Publications

ABSTRACT Controlling fracture permeability plays a critical role in subsurface energy applications, particularly in geothermal energy production and enhanced carbon sequestration, where regulating fluid flow is essential. The use of microcapsules has become a promising solution to enhance fracture permeability by providing a controlled sealing mechanism. This study employs a coupled Computational Fluid Dynamics Discrete Element Method (CFD‐DEM) approach to investigate the thermo‐hydro transport behavior of microcapsules in fractured environments, focusing on the influence of temperature, particle size, and concentration. The results show that temperature significantly affects microcapsules transport dynamics, with low temperatures promoting clustering due to increasing fluid viscosity, while high temperatures lead to excessive dispersion and reduce sealing. The medium temperature conditions create a balance between mobility and clustering, which controls the sealing behavior to suit the desired goal. Additionally, large microcapsules exhibit stronger sealing characteristics, whereas small ones maintain high mobility but are less effective for sealing. An interesting stagnation effect is also observed for medium size microcapsules, where the interaction of drag, inertia, and gravity can contribute to the control of the sealing behavior of the particles. Furthermore, high microcapsule concentrations can enhance aggregation at low temperatures, but may cause over‐dispersion at high temperatures, due to the collisional forces between the particles. These findings are extremely valuable for devising conditions for particles suitable for different purposes in controlling the transport and sealing behavior of particles in fractures in geothermal environments.

Geothermal energy has gained significant attention as a sustainable alternative to fossil fuels for mitigating energy and environmental crises. However, factors such as production temperature and thermal breakthrough can significantly affect its efficiency. Polymer-based microcapsules have been proposed as a strategy to enhance fracture permeability and mitigate thermal breakthrough in geothermal systems. In this study, we investigate microcapsule transport in fractured networks using a fully coupled CFD–DEM framework at temperatures relevant to geothermal fields. Simulations were conducted at discrete temperatures spanning near-ambient to elevated geothermal conditions (20, 50, 90, 150, and 200 °C), particle concentrations ( ϕ p = 0.05-0.2), and two injection configurations: direct injection into the fracture network (IDF) and injection near the fracture network (INF). The results reveal a clear concentration-dependent transition in the mechanisms controlling particle transport and retention. At low concentration ( ϕ p = 0.05), temperature strongly governs particle motion, while injection scenario plays a minor role. At medium concentration ( ϕ p = 0.1), both temperature and injection scenarios jointly determine particle accumulation, and preferential transport pathways. At high concentration ( ϕ p = 0.1), frequent particle–particle interactions dominate the dynamics, suppressing thermal sensitivity and making injection strategy the primary factor that controls whether particles pass through the network or form early clogging. These findings highlight how concentration, temperature, and injection scenarios interact to shape microcapsule motion in fractured systems, providing practical guidance for designing particle-based thermal breakthrough mitigation strategies in geothermal and subsurface energy applications.

This work examines and discerns variation in brittle fracture behavior of porous materials made of either idealized or realistic, microscale, pore morphologies. Constitutive anisotropy owed to a material’s heterogeneous microstructure is captured via classical asymptotic homogenization and relayed to a phase-field model of linear elastic brittle fracture. Various effective constitutive tensors are input into a finite element model of a 2-D, edge-cracked plate in tension to ascertain how microscale pore morphology affects macroscale fracture behavior. Despite uniform porosity values, the effective constitutive tensors computed showed a clear trend for idealized and realistic RVE morphologies. When diagonal and off-diagonal terms of these tensors are evaluated, each term is consistently lower for realistic pore morphologies versus idealistic cases. Such results contribute to lower forces and longer plate extensions required to propagate a crack for realistic pore morphologies.

Biopolymer-amended soils have shown promise as sustainable construction materials; however, their durability and recyclability under cyclic moisture exposure, particularly in relation to soil gradation effects, remain poorly understood. This study presents, an integrated, multiscale investigation of xanthan gum (XG)–treated sands with differing particle-size distributions: less-uniform sand (Sand Type 1, ST1) and a uniform sand (Sand Type 2, ST2), amended with 0.5, 1, and 2% XG by dry mass. Mechanical performance was evaluated through unconfined compression and oedometer testing to quantify strength, stiffness, compressibility, durability, and reuse potential under wetting–drying cycles, while micro-computed tomography (μCT) was employed to directly link pore-scale evolution to macroscopic response. Unlike prior studies that primarily focus on initial strength, this work simultaneously evaluates durability degradation, recyclability through mechanical reconstitution, and microstructural mechanisms governing performance loss. All mixtures exhibited strength reduction with wetting-drying cycles; however, ST1 treated with 1% XG retained the highest fraction of its initial strength (≈40 % after two cycles), reflecting the combined benefits of moderate biopolymer dosage and enhanced particle interlocking in the less-uniform sand. After recycling, ST1 specimens converged to similar strengths regardless of initial XG content, indicating that mechanical reprocessing disrupts the gradation-dependent bonding advantages. In contrast, ST2 specimens with 1% XG retained comparatively higher post-recycling stiffness, suggesting that the more uniform particle-size distribution promotes more homogeneous deformation and improved preservation of biopolymer bonds at moderate dosage. μCT analysis revealed progressive pore coarsening and solid-phase loss with increasing XG content, consistent with swelling–shrinkage-induced bond disruption during moisture cycling. Overall, results indicate a clear gradation–dosage trade-off: less-uniform sands achieve higher initial strength, while uniform sands exhibit improved durability and recyclability under cyclic moisture exposure.

Geothermal systems provide continuous, low-carbon energy by harnessing the Earth’s renewable heat, but their efficiency can be hindered by issues such as limited heat production and thermal breakthrough. A promising approach to overcome these issues is to inject polymer-based microcapsules into fractures to modify permeability, which requires a clear understanding of particle transport within the fracture network. To do so, this study used Computational Fluid Dynamics–Discrete Element Method (CFD–DEM) simulations combined with machine learning (ML) to capture particle transport behavior under varying temperature conditions. The dataset comprises 45 CFD–DEM test cases, which are generated by coupling OpenFOAM (for fluid dynamics) and LIGGGHTS (for particle tracking), enabling detailed modeling of thermo-hydro processes and particle interactions. To assess their influence on transport behavior, key parameters include particle diameter ( D ), formation temperature ( T ), and particle volume fraction ( ϕ ). Supervised learning models, including random forest and interpretable decision tree classifiers, were trained to classify flow blockage. Feature importance analysis identified ϕ and D as the most critical factors impacting the particle transports. To avoid sealing progression, the accumulation of low-velocity particles over time was fit with a sigmoid function. Results show that higher particle concentrations and larger diameters reduce transport efficiency, while elevated inlet velocities enhance particle mobility and prolong transport through the fracture. This interpretable data-driven approach, grounded in CFDEM simulations, offers a predictive tool for particle transport in fractures subject to complex geothermal environments.

Porous materials are essential in applications ranging from energy storage to healthcare and play a crucial role in advancing technology and enhancing the quality of life. Understanding the impact of pore morphology across different length scales on mechanical properties is necessary for the efficient design of porous structures and also to ensure the structural integrity of the structures. This study investigates the impact of morphological complexities on the mechanical properties of nature-inspired architected porous materials through pillar compression tests at micro and macro scales. Complexity was determined through the surface fractal analysis of each sample, resulting in idealistic, semi-realistic, and realistic complexity definitions. Results show that semi-realistic and realistic structures exhibit similar stress–strain behavior and micromechanical values, while idealized structures demonstrate lower properties. Moreover, for the same porosity level, loading–unloading loops reveal similar degradation of Young’s modulus across each morphology. However, this impact is significantly influenced by the porosity level and becomes more pronounced at lower strain values for lower porosity. Furthermore, macroscale investigation confirms that semi-realistic and realistic structures exhibit identical behaviors. Additionally, our finite element models demonstrate the power of numerical methods in predicting the behavior of complex pore morphologies. These insights into the structure–property relationships can inform the design of more efficient materials and structures.

