Fracture Plane Research Articles

Numerical simulation on the mechanical and fracture behavior of bedding argillaceous sandstone containing two pre-existing flaws

The overlying strata will move and generate flaws as the coal mining workings advance, and the development of flaws can affect the collapse process of the overlying strata, studying the fracture behavior under different pre-existing flaws conditions is crucial to maintain the stability of coal mining workings. In this work, a series of bedding argillaceous sandstone models containing two pre-existing flaws (i.e. bottom flaw length, included angle between upper and bottom flaw, and loading rate) were simulated under uniaxial compression experiments based on the discrete element method (DEM) under the moment tensor theory. The research results show that the increasing in included angle and loading rate lead to an increase in peak strength and a decrease in the angle of the main fracture plane. The variation of peak strength and b-value decreases with the bottom flaw length, with smaller tensile acoustic emission (AE) event and larger shear AE event for interlayer and bedding cracking, respectively. The crack-in-matrix presents a concave tendency with bedding angle, leading to a failure pattern change from matrix-dominated, matrix-bedding to bedding-dominated in a lower b-value. Loading rate promotes the change of AE event from tensile to shear mode with a wider fracture plane. In terms of brittleness, the range of brittleness is mainly between moderate brittleness and brittleness, and decreases and increases as the bottom flaw length and the included angle, respectively, exhibit a linear correlation in strength, independent of the loading rate to models. The research results could contribute to the comprehension of cracking mechanisms and improve safe production at coal mine workings of bedding strata.

High Complication Rate After Percutaneous Screw Fixation for Valgus-Impacted Femoral Neck Fractures Without Sagittal Malalignment.

To evaluate the rate of reoperation in patients without sagittal plane malalignment who underwent percutaneous screw fixation of a valgus-impacted femoral neck fracture. Retrospective case series. Two Level 1 academic trauma centers. Two hundred seven patients >50 years of age with valgus-impacted femoral neck fractures treated with at least 3 large-diameter (>6.5 mm) cancellous screws from 2013 to 2019. Patients were excluded if there was a sagittal plane fracture deformity. The primary outcome was reoperation. Secondary outcomes considered "major complications" included: avascular necrosis, varus collapse or implant cutout, nonunion, deep infection, and hematoma requiring reoperation. Surgical fixation strategies (screw configuration, aim) and implant type (partial vs. fully threaded cancellous screws) were secondarily compared. Average patient age was 77 years, and median clinical follow-up was 658 days. Thirty-one patients (15%) required reoperation, and the major complication rate was 17.3% (36 complications in 33 patients). Logistic regression analysis demonstrated a higher risk of reoperation with constructs consisting of all partially threaded screws (17.0%) compared with the use of at least 1 fully threaded screw (7.5%) when an inverted triangle configuration was used (odds ratio, 2.50; 95% CI, 0.81-7.77). This study demonstrated a relatively high rate of reoperation and major complications in patients with valgus-impacted femoral neck fractures without sagittal malalignment treated with in situ percutaneous screw fixation. Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Computed Tomography Analysis of Distal Tibia Physeal Fracture Patterns: A Classification and Technique for Optimizing Screw Trajectory.

