Stress Field Research Articles

An enhanced numerical model for considering coupled strain-softening and seepage effects on rock masses surrounding a submarine tunnel

The seepage of groundwater and the strain-softening of rock mass in a submarine tunnel expand the plastic region of rock, thereby affecting its overall stability. It is therefore essential to study the stress and strain fields in the rocks surrounding the submarine tunnel by considering the coupled effect of strain-softening and seepage. However, the evolution equation for the hydro-mechanical parameters in the existing fully coupled solution is a uniform equation that is unable to reproduce the characteristics of rock mass in practice. In this study, an updated numerical procedure for the submarine tunnel is derived by coupling strain-softening and seepage effect based on the experimental results. According to the hydro-mechanical coupling theory, the hydro-mechanical parameters such as elastic modulus, Poisson's ratio, Biot's coefficient and permeability coefficient of rocks are characterized by the fitting equations derived from the experimental data. Then, the updated numerical procedure is deduced with the governing equations, boundary conditions, seepage equations and fitting equations. The updated numerical procedure is verified accurately compared with the previous analytical solution. By utilizing the updated numerical procedure, the characteristics of stress field and the influences of initial pore water pressure, Biot's coefficient, and permeability coefficient on the stress, displacement and water-inflow of the surrounding rocks are discussed. Regardless of the variations in hydro-mechanical parameters, the stress distribution has a similar trend. The initial permeability coefficient exerts the most significant influence on the stress field. With the increases in initial pore water pressure and Biot's coefficient, the plastic region expands, and the water-inflow and displacement increase accordingly. Given the fact that the stability of the tunnel is more sensitive to the seepage force controlled by the hydraulic parameters, it is suggested to dewater the ground above the submarine tunnel to control the initial pore water pressure.

Numerical simulation of the coupled thermal-hydro-mechanical fields for evaluating CO2 geo-sequestration storage in deep saline aquifers of Hainan Fushan Sag, China

Geo-sequestration storage of CO2 in saline aquifers is an important technological option to reduce carbon emissions in China in the future. The theory of geo-sequestration storage of CO2 in saline aquifers involves complex physical operations and chemical phenomena among reservoir stress, seepage, and temperature fields, and the numerical simulation models coupling thermal-hydro-mechanical (THM) fields are widely applied to analyze the evolution of multiphysical processes in CO2 reservoirs. Based on the geo-sequestration storage project of saline aquifer CO2 in Fushan Sag, Hainan Province, under the premise of considering the change of permeability and porosity after the mineralization of CO2 in the rock reservoirs, this study simulates the evolution of temperature, stress, and seepage fields during the sequestration process of saline aquifer Continuous CO2 injection wells clarifies the range of influence of the temperature field, seepage field, and the boundary of its stress field of saline aquifer Continuous CO2 injection wells in different sequestration periods. It reveals the influence mechanism of the fault structure on the reservoir CO2 sequestration pressure and capacity, and evaluates and estimates the CO2 injection storage capacity of Fu 1# well in Fushan Sag and on this basis. The THM numerical simulation model proposed in this study plays a crucial role in guiding theoretical evaluations of the CO2 geo-sequestration potential in saline aquifers and determining its technical parameters, thereby offering significant value for engineering applications.

Characteristics of rock strength failure and identification of hazardous areas in the roof of deep mining stope

