Organizational Unit:

School of Civil and Environmental Engineering

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https://hdl.handle.net/1853/70760

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College of Engineering

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Organizational Unit

Georgia Water Resources Institute

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Georgia Transportation Institute

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Environmental Microbial Genomics Laboratory

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https://finding-aids.library.gatech.edu/agents/corporate_entities/385

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Publication Search Results

Now showing 1 - 10 of 21

Simulation of compound anchor intrusion in dry sand by a hybrid FEM+SPH method

( 2022-09) He, Haozhou ; Karsai, Andras ; Liu, Bangyuan ; Hammond III, Frank L. ; Goldman, Daniel I. ; Arson, Chloé

The intrusion of deformable compound anchors in dry sand is simulated by coupling the Finite Element Method (FEM) with Smoothed Particle Hydrodynamics (SPH). This novel approach can calculate granular flows at lower computational cost than SPH alone. The SPH and FEM domains interact through reaction forces calculated from balance equations and are assigned the same soil constitutive model (Drucker-Prager) and the same constitutive parameters (measured or calibrated). Experimental force-displacement curves are reproduced for penetration depths of 8 mm or more (respectively, 20 mm or more) for spike-shaped (respectively, fan-shaped) anchors with 1 to 6 blades. As the number of blades increases, simulations reveal that the granular flow under the anchor deviates from the vertical and that the horizontal granular flow transitions from orthoradial to radial. We interpret the strain field distribution as the result of soil arching, i.e., the transfer of stress from a yielding mass of soil onto adjoining stationary soil masses. Arching is fully active when the radial distance between blade end points is less than a critical length. In that case, the normal stress that acts on the compound anchor at a given depth reaches the normal stress that acts on a disk-shaped anchor of same radius. A single-blade anchor produces soil deformation and failure similar to Prandtl’s foundation sliding model. Multiblade anchors produce a complex failure mechanism that combines sliding and arching.
Self-consistent approach for modeling coupled elastic and visco-plastic processes induced by dislocation and pressure solution

( 2021) Xu, Tingting ; Arson, Chloé

This paper pesents a self-consistent approach in which coupled non-linear time-dependent deformation mechanisms are estimated by an affine approximation and elastic and visco-plastic macroscopic properties are calculated for the most general form of anisotropy. Phase changes from crystal to pore are accounted for, via a grain breakage mechanism. As an example, we study dislocation and pressure solution, two non-linear deformation mechanisms common to a wide range of polycrystalline materials. To this date, the couplings between the two are not fully understood. We analyze the sensitivity of the behavior of halite polycrystals to stress, brine content, grain size and grain breakage. Results indicate that: Pressure solution yields mechanical healing only if grain breakage is ignored; Otherwise, pressure solution accelerates dislocation creep, which results in an abrupt increase of elastic and viscoplastic compliance components; Higher stress and/or higher brine content enhance the coupled effects of pressure solution and dislocation; Pressure solution is delayed by the occurrence of larger grains and by the entrapment of fluid in isolated pores. An interesting feature of the model is the representation of the pore space, which allows distinguishing the deformation mechanisms of these isolated pores from those of the pores where precipitation occurs.
Finite Element model of concrete repaired by High Molecular Weight Methacrylate (HMWM)

( 2021) Ji, Koochul ; Gao, Nan ; Stewart, Lauren ; Arson, Chloé

Epoxy is widely used to fill concrete cracks that are less than a millimeter in width to protect the steel rebars from corrosion. However, the mechanical behavior of epoxy-repaired concrete remains vastly unknown. In order to understand whether or not epoxy can be used to recover the mechanical properties of damaged concrete, we provide a quantitative assessment of concrete repaired by injection of High Molecular Weight Metacrylate (HMWM). Uniaxial compression tests and three-point bending tests were conducted on cut-and-repaired specimens. The experiments were simulated with the Finite Element Method (FEM), in which concrete was assigned a constitutive model that combines continuum damage mechanics and plasticity and in which the concrete/HMWM interface was modeled with bilinear softening cohesive zone elements (CZEs). The numerical model was calibrated and validated against the experimental results. Steel-reinforced concrete (RC) beams were subjected to three-point bending to produce cracks. The beams were then repaired and reloaded. We used Digital Image Correlation (DIC) to identify the zones of high maximum principal strain after the first loading cycle. These zones were modeled with repaired concrete elements and HMWM CZEs to simulate the second load cycle. The load-displacement curves, damage distributions and strain fields obtained numerically are in agreement with those obtained experimentally, which validates the proposed model. Our simulation results suggest that HMWM can penetrate cracks of width 0.01 mm and above by gravity. We also found that HMWM reparation increases concrete stiffness and strength if crack in concrete members are over 0.1 mm in width, in which case, the load capacity of repaired RC beams is 30 to 40% higher than that of as-built RC beams.
Tensile strength of calcite/HMWM and silica/HMWM interfaces: A Molecular Dynamics analysis

(Georgia Institute of Technology, 2020-03) Arson, Chloé ; Ji, Koochul (K.)

