Reverse Shear Research Articles

Shear band development under simple shear and the intrinsicality of strain softening of amorphous glassy polymers

The development of shear bands that induced by localized strain inhomogeneity is a characteristic deformation mechanism and determines ductility of amorphous glassy polymers. To investigate the essence of intrinsic strain softening and its influence on shear band evolution under shearing and reverse shearing, a full-network constitutive model based on the micro-mechanism is implemented into the material point method and finite element method respectively. The results show that the shear band nucleates and propagates in forward shearing, and gradually fades until disappears in following reverse shearing when the specimen regains its original geometry. As reverse shearing proceeds or there is a second forward shearing, the homogeneous plastic deformation occurs preferentially in the previously deformed band but it doesn't display any shear band like the initial forward shearing. It means the glassy polymers undergoing plastic deformation cannot be recovered by reverse straining. In further shearing, new shear bands tend to be initiated outside the existing band and then propagates to merge with the previous band. The initiation and propagation of shear band along the shearing direction is caused by the intrinsic strain softening, independent of loading histories and boundary conditions. The widening of shear band is related to the strain hardening. • Origin of intrinsic strain softening lies in the saturation of plastic shear strain. • Amount of intrinsic strain softening keeps fixed. • Glassy polymers undergoing plasticity cannot be recovered by reverse straining. • Full-network model can capture the shear band evolution under reverse shearing.

Analysis of ESAFORM 2021 cup drawing benchmark of an Al alloy, critical factors for accuracy and efficiency of FE simulations

This article details the ESAFORM Benchmark 2021. The deep drawing cup of a 1 mm thick, AA 6016-T4 sheet with a strong cube texture was simulated by 11 teams relying on phenomenological or crystal plasticity approaches, using commercial or self-developed Finite Element (FE) codes, with solid, continuum or classical shell elements and different contact models. The material characterization (tensile tests, biaxial tensile tests, monotonic and reverse shear tests, EBSD measurements) and the cup forming steps were performed with care (redundancy of measurements). The Benchmark organizers identified some constitutive laws but each team could perform its own identification. The methodology to reach material data is systematically described as well as the final data set. The ability of the constitutive law and of the FE model to predict Lankford and yield stress in different directions is verified. Then, the simulation results such as the earing (number and average height and amplitude), the punch force evolution and thickness in the cup wall are evaluated and analysed. The CPU time, the manpower for each step as well as the required tests versus the final prediction accuracy of more than 20 FE simulations are commented. The article aims to guide students and engineers in their choice of a constitutive law (yield locus, hardening law or plasticity approach) and data set used in the identification, without neglecting the other FE features, such as software, explicit or implicit strategy, element type and contact model.

Mesomorphic Polymer Hydrogel Stabilizing Ionic Surfactant Self-Assembly for Fuel Cells

Lyotropic self-assembly of ionic surfactants benefits the construction of ion-conductive pathways but suffers from poor mechanical stability owing to the intrinsic fluidity. Here, a novel mesomorphic polymer hydrogel, featuring a porous network of the cross-linked polymer trapping lyotropic self-assembly of ionic surfactants, is presented for fuel cells. The mesomorphic hydrogel, which is facilely derived from radical polymerization of an acrylamide monomer and a cross-linker in an aqueous solution of 1-tetradecyl-3-methylimidazolium hydrogen sulfate, exhibits not only a lamellar lyotropic liquid crystal phase but also reversible tensile, compressive, and shear deformations. Macroscopic alignment of the mesomorphic hydrogel is achieved by low-frequency shear, and ionic conductivity is promoted to 166 mS cm–1 by virtue of the aligned ion-conductive channels. A hydrogen fuel cell is fabricated from the mesomorphic polymer hydrogel, and a peak power density of 48 mW cm–2 is achieved. Overall, this work provides a strategy to endow functional lyotropic self-assembly with mechanical strengths for diverse electrochemical applications.

