granular flow
https://resolver.caltech.edu/CaltechAUTHORS:20200505-070336456
Authors: {'items': [{'id': 'Li-Liuchi', 'name': {'family': 'Li', 'given': 'Liuchi'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}]}
Year: 2020
DOI: 10.1007/s10035-020-01013-1
It is well known that heterogeneous granular flows exhibit collisional, dense and creep regimes that can coexist in space. How to correctly predict and control such complex phenomena has many applications in both mitigation of natural hazards and optimization of industrial processes. However, it still remains a challenge to establish a predictive granular rheology model due to the lack of understanding of the internal structure variation across different regimes and its interaction with the boundary. In this work, we use DEM simulations to investigate the internal structure of heterogeneous granular flow developed at the center of rotating drum systems. By systematically varying the side wall conditions, we are able to generate various heterogeneous flow fields under different levels of boundary effects. Our extensive simulation results reveal a highly relevant micro-structural quantity δθ=|θ_c−θ_f|, where θ_c and θ_f are the preferred direction of inter-particle contacts and the preferred direction of inter-particle force transmissions, respectively. We show that δθ can characterize the internal structure of granular flow in collisional, dense and creep regimes, and its variation can identify the transition between them. In particular, in dense and collisional regimes, the classical rheological relation between bulk friction μ and inertia number I holds, while in the creep regime, such relation breaks down and μ instead depends on δθ. Our findings hold for all investigated flow fields regardless of the level of boundary effect imposed, and regardless of the amount of shear experienced. δθ thus provides a unified micro-structural characterization for heterogeneous granular flow in different regimes, and lays the foundation of establishing microstructure-informed granular rheology models.https://authors.library.caltech.edu/records/w1gpd-zrk53Effect of fabric on shear wave velocity in granular soils
https://resolver.caltech.edu/CaltechAUTHORS:20200507-073041932
Authors: {'items': [{'id': 'Mital-Utkarsh', 'name': {'family': 'Mital', 'given': 'Utkarsh'}}, {'id': 'Kawamoto-Reid', 'name': {'family': 'Kawamoto', 'given': 'Reid'}, 'orcid': '0000-0002-4936-5321'}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}]}
Year: 2020
DOI: 10.1007/s11440-019-00766-1
The small-strain elastic shear wave velocity (V_S) is a basic mechanical property of soils and is an important parameter in geotechnical engineering. Recently, V_S has been adopted as one of the indices for development of liquefaction charts. This implies that if a parameter affects V_S, it may also affect liquefaction resistance. Some of the parameters whose effects have been accounted for include relative density, stress state and geologic age. An important parameter that affects both liquefaction resistance and VS is fabric. Quantification of in situ fabric is still an open problem and hence, considerable judgement is needed in order to map laboratory test results to field conditions. In this paper, we conduct numerical simulations at the grain-scale to investigate the effect of fabric on V_S. We start by showing that two granular assemblies, with the same stress state and void ratio but different fabrics, can exhibit different trends in liquefaction behavior. Furthermore, via a numerical implementation of the bender element test, we obtain two distinct trends of V_S anisotropy for the two granular assemblies. Finally, we consider three different fabric measures based on contact properties and explore correlations between V_S anisotropy and fabric anisotropy. We also look at fabric tensors of the 'strong' and 'weak' network, respectively, of the granular assemblies. Our results suggest that for liquefiable soils, i.e., recent Holocene-age deposits with negligible cementation and with a stress history of seismic loading, a knowledge of V_S anisotropy can give information about fabric anisotropy. A knowledge of in situ fabric could help in more accurately mapping laboratory test results to field conditions.https://authors.library.caltech.edu/records/e4sqq-t2h82Level set splitting in DEM for modeling breakage mechanics
https://resolver.caltech.edu/CaltechAUTHORS:20200325-123343396
Authors: {'items': [{'id': 'Harmon-J-M', 'name': {'family': 'Harmon', 'given': 'John M.'}}, {'id': 'Arthur-D', 'name': {'family': 'Arthur', 'given': 'Daniel'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}]}
Year: 2020
DOI: 10.1016/j.cma.2020.112961
Brittle breakage of particles in granular materials has often been modeled using the discrete element method (DEM). DEM is often limited however in its ability to capture particle shape, particularly when used for breakage. This paper presents the first brittle breakage technique where level set functions will allow for the description of arbitrary shape for both particles and fracture surfaces. The breakage model to be described here uses fracture surfaces defined by level sets to take advantage of simple intersection and difference set operations to split particles in both two and three dimensions. We show how this method is implemented and how we can use it to define and apply arbitrary fracture surface shapes. We then give qualitative examples of using the method in both simple and exotic ways. Finally, we model oedometric tests and rock crushing, both very common uses for previous DEM breakage techniques, to present a validation that the method captures the physics of the problem.https://authors.library.caltech.edu/records/r9hxm-g8h61Investigating the Incremental Behavior of Granular Materials with the Level-Set Discrete Element Method
https://resolver.caltech.edu/CaltechAUTHORS:20200810-135425147
Authors: {'items': [{'id': 'Karapiperis-Konstantinos', 'name': {'family': 'Karapiperis', 'given': 'Konstantinos'}, 'orcid': '0000-0002-6796-8900'}, {'id': 'Harmon-John', 'name': {'family': 'Harmon', 'given': 'John'}}, {'id': 'Andò-Edward', 'name': {'family': 'Andò', 'given': 'Edward'}, 'orcid': '0000-0001-5509-5287'}, {'id': 'Viggiani-Gioacchino', 'name': {'family': 'Viggiani', 'given': 'Gioacchino'}, 'orcid': '0000-0002-2609-6077'}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}]}
Year: 2020
DOI: 10.1016/j.jmps.2020.104103
A computational framework is presented for high-fidelity virtual (in silico) experiments on granular materials. By building on i) accurate mathematical representation of particle morphology and contact interaction, ii) full control of the initial state of the assembly, and iii) discrete element simulation of arbitrary stress paths, the proposed framework overcomes important limitations associated with conventional experiments and simulations. The framework is utilized to investigate the incremental response of sand through stress probing experiments, focusing on key aspects such as elasticity and reversibility, yielding and plastic flow, as well as hardening and fabric evolution. It is shown that reversible strain envelopes are contained within elastic envelopes during axisymmetric loading, the yield locus follows approximately the Lade-Duncan criterion, and the plastic flow rule exhibits complex nonassociativity and minor irregularity. Hardening processes are delineated by examining the stored plastic work and the fabric evolution in the strong and weak networks. Special attention is given to isolating in turn the effect of particle shape and interparticle friction on the macroscopic response. Interestingly, idealization of particle shape preserves qualitatively most aspects of material behavior, but proves quantitatively inadequate especially in anisotropic stress states. The results point to the importance of accurately resolving particle-scale interactions, that allows macroscopic behavior to emerge free from spurious micromechanical artifacts present in an idealized setting.https://authors.library.caltech.edu/records/vfdky-y1z79Effect of Confinement on Capillary Phase Transition in Granular Aggregates
https://resolver.caltech.edu/CaltechAUTHORS:20200908-135709048