Although deep learning has achieved remarkable success in various scientific machine learning applications, its opaque nature poses concerns regarding interpretability and generalization capabilities beyond the training data. Interpretability is crucial and often desired in modeling physical systems. Moreover, acquiring extensive datasets that encompass the entire range of input features is challenging in many physics-based learning tasks, leading to increased errors when encountering out-of-distribution (OOD) data. In this work, motivated by the field of functional data analysis (FDA), we propose generalized functional linear models as an interpretable surrogate for a trained deep learning model. We demonstrate that our model could be trained either based on a trained neural network (post-hoc interpretation) or directly from training data (interpretable operator learning). A library of generalized functional linear models with different kernel functions is considered and sparse regression is used to discover an interpretable surrogate model that could be analytically presented. We present test cases in solid mechanics, fluid mechanics, and transport. Our results demonstrate that our model can achieve comparable accuracy to deep learning and can improve OOD generalization while providing more transparency and interpretability. Our study underscores the significance of interpretable representation in scientific machine learning and showcases the potential of functional linear models as a tool for interpreting and generalizing deep learning.

Abstract Geothermal energy is sustainable and gaining momentum as a solution to energy crises and environmental issues. However, challenges like production temperature and thermal breakthrough can impact geothermal project efficiency. One innovative solution to alleviate the thermal breakthrough is to inject polymer‐based materials that are encapsulated in microcapsules into fractures to modify fracture permeability and prevent preferential flow. In our study, we utilized a coupled computational fluid dynamics and discrete element method to simulate the transport of microcapsules under various scenarios controlled by microcapsule size, microcapsule concentration, and fracture roughness. For a smooth fracture, the results indicate that small microcapsules can travel through a smooth fracture regardless of their concentrations. Large microcapsules can transport through a smooth fracture when present in lower concentrations. However, medium and mixed‐size microcapsules tend to cause the sealing of a smooth fracture, irrespective of their concentrations. For a rough fracture, the transport of microcapsules is complicated by their interactions with the rough fracture walls. The presence of two sealing positions in a rough fracture adds further complexity to this transport phenomenon. The size and concentration of microcapsules control one sealing location, while the rough fracture walls determine the other sealing location. The rough walls substantially affect microcapsule transport, rendering the role of microcapsule size and concentration less significant. The simulation results suggest that complex fracture surfaces significantly elevate the occurrence of sealing behavior. To mitigate sealing behavior within more complex fractures, it would be beneficial to use smaller and lower concentrations of microcapsules. Plain Language Summary Geothermal energy is a sustainable solution to energy and environmental challenges, but it faces efficiency issues due to factors like production temperature and thermal breakthrough. A novel solution involves injecting polymer‐based microcapsules into fractures to modify permeability and prevent preferential flow. Our study used numerical simulations to explore how different factors, such as microcapsule size, microcapsule concentration, and rough fracture, affect microcapsule transport. In a smooth fracture, small microcapsules can travel easily, while large microcapsules transport at lower concentrations. However, middle and mixed‐size microcapsules tend to seal a smooth fracture. A rough fracture complicates the transport, with sealing positions influenced by microcapsule size, concentration, and interactions with rough walls. It is favorable to use smaller microcapsules at lower concentrations for complex fractures to mitigate sealing behavior. Key Points Middle and mixed‐size microcapsules have a higher propensity for sealing a smooth fracture compared to small or large microcapsules In the case of a rough fracture, the presence of rough fracture walls substantially increases the likelihood of sealing the fracture In certain rough fracture cases, two sealing locations can be observed

Porous non-woven fibrous media are widely used in various industrial applications such as filtration, insulation, and medical textiles due to their unique structural and functional properties. However, predicting the mechanical behavior of these materials is challenging due to their complex microstructure and anisotropic nature. In this study, a computational model is developed to simulate the mechanical response of porous non-woven fibrous media under external loading. The model is based on the finite element method and takes into account the geometric and material properties of the fibers and the void spaces between them. The effects of various factors such as fiber size, porosity, and fibers’ intersection ratio on the mechanical behavior of the material are investigated. The results reveal that the material’s porosity and fibers’ intersection ratio are the most significant factors influencing its mechanical properties. Additionally, the increase in fiber diameter has a relatively minor effect on the material’s elastic properties. However, such changes in elastic properties are primarily attributed to the increase in randomness within the fibrous network, which is directly related to the fiber diameter for the investigated structure. The proposed computational model predicts the mechanical properties of porous non-woven fibrous media and can provide invaluable insights into the design and optimization of porous non-woven fibrous media for various scientific and engineering applications.

This study aimed to analyze how the addition of titanium (Ti) to TiAlTa alloys affects their mechanical properties (Young’s modulus and hardness) and oxidation behavior. Alloys with three different Ti additions and equi-atomic Al and Ta were fabricated with nominal compositions of 33Ti-33Al-33Ta at%, 50Ti-25Al-25Ta at%, and 70Ti-15Al-15Ta at%. Phase identification of as-processed and compositionally homogenized alloys was conducted by coupling various electron microscopy, diffraction, and chemical analysis techniques. Composition and structures were modeled using CALPHAD-based phase predictions and compared with experimental results. Each of the alloys exhibited a unique set of microstructures with distinctly different ordered precipitates, dependent on cooling rate and chemical composition. Subsequently, nanoindentation tests were performed at temperatures of 25 °C, 250 °C, 500 °C, and 750 °C. Oxidation studies were conducted under static air at 750°C for up to 200 h. 33Ti-33Al-33Ta at% and 70Ti-15Al-15Ta at% alloys showed higher hardness and modulus than 50Ti-25Al-25Ta at% at room temperature. The 50Ti-25Al-25Ta at% alloy exhibited higher hardness and modulus values but lower oxidation resistance at 750°C when compared with the other specimens. The X-ray photoelectron spectroscopy experiments were conducted to further analyze the oxides present in the samples. Despite each sample displaying combinations of mixed oxide layers, TiO2 was the preferred oxide forming in the 50Ti-25Al-25Ta composition, while the other samples preferred to form Al2O3. The findings from this systematic exploration of phase evolution in the TiAlTa alloy space provide insights for optimized material chemistries, processing, and properties.

Calcite (CaCO3) is one of the most common minerals in geologic and engineered systems. It is often in contact with aqueous solutions, causing chemically assisted fracture that is critical to understanding the stability of subsurface systems and manmade structures. Calcite fracture was evaluated with reactive molecular dynamics simulations, including the impacts of crack tip geometry (notch), the presence of water, and surface hydroxyl groups. Chemo-mechanical weakening was assessed by comparing the loads where fracture began to propagate. Our analyses show that in the presence of a notch, the load at which crack growth begins is lower, compared to the effect of water or surface hydroxyls. Additionally, the breaking of two adjacent Ca–O bonds is the kinetic limitation for crack initiation, since transiently broken bonds can reform, not resulting in crack growth. In aqueous environments, fresh (not hydroxylated) calcite surfaces exhibited water strengthening. Manual addition of H+ and/or OH– species on the (104) calcite surface resulted in chemo-mechanical weakening of calcite by 9%. Achieving full hydroxylation of the calcite surface was thermodynamically and kinetically limited, with only 0.17–0.01 OH/nm2 surface hydroxylation observed on the (104) surface at the end of the simulations. The limited reactivity of pure water with the calcite surface restricts the chemo-mechanical effects and suggests that reactions between physiosorbed water and localized structural defects may be dominating the chemo-mechanical process in the studies where water weakening has been reported.

