In-situ measurement of texture development rate in CaIrO3 post-perovskite
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Hunt, Simon A.↗
SEARCH · Engineering Papers
Results for “SLIP”
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Modeling of fault reactivation and induced seismicity during hydraulic fracturing of shale-gas reservoirs
We have conducted numerical simulation studies to assess the potential for injection-induced fault reactivation and notable seismic events associated with shale-gas hydraulic fracturing operations. The modeling is generally tuned towards conditions usually encountered in the Marcellus shale play in the Northeastern US at an approximate depth of 1500 m (~;;4,500 feet). Our modeling simulations indicate that when faults are present, micro-seismic events are possible, the magnitude of which is somewhat larger than the one associated with micro-seismic events originating from regular hydraulic fracturing because of the larger surface area that is available for rupture. The results of our simulations indicated fault rupture lengths of about 10 to 20 m, which, in rare cases can extend to over 100 m, depending on the fault permeability, the in situ stress field, and the fault strength properties. In addition to a single event rupture length of 10 to 20 m, repeated events and aseismic slip amounted to a total rupture length of 50 m, along with a shear offset displacement of less than 0.01 m. This indicates that the possibility of hydraulically induced fractures at great depth (thousands of meters) causing activation of faults and creation of a new flow path that can reach shallow groundwater resources (or even the surface) is remote. The expected low permeability of faults in producible shale is clearly a limiting factor for the possible rupture length and seismic magnitude. In fact, for a fault that is initially nearly-impermeable, the only possibility of larger fault slip event would be opening by hydraulic fracturing; this would allow pressure to penetrate the matrix along the fault and to reduce the frictional strength over a sufficiently large fault surface patch. However, our simulation results show that if the fault is initially impermeable, hydraulic fracturing along the fault results in numerous small micro-seismic events along with the propagation, effectively preventing larger events from occurring. Nevertheless, care should be taken with continuous monitoring of induced seismicity during the entire injection process to detect any runaway fracturing along faults.
03 NATURAL GAS↗
Orientation influence on grain size-effects in ultrafine-grained magnesium
The mechanical behavior of ultrafine-grained magnesium was studied by discrete dislocation dynamics (DDD) simulations. Our results show basal slip yields a strong size effect, while prismatic and pyramidal slips produce a weak one. We developed a new size-strength model that considers dislocation transmission across grain boundaries. Good agreement between this model, current DDD simulations and previous experiments is observed. These results reveal that the grain size effect depends on 3 factors: Peierls stress, dislocation source strength and grain boundary strength.
36 MATERIALS SCIENCE↗
In-situ neutron diffraction study on the tension-compression fatigue behavior of a twinning induced plasticity steel
Grain orientation dependent behavior during tension-compression type of fatigue loading in a TWIP steel was studied using in-situ neutron diffraction. Orientation zones with dominant behavior of (1) twinning-de-twinning, (2) twinning-re-twinning followed by twinning-de-twinning, (3) twinning followed by dislocation slip and (4) dislocation slip were identified. Jumps of the orientation density were evidenced in neutron diffraction peaks which explains the macroscopic asymmetric behavior. The asymmetric behavior in early stage of fatigue loading is mainly due to small volume fraction of twins in comparison with that at later stage. As a result, easy activation of the de-twin makes the macroscopically unloading behavior nonlinear.
36 MATERIALS SCIENCE↗
In-situ TEM observation of shear induced microstructure evolution in Cu-Nb alloy
Phase boundaries in multiphase alloys govern defect interaction and chemical intermixing across different phases during plastic deformation. Dynamic interaction of defects with phase boundaries in multiphase alloys, especially for immiscible alloys, has been topic of significant research interest in recent years. In this work, we describe a novel approach for carrying out in-situ TEM shear deformation to directly observe interfacial microstructural evolution of a Cu-Nb alloy. A unique double shear specimen geometry is microfabricated by a focused ion beam technique to apply shear deformation upon push loading inside the TEM. From the real-time observation, we discover that the phase boundary with a zigzag morphology effectively blocks stacking faults nucleated in a Cu grain from slipping into a Nb grain. Meanwhile, the Cu phase bears the most plastic deformation through slip or twinning mechanisms. This work sheds light on understanding the shear deformation and the behavior of phase boundaries in multiphase alloys during shear deformation.