Authors: {'items': [{'id': 'Monfared-Siavash', 'name': {'family': 'Monfared', 'given': 'Siavash'}, 'orcid': '0000-0002-7629-7977'}, {'id': 'Zhou-Tingtao', 'name': {'family': 'Zhou', 'given': 'Tingtao'}, 'orcid': '0000-0002-1766-719X'}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}, {'id': 'Ioannidou-Katerina', 'name': {'family': 'Ioannidou', 'given': 'Katerina'}, 'orcid': '0000-0001-5454-5418'}, {'id': 'Radjai-Farhang', 'name': {'family': 'Radjai', 'given': 'Farhang'}, 'orcid': '0000-0003-1376-7705'}, {'id': 'Ulm-Franz-Josef', 'name': {'family': 'Ulm', 'given': 'Franz-Josef'}, 'orcid': '0000-0002-7089-8069'}, {'id': 'Pellenq-Roland-J-M', 'name': {'family': 'Pellenq', 'given': 'Roland J.-M.'}}]}
Year: 2020
DOI: 10.1103/PhysRevLett.125.255501
Using a 3D mean-field lattice-gas model, we analyze the effect of confinement on the nature of capillary phase transition in granular aggregates with varying disorder and their inverse porous structures obtained by interchanging particles and pores. Surprisingly, the confinement effects are found to be much less pronounced in granular aggregates as opposed to porous structures. We show that this discrepancy can be understood in terms of the surface-surface correlation length with a connected path through the fluid domain, suggesting that this length captures the true degree of confinement. We also find that the liquid-gas phase transition in these porous materials is of second order nature near capillary critical temperature, which is shown to represent a true critical temperature, i.e., independent of the degree of disorder and the nature of the solid matrix, discrete or continuous. The critical exponents estimated here from finite-size scaling analysis suggest that this transition belongs to the 3D random field Ising model universality class as hypothesized by F. Brochard and P.G. de Gennes, with the underlying random fields induced by local disorder in fluid-solid interactions.https://authors.library.caltech.edu/records/eab0r-k7092Nonlocality in granular complex networks: Linking topology, kinematics and forces
https://resolver.caltech.edu/CaltechAUTHORS:20201105-160425508
Authors: {'items': [{'id': 'Karapiperis-Konstantinos', 'name': {'family': 'Karapiperis', 'given': 'K.'}, 'orcid': '0000-0002-6796-8900'}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'J. E.'}}]}
Year: 2021
DOI: 10.1016/j.eml.2020.101041
Dry granular systems respond to shear by a process of self-organization that is nonlocal in nature. This study reveals the interplay between the topological, kinematical and force signature of this process during shear banding in an sample of angular sand. Using Level-Set Discrete Element simulations of an in-situ triaxial compression experiment, and complex networks techniques, we identify communities of similar topology (cycles), kinematics (vortex clusters) and kinetics (force chains), and study their cooperative evolution. We conclude by discussing the implications of our observations for continuum modeling, including the identification of mesoscale order parameters, and the development of nonaffine kinematics models.https://authors.library.caltech.edu/records/n83rh-drb37Mechanical behaviour of granular media in flexible boundary plane strain conditions: experiment and level-set discrete element modelling
https://resolver.caltech.edu/CaltechAUTHORS:20200604-154745728
Authors: {'items': [{'id': 'Bhattacharya-Debayan', 'name': {'family': 'Bhattacharya', 'given': 'Debayan'}}, {'id': 'Kawamoto-Reid', 'name': {'family': 'Kawamoto', 'given': 'Reid'}, 'orcid': '0000-0002-4936-5321'}, {'id': 'Karapiperis-Konstantinos', 'name': {'family': 'Karapiperis', 'given': 'Konstantinos'}, 'orcid': '0000-0002-6796-8900'}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}, {'id': 'Prashant-Amit', 'name': {'family': 'Prashant', 'given': 'Amit'}, 'orcid': '0000-0002-0841-5951'}]}
Year: 2021
DOI: 10.1007/s11440-020-00996-8
This article presents the results of level-set (LS) discrete element method (DEM) simulations with experimental comparisons of flexible boundary plane strain tests in granular media. The grain-scale micromechanics at the particle level is captured well with LS-DEM, while the overall macroscopic response of the specimen is in quite good agreement with the simulation results. Onset and evolution of localized zones of shear strain accompanied by a significant amount of grain rotation could be well apprehended in the simulations, while the bulging of the specimen could be noticed in the experimental findings as well as in the model predictions. Multiple zones of shear strain accumulation in conjugate arrays were also observed on subsequent biaxial shearing of the sand specimen. The computational results furnish a quantitative estimate of the evolution of force chains and grain fabric orientation. Initially, these force chains were isotropic which on further deformation oriented in the direction of loading, and the grains aligned themselves in their preferred fabric orientation and remained in that fashion till the end of biaxial loading.https://authors.library.caltech.edu/records/sa5jg-sp258Data-Driven Multiscale Modeling in Mechanics
https://resolver.caltech.edu/CaltechAUTHORS:20201123-120506132
Authors: {'items': [{'id': 'Karapiperis-Konstantinos', 'name': {'family': 'Karapiperis', 'given': 'K.'}, 'orcid': '0000-0002-6796-8900'}, {'id': 'Stainier-Laurent', 'name': {'family': 'Stainier', 'given': 'L.'}, 'orcid': '0000-0001-6719-6616'}, {'id': 'Ortiz-M', 'name': {'family': 'Ortiz', 'given': 'M.'}, 'orcid': '0000-0001-5877-4824'}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'J. E.'}}]}
Year: 2021
DOI: 10.1016/j.jmps.2020.104239
We present a Data-Driven framework for multiscale mechanical analysis of materials. The proposed framework relies on the Data-Driven formulation in mechanics (Kirchdoerfer and Ortiz 2016), with the material data being directly extracted from lower-scale computations. Particular emphasis is placed on two key elements: the parametrization of material history, and the optimal sampling of the mechanical state space. We demonstrate an application of the framework in the prediction of the behavior of sand, a prototypical complex history-dependent material. In particular, the model is able to predict the material response under complex nonmonotonic loading paths, and compares well against plane strain and triaxial compression shear banding experiments.https://authors.library.caltech.edu/records/b2s76-b8s23Modelling the influence of fines content on the instability of silty sands considering grain scale interactions
https://resolver.caltech.edu/CaltechAUTHORS:20210715-194108149
Authors: {'items': [{'id': 'Le-Linh-A', 'name': {'family': 'Le', 'given': 'Linh A.'}, 'orcid': '0000-0002-3560-7481'}, {'id': 'Nguyen-Giang-D', 'name': {'family': 'Nguyen', 'given': 'Giang D.'}, 'orcid': '0000-0002-8366-1693'}, {'id': 'Bui-Ha-Hong', 'name': {'family': 'Bui', 'given': 'Ha H.'}, 'orcid': '0000-0001-8071-5433'}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}]}
Year: 2021
DOI: 10.1016/j.ijplas.2021.103020
Experimental observations have shown the significant influence of silt grains on the instability and liquefaction characteristics of the host sands, but modelling such sand-silt mixtures remains a challenge, due to the complex interactions between fine silt grains and coarse sand grains. This paper presents a constitutive model based on the mechanism of grain-to-grain contacts to capture the behaviour of silty sands in both drained and undrained conditions. Grain scale contact behaviour is modelled using intrinsic void ratio and phenomenological constitutive relationships, and explicitly connected with the macro behaviour. This paves the way for the inclusion of the influence of silt grains on the stiffness and dilation/compaction tendency of the contacts, which in turn control the evolution of macro stress and strain. As a result, the effects of fines contents, stress states and initial densities on the liquefaction characteristics of silty sands can be captured in the proposed model based on phenomenological grain scale constitutive models. Validation against experimental data demonstrates reasonable predictive capabilities of the model in capturing the responses of silty sands with different fines contents. The proposed model is shown to be effective in predicting the onset and progressive development of liquefaction, as a result of changes caused by the addition of fine grains and its interaction with host sands.https://authors.library.caltech.edu/records/qmy15-87542Structured fabrics with tunable mechanical properties