The roof of deep mining stopes is notoriously unstable and challenging to manage due to high in-situ stress and deteriorating rock conditions. To address this issue, a comprehensive approach was employed, incorporating indoor physical experiments, numerical simulations, and field tests to investigate the stope roof rock composition characteristics and strength failure modes in the Laoyingshan deep coal mine. The study revealed the distribution characteristics of the high in-situ stress field in this mining area and delineated different levels of hazards in the roof. The results indicate that, under identical lithological conditions, the mineral composition of deep rock formations is complex. Changes in some mineral components and properties were observed, leading to increased expansiveness and water absorption in clay minerals such as sodium montmorillonite and kaolinite within the basic roof layer. In simulated tests of surrounding rock strength in deep mining stopes, as stress levels approached 2 MPa, the damage factor increased, showing a trend of localized concentration. Internal damage began to exhibit noticeable spatial evolutionary expansion patterns and gradual nucleation. When stress exceeded 8 MPa, rocks transitioned from macroscopic fracture surfaces to microscopic fragmentation zones, with a sudden decrease in stiffness degradation values, internal instantaneous collapse, and phenomena akin to “rock burst” under high stress disturbance. In-situ stress testing determined that the stress field in the deep mining zone of Laoyingshan is in a thrust fault stress state, with horizontal stress predominance. The maximum stress direction is predominantly southwest-northeast, with stress magnitude reaching 25.49 MPa. By arranging post-mining and pre-mining borehole observation stations and utilizing image grayscale fracture recognition technology in MATLAB, the roof was classified into four danger levels: “extremely broken,” “broken,” “significant fractures,” and “minor fractures.” Main control measures for coupling grouting in deep-shallow zonation rigidity were proposed based on these classifications.

Workflow Helps Predict Casing Deformation During Hydraulic Fracturing in Shale Gas

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper URTeC 4043054, “Casing-Deformation-Risk Prediction With Numerical Simulation During Hydraulic Fracturing in Deep Shale Gas Reservoirs,” by Jianfa Wu, Xuewen Shi, and Qiyong Gou, PetroChina, et al. The paper has not been peer reviewed. _ In this study, a numerical simulation workflow was established based on comprehensive modeling of a time-lapse stress field, hydraulic fracturing simulation, natural fractures, and other weak interfaces to analyze casing-deformation mechanisms of shale gas horizontal wells during the multistage hydraulic fracturing process. The authors write that they aim to guide the prediction of, and provide mitigating solutions for, casing-deformation risks while improving stimulation efficiency. Introduction The burial depth of deep shale gas reservoirs in the southern Sichuan Basin is approximately 3500 to 4500 m. These have complex geological conditions with developed faults and fractures and high in-situ horizontal stresses. During multistage hydraulic fracturing operations in horizontal wells, establishing an effective prediction method for casing-deformation risks in these reservoirs is a challenge. An integrated workflow is proposed to evaluate and predict casing-deformation risks, effectively support hydraulic fracturing operations, and reduce and mitigate casing failure in these reservoirs. Modeling Methodology It is essential to consider the effects of multiscale natural fractures when constructing a 3D stress model. Natural-fracture stability can be evaluated and used to identify unstable fractures that may cause casing failures. The fundamental workflow of predicting and preventing the casing failure is as follows: 1. Build a 3D geological model characterizing the spatial distribution and geometry of faults and natural fractures 2. Construct a 3D stress model to characterize the in-situ stress state 3. Perform numerical simulations of hydraulic fracturing and 4D coupled stress simulation to obtain the stress field during and after hydraulic fracturing 4. Quantitatively analyze the shear slip risks of natural fractures by calculating slip tolerance as an indicator to determine risk levels of casing deformation 5. Optimize and adjust engineering parameters for hydraulic fracturing to reduce and mitigate casing deformation Natural-Fracture Distribution and Model Construction. In this study, natural fractures parameters such as density, strike, inclination, length of extension, and height were obtained. The natural fractures were calibrated and verified with cores and wellbore images. Natural-fracture distribution was then validated with the expected tectonic history and present-day stress regime. In Fig. 1, the left-hand plot depicts the ant-tracking results by seismic attribute, the central plot portrays natural fractures validated by microseismic events, and the right-hand plot illustrates the 3D natural-fracture model. Results showed two major fracture strikes, one in the northeast and the other in the northwest, forming a mesh network distribution that will be used in the stress model, fracturing simulation, and slip analysis.