Characterization of kinematic and distortional hardening by cyclic twin-bridge shear tests for sheet metal with inverse engineering approach

This study characterizes the plastic behavior under cyclic loading for an aluminum alloy of 5182-O and advanced high strength steel of QP1180. Twin-bridge shear specimens were loaded cyclically to evaluate the reverse shear loading behavior of the tested materials with different pre-strain from small (0.05 major strain) to large (0.15). The plastic behavior under cyclic loading is modelled by kinematic and distortional hardening models under the non-associated flow rule (NAFR) by anisotropic Drucker (Aniso-Drucker) yield function. An additional shear constraint proposed by (Abedini et al., 2018) is imposed on the plastic potential of NAFR. The Zang and HAH20 models are selected as kinematic and distortional hardening models respectively. They are calibrated inversely by the reverse torque-torsion angle curves from experiments. Finally, V-bending tests with the pre-strained strips were carried out and simulated by the calibrated hardening model to evaluate its predicting accuracy. The results show that twin-bridge shear test combined with the recommended inverse engineering approach is implementable to overcome the drawback of the simple shear test due to inhomogeneous deformation in large strain. The constitutive models are critical for the inverse calibration. It is found that the calibration accuracy under NAFR is higher than the associated flow rule (AFR) especially for large strain conditions. Also, the additional shear constraint imposed on the plastic potential of NAFR is found to be an effective approach to enforce the simulated shear stress at zero hydrostatic pressure. As for hardening model, the HAH model has more flexibility compared to the kinematic hardening model benefiting from its distortional hardening form. Also, parameters related to permanent softening in the new HAH20 model need to be evaluated carefully at the large deformations.

Shear Failure Mechanism and Numerical Simulation Analysis of Rock-like Materials with an Embedded Flaw

In this study, the failure characteristics of self-made rock with internal flaws under shear were studied and a numerical simulation analysis was carried out. Firstly, based on basic physical and mechanical tests, the shear strength characteristics of rocks with built-in 3D defects were summarized. PFC3D simulation software was used to model the samples with flaws, and the microscopic parameters were calibrated according to the test results. From the simulation results, it was found that the generation mode of microcracks from the flaw tip was different. The microcracks of forward shear and reverse shear were mainly generated from the horizontal direction, while the microcracks of lateral shear gradually increased from the upper and lower ends of the flaw in the opposite direction. When the peak shear strength was reached, the total number of cracks was the largest in lateral shear and the smallest in forward shear. When studying the particle velocity vector field, it was found that when reaching the peak shear strength, the particles on both sides of the prefabricated flaw appeared to be in vortex motion. When α = 45° and σn = 2 MPa, the failure mode of forward shear and lateral shear was shear-tensile-shear (S-T-S), and that of reverse shear and the intact specimen was shear-shear-shear (S-S-S). The lateral shear tensile effect was the most obvious and was mainly concentrated in the middle part of the sample.

Identification Protocol of Yoshida-Uemori Hardening Model

The Yoshida-Uemori model is a combined hardening model coupled with the elastic modulus evolution which depends on the equivalent plastic strain. A lot of publications show that it allows to improve the springback prediction compared to a classical isotropic hardening model. It is implemented in the most used FEA stamping codes (Autoform®, Ls-Dyna® and Pamstamp®) with some variations and it is more and more used in automotive industry. ArcelorMittal decided to provide material cards to its customers. To achieve this goal, ArcelorMittal has at one’s disposal the equipment to perform reverse shear tests and hysteresis loops for all steel grades. An in-house methodology has been developed to identify the Yoshida-Uemori adjusting parameters in a very precise and robust manner. The material cards are produced for each FEA stamping code, considering the specificities of the implementations.

A comparative study on the microstructural features and mechanical properties of an Mg–Zn alloy processed by ECAP and SSE

The influence of the equal channel angular pressing (ECAP) and simple shear extrusion (SSE) processes on the microstructural and textural developments, as well as mechanical properties of Mg–4Zn alloy was studied. Application of 1, 2, and 4 passes of ECAP and SSE resulted in remarkable grain refinement of the initial microstructure of extruded material. Due to the greater shear strain and finer second phase particles, acting as obstacles to grain growth, smaller grain sizes were developed in the SSEed samples compared to the ECAPed counterparts. The fiber texture component of the extruded alloy was gradually transformed to a shear texture component after 4 ECAP passes, while 1, 2, and 4 passes of SSE produced a semi-fiber texture, in which basal planes were parallel to the longitudinal axis of the processed sample. Due to the applied reversal shear strain to the sample inside the SSE die, the volume fraction of the dynamically recrystallized (DRXed) regions was lower than that in the ECAP process which exerted a one-step shear strain to the sample. Shear punch test (SPT) results indicated that both ECAP and SSE improved the strength of the extruded alloy due to the grain boundary strengthening, texture hardening, and dislocation-dislocation interaction mechanisms. The strength of the SSEed samples was greater than ECAPed specimens, due to the finer grain size, higher volume fraction of un-DRXed grains, and lower Schmid factor of the semi-fiber texture component of the former.