36 MATERIALS SCIENCE↗
Identifying geological structures through microseismic cluster and burst analyses complementing active seismic interpretation
At the Decatur carbon capture and storage site (IL, USA) CO 2 has been injected from 2011–2014 and from 2017 to present near the base of the Lower Mt. Simon Sandstone saline reservoir, resulting in microseismicity. Microseismicity is mainly located in the basement and distributed in distinct spatial clusters. The lack of significant impedance contrasts within the basement makes the interpretation of active-source seismic reflection data challenging, however, recent reprocessing allowed to resolve faults above and at the top of the basement. These faults generally do not coincide with the location of microseismic events and their continuation to the general depth of the seismic events cannot be assumed. This paper shows how the interpretation of the microseismicity can complement structural interpretations of active-source seismic reflection data. In particular, we analyze clusters and bursts (abrupt increases) of microseismicity, identify unresolved, smaller-scale weaknesses and extract statistical parameters. These parameters allow comparisons with the interpreted faults, and with fracture sets intercepted by boreholes. During injection at the Decatur site, the injection pressure was kept far below fracture pressure, nevertheless, seismic events were induced and spread far beyond the expected extent of the CO 2 plume. We argue that local stress transfers related to the CO 2 injection reactivated pre-existing fractures within the critically stressed basement. Finally, we conducted a slip tendency analysis for faults interpreted from active seismic, selected cluster, bursts and nodal planes from focal mechanisms to determine if the interpreted structures are optimally oriented with respect to the stress regime. Our results suggest that the orientation of fractures close to the injection well, generally shows slight deviations from the optimal orientation for slip. This might indicate either slight local deviations of the maximum horizontal stress azimuth from the average direction used in the analysis, or the lack of optimally oriented fractures at this location.
58 GEOSCIENCES↗
CFD simulation of MSW combustion and SNCR in a commercial incinerator
Highlights: • Presented a CFD scheme for modeling MSW incinerator including SNCR process. • Performed a sensitivity analysis of SNCR operating conditions. • Non-uniform distributions of gas velocity, temperature and NO{sub x} in the incinerator. • The injection position of reagent was critical for a desirable performance of SNCR. • A NSR 1.5 was recommended as a compromise of NO{sub x} reduction rates and NH{sub 3} slip. - Abstract: A CFD scheme was presented for modeling municipal solid waste (MSW) combustion in a moving-grate incinerator, including the in-bed burning of solid wastes, the out-of-bed burnout of gaseous volatiles, and the selective non-catalytic reduction (SNCR) process between urea (CO(NH{sub 2}){sub 2}) and NO{sub x}. The in-bed calculations provided 2-D profiles of the gas–solid temperatures and the gas species concentrations along the bed length, which were then used as inlet conditions for the out-of-bed computations. The over-bed simulations provided the profiles of incident radiation heat flux on the top of bed. A 3-dimensional benchmark simulation was conducted with a 750 t/day commercial incinerator using the present coupling scheme incorporating with a reduced SNCR reduction mechanism. Numerical tests were performed to investigate the effects of operating parameters such as injection position, injection speed and the normalized stoichiometric ratio (NSR) on the SNCR performance. The simulation results showed that the distributions of gas velocity, temperature and NO{sub x} concentration were highly non-uniform, which made the injection position one of the most sensitive operating parameters influencing the SNCR performance of moving grate incinerators. The simulation results also showed that multi-layer injections were needed to meet the EU2000 standard, and a NSR 1.5 was suggested as a compromise of a satisfactory NO{sub x} reduction and reasonable NH{sub 3} slip rates. This work provided useful guides to the design and operation of SNCR process in moving-grate incinerators.
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
Heat transport and temperature boundary-layer profiles in closed turbulent Rayleigh–Bénard convection with slippery conducting surfaces
Here, we report direct numerical simulations (DNS) of the Nusselt number Nu , the vertical profiles of mean temperature Θ(z) and temperature variance Ω(z) across the thermal boundary layer (BL) in closed turbulent Rayleigh–Bénard convection (RBC) with slippery conducting surfaces ( z is the vertical distance from the bottom surface). The DNS study was conducted in three RBC samples: a three-dimensional cuboid with length L=H and width W=H/4 ( H is the sample height), and two-dimensional rectangles with aspect ratios Γ≡L/H=1 and 10. The slip length b for top and bottom plates varied from 0 to ∞ . The Rayleigh numbers Ra were in the range 10 6 $⩽$Ra$⩽$10 10 and the Prandtl number Pr was fixed at 4.3 . As b increases, the normalised Nu/Nu 0 ( Nu 0 is the global heat transport for b =0 ) from the three samples for different Ra and Γ can be well described by the same function Nu/Nu 0 = N 0 tanh( b /λ 0 )+1 , with N 0 =0.8±0.03 . Here λ 0 ≡ L /(2 Nu 0 ) is the thermal boundary layer thickness for b =0 . Considering the BL fluctuations for Pr >1, one can derive solutions of temperature profiles Θ(z) and Ω(z) near the thermal BL for b $⩾$ 0 . When b =0 , the solutions are equivalent to those reported by Shishkina et al. ( Phys. Rev. Lett. , vol. 114, 2015, 114302) and Wang et al. ( Phys. Rev. Fluids , vol. 1, 2016, 082301(R)), respectively, for no-slip plates. For b >0, the derived solutions are in excellent agreement with our DNS data for slippery plates.