Southeastern extension of Singhbhum Shear Zone, Eastern Indian Shield: A detailed appraisal

Trans-crustal, northerly dipping, arcuate Singhbhum Shear Zone (SSZ) constituting the interface of Proterozoic North Singhbhum Mobile Belt (NSMB) and Singhbhum Craton (SC) is established over a strike length of about ∼200 km from Baharagorato Chakradharpur in the west beyond which it bifurcates around the wedge shaped Chakradharpur granite. Based on geological mapping and meso to micro scale structural analysis, present work examines the SSZ’s southeastern extension beyond Baharagora, indicating its southward continuation for about 50 km to Dubukidihi within the NSMB lithopackage. Bangriposi Shear Zone (BSZ) which defines the terrane boundary between the SC and NSMB in this sector, splays towards north as Bangriposi West Shear Zone (BWSZ) and both transects the Dhanjori Basin longitudinally. BSZ and BWSZ are interpreted to be cogenetic with SSZ. NSMB in this area comprises of pelitic and psamopelitic rocks intruded by mafic–ultramafic magmatism and granitoids. Considering a north to south compression regime during accretion of NSMB with SC, the study area, which forms the interface between the craton and mobile belt, is at an acute to obtuse angle with the direction of overall stress field. It is marked by several high strain zones characterized by N-S shear band cleavages with moderate easterly dips, and northerly pitching stretching/mineral lineation. Consistent westerly vergent folds on mylonitic plane and orientation of stretching lineation indicates top to WSW movement in the shear zones. Tectonically interleaved mafic–ultramafic schist within the Romapahari granite are sites of copper mineralization with enhanced nickel concentration pointing towards future exploration sites for epigenetic copper, uranium mineralization which is so characteristic of SSZ.

Lithological control and structural inheritance on faults growth in multilayer foreland sequences

Foreland sectors and foredeep-forebulge systems are affected, as the orogenic wedge migrates, by successive stages of stress states and tectonic deformation, resulting in the development of complex fault networks, even if characterized by limited deformation. The role played by structural inheritance and changes in stress field through time, in influencing the successive re-activations of fault segments, is still a topic to be thoroughly investigated. In this work, thanks to an extensive database made available by courtesy of Energean, we were able to investigate a foreland sector at the margin of the southern Apennines. By means of thickness analysis of the Neogene foredeep sequence and of displacement analysis along the fault network, we documented a shift from forebulge-related extension, in Early Pliocene, to a new tectonic phase, since Middle Pliocene, related to a strike slip stress field, possibly related to the activity of the Tremiti Fault Zone. We also characterized the geometry and connectivity of the cover-restricted faults, developing above propagating normal faults and observed a clear correlation between fault propagation tendency and lithological/mechanical layering within the cover units.

Tectonomagmatic evolution of Pune – Nasik Deccan Dykes: Insights from structure and dimension scaling

The Deccan Continental Flood Basalt of the Indian Peninsula is characterized by extensive basaltic eruptions ornamented with three spectacular distinct dyke swarms: the Pune – Nasik, Narmada – Tapi, and Western Coastal dyke swarms. Our study area is the Pune – Nasik dyke swarm, which has ~465 mappable dykes. These dykes exhibit different orientations with a predominant trend of N101° and vary in length from less than 1 km to ~64 km. These dykes are massively jointed and occasionally contain vesicles filled with secondary minerals like quartz and calcite. The host rock is weathered basalt of various older Deccan flows. In this study, we have calculated magmatic overpressures and magma chamber depths using the aspect ratios (length/thickness) of the dykes. The average estimated source depth is ~13 km, based on an average Young's modulus for the host rock basalt (Eavg, 7.5 GPa). Additionally, we compared the inferred magma source depths of the Pune – Nasik, and Narmada-Tapi dyke swarms which include the Nandurbar – Dhule, and Pachmarhi dykes of the Deccan Flood Basalt Province. Our findings indicate that the magma chamber source depth is greater in the Pune – Nasik dyke swarm compared with other dyke swarms. The variation in strike distribution of the Pune-Nasik dyke swarm may be attributed to several factors, including a larger magma chamber, local stress fields generated by shallow magma chamber, or the superimposition of tectonic stress fields (N-S and E-W extension) during the emplacement of dykes. This contrasts with the commonly held belief that the dykes are solely connected to a central edifice of the Reunion hotspot.