https://resolver.caltech.edu/CaltechAUTHORS:20210519-124245707
Authors: {'items': [{'id': 'Wang-Yifan', 'name': {'family': 'Wang', 'given': 'Yifan'}, 'orcid': '0000-0001-9965-9777'}, {'id': 'Li-Liuchi', 'name': {'family': 'Li', 'given': 'Liuchi'}, 'orcid': '0000-0002-1360-4757'}, {'id': 'Hofmann-Douglas-C', 'name': {'family': 'Hofmann', 'given': 'Douglas'}, 'orcid': '0000-0002-0872-5239'}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}, {'id': 'Daraio-C', 'name': {'family': 'Daraio', 'given': 'Chiara'}, 'orcid': '0000-0001-5296-4440'}]}
Year: 2021
DOI: 10.1038/s41586-021-03698-7
Structured fabrics, such as woven sheets or chain mail armours, derive their properties both from the constitutive materials and their geometry. Their design can target desirable characteristics, such as high impact resistance, thermal regulation, or electrical conductivity. Once realized, however, the fabrics' properties are usually fixed. Here we demonstrate structured fabrics with tunable bending modulus, consisting of three-dimensional particles arranged into layered chain mails. The chain mails conform to complex shapes, but when pressure is exerted at their boundaries, the particles interlock and the chain mails jam. We show that, with small external pressure (about 93 kilopascals), the sheets become more than 25 times stiffer than in their relaxed configuration. This dramatic increase in bending resistance arises because the interlocking particles have high tensile resistance, unlike what is found for loose granular media. We use discrete-element simulations to relate the chain mail's micro-structure to macroscale properties and to interpret experimental measurements. We find that chain mails, consisting of different non-convex granular particles, undergo a jamming phase transition that is described by a characteristic power-law function akin to the behaviour of conventional convex media. Our work provides routes towards lightweight, tunable and adaptive fabrics, with potential applications in wearable exoskeletons, haptic architectures and reconfigurable medical supports.https://authors.library.caltech.edu/records/t74qg-92f12Implications of Buckingham's Pi Theorem to the Study of Similitude in Discrete Structures: Introduction of the R_F^N, μ^N, and S^N Dimensionless Numbers and the Concept of Structural Speed
https://resolver.caltech.edu/CaltechAUTHORS:20210929-175142710
Authors: {'items': [{'id': 'Rosakis-A-J', 'name': {'family': 'Rosakis', 'given': 'Ares J.'}, 'orcid': '0000-0003-0559-0794'}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}, 'orcid': '0000-0003-3741-0364'}, {'id': 'Gabuchian-Vahe', 'name': {'family': 'Gabuchian', 'given': 'Vahe'}}, {'id': 'Harmon-John-M', 'name': {'family': 'Harmon', 'given': 'John M.'}}, {'id': 'Conte-Joel-P', 'name': {'family': 'Conte', 'given': 'Joel P.'}, 'orcid': '0000-0003-2068-7965'}, {'id': 'Restrepo-José-I', 'name': {'family': 'Restrepo', 'given': 'José I.'}}, {'id': 'Rodriguez-Andrés', 'name': {'family': 'Rodriguez', 'given': 'Andrés'}}, {'id': 'Nema-Arpit', 'name': {'family': 'Nema', 'given': 'Arpit'}}, {'id': 'Pedretti-Andrea-R', 'name': {'family': 'Pedretti', 'given': 'Andrea R.'}}]}
Year: 2021
DOI: 10.1115/1.4051338
Motivated by the need to evaluate the seismic response of large-capacity gravity energy storage systems (potential energy batteries) such as the proposed frictional Multiblock Tower Structures (MTS) recently discussed by Andrade et al. (2021, "Seismic Performance Assessment of Multiblock Tower Structures As Gravity Energy Storage Systems," ASME J. Appl. Mech., Submitted), we apply Buckingham's Pi theorem (Buckingham, E., 1914, "On Physically Similar Systems; Illustrations of the Use of Dimensional Equations," Phys. Rev., 4, pp. 345–376) to identify the most general forms of dimensionless numbers and dynamic similitude laws appropriate for scaling discontinuous multiblock structural systems involving general restoring forces resisting inertial loading. We begin by introducing the dimensionless "mu-number" (μ^N) appropriate for both gravitational and frictional restoring forces and then generalize by introducing the "arbitrary restoring force number" (R^N_F). R^N_F is subsequently employed to study similitude in various types of discontinuous or discrete systems featuring frictional, gravitational, cohesive, elastic, and mixed restoring forces acting at the block interfaces. In the process, we explore the additional consequences of inter and intra-block elasticity on scaling. We also formulate a model describing the mechanism of structural signal transmission for the case of rigid MTS featuring inter-block restoring forces composed of elastic springs and interfacial friction, introducing the concept of "structural speed." Finally, we validate our results by demonstrating that dynamic time-histories of field quantities and structural speeds between MTS models at various scales are governed by our proposed similitude laws, thus demonstrating the consistency of our approach.https://authors.library.caltech.edu/records/q7dmg-rs666Unearthing real-time 3D ant tunneling mechanics
https://resolver.caltech.edu/CaltechAUTHORS:20210824-153629422
Authors: {'items': [{'id': 'Buarque-de-Macedo-Robert', 'name': {'family': 'Buarque de Macedo', 'given': 'Robert'}, 'orcid': '0000-0002-2218-4117'}, {'id': 'Andò-Edward', 'name': {'family': 'Andò', 'given': 'Edward'}, 'orcid': '0000-0001-5509-5287'}, {'id': 'Joy-Shilpa', 'name': {'family': 'Joy', 'given': 'Shilpa'}, 'orcid': '0000-0002-0169-7036'}, {'id': 'Viggiani-Gioacchino', 'name': {'family': 'Viggiani', 'given': 'Gioacchino'}, 'orcid': '0000-0002-2609-6077'}, {'id': 'Pal-Raj-Kumar', 'name': {'family': 'Pal', 'given': 'Raj Kumar'}, 'orcid': '0000-0001-5039-7710'}, {'id': 'Parker-J', 'name': {'family': 'Parker', 'given': 'Joseph'}, 'orcid': '0000-0001-9598-2454'}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}, 'orcid': '0000-0003-3741-0364'}]}
Year: 2021
DOI: 10.1073/pnas.2102267118
PMCID: PMC8433525
Granular excavation is the removal of solid, discrete particles from a structure composed of these objects. Efficiently predicting the stability of an excavation during particle removal is an unsolved and highly nonlinear problem, as the movement of each grain is coupled to its neighbors. Despite this, insects such as ants have evolved to be astonishingly proficient excavators, successfully removing grains such that their tunnels are stable. Currently, it is unclear how ants use their limited information about the environment to construct lasting tunnels. We attempt to unearth the ants' tunneling algorithm by taking three-dimensional (3D) X-ray computed tomographic imaging (XRCT), in real time, of Pogonomyrmex ant tunnel construction. By capturing the location and shape of each grain in the domain, we characterize the relationship between particle properties and ant decision-making within an accurate, virtual recreation of the experiment. We discover that intergranular forces decrease significantly around ant tunnels due to arches forming within the soil. Due to this force relaxation, any grain the ants pick from the tunnel surface will likely be under low stress. Thus, ants avoid removing grains compressed under high forces without needing to be aware of the force network in the surrounding material. Even more, such arches shield tunnels from high forces, providing tunnel robustness. Finally, we observe that ants tend to dig piecewise linearly downward. These results are a step toward understanding granular tunnel stability in heterogeneous 3D systems. We expect that such findings may be leveraged for robotic excavation.https://authors.library.caltech.edu/records/nm7th-hgm94Undrained instability detection under general stress conditions
https://resolver.caltech.edu/CaltechAUTHORS:20210727-192410218
Authors: {'items': [{'id': 'Leguizamón-Barreto-Luis-C', 'name': {'family': 'Leguizamón-Barreto', 'given': 'Luis C.'}, 'orcid': '0000-0002-3316-3768'}, {'id': 'Ramos-Cañón-Alfonso-M', 'name': {'family': 'Ramos-Cañón', 'given': 'Alfonso M.'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}]}
Year: 2021
DOI: 10.1007/s11440-021-01241-6