42 ENGINEERING↗
Resistive evolution of toroidal field distributions and their relation to magnetic clouds
We study the resistive evolution of a localized self-organizing magnetohydrodynamic equilibrium. In this configuration the magnetic forces are balanced by a pressure force caused by a toroidal depression in the pressure. Equilibrium is attained when this low-pressure region prevents further expansion into the higher-pressure external plasma. We find that, for the parameters investigated, the resistive evolution of the structures follows a universal pattern when rescaled to resistive time. The finite resistivity causes both a decrease in the magnetic field strength and a finite slip of the plasma fluid against the static equilibrium. This slip is caused by a Pfirsch–Schlüter-type diffusion, similar to what is seen in tokamak equilibria. The net effect is that the configuration remains in magnetostatic equilibrium whilst it slowly grows in size. The rotational transform of the structure becomes nearly constant throughout the entire structure, and decreases according to a power law. In simulations this equilibrium is observed when highly tangled field lines relax in a high-pressure (relative to the magnetic field strength) environment, a situation that occurs when the twisted field of a coronal loop is ejected into the interplanetary solar wind. In this study we relate this localized magnetohydrodynamic equilibrium to magnetic clouds in the solar wind.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Fractal Model for Drag Reduction on Multiscale Nonwetting Rough Surfaces
Rough surfaces in contact with a flow of fluid exhibit alternating no-slip and free shear boundary conditions at the solid–liquid and air–liquid interfaces, respectively, thereby potentially offering drag reduction benefits. The balance between the dynamic pressure in the flow and the restoring capillary pressure in the interasperity spaces determines the stability of the Cassie state of wettability and is a function of the relative extent of no-slip and free shear regions per unit surface area. In the present study, using a fractal representation of rough surface topography, an analytical model is developed to quantify the stability of the Cassie state of wettability as well as drag reduction and the friction factor for laminar flow in a rectangular channel between nonwetting multiscale rough surfaces. A systematic study is conducted to quantify the effects of fractal parameters of the surfaces and the flow Reynolds number on drag reduction and the friction factor. The studies are used to develop friction factor curves extending the classical Moody diagram to hydrophobic and superhydrophobic surfaces. On the basis of the studies, regime maps are derived for estimating the extent of drag reduction offered by hydrophobic and superhydrophobic surfaces, revealing that superhydrophobic surfaces do not always offer the best drag reduction performance. The application of the fractal model to practical topographies of nonwetting surfaces of copper, aluminum, and zinc oxide fabricated via electrodeposition and etching is also discussed.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Degradation by Kinking in Layered Cathode Materials
Layered cathode materials are commonly used in lithium and sodium ion batteries, but they are prone to degradation under electrochemical cycling during battery operation. Here we report a new type of degradation mechanism through the electrochemically induced mechanical buckling and delamination cracking of intercalation layers in a P2 Na 0.7 -Ni 0.3 Mn 0.6 Co 0.1 O 2 (Na-NMC) cathode material. Kinks form in the delaminated layers due to severe local bending, and each kink consists of a vertical array of dislocations, resulting from an easy slip between transition metal oxide layers. In situ mechanical compression experiments directly reveal the kink formation due to strong mechanical anisotropy parallel and perpendicular to the intercalation layers in single-crystal Na-NMC. In situ electrochemical experiments indicate that kinks form during the desodiation process. Our results unveil a new mechanism of electrochemically induced mechanical degradation stemming from weak interlayer bonding in layered cathode materials. In conclusion, this work has broad implications for the mitigation of degradation associated with irreversible interlayer slip in layered cathode materials.