Critical length prediction for fiber breaking in injection molded of long-fiber reinforced thin-walled products

Fiber length is one of the vital factors in determining the properties of long fiber reinforced thermoplastics (LFRT). However, many factors may generate fiber breakage in the injection molding process of LFRT, such as friction, melt shear, injection rate, etc. Especially for thin-walled products, owing to the relatively narrow mold cavity and frozen layer near the mold wall, it’s usually difficult for the fibers to move freely with the melt, leading to fiber breakage under the shear stress of the flow field eventually. In such a situation, the existing buckling breakage model based on the assumption fibers immersed in the flow field being in an unconstrained state is no longer applicable. In this paper, a new model for calculating the critical length of constrained fiber in thin-walled injection molded products is developed. A typical long glass fiber reinforced polypropylene thin-walled product was employed to verify the reliability of the model. The high-precision fiber length analyzer was used to calculate the fiber length distribution at different distances from the injection port. At the same time, the length distribution at the corresponding position was predicted via the model. The average prediction accuracy in the three sampling sections is 87.8%, 91.4% and 83.6%, respectively. The results show that the proposed model can effectively predict the fiber length distribution of injection molded thin-walled products. This conclusion provides important support for further accurate calculation of the mechanical properties of products.

Numerical simulation of gas tungsten arc welding for ZW61 magnesium alloy thin plates

Mg-Zn-Y alloy has become the favorite of magnesium alloy research due to its excellent comprehensive performance and increasingly mature deformation process. For the gas tungsten arc welding (GTAW) process of ZW61 magnesium alloy thin plates, the physical field and microstructure evolution is simulated with the finite volume method and the cellular automata (CA) method in this paper. The flow field results show that the Marangoni force dominates the flow of liquid metal in the molten pool from the center of the molten pool to the edge of the molten pool. The increase in welding speed significantly increases the temperature gradient in the molten pool. In addition, from the results of the stress field, the residual stresses are mainly distributed in the fusion zone (FZ) and heat-affected zone (HAZ). The maximum longitudinal residual stress occurs in the HAZ, about 82 MPa. While the maximum transverse residual stress occurs at the end of the plate, about 104 MPa. Neither exceeds the tensile strength of ZW61 alloy, so no cracks appear in the joint. The temperature gradient of the welded plate and the solidification rate of the molten metal in the molten pool are regulated by adjusting the welding process parameters, to improve the microstructure in the FZ. The minimum average grain size of the FZ is only 29.50 μm under the optimum welding process conditions set in this paper.

Numerical Investigation of the Cohesive Strength Regime of the Bilobated Arrokoth after the Sky-crater-forming Impact Event

Abstract In 2019, NASA’s New Horizons mission, using the Long Range Reconnaissance Imager, revealed Arrokoth’s bilobated shape and a large impact-crater-like region (“Sky”) on the small lobe, which is ∼7 km wide and ∼1 km deep. Given that this depression takes up ∼7% of the entire volume of the small lobe, Arrokoth’s neck, the most structurally sensitive area to failure, might have been subject to substantial structural modification if the Sky-crater-forming event occurred after the bilobate shape had formed. Using the π-scaling law, we quantified the linear momentum imparted to the small lobe by the Sky-crater-forming event, which was in the range of (2.4–4.0) × 1013 kg m s−1, depending on Arrokoth’s bulk density of 250–500 kg m−3 and impact speeds of 100 m s−1, 300 m s−1, and 1 km s−1. If the linear momentum was fully transferred to Arrokoth’s small lobe, it would have given the small lobe an impulse velocity of approximately 0.1 m s−1 relative to the large lobe. To assess the structural impact of this event, we used a finite-element modeling approach to simulate post-impact stress fields driven by the estimated impulse velocity on the small lobe and constrained the critical cohesive strength required to prevent structural failure. Based on the current parameter space, our results suggest that the Sky-crater-forming event could have required the critical cohesive strength of up to ∼20 kPa for Arrokoth’s neck to avoid structural failure, which is higher than the typical cohesive strength estimated for small bodies (usually less than 1 kPa for asteroids and comets).