This work proposes a criterion for the detection of undrained instability under multiaxial stress conditions at elemental level. To do so, it develops the application of the proposed criterion to the implicit implementation of a multiaxial elastoplastic constitutive model, which considers the effect of inherent anisotropy for the simulation of monotonic loading. The general criterion proposed is validated through the simulation of undrained torsional shear tests in Toyoura sand. The application of the criterion shows precision at onset of both liquefaction and phase transformation mechanisms, in general stress conditions through the variation of the intermediate principal stress ratio b. By considering different ranges of the initial void ratio and confining pressure, the representation of the collapse surface in three-dimensional stress space and in critical state space is shown and the phase transformation surface is presented in the critical state space. The interaction of the collapse and phase transformation surfaces offers the possibility of better understanding the influence of the initial void ratio and the confining pressure in the mechanical behavior of geomaterials in undrained conditions and the occurrence of the related instability processes.https://authors.library.caltech.edu/records/wya5v-vcp96Tunnel excavation in granular media: the role of force chains
https://resolver.caltech.edu/CaltechAUTHORS:20210930-191255538
Authors: {'items': [{'id': 'Pal-Raj-Kumar', 'name': {'family': 'Pal', 'given': 'Raj Kumar'}, 'orcid': '0000-0001-5039-7710'}, {'id': 'de-Macedo-Robert-Buraque', 'name': {'family': 'de Macedo', 'given': 'Robert Buraque'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}, 'orcid': '0000-0003-3741-0364'}]}
Year: 2021
DOI: 10.1007/s10035-021-01141-2
We investigate how force chains in a granular packing influence and change during a tunnel excavation process. A two-dimensional (2D) frictional cohensionless packing is considered under gravity and a set of contiguous particles are removed in the interior. Using discrete element simulations on realistic non-spherical soil grains, we investigate the role of force chains in the stability of the resulting tunnel. We illustrate that force disturbance due to excavation is transmitted over considerable distance by force chains. Such force chains behave as one-dimensional (1D) load carrying members, leading to nonlocal influences on tunnel stability as these chains rearrange around tunnels. Based on these observations, we posit the non-existence of a local stability prediction criterion that examines only the set of grains adjacent to the tunnel boundary. Finally, we study the mechanics of transition to the new equilibrium configuration by examining how the various components of force disturbance vary with distance from the tunnel. This work lays the framework for a systematic analysis of granular excavation process by examining how forces applied in the domain interior are transmitted into the granular media.https://authors.library.caltech.edu/records/mbsg7-qzm34Emerging contact force heterogeneity in ordered soft granular media
https://resolver.caltech.edu/CaltechAUTHORS:20210927-225706408
Authors: {'items': [{'id': 'Li-Liuchi', 'name': {'family': 'Li', 'given': 'Liuchi'}, 'orcid': '0000-0002-1360-4757'}, {'id': 'Karapiperis-Konstantinos', 'name': {'family': 'Karapiperis', 'given': 'Konstantinos'}, 'orcid': '0000-0002-6796-8900'}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}, 'orcid': '0000-0003-3741-0364'}]}
Year: 2021
DOI: 10.1016/j.mechmat.2021.104055
Under external perturbations, inter-particle forces in disordered granular media are well known to form a heterogeneous distribution with filamentary patterns. Better understanding these forces and the distribution is important for predicting the collective behavior of granular media, the media second only to water as the most manipulated material in global industry. However, studies in this regard so far have been largely confined to granular media exhibiting only geometric heterogeneity, leaving the dimension of mechanical heterogeneity a rather uncharted area. Here, through a FEM contact mechanics model, we show that a heterogeneous inter-particle force distribution can also emerge from the dimension of mechanical heterogeneity alone. Specifically, we numerically study inter-particle forces in packing of mechanically heterogeneous disks arranged over either a square or a hexagonal lattice and under quasi-static isotropic compression. Our results show that, at the system scale, a hexagonal packing exhibit a more heterogeneous inter-particle force distribution than a square packing does; At the particle scale, for both packing lattices, preliminary analysis shows the consistent coexistence of outliers (i.e., softer disks sustaining larger forces while stiffer disks sustaining smaller forces) in comparison to their homogeneous counterparts, which implies the existence of nonlocal effect. Further analysis on the portion of outliers and on spatial contact force correlations suggest that the hexagonal packing shows more pronounced nonlocal effect over the square packing under small mechanical heterogeneity. However, such trend is reversed when assemblies becomes more mechanically heterogeneous. Lastly, we confirm that, in the absence of particle reorganization events, contact friction merely plays the role of packing stabilization while its variation has little effect on inter-particle forces and their distribution.https://authors.library.caltech.edu/records/v7sdk-aez24An Experimental Study of the Effect of Particle Shape on Force Transmission and Mobilized Strength of Granular Materials
https://resolver.caltech.edu/CaltechAUTHORS:20211022-213955248
Authors: {'items': [{'id': 'Marteau-Eloïse', 'name': {'family': 'Marteau', 'given': 'Eloïse'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}, 'orcid': '0000-0003-3741-0364'}]}
Year: 2021
DOI: 10.1115/1.4051818
Force chains have been regarded as an important hallmark of granular materials. Numerous studies have examined their evolution, properties, and statistics in highly idealized, often circular-shaped, granular assemblies. However, particles found in nature and handled in industries come in a wide variety of shapes. In this article, we experimentally investigate the robustness of force chains with respect to particle shape. We present a detailed analysis on the particle- to continuum-scale response of granular materials affected by particle shape, which includes the force transmission and mobilized shear strength. The effect of shape is studied by comparing experimental results collected from shear tests performed on 2D analog circular- and arbitrarily shaped granular assemblies. Particle shapes are directly discretized from X-ray CT images of a real sand sample. By inferring individual contact forces using the granular element method (GEM), we provide a direct visualization of the force network, a statistical characterization of the force transmission and a quantitative description of the shear strength in terms of rolling, sliding, and interlocking contact mechanisms. We report that force chains are less prevalent in assemblies of arbitrarily-shaped particles than in circular-shaped samples. Furthermore, interlocking is identified as the essential contact mechanism that (1) furnishes a stable structure for force chains to emerge and (2) explains the enhanced shear strength observed in the arbitrarily-shaped samples. These findings highlight the importance of accounting for particle shape to capture and predict the complex mechanical behavior of granular materials across scales.https://authors.library.caltech.edu/records/8znea-e4y09Data-Driven nonlocal mechanics: Discovering the internal length scales of materials
https://resolver.caltech.edu/CaltechAUTHORS:20210908-171123194
Authors: {'items': [{'id': 'Karapiperis-Konstantinos', 'name': {'family': 'Karapiperis', 'given': 'K.'}, 'orcid': '0000-0002-6796-8900'}, {'id': 'Ortiz-M', 'name': {'family': 'Ortiz', 'given': 'M.'}, 'orcid': '0000-0001-5877-4824'}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'J. E.'}}]}
Year: 2021
DOI: 10.1016/j.cma.2021.114039