25 ENERGY STORAGE↗
Substituent and Heteroatom Effects on π–π Interactions: Evidence That Parallel-Displaced π-Stacking is Not Driven by Quadrupolar Electrostatics
Stacking interactions are a recurring motif in supramolecular chemistry and biochemistry, where a persistent theme is a preference for parallel-displaced aromatic rings rather than face-to-face π-stacking. This is usually explained in terms of quadrupole–quadrupole interactions between the arene moieties but that interpretation is inconsistent with accurate calculations, which reveal that the quadrupolar picture is qualitatively wrong. At typical π-stacking distances, quadrupolar electrostatics may differ in sign from an exact calculation based on charge densities of the interacting arenes. We apply symmetry-adapted perturbation theory to dimers composed of substituted benzene and various aromatic heterocycles, which display a wide range of electrostatic interactions, and we investigate the interplay of Pauli repulsion, dispersion, and electrostatics as it pertains to parallel-displaced π-stacking. Profiles of energy components along cofacial slip-stacking coordinates support a prominent role for the “van der Waals model” (dispersion in competition with Pauli repulsion), even for polar monomers where electrostatic interactions are significant. While electrostatic interactions are necessary to explain the optimal face-to-face π-stacking distance and to account for the relative orientation of one polar arene with respect to another, we find no evidence to support continued invocation of quadrupolar electrostatics as a basis for π-stacking. Our results suggest that a driving force for offset-stacking exists even in the absence of electrostatic interactions. Consequently, tuning electrostatics via functionalization does not guarantee that slip-stacking can be avoided. This has implications for rational design of soft materials and other supramolecular architectures.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Ensemble Shear Strength, Stability, and Permeability of Mixed Mineralogy Fault Gouge Recovered From 3D Granular Models
We conduct numerical shear experiments on mixtures of quartz and talc gouge using a three-dimensional (3D) distinct element model. A modified slip-weakening constitutive law is applied at contacts. We perform velocity-stepping experiments on both uniform and layered mixtures of quartz and talc analogs. We separately vary the proportion of talc in the uniform mixtures and talc layer thickness in the layered mixtures. Shear displacements are cycled through velocities of 1 and 10 μm/s. We follow the resulting evolution of ensemble shear strength, slip stability, and permeability of the gouge mixture and explore the mesoscopic mechanisms. Simulation results show that talc has a strong weakening effect on shear strength—a thin shear-parallel layer of talc (three particles wide) can induce significant weakening. However, the model offsets laboratory-derived strong weakening effects of talc observed in uniform mixtures, implying the governing mechanisms may be the shear localization effect of talc, which is enhanced by its natural platy shape or preimposed layered structure. Ensemble stability (a – b ) can be enhanced by increasing talc content in uniform talc-quartz mixtures. Reactivation-induced permeability increase is amplified with increased quartz content before the maturation of shear localization. Postmaturation permeability enhances on velocity upsteps and diminishes on velocity downsteps. Talc enhances compaction at velocity downsteps, potentially reducing fault permeability. Evolution trends of stability relating to the composition and structure of the fault gouge are straightforwardly obtained from the 3D simulation. Local friction evolution indicates that talc preferentially organizes and localizes in the shear zone, dominating the shear strength and frictional stability of faults
58 GEOSCIENCES↗
The Effects of Earthquakes and Fluids on the Metamorphism of the Lower Continental Crust
Rock rheology and density have first-order effects on the lithosphere's response to plate tectonic forces at plate boundaries. Changes in these rock properties are controlled by metamorphic transformation processes that are critically dependent on the presence of fluids. At the onset of a continental collision, the lower crust is in most cases dry and strong. However, if exposed to internally produced or externally supplied fluids, the thickened crust will react and be converted into a mechanically weaker lithology by fluid-driven metamorphic reactions. Fluid introduction is often associated with deep crustal earthquakes. Microstructural evidence, suggest that in strong highly stressed rocks, seismic slip may be initiated by brittle deformation and that wall-rock damage caused by dynamic ruptures plays a very important role in allowing fluids to enter into contact with dry and highly reactive lower crustal rocks. The resulting metamorphism produces weaker rocks which subsequently deform by viscous creep. Volumes of weak rocks contained in a highly stressed environment of strong rocks may experience significant excursions toward higher pressure without any associated burial. Slow and highly localized creep processes in a velocity strengthening regime may produce mylonitic shear zones along faults initially characterized by earthquake-generated frictional melting and wall rock damage. However, stress pulses from earthquakes in the shallower brittle regime may kick start new episodes of seismic slip at velocity weakening conditions. These processes indicate that the evolution of the lower crust during continental collisions is controlled by the transient interplay between brittle deformation, fluid-rock interactions, and creep flow.