Fractures involving the anterolateral distal tibia, often referred to as Tillaux or Triplane fractures, are often treated operatively to achieve an anatomic reduction of the ankle joint articular surface. Although axial images from computed tomography scans are commonly obtained to measure displacement, no studies have examined these fracture patterns in the axial plane. This information may be useful to guide screw trajectory with only fluoroscopic imaging intraoperatively. We queried an institutional radiology report database for all "Tillaux" or "triplane" fractures and manually reviewed to identify fractures with an anterolateral tibia fragment. The axial image immediately caudal to the physis or physeal scar was used for measurements. The angle between the incisura and the fracture line exiting the incisura was measured. The width of the fracture fragment and the anterior distal tibia was then measured perpendicular to the incisura, representing the width that would be seen on an intraoperative mortise. A cluster analysis was performed to identify fracture patterns. The average age of patients included in the study was 16 ± 2 years. Sixty-nine patients met inclusion criteria 32 patients with Tillaux fractures (46.4%) and 37 patients with triplane fractures (53.6%) met study inclusion criteria for a total of 69 patients. The cluster analysis demonstrated 3 fracture patterns. For type 1 (n=16), the mean was 24.5 ± 6.5 degrees from the incisura and the mean distance from the tibiofibular joint was 21.1 ± 6.3%. For type 2 (n=20), the mean was 58.6 ± 7.2 degrees and the mean distance was 48.7 ± 8.9%. For type 3 (n=33), the mean was 88.6 ± 6.3 degrees and the mean distance was 49.1 ± 9.7%. This is the first study to identify that pediatric distal tibia physeal fractures occur in 3 common patterns with consistent fragment sizes and fracture planes. This information can optimize screw start point and trajectory in the axial plane when referencing a mortise x-ray and C-arm beam. Diagnostic, Level III.

A Fast Workflow for Automatically Extracting the Apparent Attitude of Fractures in 3-D Digital Core Images

Fractures play a crucial role as fluid conduits and reservoir spaces in reservoirs. The distribution and characteristics of fractures determine the presence of high-quality reservoirs. To accurately analyze and observe fracture parameters, three-dimensional (3-D) digital cores generated from computed tomography (CT) are utilized. However, the current process of extracting fracture properties from these digital cores is time-consuming and labor-intensive. This paper introduces a new, fast, and automatic workflow for extracting the apparent dip angle and direction of fractures from 3-D digital core images. The proposed workflow involves several steps. Firstly, two perpendicular cross-sections are obtained from the digital core and converted into binary images. Next, the coordinates of four fracture feature points within the core image are automatically extracted. The fracture plane is then fitted using the least squares method based on the extracted coordinates. Finally, the apparent dip angle and direction of the fracture are calculated using the plane’s normal vector. By comparing and analyzing the proposed workflow with the original method, it becomes evident that the method proposed in this paper allows for quick, automated, and accurate extraction of the apparent dip angle and direction of fractures. The application of this workflow to extract fracture attitudes in 3-D micro-CT and full-hole digital core images significantly enhances efficiency.

Meso to macro connections to capture fatigue damage in cemented materials

Fatigue-induced damage is a common issue in cemented materials, involving the progressive formation and complicated propagation of fatigue cracks. These cracks typically localise on weak or fracture planes, leading to inhomogeneous deformation within the material. Thus, accurately predicting the fatigue phenomenon becomes challenging due to the material’s inhomogeneity and the complex evolution of cracks, from initiation to propagation and eventual failure. To address this challenge, this paper presents a constitutive model that accounts for strain discontinuity across fracture planes by employing kinematic enrichment. This enhancement facilitates interaction between the material responses of cracks and the outer bulk, thereby contributing to the overall macro behaviour of the materials. Moreover, the proposed model incorporates a new cohesive-frictional fatigue model that couples damage mechanics and bounding surface plasticity to describe the fatigue behaviour of fracture planes/cracks. Since the proposed model features a characteristic length scale, it exhibits size-dependent behaviour and helps overcome the issue of mesh dependence. The model's validity is demonstrated through its ability to capture nonlinear fatigue damage under constant/variable cyclic loading and to simulate the propagation of fatigue fracture process zones. Furthermore, the model effectively captures the significant influence of stress amplitudes on the fatigue lives of materials, making it an essential tool for predicting and mitigating fatigue-induced damage in cemented materials.