Micropores play critical roles in both natural and man-made materials. Such pores take on a variety of shapes and sizes ranging from spherical to irregular sphere-like voids with diameters spanning from the nanometer to millimeter scales. When porous structures are mechanically loaded, the pores direct the stress around their free surfaces, altering the material’s mechanical response relative to fully dense materials. In this study, for the first time, we create micro-architected porous samples using nanolithography and investigate the role of pore morphology by conducting a series of in situ micropillar compression tests in scanning electron microscopy. The findings demonstrate that porosity is the primary factor influencing the mechanical response of these micro-architected materials, as often seen on a macroscopic level. Additionally, we observed that pore geometry had a significant impact on Young’s modulus, yield stress, and strain energy density as a secondary parameter. Then, the extracted Young’s modulus was compared to macroscopic empirical models and determined the analytical models sufficiently described the impact of porosity in the microscopic scale but failed to capture the impact of second-order parameters. These results suggest how porous materials can be tailored to achieve desired mechanical properties based on the engineering applications of interest.

Advances in additive manufacturing create unique opportunities for the investigation of permeability of fine-grained soils. The permeability of fine-grained soils, such as clays, plays an important role in various design considerations in the geotechnical, environmental, and stormwater management systems. This research investigates the application of 3D printed specimens in studying the hydraulic and mechanical properties of clayey soils. The effects of 3D printing, specifically direct binder jet printing, on the permeability, and other physical properties of clay were investigated. Cylindrical clay specimens were prepared using an advanced direct binder jet printing and tested in a flexible wall permeameter and triaxial compression setup under effective confining stresses representing clay at very shallow depths. The results of this study show that the 3D printing process affects the permeability of clay through changes in physical properties such as the specific surface area. However, the printing provides consistent and repeatable specimens with very low disturbance and efficient controlled geometry. Also, due to stiffer 3D printed specimen, less confinement impact was observed in 3D printed specimens. Also, 3D printed specimens showed significantly higher shear strength and friction angle. The outcome of this research could pave the path for future studies dealing with flow through fractured clays.Article Highlights3D printing and sintering change the physical properties of clay powder leading to higher permeability.The impact of confining pressure on 3D printed specimens is considerably low.3D printing increases the shear strength of soil specimens.

In the era of big data, materials science workflows need to handle large-scale data distribution, storage, and computation. Any of these areas can become a performance bottleneck. We present a framework for analyzing internal material structures (e.g., cracks) to mitigate these bottlenecks. We demonstrate the effectiveness of our framework for a workflow performing synchrotron X-ray computed tomography reconstruction and segmentation of a silica-based structure. Our framework provides a cloud-based, cutting-edge solution to challenges such as growing intermediate and output data and heavy resource demands during image reconstruction and segmentation. Specifically, our framework efficiently manages data storage, scaling up compute resources on the cloud. The multi-layer software structure of our framework includes three layers. A top layer uses Jupyter notebooks and serves as the user interface. A middle layer uses Ansible for resource deployment and managing the execution environment. A low layer is dedicated to resource management and provides resource management and job scheduling on heterogeneous nodes (i.e., GPU and CPU). At the core of this layer, Kubernetes supports resource management, and Dask enables large-scale job scheduling for heterogeneous resources. The broader impact of our work is four-fold: through our framework, we hide the complexity of the cloud’s software stack to the user who otherwise is required to have expertise in cloud technologies; we manage job scheduling efficiently and in a scalable manner; we enable resource elasticity and workflow orchestration at a large scale; and we facilitate moving the study of nonporous structures, which has wide applications in engineering and scientific fields, to the cloud. While we demonstrate the capability of our framework for a specific materials science application, it can be adapted for other applications and domains because of its modular, multi-layer architecture.

This paper develops a numerical model based on two-parameter extended bond-based peridynamics with a new bond-breakage criterion to simulate mixed-mode fracture in rock-like materials. This model requires only four basic parameters: Young’s modulus, Poisson’s ratio, and Mode-I and Mode-II energy release rates. Tensile and shear cracks can be distinguished explicitly from mixed-mode fracture phenomena by decomposing the bond potential into dilatational and deviatoric terms. The m - and δ -convergence studies are first performed on the gypsum specimen with a single flaw subjected to uniaxial compression. The initialization and propagation of wing cracks (tensile cracks), quasi-coplanar and oblique secondary cracks (shear cracks) are successfully captured. As an example application, the crack initiation, propagation and coalescence processes of gypsum specimens with various double-flaw configurations are investigated. Under uniaxial compression, three typical types of crack coalescence patterns characterized by shear cracking or mixed tensile-shear cracking are obtained. In all cases, the numerical results predicted by the developed approach agree well with the experimental observations, both qualitatively and quantitatively.

Even though the development of novel materials that mimic nature is widely used in a variety of engineering and scientific fields, the relationship between effective material properties and underlying, often complex pore morphology is still not fully understood. To address this knowledge gap and accelerate the development of novel nature-inspired materials, this paper adopts a higher-order asymptotic homogenization method to numerically investigate the effect of complex micropore morphology on the effective mechanical properties of a porous system. Specifically, we create unique pore morphologies with varying levels of complexity that serve as a more realistic representation of natural materials. We then use the second-order homogenization method to capture the role of pore size, shape, orientation, and distribution on effective properties. By creating different pore morphologies, we systematically studied the relationship between morphology and effective mechanical properties. The results highlight the necessity of higher-order parameters to fully capture the role of realistic pore morphologies on effective mechanical properties and provide a path forward in the design of nature-inspired materials.

The interaction between crack propagation and interfaces is one of the critical problems in bimaterial systems. In this paper, interfacial and subinterfacial fracture behaviors are simulated to investigate this interaction. The modeling approach for bimaterial structures is first introduced, where the extended bond-based peridynamic model is adopted. Then a convergence study is carried out with a bimaterial plate containing two asymmetric inclusions under tensile load. The comparison with the finite element solution validates the proposed modeling approach. Subsequently, several interfacial and subinterfacial fracture cases are considered to pinpoint the influence of interfaces on crack propagation. The numerical results show that the proposed method can satisfactorily capture the interplay between interfaces and crack propagation. Furthermore, in the subinterfacial fracture case, an equilibrium state of mode-I crack growth is successfully obtained, implying that a specific loading condition can counteract the effect of the interface.

Many important engineering and scientific applications such as cement slurries, foams, crude oil, and granular avalanches involve the concept of yield stress. Therefore, modeling yield stress fluids in different flow configurations, including the accurate prediction of the yield surface, is important. In this paper, we present a computational model based on the finite element method to study the flow of yield stress fluids in a thin mold and compare the results with data from flow visualization experiments. We use the level set method to describe the interface between the filling fluid and air. We use polypropylene glycol as a model Newtonian fluid and Carbopol for the model yield stress fluid, as the Carbopol solution demonstrates yielding without thixotropy. To describe the yielding and shear-thinning behavior, we use a generalized Newtonian constitutive equation with a Bingham–Carreau–Yasuda form. We compare the results obtained from the mold filling experiments with the results from the three-dimensional (3D) model and from a reduced-order Hele-Shaw (HS) model that is two-dimensional, including the effect of shear-thinning along the thin direction only approximately. We show that both the 3D and the HS model can capture the experimental meniscus shape reasonably well for all the fluids considered at three different flow rates. This indicates that the shape evolution is insensitive to the dimensionality of the model. However, the viscosity and yield surfaces predicted by the 3D and HS models are different. The HS model underestimates the high viscosity and unyielded regions compared to the estimation by the 3D model.