Nonlocal effects permeate most microstructured materials, including granular media, metals and foams. The quest for predictive nonlocal mechanical theories with well-defined internal length scales has been ongoing for more than a century since the seminal work of the Cosserats. We present here a novel framework for the nonlocal analysis of material behavior, which bypasses the need to define any internal length scale. This is achieved by extending the Data-Driven paradigm in mechanics, originally introduced for simple continua, into generalized continua. The problem is formulated directly on a material data set, comprised of higher-order kinematics and their conjugate kinetics, which are identified from experiments or inferred from lower scale computations. The case of a micropolar continuum is used as a vehicle to introduce the framework, which may also be adapted to strain-gradient and micromorphic media. Two applications are presented: a micropolar elastic plate with a hole, which is used to demonstrate the convergence properties of the method, and the shear banding problem of a triaxially compressed sample of quartz sand, which is used to demonstrate the applicability of the method in the case of complex history-dependent material behavior.https://authors.library.caltech.edu/records/mvx1v-5qg28Bridging length scales in granular materials using convolutional neural networks
https://resolver.caltech.edu/CaltechAUTHORS:20210506-104707586
Authors: {'items': [{'id': 'Mital-Utkarsh', 'name': {'family': 'Mital', 'given': 'Utkarsh'}, 'orcid': '0000-0001-9794-382X'}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}}]}
Year: 2022
DOI: 10.1007/s40571-021-00405-1
Granular materials are complex systems whose macroscopic mechanics are governed by particles at the grain-scale. The need to understand their grain-scale behavior has motivated significant experimental and modeling efforts. Bridging the grain-scale with the continuum scale is important in order to develop constitutive theories based on grain-scale behavior, as well as for interpreting the results of grain-scale models and experiments from a macroscopic context. In this work, we present a new data-driven framework based on convolutional neural networks to bridge the grain-scale and continuum scale in granular materials. We use this framework to obtain a micromechanical model of stress and demonstrate that spatial correlations at the grain-scale are critical for bridging length scales. Our results suggest that it is possible to learn data-driven relationships between the grain-scale and macroscale even if we have limited knowledge about the physical state of a granular system. We also observed that it is possible to train a model to predict macroscopic stress using only a subset of the contact data for each time step. This points to the discovery of a new pattern in granular systems, whereby any spatially correlated subset of contact data is sufficient to model macroscopic stress, regardless of how much force they may be carrying. Finally, we demonstrated that our framework is robust with potential for generalizability in time.https://authors.library.caltech.edu/records/82kw8-sfw64Localised failure of geomaterials: how to extract localisation band behaviour from macro test data
https://resolver.caltech.edu/CaltechAUTHORS:20220715-744243000
Authors: {'items': [{'id': 'Le-Linh-A', 'name': {'family': 'Le', 'given': 'Linh A.'}, 'orcid': '0000-0002-3560-7481'}, {'id': 'Nguyen-Giang-D', 'name': {'family': 'Nguyen', 'given': 'Giang D.'}, 'orcid': '0000-0003-2348-7563'}, {'id': 'Bui-Ha-Hong', 'name': {'family': 'Bui', 'given': 'Ha H.'}, 'orcid': '0000-0001-8071-5433'}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}, 'orcid': '0000-0003-3741-0364'}]}
Year: 2022
DOI: 10.1680/jgeot.20.p.105
The formulation and calibration of constitutive models for geomaterials require material behaviour from experiments under a wide range of triaxial loading conditions. However, failure of geomaterials usually involves localisation of deformation that leads to very strong inhomogeneous behaviour. Therefore, the experimentally measured macro (specimen) behaviour is a mix between very different responses inside and outside the localisation zone and thus should not be used as a true representation of the material responses. This paper proposes a theoretical framework that provides links between mechanical responses inside and outside the localisation band, alongside their contributions toward the overall behaviour of a specimen undergoing localised deformation. This meso–macro connection allows the quantification of behaviour inside the localisation band, which is the main source of material inelasticity, from experimentally measured specimen behaviour. Correlation between the thickness of the localisation band and its behaviour is shown, bounded by a unique stress–deformation relationship describing the behaviour of an idealised zero-thickness localisation band.https://authors.library.caltech.edu/records/3x2e0-33192Insight into contact forces in crushable sand using experiments and predictive particle-scale modelling
https://resolver.caltech.edu/CaltechAUTHORS:20220715-744256000
Authors: {'items': [{'id': 'Harmon-John-M', 'name': {'family': 'Harmon', 'given': 'John M.'}}, {'id': 'Seo-Dawa', 'name': {'family': 'Seo', 'given': 'Dawa'}}, {'id': 'Buscarnera-Giuseppe', 'name': {'family': 'Buscarnera', 'given': 'Giuseppe'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}, 'orcid': '0000-0003-3741-0364'}]}
Year: 2022
DOI: 10.1680/jgeot.21.00212
In this paper, an attempt is made to predict the evolving statistics of inter-particle contact forces during comminution using grain-scale computational modelling. A validation is first carried out by creating a one-to-one virtual avatar of an Ottawa sand specimen from three-dimensional X-ray tomography with level sets and comparing the data from an oedometric test to the model's prediction. The predictive capabilities are confirmed by comparing the constitutive response, grain size distribution and changes in particle shapes in both the experiment and model. Once validated, the predicted contact forces and particle stresses are investigated. It is found that the largest particles experience the largest forces. Despite larger particles being weaker on average, many survive because they are on the stronger side of the particle strength distribution and also have a higher coordination number producing a more isotropic stress state in the particle. These highest forces are largely aligned with the specimen axis, demonstrating that larger particles provide the strength in the loading direction. Meanwhile forces in the radial direction are more broadly distributed, indicating that small particles play a significant part in providing radial stability.https://authors.library.caltech.edu/records/rayer-9v081Stress transmission in entangled granular structures
https://resolver.caltech.edu/CaltechAUTHORS:20220714-369159000
Authors: {'items': [{'id': 'Karapiperis-Konstantinos', 'name': {'family': 'Karapiperis', 'given': 'K.'}, 'orcid': '0000-0002-6796-8900'}, {'id': 'Monfared-Siavash', 'name': {'family': 'Monfared', 'given': 'S.'}, 'orcid': '0000-0002-7629-7977'}, {'id': 'Buarque-de-Macedo-Robert', 'name': {'family': 'Buarque de Macedo', 'given': 'R.'}, 'orcid': '0000-0002-2218-4117'}, {'id': 'Richardson-S', 'name': {'family': 'Richardson', 'given': 'S.'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'J. E.'}, 'orcid': '0000-0003-3741-0364'}]}
Year: 2022
DOI: 10.1007/s10035-022-01252-4
We study the transmission of compressive and tensile stresses, and the development of stress - induced anisotropy in entangled granular structures composed of nonconvex S-shaped hooks and staples. Utilizing discrete element simulations, we find that these systems exhibit fundamentally different behavior compared to standard convex particle systems, including the ability to entangle which contributes to a lower jamming packing fraction and facilitates the transmission of tensile stresses. We present direct evidence of tensile stress chains, and show that these chains are generally sparser, shorter and shorter-lived than the compressive chains found in convex particle packings. We finally study the probability distribution, angular density and anisotropic spatial correlation of the minor (compressive) and major (tensile) particle stresses. The insight gained for these systems can help the design of reconfigurable and recyclable granular structures capable of bearing considerable loads, without any need for reinforcement.https://authors.library.caltech.edu/records/jdnx9-8q259Measuring Terzaghi's effective stress by decoding force transmission in fluid-saturated granular media
https://resolver.caltech.edu/CaltechAUTHORS:20220517-424836000