Unveiling the mechanism of the carbon ordering and martensite tetragonality in Fe–C alloys studied via deep-potential molecular dynamics simulations

The martensitic transformation plays a pivotal role in the strengthening and hardening of steels, yet an accurate interatomic potential for a comprehensive description of the martensitic phase formation in Fe–C alloys is lacking. Herein, we develop a deep learning-based interatomic potential to perform molecular dynamics (MD) simulations to study the martensitic phase transformation across a range of carbon (C) concentrations. The results reveal that an increased C concentration leads to a suppression of phase boundary movement and a deceleration of the phase transformation rate. To overcome the timescale limitations inherent in MD simulations, metadynamics sampling was employed to accelerate the simulations of C diffusion. We find that C atoms tend to cluster at distances equivalent to the lattice parameter of Fe with the same sublattice occupation, leading to local lattice tetragonality. Such C-ordered structures effectively inhibit dislocation movement and enhance strength. The stress field induced by dislocations facilitates a higher degree of ordering. The formation of C-ordered structures is identified as a potentially crucial strengthening mechanism for martensitic steels. The consistency between our simulation results and reported experimental observations underscores the effectiveness of the developed DP model in simulating martensitic phase transformation in Fe–C alloys, providing detailed insights into the mechanisms underlying this process.

Residual stress release and corresponding microstructural changes in high-energy impact-modified GH4169 after aging at 425 °C and 650 °C

The nickel-based superalloy is a critical material in aero-engines, where enhanced durability and resistance to stress relaxation are essential. This study evaluates the effectiveness of a high-energy composite modification technique, applied through dual surface friction methods, to induce residual stress and examines the stability of this stress under medium-temperature aging conditions. GH4169 was selected and a foundational study was conducted to quantify residual stress relaxation under medium-temperature aging treatment. The surface strengthening method used was a high-energy composite modification known for its significant post-treatment effects. The specific temperatures for medium-temperature aging treatment were 425 °C and 650 °C. The test results of the residual stress field confirmed the phenomenon of residual stress relaxation under the influence of temperature. Correspondingly, the different degrees of stress relaxation caused by varying aging treatment conditions are closely related to the microstructural changes within the material. Areas with a higher number of annealing twins exhibited a more pronounced degree of residual stress relaxation. By elucidating the link between stress relaxation and microstructural changes, this research offers a theoretical foundation for optimizing surface-strengthening processes and setting optimal operational temperatures for advanced structural materials.

Advances in defect characterization techniques using polarized light observation in SiC wafers for power devices

This short review provides an overview of advancements in the characterization of defects in silicon carbide (SiC) wafers using polarized light observation. SiC, which has a wide bandgap and excellent thermal and electrical properties, is widely used in power devices. However, various defects such as threading screw dislocations (TSD), threading edge dislocations (TED), and basal plane dislocations (BPD) can significantly affect device performance and reliability. Polarized light observation offers a nondestructive method for visualizing these defects and analyzing the stress fields induced within the SiC crystal structure. This paper summarizes recent developments in this technique, including the application of analyzer rotation to enhance the contrast in defect visualization. Furthermore, the development of automated systems for rapid wafer evaluation is discussed, highlighting the role of polarized light observation in improving quality control and production efficiency in SiC power device manufacturing.