Applying deep bed filtration theory to study long-term impairment of fracture conductivity caused by reservoir fines

This paper examines conductivity/permeability impairment of hydraulically-created fractures owing to intrusion of reservoir fine particle. The blockage of fracture network by the reservoir fines will cause productivity loss. Understanding the mechanism upon which the fracture conductivity is reduced owing to intrusion of reservoir fines is essential for operation design and accurate prediction of stimulation performance in reservoirs with unconsolidated sand pockets.In this study, the deep bed filtration network model is used to study transport and distribution of the intruded reservoir particles into a propped fracture plane. The fracture plane was discretized into a series of flow bed elements/units wherein transportation and distribution of particles and capturing coefficient were determined. The bilinear flow model was adopted to explain particulate flow transport into the fracture plane from disrupted sand pockets.An experimental approach was further used to validate the model predictions. A sensitivity analysis was performed to study impacts of proppant size, production/flow rates, fluid viscosity, and the fracture length on the long-term fracture conductivity damage caused by intrusion of reservoir fines. It is anticipated that the approach presented in this paper can immensely contribute to development of a computationally viable method to study productivity impairment due to fines migration and selection of candidate wells for refracturing operation.

Deformation and Fracturing Behaviors of Sandstone Disc Containing a Circular Inclusion under Diametrical Compression: Insights from Integrated SG and DIC Experiments

Weak inclusions play a significant role in regulating the deformation and fracturing behavior of rock masses. In this study, sandstone specimens filled with circular inclusions were subjected to diametrical compression until failure. The local strain concentration intensity and cracking process at the rock-inclusion interface were specifically investigated using the integrated strain gauge (SG) and digital image correlation (DIC) techniques. The experimental results reveal that the presence of inclusions introduces more complex deformation and fracturing behaviors in the infilled sandstone specimens. The stiffness of the infilled sandstones, with either low-strength or high-strength inclusions, initially increases and then decreases as the inclusion diameter increases. The effective load-carrying capacity of the infilled sandstone is influenced by the competing effects of inclusion enhancement and hole weakening. Moreover, a more pronounced strain concentration occurs at the inclusion boundary when the inclusion diameter is larger and the inclusion strength is lower. The crack mode in the infilled red sandstone is independent of the strength of the inclusion. For larger hole diameters, fracture planes form along the compression line, whereas interfacial debonding occurs in red sandstone with smaller hole diameters. Finally, the stress distribution characteristics along the loaded diameter and transverse diameter were analyzed using elastic finite element analyses, which can well explain the cracking mechanism of the infilled disc specimens.

Segregation-enhanced grain boundary embrittlement of recrystallised tungsten evidenced by site-specific microcantilever fracture

Tungsten stands a prime candidate for plasma-facing applications in fusion reactors, attributed to its capacity to withstand high temperatures and intensive particle fluxes. The operational heat flux, however, can induce recrystallisation of the initial microstructure, increasing the brittle-to-ductile transition temperature. Although such a phenomenon is thought to result from impurity segregation to grain boundaries, direct evidence of impurity-induced grain boundary embrittlement has not yet been reported. Addressing this, our study employs microcantilever testing, coupled with local chemical analysis via atom probe tomography, to unveil the impact of impurity segregation on the fracture toughness of recrystallised tungsten with a purity of 99.98 at.%. The in situ fracture toughness measurements were performed with the notch placed directly at random high-angle grain boundaries, revealing brittle failure regardless of grain boundary misorientation or grain orientation. Notably, both single-crystalline microcantilevers and the as-received material exhibited significant plasticity before failure, with instances without crack propagation. In contrast, recrystallised grain boundaries displayed a fracture toughness of 4.7 ± 0.4 MPa·√m, determined using a linear elastic approach - notably lower than for cleavage plane fracture in tungsten microcantilevers. Local atom probe analysis of the high-angle grain boundaries exposed phosphorous segregation exceeding 2 at.% at the recrystallised interfaces, stemming from recrystallisation. Atomistic simulations confirmed the role of phosphorous in embrittling high-angle grain boundaries in tungsten, while additionally revealing mechanisms of crack-grain boundary interactions and their dependence on phosphorous segregation.