This perspective article presents the vision of combining findable, accessible, interoperable, and reusable (FAIR) Digital Objects with the National Science Data Fabric (NSDF) to enhance data accessibility, scientific discovery, and education. Integrating FAIR Digital Objects into the NSDF overcomes data access barriers and facilitates the extraction of machine-actionable metadata in alignment with FAIR principles. The article discusses examples of climate simulations and materials science workflows and establishes the groundwork for a dataflow design that prioritizes inclusivity, web-centricity, and a network-first approach to democratize data access and create opportunities for research and collaboration in the scientific community.

A fundamental understanding of the interaction between microstructure and underlying physical mechanisms is essential, especially for developing more accurate multi-physics models for heterogeneous materials. Effects of microstructure on the material response at the macroscale are modeled by using the generalized thermomechanics. In this study, strain gradient theory is employed as a higher-order theory on the macroscale with thermodynamics modeled as a first-order theory on the microscale. Hence, energy depends only on the temperature such that we circumvent an extension of Fourier’s law and analyze the “simplest” thermo-mechanical model in strain gradient elasticity. Developing multiphysics models for heterogeneous materials is indeed a challenge and even this “simplest” model in generalized thermomechanics creates dozens of parameters to be determined. We develop a thermo-mechanical framework, in which microstructure is modeled as a periodic structure and through asymptotic homogenization approach, higher-order parameters at macroscopic scale are calculated. To illustrate the importance of higher-order parameters in overall thermo-mechanical response of a heterogeneous materials, finite element method (FEM) is employed with the aid of open-source codes (FEniCS). Verification example of a bulk system and several case studies of porous structures demonstrate how such numerical framework can be beneficial in the design of materials with tailored microstructures.

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Microscopic features (e.g., pore shapes, sizes, and distribution) in porous material substantially affect the overall mechanical properties such as stiffness and strength. In turn, these material properties determine the macroscopic behaviors of fracture in the porous material. In certain cases, macroscopic properties can be derived from the porous skeleton and void ratio (i.e., porosity), but in many other cases, such derivation is a challenging task. This paper presents a numerical investigation of microporosity and micropore shapes effect on the macrofracture behavior in porous amorphous silica. For this study, we extend the recently proposed combined molecular dynamic (MD) and phase-field (PF) fracture modeling approach by including different pore shapes in the atomistic domain. In the MD simulations, we adopt ReaxFF to evaluate the material properties, where four different micropore cases are considered. Based on the material properties derived from MD simulations, the macrofracture propagation of porous media is studied using hybrid PF simulation. In the characterization of the pore structure, the concept of pore ligament is proposed to relate the pore shape and the critical energy release rate. Two classical fracture problems were used to evaluate the effect of micropore shape on the macrofracture behavior. The results of the case studies show that although the micropore shapes change the macrofracture behaviors, these effects vary with the geometry and loading conditions of macroscopic boundary value problems. The case study also shows that the influence of micropore structure can be captured at the macroscopic level through the material properties derived from the MD simulations.

Even though heterogeneous porous materials are widely used in a variety of engineering and scientific fields, such as aerospace, energy-storage technology, and bio-engineering, the relationship between effective material properties of porous materials and their underlying morphology is still not fully understood. To contribute to this knowledge gap, this paper adopts a higher-order asymptotic homogenization method to numerically investigate the effect of complex micropore morphology on the effective mechanical properties of a porous system. Specifically, we use the second-order scheme that is an extension of the first-order computational homogenization framework, where a generalized continuum enables us to introduce length scale into the material constitutive law and capture both pore size and pore distribution. Through several numerical case studies with different combinations of porosity, pore shapes, and distributions, we systematically studied the relationship between the underlying morphology and effective mechanical properties. The results highlight the necessity of higher-order homogenization in understanding the mechanical properties and reveal that higher-order parameters are required to capture the role of realistic pore morphologies on effective mechanical properties. Furthermore, for specific pore shapes, higher-order parameters exhibit dominant influence over the first-order continuum.

Reinforced concrete is one of the most widely used materials in engineering construction and reinforced concrete structures can be degraded by CO2 in a humid environment. This article reviews previous studies that investigated the evolution of the chemical, structural, and mechanical properties of concrete and steel reinforcement experiencing CO2-induced reaction. The major findings can be summarized as follows: 1) CO2 causes changes in the mineral phases of concrete and steel reinforcement, eventually leading to the deterioration of their structure and strength. 2) Because of the CO2 reaction, the compressive strength of concrete increases first and then decreases, whereas the tensile strength of the steel reinforcement decreases. 3) The corrosion reaction at the interface (i.e., the interface between soil/rock and concrete or that between concrete and reinforcement steel) causes the interfacial bonding strength to increase first and then decrease. 4) Reinforced concrete degradation caused by high-concentration CO2 is considerably more severe than that caused by atmospheric CO2, and more studies are required to understand the reaction mechanism.

Materials which exhibit elastic and yielding behavior are present in many industrial processes including thin-film coating, oil extraction, manufacturing of consumer products, and food processing. Numerical simulation is a powerful tool for gaining insights into the flow behavior of complex fluids and can facilitate the design of commercially relevant processes, such as mold filling and coating flows. In this study, we perform numerical simulations of an elastoviscoplastic fluid expanding into a thin, rectangular mold. We use a Saramito model to describe the rheology of the fluid (Saramito, 2007) as well as the Bingham–Carreau–Yasuda generalized Newtonian model. The Saramito model used describes the material as an Oldroyd-B fluid above yield and an elastic solid below yield; the yield criterion is based on the von Mises stress. Conservation equations for momentum and mass and the Saramito constitutive equations for stress are solved using the finite element method coupled to a free surface moving mesh algorithm. We assess our Saramito model implementation by comparing computations to benchmarks in the literature, including flow past a cylindrical obstacle and channel flow. We compare results from two and three-dimensional mold filling simulations to flow visualization experiments where fluid fills a thin gap between transparent plates. For both two and three-dimensional, the Saramito model is generally more predictive of the shape of the growing fluid droplet than the Bingham–Carreau–Yasuda model. Saramito model results for 2D computations match experimental droplet shapes well with the addition of a model for the drag terms to capture the effects of the unresolved third dimension. For fully 3D computations, the Saramito model is able to reproduce experimentally-observed droplet shapes for the smallest (5 mL/min) and largest (20 mL/min) flow rates, but struggles to accurately reproduce experimental observations at an intermediate flow rate (10 mL/min). This discrepancy is probably due to the over prediction of slip from the wetting model.

Microstructure related deviation from elastic response is known as “size-effect.” Metamaterials – for example modeled by strain gradient elasticity – capture this effect adequately by means of additional parameters to be determined. We employ a methodology based on asymptotic homogenization in order to obtain metamaterials parameters and then present the influence of these additional parameters by using simulations. By means of the finite element method, we solve metamaterials deformation modeled by the strain gradient elasticity. The implementation is established by open-source packages (FEniCS) for a realistic, composite structure with round and oval inclusions.