58 GEOSCIENCES↗
Basement Fault Reactivation by Fluid Injection Into Sedimentary Reservoirs: Poroelastic Effects
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.
Fan, Zhiqiang↗
Fault Stability Perturbation by Thermal Pressurization and Stress Transfer Around a Deep Geological Repository in a Clay Formation
The increase of temperature of a low-permeability, fluid-saturated media may trigger significant thermal pressurization, where the expansion of pore fluid cannot be accommodated by the thermal expansion of the pore space. With the aid of a coupled thermohydromechanical numerical simulator, we investigate the possible impact of thermal pressurization during the life of a deep geological repository (DGR) for high-level radioactive waste, characterized by the emplacement of radioactive material-filled canisters in a series of parallel tunnels, excavated in a low-permeability clay formation. We represent the fault as a planar structure embedded in a thermoporoelastic material and shear activation evaluated by a strain-softening Mohr-Coulomb failure criterion. The results show that stress changes caused by temperature and thermal pressurization of a rock mass around the emplacement tunnels may trigger a slip event on a fault plane in proximity of the geological disposal site: Rupture nucleates at depth, hundreds of meters below the DGR. Stress transfer plays a key role, while a direct hydraulic connection between the repository and the nucleation zone is not necessary in order to trigger rupture. A low stress ratio may favor the occurrence of slip up to a distance of 600 m of the fault from the outermost tunnel. Furthermore, these results highlight the need of investigating hydromechanical properties and local stress conditions at depth to characterize the geomechanical response of weak planes located in the surroundings of a high-level radioactive waste repository and to provide sufficient knowledge for the safe development of the DGR site.
58 GEOSCIENCES↗
Acoustic Energy Release During the Laboratory Seismic Cycle: Insights on Laboratory Earthquake Precursors and Prediction
Abstract Machine learning can predict the timing and magnitude of laboratory earthquakes using statistics of acoustic emissions. The evolution of acoustic energy is critical for lab earthquake prediction; however, the connections between acoustic energy and fault zone processes leading to failure are poorly understood. Here, we document in detail the temporal evolution of acoustic energy during the laboratory seismic cycle. We report on friction experiments for a range of shearing velocities, normal stresses, and granular particle sizes. Acoustic emission data are recorded continuously throughout shear using broadband piezo‐ceramic sensors. The coseismic acoustic energy release scales directly with stress drop and is consistent with concepts of frictional contact mechanics and time‐dependent fault healing. Experiments conducted with larger grains (10.5 μm) show that the temporal evolution of acoustic energy scales directly with fault slip rate. In particular, the acoustic energy is low when the fault is locked and increases to a maximum during coseismic failure. Data from traditional slide‐hold‐slide friction tests confirm that acoustic energy release is closely linked to fault slip rate. Furthermore, variations in the true contact area of fault zone particles play a key role in the generation of acoustic energy. Our data show that acoustic radiation is related primarily to breaking/sliding of frictional contact junctions, which suggests that machine learning‐based laboratory earthquake prediction derives from frictional weakening processes that begin very early in the seismic cycle and well before macroscopic failure.
58 GEOSCIENCES↗
Variations of Stress Parameters in the Southern California Plate Boundary Around the South Central Transverse Ranges
We examine the stress field in Southern California with a focus on the region near the South Central Transverse Ranges (SCTR), using a refined stress inversion methodology. We independently invert declustered and aftershocks focal mechanisms from the years 1981 to 2017. Comparisons between the stress field orientations and the stress ratios from these inversions provide information on local sources of the stress field. Regionally, the SHmax tends to be toward NNE and the stress ratios vary from transtensional stress regime near the Eastern California Shear Zone (ECSZ), to strike-slip faulting near the SCTR, and toward transpression near the Western Transverse Ranges. Detailed analysis of stress parameters near the SCTR indicates deviations from the regional strike-slip faulting including the following: (1) The San Bernardino Mountain area shows S Hmax direction toward NNW and transpressional stress components likely associated with the motions of the San Andreas Fault and ECSZ; (2) the Cajon Pass and San Gorgonio Pass show transpressional stress regime near the bottom of the seismogenic zone likely associated with the elevated topography; and (3) in Crafton Hills, rotation of the principal stress plunges and SHmax direction and transtensional stress regime below ~10 km, along with lower estimated apparent friction coefficient, suggest a weak fault possibly associated with deep creep. The performed multiscale analysis resolves effects of regional and local loadings. The average stress parameters in the analyzed 37 years do not show significant temporal variations of stress field near the SCTR region.
58 GEOSCIENCES↗