Modelling intralaminar damage mechanisms in fibre reinforced polymers at finite strains

An approach to predict intralaminar failure mechanisms in laminate fibre-reinforced composites, at finite strains, is proposed. Transverse matrix cracking is described by a smeared crack model, activated by an invariant-based failure criterion, where an embedded cohesive crack is considered in the continuum description. A deformation gradient decomposition based on homogenisation considerations is developed for a more objective finite strain kinematic description of transverse cracks. The local equilibrium problem is established in the reference configuration to naturally include re-orientation of the fracture plane, and the employed cohesive law is able to deal with non-monotonic loading. Moreover, a continuum damage model formulated in terms of the Green–Lagrange strain tensor is used for longitudinal failure. The simulation of an open-hole multi-directional specimen subjected to tension illustrates the ability of the proposed constitutive equations to capture experimental observations.

Anatomy of an obducted ultramafic unit (Tiébaghi Massif – Peridotite Nappe – New Caledonia): Polyphase brittle tectonics constrained by fault-slip data and crack seal mineralogy

ABSTRACT New data collected in the mining areas of the Tiébaghi Massif, a klippe of the Peridotite Nappe located in the north of New Caledonia, are presented. Data were collected in open cast nickel mine pits and chromite underground works, notably along a 1.2-km long tunnel which penetrates the deep geological structure of the massif. Surface and sub-surface geology, microtectonic observations and kinematic analysis of fracture planes, Electrical Resistivity Tomography, micron-scale Raman spectroscopy and Transmission Electron Microscopy were used to characterise the different tectonic regimes and associated mineralisations. Three stages of deformation and their kinematic axes are identified. Fractures coated with antigorite-tremolite minerals are associated to supra-subduction melt intrusions in a compressional regime characterised mainly by thrust and transcurrent faults. They are followed by fractures coated with polygonal serpentine formed in an extensional regime. The two former mineral phases are commonly superimposed on the same plane. Third-stage consist of fractures associated with supergene minerals deposited in an extensional regime, associated with gravity driven normal faulting. Fractures associated with this supergene stage have reactivated the former hypogene network.

Geophysical characteristics of a fault system in the northern Central Range of Taiwan and its applications for geothermal energy exploration

The northern Central Range of Taiwan is a high-potential geothermal region. Since the formations are mainly tight metasandstone and slate, permeable structures associated with faults are commonly considered as conduits of geothermal fluids. This study determines the characteristics and orientations of the permeable fault zones by analyzing the geophysical logs and microresistivity formation image log (FMI) of the JT-4 well in Jentse, an important geothermal area in the northern Central Range. Between 720 and 1480 m measured depth (MD), the effective porosity of the intact host rock is mostly below 3% calculated by the geophysical log. Zones with porosity greater than 5% are only clustered within a few thin intervals. The FMI interpretations show these porous zones are in the interior of the fractured and faulted intervals. These porous fault zones comprise fault damage zones with a high density of open fracture planes and fault cores with porous fault breccias. There is a highly brecciated fault core in 1334–1339 m MD, which would be the most permeable interval of the well. Additionally, some healed fault zones with sealed fractures are observed. The picked drilling-induced tensile fractures signify that the direction of the present-day maximum horizontal principal stress is N40–50°E, and most of the open fractures also strike parallel to the NE–SW direction. The study results show that the open fractures are concentrated in the four fault zones belonging to one major normal fault system. After integrating the orientations and locations of the fault zones, we propose that the permeable normal fault system is about 200 m wide, trends N50–70°E, and dips 70–80° to the NW. The development of the open fractures and the permeable fault system in the northern Central Range may be controlled by the current rifting of the Okinawa Trough offshore northeastern Taiwan. The study exhibits the characteristics of fractured fluid conduits of the regional geothermal system, which will benefit future geothermal exploration in northeastern Taiwan.