Armillaria ostoyae (Romagn.) Herink is a highly pathogenic fungus that uses exploratory, cordlike structures called rhizomorphs to seek out new sources of nutrition, posing a parasitic threat to natural stands of trees, orchards, and vineyards. Rhizomorphs are notoriously difficult to destroy, and this resilience is due in large part to a melanized layer that protects the rhizomorph. While this structure has been previously observed, its structural and chemical defenses are yet to be discerned. Research was conducted on both lab-cultured and wild-harvested rhizomorph samples. While both environments produce rhizomorphs, only the wild-harvested rhizomorphs produced the melanized layer, allowing for direct investigation of its structure and properties. Imaging, chemical analysis, mechanical testing, and finite element modeling were used to understand the defense mechanisms provided by the melanized layer. Imaging showed a porous outer layer in both types of rhizomorphs, though the pores were smaller in the harvested melanized layer. This melanized layer contained calcium, which provides chemical defense against both human and natural control methods, but was absent from cultured samples. Nanoindentation resulted in a larger variance of hardness values for cultured rhizomorphs than for wild-harvested. Finite element analysis proved that the smaller pore structure of the melanized porous layer had the best balance between maximum deformation and resulting permanent deformation. These results allow for a better understanding of the defenses of this pathogenic fungus, which may lead to better control methods.

Shale can be a potential buffer for high-level radioactive nuclear wastes. To be an effective buffer while subject to waste heat, shale's mechanical response at elevated temperature must be known. Many researchers have experimentally characterized the mechanical behavior of various shales at different length scales in adiabatic conditions. However, its mechanical performance at elevated temperatures at the nano-scale remains unknown. To investigate the temperature dependency of nanomechanical properties of shale, we conducted both experimental and numerical studies. In this study, we measured mechanical and fracture properties of shale, such as hardness, elastic modulus, anisotropy, and fracture toughness from 25 °C up to 300 °C at different bedding planes. Statistical analysis of the results suggests that hardness and fracture toughness significantly increased at temperatures from 100 to 300 °C; while, temperature does not have a significant impact on elastic modulus. Data also shows that the bedding plane orientations have a substantial impact on both mechanical and fracture properties of shale at the nano-scale leading to distinct anisotropic behavior at elevated temperature below 100 °C. Additionally, we numerically investigated the mechanical performance of the shale samples at room temperature to gain an insight into its mechanical response through the thickness. Numerical results were validated against the experimental results, confirming the simulation can be used to predict shale deformation at the nano-scale or potentially be used in multi-scale simulations.

The collapse of the Champlain Towers South condominium in South Florida shocked the world. Many families lost loved ones or are still holding their breath. The question remains: what was the cause of this catastrophic failure?

Porous amorphous silica (a-SiO2) is of both fundamental and practical interests, as they exhibit a large specific surface area and tunable porous network. However, the brittle nature of a-SiO2 and the presence of pre-existing cracks at both micro- and nano-scales lead to complex mechanical behavior. In this study, we systematically investigate the effects of pre-existing crack and its orientation on the mechanical properties of a-SiO2 with varying pore shapes using reactive molecular dynamics simulations. We demonstrate that pore shape will primarily influence the Young’s modulus (E) and critical energy release rate ( G IC ). We further investigate the impact of pore shape and crack orientation by local characterization of the structural parameters. By defining the high stress and inter-mediate regions, the overall mechanical properties are found to be greatly influenced by the pore shape which can be reflected through the spatial distribution of von Mises stress. Overall, G IC is found to increase with the increase of ligament length (also known as pore wall thickness). Meanwhile, the effect of the pre-existing crack on the crack propagation process is confirmed by analyzing the density distribution evolution. These results highlight the interplay between pore morphology and crack orientation in controlling the fracture behaviors in brittle porous materials.

Porous materials are typically heterogeneous and they contain large variations of micro-/nano-pore structures, causing complicated behaviors. In continuum models, most mechanical properties of porous materials are estimated based on porosity, while the variations of micro/nano structures are ignored. That could be problematic as the microscopic heterogeneity may affect the mechanical response of porous materials. Thus, understanding micro/nano heterogeneity impact has been the focus in many scientific and engineering subjects. In the present study, we investigated the effect of nanopore structure (including pore shape and orientation) as well as porosity on mechanical properties of amorphous silica (a-SiO2). The pore sizes in our simulations are comparable to the corresponding ones observed in a-SiO2 based materials. We found that the existing of nanopores strongly influences Young’s modulus (E) and critical energy release rate ( G IC ). These properties decrease with increasing porosity. Importantly, the impact of nanopores was characterized by structural parameters of porous materials. In addition to dependency on porosity, Young’s modulus also was found to vary as a function of potential energy per atom, which highly depends on nanopore shape. Furthermore, critical energy release rate was found to increase with increasing ligament length (also known as pore wall thickness). The results highlighted the importance of nanopore structures, which must be taken into account when studying fracture mechanisms in porous materials. Based on our findings, it was proposed that mechanical properties of porous materials can be controlled by nano-engineering pore structures.

Most porous media, such as geomaterials and biomaterials are highly heterogeneous in nature, and they contain large variations of microscopic pore structures, such as pore sizes, pore distribution, and pore shapes. The oscillation of microscopic structures is a substantial challenge in theoretical characterization and is usually ignored in continuous modeling. However, mechanical behavior of porous media such as deformation and failure, are essentially impacted by the microscopic heterogeneity which needs to be considered in modeling a porous media. This research proposes a numerical modeling framework with a capability to investigate the effect of microscopic heterogeneity on the macroscopic fracture behavior in porous media by using a numerical homogenization technique, combined with the phase-field fracture modeling method. This numerical modeling strategy computes a homogenized elasticity tensor based on microscopic heterogeneous pore structures heterogenous porous domain by solving boundary value problems at microscopic domain. The strain energy and subsequent propagation of macroscopic fractures will be updated using homogenized stiffness information. Using this numerical scheme, the microscopic pore structure’s impact on the fracture behavior through the homogenized elastic tensor will be taken into account. This multiscale technique is benchmarked against classical problems. The results highlight the importance of the underlying pore structure and reveal that both fracture strength and propagation path can be influenced by the microscopic heterogeneity.

The development of fractures in materials is controlled by stress, as well as chemical environment to which materials might be exposed. Chemical dissolution reactions have proven to affect the integrity of various materials, including porous rocks. The goal for this study is to develop a novel phase-field formulation to deal with fracture propagation in a chemically reactive environment. We formulated a numerical model for coupling chemical damage and mechanical damage defined based on the diffusive phase-field fracture method. Furthermore, the chemical damage is linked to the change in porosity due to dissolution. The developed theoretical framework was numerically implemented and applied to subsurface undergoing calcite dissolution due to exposure to CO 2 , as a real-world example where understanding chemo-mechanical damage is crucial. The chemical damage assists mechanical damage obtained from phase-field in degradation of the material. This application of the phase-field method to subsurface rocks demonstrates its ability to predict chemo-mechanical coupling, and to quantify the impact of chemical alteration on fracture behavior.

One potential risk in CO2 sequestration is the leakage of carbon dioxide, which can result in contamination of underground water, creating potential threats to existing ecosystems. The common leakage pathway is through the pre-existing fractures or discontinuities within cement in the wellbore, incurred by the environmental conditions imposed on the cement. Injecting nanoparticles into pre-existing cracks is one of the most recently proposed ideas for mitigating fracture propagation in cement CO2 sequestration. To demonstrate the feasibility of this new technology, a numerical approach was taken in this work, as it is challenging to investigate it in a laboratory setting. We proposed a coupled ALE (Arbitrary Lagrangian–Eulerian)–DEM (Discrete Element Method)–peridynamic modeling strategy within the LS-Dyna package to investigate the intertwined interaction among the CO2 fluid flow, native fluid (e.g., brine), particle clusters, and cracks within the cement. The numerical results demonstrate that injected nanoparticles can effectively reduce the pressure exerted on the crack surface. Accordingly, the potential fracture propagation at the crack tip would be reduced compared to corresponding cases without nanoparticels as pressurized by fluid flow. This result verifies the effectiveness of proposed nanoparticle injection technology. Finally, using this established modeling strategy, the effect of filling particles on the fracture mitigation for different crack geometries (e.g. particle cluster patterns, aspect ratio of crack aperture and length) and CO2 reservoir pressure are examined. The result shows that injected particles successfully reduce the fracture propagation in these scenarios.