Effects of the 2022 Mw 7.0 Chihshang Earthquake on the Shallow Creeping of the Central Longitudinal Valley Fault in Eastern Taiwan: Insights from Precise Leveling Measurements

Abstract This study investigated the effects of the 2022 Mw 7.0 Chihshang earthquake in eastern Taiwan on the shallow creeping of the central Longitudinal Valley fault (LVF). Precise leveling surveys were conducted along the Ruisui-Dewu, Yuli, and Dongzhu routes over the LVF. Before the earthquake, previous leveling surveys had detected deformations caused by stable fault creeping of the LVF. Interseismic linear trends and coseismic deformations were removed from the leveling data. Two shallow faults at 1 km were estimated from the corrected-coseismic deformation for the Yuli route. A shallow fault at 1 km and a deep fault at 5 km were estimated from the interseismic deformation. A positive delta Coulomb failure function change was calculated for shallow faults due to the creeping movement on the deep fault before the earthquake, and the creeping movement on the deep fault before the earthquake may have promoted the rupture of the shallow fault. The strong Chihshang earthquake most likely triggered the rupture of the shallow fault, on which strain had been concentrated by the interseismic creeping of the deeper fault. In contrast, the accumulated total strain at the deeper part might be quite low due to a strain release process for a steady creeping movement on deep fault in the interseismic period. The significant slip was not induced in the coseismic period. Although significant slip occurred in the shallower part, the slip might not be induced in the deeper part adjacent to the asperity of the LVF. In the Dewu route, the observed large west-side-uplift is attributed to the coseismic rupture of the Chihshang earthquake. In the Dongzhu route, an interseismic east-side-uplift by a creeping fault and a coseismic west-side-uplift were observed at the same location, indicating a local tensile stress field by the Chihshang earthquake.

Role of molecular damage in crack initiation mechanisms of tough elastomers

Tough soft materials such as multiple network elastomers (MNE) or filled elastomers are typically stretchable and include significant energy dissipation mechanisms that prevent or delay crack growth. Yet most studies and fracture models focus on steady-state propagation and damage is assumed to be decoupled from the local stress and strain fields near the crack tip. We report an in situ spatial-temporally resolved 3D measurement of molecular damage in mechanophore-labeled MNE just before a crack propagates. This technique, complemented by digital image correlation, allows us to compare the spatial distribution of both damage and deformation in single network (SN) elastomers and in MNE. Compared to SN, MNE have a wide-spread damage in front of the crack and, surprisingly, delocalize strain concentration. A continuum model, where damage distribution is fully coupled to the crack tip fields, is proposed to explain these results. Additional measurements of time-dependent molecular damage during fixed grips relaxation in the presence of a crack reveal that the less localized damage distribution delays fracture initiation. The observations and exploratory modeling reveal the dynamic fracture mechanism of MNE, providing guidance for rational design of high-performance tough elastomers.

Numerical Study on the Development of Adiabatic Shear Bands During High Strain-Rate Compression of AISI 1045 Steel: A Comparative Analysis Between Plane-Strain and Axisymmetric Problems

This work studies numerically the development of adiabatic shear banding (ASB) during high strain-rate compression of AISI 1045 steel. Plane strain and cylindrical axisymmetric compressions are simulated in LS-DYNA, considering rectangular and cylindrical steel samples, respectively. Also, a parametric analysis in height-to-base ratio is conducted in order to evaluate the effect of geometry and dimensional ratio of the sample on ASB formation. Doubly structural-thermal-damage coupled finite element models are developed for the numerical simulations, implementing the thermo-viscoplastic Modified Johnson–Cook constitutive relation and damage criterion, while further damage-equivalent stress and strain fields are introduced for the damage coupling. The simulations revealed that plane strain compression promotes more ASB formation, providing lower critical strain for ASB initiation and wider and stronger ASBs compared with axisymmetric compression. Further, X-shaped ASBs initially form during plane strain compression, while as deformation increases, they transform into S-shaped ASBs in contrast to axisymmetric compression, where parabolic ASBs are developed. Also, a lower height-to-base ratio leads to greater ASB propensity, reducing critical strain in axisymmetric compression. Finally, thermal softening is found to precede damage softening and dominate the ASB genesis and its early evolution, while in contrast damage softening drives later ASB evolution and its transition to fracture.