Efficient fracture network characterization in enhanced geothermal reservoirs by the integration of microseismic and borehole logs data

Characterization of 3D fracture networks induced by hydraulic fracturing in enhanced geothermal reservoirs is crucial for safe and effective energy recovery from deep geothermal reservoirs. Microseismic monitoring is one of the most promising ways to infer the geometry of fracture network. However, the identification of fracture network from microseismic events is still a challenging task, attributed to high noises in microseismicity interpretation and fuzzy relationships between microseismic event locations and fracture planes. This study proposed a novel methodology to identify fracture network from the spatial distribution of microseismic events. The method was composed by (1) density-based spatial clustering algorithm for microseismic data denoising, (2) Monte Carlo optimization algorithm for fractures localization by minimizing the total distance between denoised microseismic events and fracture planes, and (3) Elbow method to decide the most likely number of fractures. Moreover, the method employed the prior knowledge of geo-stresses and initial fracture patterns inferred from borehole logs to constrain the geometry of fracture network. Following verifications with synthetic fractures and microseismic events, the method was implemented in a realistic enhanced geothermal system, which reliably identified the geometry of 3D fracture network induced by hydraulic fracturing.

An inversion for asymmetric hydraulic fracture growth and fracture opening distribution from tilt measurements

The eigenstrain tensor is defined in terms of the unit vector normal to the fracture plane and the dislocation vector to characterize the fracture geometry and to determine the fracture induced deformation field. Compared to the conventional nonlinear fracture model, the forward fracture model provides a linear relationship between fracture geometry parameters (eigenstrain) and the induced deformation. Therefore, a linear inverse problem needs to be tackled in mapping the fracture geometry by inversion of tilt observations. The fracture orientation and opening distribution of a tensile-dominated hydraulic fracture can be mapped iteratively in a coupled way by using the forward model defined in terms of the dislocation vector. The proposed analysis method is applied to field tilt data collected for monitoring the growth of a hydraulic fracture placed in the preconditioning of a roof rock over a coal longwall panel at a test site. Inversion of the tilt data produces a low fracture dip angle of 6.8°, which agrees with a nearly horizontal fracture orientation confirmed by intersection data collected in offset monitoring boreholes. Tikhonov regularization technique is applied to stabilize the discrete ill-posed inverse problem. The regularized solution provides information on the fracture opening distribution and asymmetric fracture growth. The inversion shows that the fracture grows uniformly and roughly in a radial pattern at early injection times, but grows asymmetrically, preferentially, and consistently to the northwest during later times. The predicted fracture growth agrees with the temperature logging to measure fracture intersections with the offset monitoring boreholes.

Diffusion characteristics of shale mixed gases on the wall of microscale fractures

Shale reservoirs are rich in organic and inorganic matter, causing a large amount of gas to exist on the surface of microscale cracks in an adsorbed state. Revealing the surface diffusion characteristics of adsorbed gas is of great significance for the microscale numerical simulation of shale gas reservoir. In this paper, the unconventional gas reservoir is taken as the research object, and the characteristics of gas surface diffusion on surface wall of microscale fractures is systematically studied. There are two innovations in this paper: (a) the characteristics of gas surface diffusion inside the planar microscale fractures are analyzed; (b) The influence of mixed gas effect on gas surface diffusion is considered. Research results show that: (a) when the fracture opening is 2 nm or 5 nm, the influence of the opening of microscale fractures on the thickness of adsorption layer can be ignored. (b) The interaction between components refers to the frictional force generated by the relative motion of molecules. (c). The magnitude of frictional force is related to the Maxwell Stefan diffusion term and is proportional to the velocity difference. Due to the interaction between components, fast-moving molecules will accelerate the movement of slow-moving molecules.

Lattice discrete particle modeling of the cycling behavior of strain-hardening cementitious composites with and without fiber reinforced polymer grid reinforcement