Coupled fluid-flow and geomechanical analysis of caprock integrity has gained a lot of attention among scientists and researchers investigating the long-term performance of geologic carbon storage systems. Reactivation of pre-existing fractures within the caprock or re-opening of faults can create permeable pathways which can influence the seal integrity. Stability of the caprock during and after injection of super-critical CO 2 , and the impact of pre-existing fractures in the presence or absence of one or multiple faults have been investigated in this study. The impact of the wellbore orientation and the injection rate are among other key factors in understanding the structural trapping mechanisms within such geological formations. In this study, we numerically investigated the impact of each of these factors. This study revealed the interplay between joints and faults and how different leakage pathways are formed and under which scenario they play a dominant role in terms of CO 2 leakage. This study also highlights the role of one versus multiple faults in the domain and the importance of the fault hydrological property in forming leakage pathway.

Mechanical properties are very important when choosing a material for a specific application. They help to determine the range of usefulness of a material, establish the service life, and classify and identify materials. The size effect on mechanical properties has been well established numerically and experimentally. However, the role of the size effect combined with boundary and loading conditions on mechanical properties remains unknown. In this paper, by using molecular dynamics (MD) simulations with the state-of-the-art ReaxFF force field, we study mechanical properties of amorphous silica (e.g., Young's modulus, Poisson's ratio) as a function of domain size, full-/semi-periodic boundary condition, and tensile/compressive loading. We found that the domain-size effect on Young's modulus and Poisson's ratio is much more significant in semi-periodic domains compared to full-periodic domains. The results, for the first time, revealed the bimodular and anisotropic nature of amorphous silica at the atomic level. We also defined a "safe zone" regarding the domain size, where the bulk properties of amorphous silica can be reproducible, while the computational cost and accuracy are in balance.

Abstract To investigate mechanisms of seismic fault reactivation in crystalline basement in response to fluid injection in overlying sedimentary reservoirs, we conducted three‐dimensional finite element simulations to assess the effects of direct pore pressure communication and indirect poroelastic stress transfer on the change in Coulomb failure stress of favorably oriented faults of varying permeability structure in normal, strike‐slip, and reverse faulting stress regimes. We demonstrate that the direct pore pressure effect transmitted along a hydraulically conductive fault exceeds the indirect poroelastic effect, but alone is insufficient for fault reactivation in the basement. The poroelastic effect on the Coulomb failure stress results from induced normal tractions and, to a lesser extent, from induced shear tractions that relate to the flexing of the fault as the reservoir expands poroelastically with fluid injection. Assuming a higher Biot coefficient for reservoir over basement rock as previously reported, the combined direct pore pressure and indirect poroelastic effects result in reactivation of hydraulically conductive faults in the basement in normal and strike‐slip faulting stress regimes and in the reservoir in reverse faulting regimes. Sealing normal faults that are not preferentially conductive also preferentially reactivate in the reservoir. These findings apply to injection in either hanging or footwall of normal and reverse faults. Reducing the contrast in Biot coefficient between reservoir and basement favors fault reactivation in the reservoir for injection in the footwall in normal faulting stress regimes. These simulations demonstrate that geomechanical models without coupled poroelasticity underestimate the potential of fault reactivation in crystalline basement. Key Points Poroelastic stress changes favor fault reactivation in basement in normal and strike‐slip faulting regimes for conduit‐barrier faults Sealing normal fault and reduced material contrast between reservoir and basement favor reactivation in reservoir over basement Direct pore pressure effects prevail over poroelastic stress in increasing Coulomb failure stress but are insufficient to lead to basement fault reactivation

Three computational methods for modeling fracture are compared in the context of a class’ participation in the Third Sandia Fracture Challenge (SFC3). The SFC3 was issued to assess blind predictions of ductile fracture in a complex specimen geometry produced via additive manufacturing of stainless steel 316L powder. In this work, three finite-element-based methods are investigated: (1) adaptive remeshing, with or without material-state mapping; (2) element deletion; and (3) the extended finite element method. Each student team was tasked with learning about its respective method, calibrating model parameters, and performing blind prediction(s) of fracture/failure in the challenge-geometry specimen. Out of 21 teams who participated in the SFC3, three of the seven student teams from this class project ranked among the top five based on either global force-displacement or local strain predictions. Advantages and disadvantages of the three modeling approaches are identified in terms of mesh dependency, user-friendliness, and accuracy compared to experimental results. Recommendations regarding project management and organization are offered to facilitate future classroom participation in the Sandia Fracture Challenge or similar blind round-robin exercises.

The Sandia Fracture Challenges provide a forum for the mechanics community to assess its ability to predict ductile fracture through a blind, round-robin format where mechanicians are challenged to predict the deformation and failure of an arbitrary geometry given experimental calibration data. The Third Challenge (SFC3) required participants to predict fracture in an additively manufactured (AM) 316L stainless steel bar containing through holes and internal cavities that could not have been conventionally machined. The volunteer participants were provided extensive data including tension and notched tensions tests of 316L specimens built on the same build-plate as the Challenge geometry, micro-CT scans of the Challenge specimens and geometric measurements of the feature based on the scans, electron backscatter diffraction (EBSD) information on grain texture, and post-test fractography of the calibration specimens. Surprisingly, the global behavior of the SFC3 geometry specimens had modest variability despite being made of AM metal, with all of the SFC3 geometry specimens failing under the same failure mode. This is attributed to the large stress concentrations from the holes overwhelming the stochastic local influence of the AM voids and surface roughness. The teams were asked to predict a number of quantities of interest in the response based on global and local measures that were compared to experimental data, based partly on Digital Image Correlation (DIC) measurements of surface displacements and strains, including predictions of variability in the resulting fracture response, as the basis for assessment of the predictive capabilities of the modeling and simulation strategies. Twenty-one teams submitted predictions obtained from a variety of methods: the finite element method (FEM) or the mesh-free, peridynamic method; solvers with explicit time integration, implicit time integration, or quasi-statics; fracture methods including element deletion, peridynamics with bond damage, XFEM, damage (stiffness degradation), and adaptive remeshing. These predictions utilized many different material models: plasticity models including J2 plasticity or Hill yield with isotropic hardening, mixed Swift-Voce hardening, kinematic hardening, or custom hardening curves; fracture criteria including GTN model, Hosford-Coulomb, triaxiality-dependent strain, critical fracture energy, damage-based model, critical void volume fraction, and Johnson-Cook model; and damage evolution models including damage accumulation and evolution, crack band model, fracture energy, displacement value threshold, incremental stress triaxiality, Cocks-Ashby void growth, and void nucleation, growth, and coalescence. Teams used various combinations of calibration data from tensile specimens, the notched tensile specimens, and literature data. A detailed comparison of results based of these different methods is presented in this paper to suggest a set of best practices for modeling ductile fracture in situations like the SFC3 AM-material problem. All blind predictions identified the nominal crack path and initiation location correctly. The SFC3 participants generally fared better in their global predictions of deformation and failure than the participants in the previous Challenges, suggesting the relative maturity of the models used and adoption of best practices from previous Challenges. This paper provides detailed analyses of the results, including discussion of the utility of the provided data, challenges of the experimental-numerical comparison, defects in the AM material, and human factors.