Authors: {'items': [{'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'J. E.'}, 'orcid': '0000-0003-3741-0364'}, {'id': 'Gu-Zichen', 'name': {'family': 'Gu', 'given': 'Z.'}}, {'id': 'Monfared-Siavash', 'name': {'family': 'Monfared', 'given': 'S.'}, 'orcid': '0000-0002-7629-7977'}, {'id': 'Mac-Donald-Kimberley-Ann', 'name': {'family': 'Mac Donald', 'given': 'K. A.'}, 'orcid': '0000-0003-4512-9740'}, {'id': 'Ravichandran-G', 'name': {'family': 'Ravichandran', 'given': 'G.'}, 'orcid': '0000-0002-2912-0001'}]}
Year: 2022
DOI: 10.1016/j.jmps.2022.104912
Force transmission between solid and fluid phases in fluid-saturated granular systems is yet to be fully resolved. This is rooted in our inability to measure inter-particle forces in opaque systems in the presence of fluids. At the same time, the concept of effective stress was introduced by Karl Terzaghi a century ago, but this empirical approach is yet to be linked to grain-scale phenomena experimentally. To this end, we derive an expression for the effective stress based on inter-particle forces and use a hybrid optical–mechanical method to directly measure the evolution of inter-particle forces and effective stress, offering a new perspective on how forces are distributed between solid and fluid phases. While our derivation and measurement of effective stress focuses on the limiting case of the Terzaghi stress, the methodology presented herein could be extended to more general situations, such as unsaturated conditions, where the micro-mechanical origin of effective stress remains elusive.https://authors.library.caltech.edu/records/f417k-3v741A Framework to Assess the Seismic Performance of Multiblock Tower Structures as Gravity Energy Storage Systems
https://resolver.caltech.edu/CaltechAUTHORS:20221205-666301600.10
Authors: {'items': [{'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}, 'orcid': '0000-0003-3741-0364'}, {'id': 'Rosakis-A-J', 'name': {'family': 'Rosakis', 'given': 'Ares J.'}, 'orcid': '0000-0003-0559-0794'}, {'id': 'Conte-Joel-P', 'name': {'family': 'Conte', 'given': 'Joel P.'}, 'orcid': '0000-0003-2068-7965'}, {'id': 'Restrepo-José-I', 'name': {'family': 'Restrepo', 'given': 'José I.'}}, {'id': 'Gabuchian-Vahe', 'name': {'family': 'Gabuchian', 'given': 'Vahe'}}, {'id': 'Harmon-John-M', 'name': {'family': 'Harmon', 'given': 'John M.'}}, {'id': 'Rodriguez-Andrés', 'name': {'family': 'Rodriguez', 'given': 'Andrés'}}, {'id': 'Nema-Arpit', 'name': {'family': 'Nema', 'given': 'Arpit'}}, {'id': 'Pedretti-Andrea-R', 'name': {'family': 'Pedretti', 'given': 'Andrea R.'}}]}
Year: 2023
DOI: 10.1061/(asce)em.1943-7889.0002159
This paper proposes a framework for seismic performance assessment of mutiblock tower structures designed to store renewable energy. To perform our assessment, we deployed, in tandem, physical and numerical models that were developed using appropriate scaling for Newtonian systems that interact via frictional contact. The approach is novel, breaking away from continuum structures for which Cauchy scaling and continuum mechanics are used to model systems. We show that our discontinuous approach is predictive and consistent. We demonstrate predictiveness by showing that the numerical models can reproduce with high fidelity the physical models deployed across two different scales. Consistency is demonstrated by showing that our models can be seamlessly compared across scales and without regard for whether the model is physical or numerical. The integrated theoretical-numerical-experimental approach provides a robust framework to study multiblock tower structures, and the results of our seismic performance assessments are promising. These findings may open the door for new analysis tools in structural mechanics, particularly those applied to gravity energy storage systems.https://authors.library.caltech.edu/records/bb5m8-dbf50What is shape? Characterizing particle morphology with genetic algorithms and deep generative models
https://resolver.caltech.edu/CaltechAUTHORS:20221121-712406200.7
Authors: {'items': [{'id': 'Buarque de-Macedo-Robert', 'name': {'family': 'Buarque de Macedo', 'given': 'R.'}, 'orcid': '0000-0002-2218-4117'}, {'id': 'Monfared-Siavash', 'name': {'family': 'Monfared', 'given': 'S.'}, 'orcid': '0000-0002-7629-7977'}, {'id': 'Karapiperis-Konstantinos', 'name': {'family': 'Karapiperis', 'given': 'K.'}, 'orcid': '0000-0002-6796-8900'}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'J. E.'}, 'orcid': '0000-0003-3741-0364'}]}
Year: 2023
DOI: 10.1007/s10035-022-01282-y
Engineered granular materials have gained considerable interest in recent years. For this substance, the primary design variable is grain shape. Optimizing grain form to achieve a macroscopic property is difficult due to the infinite-dimensional function space particle shape inhabits. Nonetheless, by parameterizing morphology the dimension of the problem can be reduced. In this work, we study the effects of both intuitive and machine-picked shape descriptors on granular material properties. First, we investigate the effect of classical shape descriptors (roundness, convexity, and aspect ratio) on packing fraction ϕ and coordination number Z. We use a genetic algorithm to generate a uniform sampling of shapes across these three shape parameters. The shapes are then simulated in the level set discrete element method. We discover that both ϕ and Z decrease with decreasing convexity, and Z increases with decreasing aspect ratio across the large sampling of morphologies—including among highly non-convex grains not commonly found in nature. Further, we find that subtle changes in mesoscopic properties can be attributed to a continuum of geometric phenomena, including tessellation, hexagonal packing, nematic order and arching. Nonetheless, such descriptors alone can not entirely describe a shape. Thus, we find a set of 20 descriptors which uniquely define a morphology via deep generative models. We show how two of these machine-derived parameters affect ϕ and Z. This methodology can be leveraged for topology optimization of granular materials, with applications ranging from robotic grippers to materials with tunable mechanical properties.https://authors.library.caltech.edu/records/e4cab-9t285Level Set Discrete Element Method for modeling sea ice floes
https://resolver.caltech.edu/CaltechAUTHORS:20230302-364814000.2
Authors: {'items': [{'id': 'Moncada-Rigoberto', 'name': {'family': 'Moncada', 'given': 'Rigoberto'}, 'orcid': '0000-0001-7655-5406'}, {'id': 'Gupta-Mukund', 'name': {'family': 'Gupta', 'given': 'Mukund'}, 'orcid': '0000-0003-0181-9504'}, {'id': 'Thompson-A-F', 'name': {'family': 'Thompson', 'given': 'Andrew'}, 'orcid': '0000-0003-0322-4811'}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'Jose E.'}, 'orcid': '0000-0003-3741-0364'}]}
Year: 2023
DOI: 10.1016/j.cma.2023.115891
Understanding and projecting seasonal variations in sea ice is necessary to improve global climate predictions. However, accurately capturing changes in sea ice and its interactions with ocean and atmosphere variability remains a challenge for models, notably due to its complex behavior at the floe scale. In this work, we introduce a method to capture the floe-like behavior of sea ice, named the 'Level Set Discrete Element Method for Sea Ice' (LS-ICE). This model can resolve individual sea ice floes with realistic shapes, and represent their physical interactions by leveraging level-set functions for detecting contact between floes. LS-ICE can also be coupled to heat and momentum forcings from the atmosphere and the ocean, and simulate associated melt and breakage processes. The discrete representation of sea ice floes reveals melt dynamics, associated with their shapes and thickness distributions, which are currently not well represented by continuum models. We illustrate the model capabilities for two different years involving the spring to summer transition in Baffin Bay, where the sea ice concentration declines from approximately 80% to 0% between the months of June and July. Satellite imagery, along with oceanographic reanalysis data based on field measurements, are used to initialize the model and validate its subsequent evolution during these months. For an appropriate set of parameters, the model can reproduce the evolution of sea ice concentration, floe size distribution, oceanic temperature and mean sea ice thickness, despite only a small number of tunable parameters. This study identifies the potential for LS-ICE to simulate the interaction between floe shape, melt and breakage, to enhance seasonal scale forecasts for sea ice floes.https://authors.library.caltech.edu/records/my8pq-zzf48Mechanical basis and topological routes to cell elimination