Strain-hardening cementitious composites (SHCC) has become increasingly prevalent in structural design. Compared to ordinary concrete, SHCC exhibits ultra-high tensile ductility, significant strain-hardening behavior, very fine multi-point cracking, high energy dissipation, and good durability. One robust model for simulating reinforced concrete behavior is the so-called Lattice Discrete Particle Model (LDPM), and specifically LDPM-F which includes the effect of fiber reinforcement. The present cycling constitutive law implemented in LDPM and the cycling fiber-bridging law in LDPM-F though cannot accurately capture the residual tensile plastic strain, loading–unloading path, and energy dissipation of SHCC during cyclic tension. To solve these concerns, the cycling tension–compression constitutive law and the nonlinear cycling fiber-bridging law were reformulated. Further, the new model was used to simulate the cycling tensile behavior of plain concrete, SHCC, and Fiber-Reinforced Polymer (FRP) grid reinforced SHCC (FRP-SHCC). Simulation results show that the multi-point cracking, crack widths, and ultra-high ductility properties are correctly captured by LDPM-F. In addition, LDPM-F with the modified cycling constitutive model can effectively simulate the cycling tension–compression behavior, accurately reproducing the stress–strain relationship, residual plastic strain, and overall dissipated energy. Finally, the simulated failure modes agree well with the actual fracture planes of these materials under cyclic tension.

Physical and numerical models of pressure during waterproofing injections with polymer into concrete fractures

ABSTRACT Polymer injections in concrete fractures are commonly used for the waterproofing of tunnels. The pressure during the injection needs to be high enough to ensure polymer penetrability. This paper introduces two physical models for the study of the pressure inside concrete fractures during polymer injections. The injection parameters that were varied include pressure, injection duration, injection volume, location of the injection and pressure reading ports, and fluid dynamic viscosity. Water and water-glycerol mixtures were used to verify the influence of viscosity on flow. Tests were performed with both open and sealed fractures. The pressure inside the fracture during the injection was influenced by the dynamic viscosity, boundary conditions and the saturation level of the fracture. Sealed and initially moist fractures led to a higher pressure gain inside the fracture after achieving saturation. More than 40% of the injection pressure was already lost when the liquid entered the model. A numerical model of liquid flow in the fracture plane was developed with the finite element code COMSOL Multiphysics. It was able to replicate the influence of boundary conditions and initial fracture saturation on pressure. The model also shows how aperture and roughness influence the flow conditions in the fracture.

Fabrication of graphene oxide-modified self-healing microcapsules for Cardanol-based epoxy anti-corrosion coatings

In this paper, graphene oxide (GO) modified microcapsules have been developed for use in self-healing Cardanol-based epoxy anti-corrosion coatings on steel substrates. The microcapsules had a polymethyl methacrylate (PMMA) shell, covered with aminated GO flakes and contained either of the two complementary healing agents mixed with nanosized GO flakes. One set of capsules contained epoxidized nanosized GO and Cardanol-based epoxy resin, while the other contained aminated nanosized GO and Cardanol-based amine curing agent. The microcapsules had a narrow size distribution with a peak value of 4 μm. The Cardanol-based coatings containing various fractions of up to 20 wt% microcapsules in their stoichiometric ratio showed excellent anti-corrosion and self-healing properties. FT-IR, XPS, AFM, and Raman spectroscopy were used to characterize the size and chemical composition of the GO. Optical microscopy and SEM were used for morphological characterization. Double cantilever test upon bulk samples showed an excellent load transfer across the fracture plane after only 1 day curing at room temperature. The anti-corrosion properties of the Cardanol-based coating containing the two-component microcapsules were tested using electrochemical impedance spectroscopy (EIS). It was found that, after 60-day immersion in 3.5 wt% NaCl solution, the low-frequency impedance modulus |Z|0.01Hz of the Cardanol-based coating containing GO-modified microcapsules was three orders of magnitude higher than that of the systems with capsules without GO. After scratching the coating containing 20 wt% GO-modified microcapsules and exposing it to an aqueous 3.5 wt% NaCl solution, the |Z|0.01Hz of the Cardanol-based coating returned over a period of 7 days to the original value.