Research on accelerated thermal fatigue testing and life prediction of Al-Si alloy pistons under start-stop cycles

As one of the most critical components in the combustion chamber of diesel engines, pistons operate under high temperature and pressure conditions for extended periods, which increases the likelihood of failures such as thermal fatigue. This paper first utilizes finite element simulation to obtain the temperature and stress field distribution of an Al-Si alloy piston under actual engine conditions. The results indicate that the throat area of the piston is the most susceptible to fatigue failure. Based on this, accelerated thermal fatigue tests were conducted to study the influence of various experimental factors on piston life, as well as to analyze the weight of each factor. Results from macroscopic and microscopic analyses of cracks using a scanning electron microscope show that fatigue cracks originate at the interface between the aluminum matrix and the detached hard particles. The cracking at the piston throat exhibits clear characteristics of ductile fracture, which is the result of cumulative fatigue damage. Therefore, from the perspective of continuum damage mechanics, it is considered to characterize the equivalent stress using the average loading rate during the loading phase and the maximum axial temperature gradient, establishing an experimental life prediction model for Al-Si alloy pistons.

Co-seismic Static Stress Field and Stress Triggering of Aftershocks in the 2022 Menyuan Ms 6.9 Earthquake

Co-seismic Static Stress Field and Stress Triggering of Aftershocks in the 2022 Menyuan Ms 6.9 Earthquake

Finite element analysis and computational fluid dynamics to elucidate the mechanism of distal stent graft-induced new entry after frozen elephant trunk technique.

Distal stent graft-induced new entry (dSINE), a new intimal tear at the distal edge of the frozen elephant trunk (FET), is a complication of FET. Preventive measures for dSINE have not yet been established. This study aimed to clarify the mechanisms underlying the development of dSINE by simulating the mechanical environment at the distal edge of the FET. The stress field in the aortic wall after FET deployment was calculated using finite element analysis. Blood flow in the intraluminal space of the aorta and FET models was simulated using computational fluid dynamics. The simulations were conducted with various oversizing rates of FET ranging from 0 to 30% under the condition of FET with elastic recoil. The elastic recoil of the FET, which caused its distal edge to push against the greater curvature of the aorta, induced a concentration of circumferential stress and increased wall shear stress (WSS) at the aorta. Elastic recoil also created a discontinuous notch on the lesser curvature of the aorta, causing flow stagnation. An increase in the oversizing rate of the FET widened the large circumferential stress area on the greater curvature and increases the maximum stress. Conversely, a decrease in the oversizing rate of the FET increased the WSS and widened the area with high WSS. Circumferential stress concentration due to an oversized FET and high WSS due to an undersized FET can cause a dSINE. The selection of smaller-sized FET alone might not prevent dSINE.

Significant spatial variation of upper crustal anisotropy in Southern Sichuan Basin, China: constraints from local shear wave splitting analysis

Summary The recent upsurge in seismic activity within the southern Sichuan Basin has garnered considerable public attention and simultaneously offers a valuable opportunity for investigating upper crustal anisotropy. Such investigations can provide critical insights into the stress field and crustal deformation in the region. We obtained a total of 1 845 high-quality local shear wave splitting measurements at 15 stations and 2 027 null measurements at 19 stations. These results indicate the presence of a single layer of anisotropy with a horizontal axis of symmetry at a depth of 3 to 7 km. The fast polarization directions display discernible spatial variations that are primarily influenced by the geographical location of earthquakes rather than changes over time. In the vicinity of the Baimazhen Syncline, the fast polarization directions coincide with the strike of the stratum, forming a circular pattern around the core of the syncline, suggesting that the observed anisotropy is structure-controlled. In contrast, stations situated in the southern Weiyuan Anticline and western Baimazhen Syncline display fast directions trending N171.7° E and N45.9° E, respectively. These directions are consistent with the P-axes of the focal mechanism of earthquakes, signifying that the anisotropy in these areas is governed by the regional stress field. The findings of this study not only deepen our understanding of the intricate geological structures in the southern Sichuan Basin but also indicate the need for greater caution when interpreting potential temporal changes in anisotropy in future research.