https://resolver.caltech.edu/CaltechAUTHORS:20230509-421333500.5
Authors: {'items': [{'id': 'Monfared-Siavash', 'name': {'family': 'Monfared', 'given': 'Siavash'}, 'orcid': '0000-0002-7629-7977'}, {'id': 'Ravichandran-G', 'name': {'family': 'Ravichandran', 'given': 'Guruswami'}, 'orcid': '0000-0002-2912-0001'}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José'}, 'orcid': '0000-0003-3741-0364'}, {'id': 'Doostmohammadi-Amin', 'name': {'family': 'Doostmohammadi', 'given': 'Amin'}, 'orcid': '0000-0002-1116-4268'}]}
Year: 2023
DOI: 10.7554/elife.82435
PMCID: PMC10112887
Cell layers eliminate unwanted cells through the extrusion process, which underlines healthy versus flawed tissue behaviors. Although several biochemical pathways have been identified, the underlying mechanical basis including the forces involved in cellular extrusion remains largely unexplored. Utilizing a phase-field model of a three-dimensional cell layer, we study the interplay of cell extrusion with cell–cell and cell–substrate interactions in a flat monolayer. Independent tuning of cell–cell versus cell–substrate adhesion forces reveals that extrusion events can be distinctly linked to defects in nematic and hexatic orders associated with cellular arrangements. Specifically, we show that by increasing relative cell–cell adhesion forces the cell monolayer can switch between the collective tendency towards fivefold, hexatic, disclinations relative to half-integer, nematic, defects for extruding a cell. We unify our findings by accessing three-dimensional mechanical stress fields to show that an extrusion event acts as a mechanism to relieve localized stress concentration.https://authors.library.caltech.edu/records/jh82r-xq686Scaling, saturation, and upper bounds in the failure of topologically interlocked structures
https://resolver.caltech.edu/CaltechAUTHORS:20230502-330322900.5
Authors: {'items': [{'id': 'Feldfogel-Shai', 'name': {'family': 'Feldfogel', 'given': 'Shai'}, 'orcid': '0000-0001-8819-6148'}, {'id': 'Karapiperis-Konstantinos', 'name': {'family': 'Karapiperis', 'given': 'Konstantinos'}, 'orcid': '0000-0002-6796-8900'}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'Jose'}, 'orcid': '0000-0003-3741-0364'}, {'id': 'Kammer-David-S', 'name': {'family': 'Kammer', 'given': 'David S.'}, 'orcid': '0000-0003-3782-9368'}]}
Year: 2023
DOI: 10.1016/j.ijsolstr.2023.112228
Topological Interlocking Structures (TIS) have been increasingly studied in the past two decades. However, some fundamental questions concerning the effects of Young's modulus and the friction coefficient on the structural mechanics of the most common type of TIS application – centrally loaded panels – are not yet clear. Here, we present a first-of-its-kind parametric study that aims to clarify how these two parameters affect multiple aspects of the behavior and failure of centrally-loaded TIS panels. This includes the evolution of the structural response up to and including failure, the foremost structural response parameters, and the residual carrying capacity. We find that the structural response parameters in TIS panels scale linearly with Young's modulus, that they saturate with the friction coefficient, and that the saturated response provides an upper-bound on the capacity of centrally loaded TIS panels reported in the literature. This, together with additional findings, insights, and observations, comprise a novel contribution to our understanding of the interlocked structural form.https://authors.library.caltech.edu/records/nzk2c-4pb20Adaptive goal-oriented data sampling in Data-Driven Computational Mechanics
https://resolver.caltech.edu/CaltechAUTHORS:20230411-695015900.6
Authors: {'items': [{'id': 'Gorgogianni-Anna', 'name': {'family': 'Gorgogianni', 'given': 'Anna'}}, {'id': 'Karapiperis-Konstantinos', 'name': {'family': 'Karapiperis', 'given': 'Konstantinos'}, 'orcid': '0000-0002-6796-8900'}, {'id': 'Stainier-Laurent', 'name': {'family': 'Stainier', 'given': 'Laurent'}, 'orcid': '0000-0001-6719-6616'}, {'id': 'Ortiz-M', 'name': {'family': 'Ortiz', 'given': 'Michael'}, 'orcid': '0000-0001-5877-4824'}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}, 'orcid': '0000-0003-3741-0364'}]}
Year: 2023
DOI: 10.1016/j.cma.2023.115949
Data-Driven (DD) computing is an emerging field of Computational Mechanics, motivated by recent technological advances in experimental measurements, the development of highly predictive computational models, advances in data storage and data processing, which enable the transition from a material data-scarce to a material data-rich era. The predictive capability of DD simulations is contingent on the quality of the material data set, i.e. its ability to closely sample all the strain–stress states in the phase space of a given mechanical problem. In this study, we develop a methodology for increasing the quality of an existing material data set through iterative expansions. Leveraging the formulation of the problems treated with the DD paradigm as distance minimization problems, we identify regions in phase space with poor data coverage, and target them with additional experiments or lower-scale simulations. The DD solution informs the additional experiments so that they can provide better coverage of the phase space of a given application.https://authors.library.caltech.edu/records/9sv03-ppf89Predicting the seismic behavior of multiblock tower structures using the level set discrete element method
https://resolver.caltech.edu/CaltechAUTHORS:20230509-291707400.3
Authors: {'items': [{'id': 'Harmon-John-M', 'name': {'family': 'Harmon', 'given': 'John M.'}}, {'id': 'Gabuchian-Vahe', 'name': {'family': 'Gabuchian', 'given': 'Vahe'}}, {'id': 'Rosakis-A-J', 'name': {'family': 'Rosakis', 'given': 'Ares J.'}, 'orcid': '0000-0003-0559-0794'}, {'id': 'Conte-Joel-P', 'name': {'family': 'Conte', 'given': 'Joel P.'}, 'orcid': '0000-0003-2068-7965'}, {'id': 'Restrepo-José-I', 'name': {'family': 'Restrepo', 'given': 'José I.'}}, {'id': 'Rodriguez-Andrés', 'name': {'family': 'Rodriguez', 'given': 'Andrés'}}, {'id': 'Nema-Arpit', 'name': {'family': 'Nema', 'given': 'Arpit'}}, {'id': 'Pedretti-Andrea-R', 'name': {'family': 'Pedretti', 'given': 'Andrea R.'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}, 'orcid': '0000-0003-3741-0364'}]}
Year: 2023
DOI: 10.1002/eqe.3883
In this paper a modeling method is validated at multiple scales for the seismic performance of multiblock tower structure (MTS). MTS are a proposed concept for large-capacity gravitational energy storage that will enable renewable energy sources. The structure modeled is a tower of 7144 nominally identical blocks arranged in a 38-layered annular pattern with no adhesive mechanisms between the blocks or the blocks and the foundation. The level set discrete element method is used to model the dynamics of the tower structure experiencing a ground motion. Experimental determination of each model parameter is shown from the use of individual blocks before construction. Close comparisons to experimental results are shown for the dynamic motion of the tower over a full ground motion time history for multiple scales, materials and ground motions. When the tower was brought to failure, the two ground motions used produced distinct failure modes of the tower showing both a peeling and buckling behavior. Both the effect of the friction coefficient and unequal block heights are investigated. Friction coefficient has a noticeable effect on the amplitude of motion of the tower while the unevenness of the block heights affects mostly the structural speed.https://authors.library.caltech.edu/records/p2hzh-mv009Shaking table tests for seismic stability of stacked concrete blocks used for radiation shielding
https://resolver.caltech.edu/CaltechAUTHORS:20230411-695015900.17