Structural Classification, Discharge Statistics, and Recession Analysis from the Springs of the Gran Sasso (Italy) Carbonate Aquifer; Comparison with Selected Analogues Worldwide

The relative importance of karst conduits and fractures in driving groundwater flow affects the discharge of springs and the long-term availability of water resources. Applying statistics to the hydrographs of the discharge and studying the recessions provide information on the degree of reliability and variability of the springs and, therefore, the flow regime within the saturated part of the carbonate aquifers. This approach was applied to six springs at the Gran Sasso aquifer in Central Italy. These springs were divided into three structural geological groups that determined the position of the permeability thresholds. The type of tectonic structures and the pattern of the permeability thresholds allow a correlation with the computed statistics. The studied springs were associated with the presence of thrusts, overturned drag folds, and a normal fault. The computed statistics describe a general scenario of reliability and steadiness for the springs. The Flow Duration Curves for the springs show limited groundwater flow through the conduits through a comparison with analogues in Slovakia. Joints and bedding plane fractures dominate the groundwater flow, fitting both the relative steadiness of the discharges and the pattern of the Flow Duration Curves. The recessions are also characterized by more gentle slopes with respect to nearby areas fitting a conceptual model of dominant fracture flow. This mathematical scenario depicts groundwater resources, which have limited exposure to episodes of summer droughts. The proposed approach is a holistic combination of structural geology and hydrologic elements and can be successfully exported to other tectonized carbonate areas for the sustainable management of groundwater resources worldwide.

Quantification of damage evolution in cross-ply polymer composites under longitudinal compression by fast computed tomography and semi-automated segmentation

Compressive failure in a notched cross-ply IM7/8552 carbon fiber reinforced polymer (CFRP) laminate is studied experimentally by time-lapse in-situ synchrotron radiation computed tomography (CT). The focus is on tracking and quantifying the fiber damage evolution in the 0° plies under compression for the first time via a specimen design that exhibits quasi-stable damage accumulation. A novel segmentation algorithm has been developed and applied to extract morphological features of interest including the kink band width, inclination angle, and the extent of propagation from the notch. In the four innermost 0∘ plies, shear-driven fiber fracture initiates from the notch tip and propagates as a single fracture plane inclined about 45° to the compression axis. This shear-driven fiber fracture transitions to a kink band at a distance of about 300μm from the notch, which propagates at a shallower angle. During the later stages of the test, the kink bands propagate in the reverse direction to areas that previously initiated by shear-driven fiber fracture, which may explain why post-mortem observations seldom reveal the fiber shear fracture mechanism. The fiber damage initiation and evolution appears distinctly different from the classical parallel plane kink bands formed by plastic microbuckling under uniaxial compression in that the dominant mechanism appears to be shear-driven fiber fracture.

Fluid flow and mass transport in fractured media with curved fractures and varying apertures: A 3D modeling approach

AbstractFractured media have been extensively studied due to their significant impact on hydraulic properties of subsurface systems. However, accurately modeling and simulating flow and transport in complex 3D fractured media still remains a challenge. For this purpose, this work aims to develop a new 3D modeling approach and investigate flow and mass transport in fractured media. First, a modeling approach is presented for generating 3D complex structures and high quality finite element grids. This approach allows for the presence of a range of complex geometries, including curved fracture, multiple fractures and the coexistence of fracture‐inclusions. The resulting models and grids are of high quality, enabling accurate simulation and analysis of complex systems. Furthermore, stress‐dependent aperture and roughness are integrated in the computational scheme using Barton–Bandis law. The Galerkin finite element method is used for numerical discretization, then pressure and concentration are calculated in a unified formulation. Later, numerical tests are performed to analyze the role of 3D fractures in flow and mass transport. Simulation results show that fractures have a larger impact on pressure distribution and flow rate compared to inclusions. Fracture roughness increases the aperture then the effective conductivity is improved as well. Curved fractures may reduce flow rate more than planar fractures due to the tortuosity effect. The variation of equivalent permeability tensor is analyzed with varying orientation, roughness, and number of fractures. The impact of stress and fracture roughness causes a variation of fracture permeability and a high pressure gradient on the fracture‐matrix interface, resulting in different patterns of concentration evolution. Overall, this investigation provides insights into the role of 3D fractures in subsurface flow and transport, with implications for various applications.