Geological carbon storage (GCS) is a promising technology for mitigating increasing concentrations of carbon dioxide (CO2) in the atmosphere. The injection of supercritical CO2 into geological formations perturbs the physical and chemical state of the subsurface. The reservoir rock, as well as the overlying caprock, can experience changes in the pore fluid pressure, thermal state, chemical reactivity and stress distribution. These changes can cause mechanical deformation of the rock mass, opening/closure of preexisting fractures or/and initiation of new fractures, which can influence the integrity of the overall geological carbon storage (GCS) systems over thousands of years, required for successful carbon storage. GCS sites are inherently unified systems; however, given the scientific framework, these systems are usually divided based on the physics and temporal/spatial scales during scientific investigations. For many applications, decoupling the physics by treating the adjacent system as a boundary condition works well. Unfortunately, in the case of water and gas flow in porous media, because of the complexity of geological subsurface systems, the decoupling approach does not accurately capture the behavior of the larger relevant system. The coupled processes include various combinations of thermal (T), hydrological (H), chemical (C), mechanical (M), and biological (B) effects. These coupled processes are time- and length-scale- dependent, and can manifest in one- or two-way coupled behavior. There is an undeniable need for understanding the coupling of processes during GCS, and how these coupled phenomena can result in emergent behaviors arising from the interplay of physics and chemistry, including self - focusing of flow, porosity collapse, and changes in fracture networks. In this chapter, the first section addresses the subsurface system response to the injection of CO2, examined at field and laboratory scales, as well as in model systems, addressed from a perspective of single disciplines. The second section reviews coupling between processes during GCS observed either in the field or anticipated based on laboratory results.

The long-term carbon dioxide storage capacity of reservoirs can be impacted by chemical reactions, mass transport, and mechanical deformation of the reservoir and caprock following the injection of CO2. Mineral mass removal can lead to microcracking and compaction, thus affecting the mechanical integrity of the reservoir–caprock system. The short-term (days, months) and long-term (hundreds to thousands of years) chemical effects, such as the dissolution of intergranular cement and mineral precipitation, can lead to a coupled chemical-mechanical response. This chemical-mechanical coupling occurs at multiple temporal and spatial scales. For instance, chemical processes at the crack-tip (micrometer) scale affect fracture networks with complex fracture architecture all the way to the reservoir scale. This chapter addresses chemical effects on the mechanical response of reservoir and caprock lithologies considered for geological carbon storage. Particular emphasis is on sandstone reservoir and mudrock (shale) caprock, as they are the most typical formations targeted for the injection of CO2. This chapter examines the existing laboratory, field, and modeling studies that address the coupled chemical-mechanical response of sandstone and mudrock lithologies to the injection of CO2. These coupled chemical-mechanical responses during geological carbon storage can result in the development of preferential flow paths and CO2leakage.

Shale gas rocks are characterized as clastic sedimentary rocks, with features such as obvious bedding planes, presence of micro-cracks, and high clay and organic content. These rocks are anisotropic and inhomogeneous, exhibiting a nonlinear response under loading. In order to optimize the required energy for hydraulic fracturing operation and production in shale gas reservoirs, and for constitutive and numerical modeling, it is important to characterize these shale gas rocks. In this study, the hysteresis, elastic-plastic, viscoelastic, and strength properties of Marcellus Shale specimens, retrieved from a deep well located in West Virginia, were evaluated through performing a series of creep, cyclic, and triaxial multi-stage failure tests on these specimens. Both elastic moduli and plastic deformations show significant levels of pressure dependency. Moreover, higher creep compliance and lower Young's modulus values were observed for clay-rich specimens. Both Power-Law and Burgers' models were found to capture the creep response of these specimens reasonably well. The dynamic moduli estimated from the ultrasonic velocity measurements at different stress levels were found to be higher than static moduli estimations. In addition, the changes in the internal micro-structure of the specimens resulted from variations in the stress condition, were found to affect the ultrasonic velocity measurements. The strength properties of the calcite/quartz-rich specimen, using multi-stage triaxial failure test, were estimated through both Mohr-Coulomb and Hoek-Brown failure criteria.

Desirable outcomes for geologic carbon storage include maximizing storage efficiency, preserving injectivity, and avoiding unwanted consequences such as caprock or wellbore leakage or induced seismicity during and post injection. To achieve these outcomes, three control measures are evident including pore pressure, injectate chemistry, and knowledge and prudent use of geologic heterogeneity. Field, experimental, and modeling examples are presented that demonstrate controllable GCS via these three measures. Observed changes in reservoir response accompanying CO2 injection at the Cranfield (Mississippi, USA) site, along with lab testing, show potential for use of injectate chemistry as a means to alter fracture permeability (with concomitant improvements for sweep and storage efficiency). Further control of reservoir sweep attends brine extraction from reservoirs, with benefit for pressure control, mitigation of reservoir and wellbore damage, and water use. State-of-the-art validated models predict the extent of damage and deformation associated with pore pressure hazards in reservoirs, timing and location of networks of fractures, and development of localized leakage pathways. Experimentally validated geomechanics models show where wellbore failure is likely to occur during injection, and efficiency of repair methods. Use of heterogeneity as a control measure includes where best to inject, and where to avoid attempts at storage. An example is use of waste zones or leaky seals to both reduce pore pressure hazards and enhance residual CO2 trapping.

Economic feasibility of geologic carbon storage demands sustaining large storage rates without damaging caprock seals. Reactivation of pre-existing or newly formed fractures may provide a leakage pathway across caprock layers. In this study, we apply an equivalent continuum approach within a finite element framework to model the fluid-pressure-induced reactivation of pre-existing fractures within the caprock, during high-rate injection of super-critical CO2 into a brine-saturated reservoir in a hypothetical system, using realistic geomechanical and fluid properties. We investigate the impact of reservoir to caprock layer thickness, wellbore orientation, and injection rate on overall performance of the system with respect to caprock failure and leakage. We find that vertical wells result in locally higher reservoir pressures relative to horizontal injection wells for the same injection rate, with high pressure inducing caprock leakage along reactivated opening-mode fractures in the caprock. After prolonged injection, leakage along reactivated fractures in the caprock is always higher for vertical than horizontal injection wells. Furthermore, we find that low ratios of reservoir to caprock thickness favor high excess pressure and thus fracture reactivation in the caprock. Injection into thick reservoir units thus lowers the risk associated with CO2 leakage.

Coupled reservoir and geomechanical simulations are significantly important to understand the long-term behavior of geologic carbon storage (GCS) systems. In this study, we performed coupled fluid flow and geomechanical modeling of CO2 storage using available field data to (1) validate our existing numerical model and (2) perform parameter estimation via inverse modeling to identify the impact of key geomechanical (Young's modulus and Biot's coefficient) and hydrogeological (permeability and anisotropy ratio) properties on surface uplift and the pore pressure buildup at In Salah in Algeria. Two sets of surface uplift data featuring low and high uplifts above two injection wells and the maximum change in the pore pressure due to CO2 injection were used to constrain the inverse model. Forward simulation results with representative parameter values from the literature match both low and high surface uplifts reasonably well and predicted the maximum change in the pore pressure. In particular, forward modeling results with estimated Biot's coefficients for reservoir and caprock layers, match the observed uplift well, highlighting the significance of Biot's coefficient in coupled reservoir and geomechanical models. Parameter estimation with 12 parameter sets for both low and high uplift data demonstrates that multiple sets of parameters can match the observed data equally well and the inclusion of the pore pressure data is critically important to constrain the parameter solution during inverse modeling. For a majority of cases, estimation results for both low and high uplift data show the vertical intrinsic permeability and Young's modulus of the reservoir remained close to 13mD (1.3×10−14m2) and 10GPa, respectively, suggesting that these parameters may represent the actual effective properties. Additionally, higher correlations between reservoir permeability and caprock's Biot's coefficient with high surface uplift data were observed consistently under the pore pressure constraint, suggesting the inclusion of the pore pressure constraint is required to estimate the proper values of coupled flow and geomechanical properties associated with different surface uplift data. Overall, this study suggests that given limited data, including Biot's coefficient, in addition to permeability and Young's modulus can enhance parameter estimation of the geomechanical response during GCS.