The mechanical behavior of interfaces between high molecular weight methacrylate (HMWM) and concrete minerals (calcite and silica) is investigated from a Molecular Dynamics (MD) perspective. MD simulations of pullout tests shows that interfaces debond at the surface of contact between HMWM and the mineral substrate, and that the interfacial strength decreases in the presence of moisture, under low strain rate, or at high temperature. Silica/HMWM interfaces are stronger than the calcite/HMWM interfaces. Additionally, the work of separation is mostly done by van der Waals forces, in agreement with previous studies. We use published experimental data at low strain rate along with our MD results at high strain rate to calibrate Richeton’s model and Johnson-Cook model. We show that, if more experimental results were available for validation, MD results could be extrapolated to predict the tensile modulus of HMWM at low strain rate and the HMWM/mineral interfacial strength for a broad range of temperatures and strain rates. The sensitivity analysis of the model confirms that HMWM should be applied on dry surfaces and in concrete exposed to lower temperatures. Additionally, MD results suggest that HMWM is more likely to last in concrete with high silica contents than in concrete with high calcite contents.
Horizontal directional drilling (HDD) alignment optimization using ant colony optimization

( 2020) Patino-Ramirez, Fernando ; Layhee, Carrie ; Arson, Chloé

Horizontal Directional Drilling (HDD) is a trenchless method that consists in drilling an inclined and curved bore from an entry point to an exit point. In practice, HDD is designed iteratively by trial and error, to minimize the cost under geometric and mechanical constraints. In this paper, we optimize the drill path with continuous implementations of an Ant Colony Optimization (ACO) algorithm that sets the depth 15 of the alignment and its entry and exit angles as the design parameters to optimize, to ensure minimal drill path length (cost), avoid collapse or instability (mechanical constraints) and remain in the construction domain (geometric constraint). We compare the ACO results to the drill paths designed in practice in two different scenarios: one in which the entry and exit points are fixed, and one in which the geometry of the central 20 segment is constrained. Results show that ACO can be used to automate the otherwise time-consuming design process while minimizing the drill path length and the costs associated to it.
Fabric evolution and crack propagation in salt during consolidation and cyclic compression tests

( 2020) Shen, Xianda ; Ding, Jihui ; Lordkipanidze, Ilia ; Arson, Chloé ; Chester, Judith ; Chester, Frederick

It is of great interest to describe and quantify the evolution of microstructure for a better understanding of rock deformation processes. In this study, 2D microstructure images of salt rock are analyzed at several stages of consolidation tests and cyclic compression tests to quantify the evolution of the magnitude and orientation of solidity, coordination, local solid volume fraction and crack volume. In both the consolidation and the cyclic compression tests, the deformation of aggregates achieved by grain rearrangement is greater than that achieved by the deformation of an individual grain. In the consolidation tests, the aggregates are rearranged into horizontal layers of coordinated grains, the orientation distribution of grain indentations is quasi-uniform, and the size of the pores reduces and becomes more uniformly distributed. As a result, salt rock microstructure becomes more homogeneous. The increase of local solid volume fraction in the lateral direction is correlated with an increase of the oedometer modulus. In the cyclic compression tests, grain-to-grain contact areas decrease due to the redistribution of grains and the propagation of intergranular cracks. Aggregates are reorganized into columns of coordinated grains. Intergranular opening-mode cracks tend to develop in the axial direction, while intergranular shear-mode cracks propagate preferentially in the lateral direction. The lateral components of the fabric tensors of coordination and local solid volume fraction decrease, which results in an increase of the Poisson's ratio. The fabric descriptors used in this work allow a better quanti cation and understanding of halite deformation processes and can be used in other types of rocks encountering similar deformation mechanisms.
DEM analysis on the role of aggregates on concrete strength

(Georgia Institute of Technology, 2019-10-02) Wang, Pei ; Gao, Nan ; Ji, Koochul ; Stewart, Lauren K. ; Arson, Chloé