Authors: {'items': [{'id': 'Sironi-Luca', 'name': {'family': 'Sironi', 'given': 'Luca'}}, {'id': 'Andreini-Marco', 'name': {'family': 'Andreini', 'given': 'Marco'}, 'orcid': '0000-0001-8474-4397'}, {'id': 'Colloca-Cristiana', 'name': {'family': 'Colloca', 'given': 'Cristiana'}}, {'id': 'Poehler-Michael', 'name': {'family': 'Poehler', 'given': 'Michael'}}, {'id': 'Bolognini-Davide', 'name': {'family': 'Bolognini', 'given': 'Davide'}, 'orcid': '0000-0003-3015-6738'}, {'id': 'Dacarro-Filippo', 'name': {'family': 'Dacarro', 'given': 'Filippo'}, 'orcid': '0000-0003-2989-3845'}, {'id': 'Lestuzzi-Pierino', 'name': {'family': 'Lestuzzi', 'given': 'Pierino'}, 'orcid': '0000-0001-8761-8708'}, {'id': 'Dubois-Frédéric', 'name': {'family': 'Dubois', 'given': 'Frédéric'}, 'orcid': '0000-0003-1977-8042'}, {'id': 'Zhou-Ziran', 'name': {'family': 'Zhou', 'given': 'Ziran'}}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}, 'orcid': '0000-0003-3741-0364'}]}
Year: 2023
DOI: 10.1016/j.engstruct.2023.115895
This paper describes the shaking table tests carried out at the European Centre for Training and Research in Earthquake Engineering (EUCENTRE) to investigate the seismic behaviour of four configurations of stacked concrete blocks, commonly used at the European Organisation for Nuclear Research (CERN) as a shielding barrier against different types of radiation. The blocks used for these configurations have been designed to guarantee an adequate level of protection to radiation and, at the same time, to be easily transported and managed for different installations. The block configuration specimens have been tested using the acceleration time-histories of two different earthquakes occurred in the Mediterranean region. Each configuration has been tested several times with acceleration amplitude increments until rigid kinematisms are triggered. This paper presents the test setup and inputs, the related experimental readings and the main results obtained by these tests. The two main mechanisms observed at the interfaces between the blocks during the tests were sliding and rocking. The data collected at the end of the experimental campaign constitute an important source to calibrate different discrete-system-models, in order to study the seismic response of block configurations used for radiation protection in particle physics research institutions.https://authors.library.caltech.edu/records/m0656-vzp14Tunable Mechanical Response of Self-Assembled Nanoparticle Superlattices
https://resolver.caltech.edu/CaltechAUTHORS:20230725-856874000.12
Authors: {'items': [{'id': 'Dhulipala-Somayajulu', 'name': {'family': 'Dhulipala', 'given': 'Somayajulu'}, 'orcid': '0000-0002-3144-8583'}, {'id': 'Yee-Daryl-W', 'name': {'family': 'Yee', 'given': 'Daryl W.'}, 'orcid': '0000-0002-4114-6167'}, {'id': 'Zhou-Ziran', 'name': {'family': 'Zhou', 'given': 'Ziran'}, 'orcid': '0009-0008-9327-3505'}, {'id': 'Sun-Rachel', 'name': {'family': 'Sun', 'given': 'Rachel'}, 'orcid': '0000-0001-6396-1720'}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}, 'orcid': '0000-0003-3741-0364'}, {'id': 'Macfarlane-Robert-J', 'name': {'family': 'Macfarlane', 'given': 'Robert J.'}, 'orcid': '0000-0001-9449-2680'}, {'id': 'Portela-Carlos-M', 'name': {'family': 'Portela', 'given': 'Carlos M.'}, 'orcid': '0000-0002-2649-4235'}]}
Year: 2023
DOI: 10.1021/acs.nanolett.3c01058
Self-assembled nanoparticle superlattices (NPSLs) are an emergent class of self-architected nanocomposite materials that possess promising properties arising from precise nanoparticle ordering. Their multiple coupled properties make them desirable as functional components in devices where mechanical robustness is critical. However, questions remain about NPSL mechanical properties and how shaping them affects their mechanical response. Here, we perform in situ nanomechanical experiments that evidence up to an 11-fold increase in stiffness (∼1.49 to 16.9 GPa) and a 5-fold increase in strength (∼88 to 426 MPa) because of surface stiffening/strengthening from shaping these nanomaterials via focused-ion-beam milling. To predict the mechanical properties of shaped NPSLs, we present discrete element method (DEM) simulations and an analytical core–shell model that capture the FIB-induced stiffening response. This work presents a route for tunable mechanical responses of self-architected NPSLs and provides two frameworks to predict their mechanical response and guide the design of future NPSL-containing devices.https://authors.library.caltech.edu/records/dpzsk-zz910Data-driven breakage mechanics: Predicting the evolution of particle-size distribution in granular media
https://authors.library.caltech.edu/records/5s9tc-v9641
Authors: {'items': [{'id': 'Ulloa-Jacinto', 'name': {'family': 'Ulloa', 'given': 'Jacinto'}, 'orcid': '0000-0001-7616-5408'}, {'id': 'Gorgogianni-Anna', 'name': {'family': 'Gorgogianni', 'given': 'Anna'}}, {'id': 'Karapiperis-Konstantinos', 'name': {'family': 'Karapiperis', 'given': 'Konstantinos'}, 'orcid': '0000-0002-6796-8900'}, {'id': 'Ortiz-M', 'name': {'family': 'Ortiz', 'given': 'Michael'}, 'orcid': '0000-0001-5877-4824'}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'José E.'}, 'orcid': '0000-0003-3741-0364'}]}
Year: 2023
DOI: 10.1016/j.jmps.2023.105328
<p>This paper presents a model-free data-driven framework for breakage mechanics. In contrast with continuum breakage mechanics, the de facto approach for the macroscopic analysis of crushable granular media, the present framework does not require the definition of constitutive models and phenomenological assumptions, relying on <a href="https://www.sciencedirect.com/topics/engineering/material-behavior">material behavior</a> that is known only through empirical data. For this purpose, we revisit the recent developments in model-free data-driven computing for history-dependent materials and extend the main ideas to materials with particle breakage. A systematic construction of the modeling framework is presented, starting from the closed-form representation of continuum breakage mechanics and arriving at alternative model-free representations. The <a href="https://www.sciencedirect.com/topics/engineering/predictive-ability">predictive ability</a> of the data-driven framework is highlighted and contrasted with continuum breakage mechanics on different boundary value problems. Moreover, an application to a real experimental test in crushable sand is presented, where the data is furnished by high-fidelity grain-scale simulations, indicating that the proposed framework provides an accurate prediction of the mechanics of crushable materials including the state of comminution.</p>https://authors.library.caltech.edu/records/5s9tc-v9641A discretization‐convergent level‐set‐discrete‐element‐method using a continuum‐based contact formulation
https://authors.library.caltech.edu/records/5spa1-57j41
Authors: {'items': [{'id': 'Feldfogel-Shai', 'name': {'family': 'Feldfogel', 'given': 'Shai'}, 'orcid': '0000-0001-8819-6148'}, {'id': 'Karapiperis-Konstantinos', 'name': {'family': 'Karapiperis', 'given': 'Konstantinos'}, 'orcid': '0000-0002-6796-8900'}, {'id': 'Andrade-J-E', 'name': {'family': 'Andrade', 'given': 'Jose'}, 'orcid': '0000-0003-3741-0364'}, {'id': 'Kammer-David-S', 'name': {'family': 'Kammer', 'given': 'David S.'}, 'orcid': '0000-0003-3782-9368'}]}
Year: 2023
DOI: 10.1002/nme.7400
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<p>The level-set-discrete-element-method (LS-DEM) was developed to overcome the shape limitation of traditional discrete element method. LS-DEM's shape generality relies on a node-based surface discretization of grain boundary, and it has been used to shed new light of a variety of granular mechanics applications with realistically shaped grains and structural assemblies made of unbonded building blocks. Due to the node-based discretization of grain boundary, the original LS-DEM is discretization-sensitive and it suffers from divergence of the response with discretization refinement, particularly for highly compressible problems. Previous studies have identified and addressed this issue in different ways, each with its own advantages and shortcomings. Here, we propose a methodologically-rigorous and computationally-efficient adapted formulation which solves LS-DEM's discretization-sensitivity issue. It adopts the classical contact description of continuum mechanics, wherein the contact interactions are traction-based. We demonstrate the convergence of the adapted LS-DEM in several highly compressible cases studies, show that it is key to correctly capturing the mechanical response, and compare it to alternative formulations.</p>
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</div>https://authors.library.caltech.edu/records/5spa1-57j41