Fracture and fragmentation are extremely nonlinear multiscale processes in which microscale damage mechanisms emerge at the macroscale as new fracture surfaces. Numerous numerical methods have been developed for simulating fracture initiation, propagation, and coalescence. Here, we present a computational approach for modeling pervasive fracture in quasi-brittle materials based on random close-packed Voronoi tessellations. Each Voronoi cell is formulated as a polyhedral finite element containing an arbitrary number of vertices and faces. Fracture surfaces are allowed to nucleate only at the intercell faces. Cohesive softening tractions are applied to new fracture surfaces in order to model the energy dissipated during fracture growth. The randomly seeded Voronoi cells provide a regularized discrete random network for representing fracture surfaces. The potential crack paths within the random network are viewed as instances of realizable crack paths within the continuum material. Mesh convergence of fracture simulations is viewed in a weak, or distributional, sense. The explicit facet representation of fractures within this approach is advantageous for modeling contact on new fracture surfaces and fluid flow within the evolving fracture network. Applications of interest include fracture and fragmentation in quasi-brittle materials and geomechanical applications such as hydraulic fracturing, engineered geothermal systems, compressed-air energy storage, and carbon sequestration.

The Mount Simon Sandstone (Mt. Simon), a basal Cambrian sandstone underlying much of Midwestern US, is a target for underground CO2 storage and waste injection which requires an assessment of geomechanical behavior. The range of depositional environments yields a heterogeneous formation with varying porosity, permeability, and mechanical properties. Experimental deformational behavior of three distinct Mt. Simon lithofacies was examined via axisymmetric compressional testing of core samples. Initial yielding was confirmed with acoustic emissions in many tests and failure envelopes were determined for each lithofacies. Evolution of elastic moduli with stress and plastic strain was determined by use of unload–reload cycles, which permit separation of total measured strains into elastic and plastic strains. The Upper Mt. Simon lithofacies yields at higher shear stresses compared to two “Lower” lithofacies, with little modulus degradation with plastic strain. Lower Mt. Simon lithofacies are weaker and deform plastically with modulus degradation. This range in constitutive response is quantified with an elasto-plasticity model. Based on these results, Mount Simon Sandstone would likely deform elastically during CO2 injection and storage, with large pore pressure increases (∼8–9MPa above hydrostatic) predicted to initiate plastic yielding. Nonetheless, near-wellbore damage could result in weaker lithofacies during injection and/or brine extraction.

Encapsulated phase change materials (PCMs) were used in concrete to improve thermal properties of the concrete, called PCM-concrete. This paper presents the predictions of the effective thermal conductivity of PCM-concrete using different composite models, such as the parallel, the series models, Maxwell model and Generalized Self-Consistent (GSC) model. Multi-phase, multi-scale internal structural models were developed and combined with GSC model to predict the effective thermal conductivity of PCM-concrete. It was found that the configuration of the internal structure for the PCM phase is very important. The PCM phase needs to be considered as a matrix (a thin shell), which can effectively block the heat flow and thus reduce the thermal conductivity of PCM-concrete. The GSC model with the suggested internal structure model can predict the effective thermal conductivity of PCM-concrete. The prediction agreed with test data quite well, and the prediction is within the upper and lower bounds.

The initial and primary trapping mechanism for long term subsurface sequestration of CO2 is structural trapping beneath a low permeability caprock layer. Maintaining caprock integrity during injection operations is paramount to successful sequestration. Evaluation of jointed/fractured caprock systems is of particular concern to CO2 sequestration because creation of fractures or reactivation of joints can lead to enhanced pathways for leakage.In this work, a joint model is introduced to describe joint reactivation during injection of CO2. The model assumes equally spaced anisotropic joint sets with non-linear normal stiffness and linear shear stiffness. Normal displacement of the joints is mapped into a dynamically evolving effective anisotropic permeability tensor, assuming a cubic law for fracture permeability as a function of joint aperture. A model problem is presented to demonstrate features of the joint model and how it affects the coupled geomechanics and flow during injection of CO2 into deep saline aquifers. The model is used to demonstrate injection reservoir properties and injection rates that have potential for inducing leakage through the caprock due to overpressures associated with CO2 injection.In situations where pore pressure approaches or exceeds lithostatic pressure under a constant-rate, 30 year injection, the model indicates between 16 and 20% of injected CO2 could leak past the primary caprock after 50 years. The model also indicates a concomitant overpressure reduction that could signal caprock leakage during the injection.

Phase change materials (PCMs) and rubber particles from recycled tires were used in portland cement mortar with a potential application as insulation mortar. Series of tests were designed and conducted including compressive strength, flexural strength, thermal conductivity, drying shrinkage, and bond strength tests at 7days and 28days of age. Different types of additives were also used in the mix designs. The experimental results showed that mechanical properties of rubberized-mortar can be improved by adjusting the size of rubber particles and the amount of additives. With the same volume fraction of PCM and rubbers, the mechanical properties of PCM-modified mortar are either the same or better than that of rubberized-mortar. In terms of thermal properties, the rubber particles can reduce thermal conductivity of the mortar significantly, while the PCM can improve heat capacity of the mortar.

This paper presents the results of experimental and analytical investigations on the long-term behavior of epoxy at the interface between the concrete and the fiber-reinforced-polymer (FRP). Double shear experiments under sustained service load were performed on nine specimens composed of two concrete blocks connected by FRP sheets bonded to concrete using epoxy. The primary investigation parameters included the ratio of shear stress to ultimate shear strength, the epoxy thickness and the epoxy time-before-loading. Loading was sustained for periods up to nine months. We show that the magnitude of shear stress to ultimate shear strength and the epoxy time-before-loading could be the most critical parameters affecting creep of epoxy at the concrete–FRP interfaces. It was also found that the creep of epoxy can result in failure at the interfaces due to the combined effect of relatively high shear stress to ultimate shear strength and thick epoxy adhesive. This can have an adverse effect on the designed performance of reinforced concrete (RC) structures strengthened with FRP. Based on the experimental observations, rheological models were developed to simulate the long-term behavior of epoxy at the concrete–FRP interfaces. It is shown that the long-term behavior of epoxy at the interfaces can be properly modeled by analytically for both loading and unloading stages.

This paper presents the results of experimental and analytical investigations of the long-term behavior of the epoxy used at the concrete–FRP interfaces. Double shear long-term test was performed on specimens composed of concrete blocks bonded to FRP sheets using epoxy. Three test replicates were examined under sustained shear stress for up to six month time period with two primary parameters: the shear stress level and the epoxy thickness. The investigation showed that shear stress level might have significant effect on the long-term behavior of epoxy at the concrete–FRP interfaces. Based on the experimental results, creep characteristics of epoxy in the concrete–FRP interfaces were evaluated. Finite element analysis was performed incorporating these creep characteristics to investigate the long-term deformations and stress redistributions in the test specimens. It was recognized that creep of epoxy might result in stress-redistribution at the concrete–FRP interfaces.