This study aims to understand the micro-mechanisms that drive fracture propagation in concrete and to assess the roles of the strength of aggregates and of the aggregate/mortar interfacial transition zone (ITZ) on concrete strength. We use the Discrete Element Method (DEM) to model concrete samples. Mortar is represented by a volume of bonded spherical elements. Bonds are governed by a new displacement-softening law. Aggregate centroids are randomly placed in the DEM sample. We use CT scan images of real aggregates to plot 3D aggregate contours. The spherical elements that are contained in 3D contours around the randomly placed centroids are replaced by clusters with aggregate properties. The number and the size of the clusters are determined from the experimental Particle Size Distribution. The DEM concrete model is calibrated against uniaxial compression tests and Brazilian tests of both mortar and concrete. It is found that: At same aggregate volume fraction, a concrete sample with randomly placed aggregates and ITZ bonds is stronger; Concrete strength is linearly related to aggregate tensile strength; A linear relationship exists between the contact ratio in the mortar/aggregate ITZ and concrete strength; The ITZ has more influence on concrete strength than aggregate tensile strength.
XFEM to couple nonlocal micromechanics damage with discrete mode I cohesive fracture

( 2019-09) Wencheng, Jin ; Arson, Chloé

A computational tool is developed to simulate the propagation of a discrete fracture within a continuum damage process zone. Microcrack initiation and propagation prior to coalescence are represented by a nonlocal anisotropic Continuum Damage Mechanics (CDM) model in which the crack density is calculated explicitly. A damage threshold is defined to mark the beginning of crack coalescence. When that threshold is reached, a cohesive segment is inserted in the mesh to replace a portion of the damage process zone by a segment of discrete fracture. Discretization is done with the extended Finite Element Method (XFEM), which makes it possible to simulate fracture propagation without assigning the fracture path a priori. Rigorous calibration procedures are established for the cohesive strength (related to the damage threshold) and for the cohesive energy release rate, to ensure the balance of energy dissipated at the micro and macro scales. The XFEM-based tool is implemented into an open source object-oriented numerical package (OOFEM), and used to simulate wedge splitting and three-point bending tests. Results demonstrate that the proposed numerical method captures the entire failure process in mode I, from a mesh-independent diffuse damage zone to a localized fracture. Future work will investigate mixed mode fracture propagation.
Structure and mechanical behavior of dentin-inspired nanoporous copper

( 2019) Ibru, Timothy ; Violante, Sarah ; Vennat, Elsa ; Arson, Chloé ; Antoniou, Antonia

Dentin possesses a hierarchical porous structure with varying cross-scale morphology and characteristic lengths ranging from nanometers to micrometers. NP Copper is fabricated with nano-sized and micron-sized features that mimic dentin’s morphology. NP Copper Young’s modulus, hardness, and plastic Poisson’s ratio are shown to be in the range characteristic of dentin. This correspondence in properties may allow use of NP metals to advance tooth restoration techniques, for example by using NP metals as model systems to study infiltration of dentin with resins. Moreover, the multi-scale porosity may inspire design of 3D catalysts with efficient reactant mass transport through the catalyst volume.
An alternative to periodic homogenization for dentin elastic stiffness

( 2019) Arson, Chloé ; Yasothan, Yannick ; Jeanneret, Romain ; Benoit, Aurelie ; Roubier, Nicolas ; Vennat, Elsa

Dentin, the main tissue of the tooth, is made of tubules surrounded by peri-tubular dentin (PTD), embedded in a matrix of inter-tubular dentin (ITD). The PTD and the ITD have different relative fractions of collagen and hydroxyapatite crystals. The ITD is typically less rigid than the PTD, which can be seen as a set of parallel hollow cylindrical reinforcements in the ITD matrix. In this paper, we extend Hashin and Rozen's homogenization scheme to a non-uniform distribution of hollow PTD cylinders, determined from image analysis. We relate the transverse isotropic elastic coeffcients of a Representative Elementary Volume (REV) of dentin to the elastic and topological properties of PTD and ITD. The model is calibrated against experimental data. Each sample tested is consistently characterized by Environmental Scanning Electron Microscopy (ESEM), nano-indentation and Resonant Ultrasound Spectroscopy (RUS), which ensures that macroscopic mechanical properties measured are correlated with microstructure observations. Despite the high variability of microstructure descriptors and mechanical properties, statistical analyses show that Hashin's bounds converge and that the proposed model can be used for back-calculating the microscopic Poisson's ratios of dentin constituents. Three-point bending tests conducted in the laboratory were simulated with the Finite Element Method (FEM). Elements were assigned transverse isotropic elastic parameters calculated by homogenization. The tubule orientation and the pdf of the ratio inner/outer tubule radius were determined in several zones of the beams before testing. The remainder of the micro-mechanical parameters were taken equal to those calibrated by RUS. The horizontal strains found experimentally by Digital Image Correlation (DIC) were compared to those found by FEM. The DIC and FEM horizontal strain fields showed a very good agreement in trend and order of magnitude, which verifies the calibration of the homogenization model. By contrast with previous studies of dentin, we fully calibrated a closed form mechanical model against experimental data and we explained the testing procedures. In elastic conditions, the proposed homogenization scheme gives a better account of microstructure variability than micro-macro dentin models with periodic microstructure.