Rational Analysis of Drag Reduction Variation Induced by Surface Microstructures Inspired by the Middle Section of Barchan Dunes at High Flow Velocity

Aerodynamic drag reduction is a key element for the design of aircrafts, and it is also considered to be affected by the flow velocity. Herein, the influence of high flow velocity on the drag reduction induced by the surface microstructure inspired by a cross-section of barchan dune was investigated by the computational fluid dynamics method in this work. Overall, the drag reduction ratio was decreased while the pressure drag and viscous resistance enhanced simultaneously with the augmentation of flow velocity. Otherwise, drag analysis revealed that the total drag was a power function of flow velocity, which meant that the effect of flow velocity on drag was extremely fierce. Additionally, the microstructure improved the thickness of the boundary layer with a growth rate of 14.2%, and then reduced the viscosity resistance with limits during the development process of flow velocity. Furthermore, the micro-vortex caused by the surface microstructure provided the reverse wall shear stress, with the maximum value ranging from −4.77 Pa to −51.27 Pa, and then reduced the velocity gradient above the microstructure, thereby improving the drag reduction. However, both Reynolds-averaged Navier-Stokes (RANS) and large eddy simulation (LES) calculations showed that the excessive velocity could lead to the dissipation of micro-vortex, which augmented the contact area between the fluid and the surface, resulting in the enlargement of viscous resistance. Finally, it was confirmed that the variation of surface microstructure height had a significant influence on drag reduction at high flow velocity. The underlying mechanism of drag reduction could also provide theoretical guidance for the design and optimization of drag reduction coatings in aeronautical applications.

A constitutive model for metallic glasses based on two-temperature nonequilibrium thermodynamics

We develop a new finite deformation constitutive model for metallic glass within the framework of irreversible nonequilibrium thermodynamics. To consider the intrinsically out-of-equilibrium characteristics of metallic glass, its total internal energy is divided into two weakly coupled configurational and kinetic subsystems, and configurational temperature coupling with configurational degrees of freedom is introduced as a thermodynamic state variable to characterize the evolution of the disordered structure. Furthermore, the classical shear transformation zone theory is extended by reasonably considering the reverse shear transformation as a form of the relaxation of the strain field, which is stored in the elastic matrix and produced by the constraint of the matrix on shear transformation. With the help of the finite element implementation for the new model, the effectiveness of the proposed model is validated by comparing the modeling stress–strain responses of the macroscopic deformations under different temperatures and strain rates with the experimental results, and the utility of the model for predicting the shear banding behavior of metallic glasses is examined as well. The results therefore show that the constructed constitutive model can not only effectively predict the deformations of metallic glass under different ambient temperatures and applied strain rates, but also reasonably explain the mechanisms of deformation mode evolution and shear band formation.

Dynamically reversible shear transformations in a CrMnFeCoNi high-entropy alloy at cryogenic temperature

Shear transformation, such as twinning and martensitic phase transformation, is generally unidirectional under monotonic thermal or mechanical loading. Here, we report the dynamically reversible shear transformations in a CrMnFeCoNi high-entropy alloy (HEA) under uniaxial tension at the extremely low temperature of 4.2 K. Since stacking fault energy (SFE) of CrMnFeCoNi HEA with a face-centered cubic (fcc) structure is low and decreases with decreasing temperature, plastic deformation is accommodated by dislocation slips and shear transformation bands, such as {111} stacking faults (SFs), {111} nano-twins and fcc → hcp (hexagonal close-packed structure) shear transformation bands. When deformed at 4.2 K, the lower SFE promotes fcc → hcp shear transformation, forming hcp grains. Besides basal and non-basal dislocation slips in hcp grains, high-density {0001} SFs and {101¯1} nano-twinning are activated to accommodate plastic deformation. More intriguingly, reverse hcp → fcc shear transformations are stimulated by deformation-induced local dissipative heating. The reversible fcc↔hcp shear transformations and both {101¯1} and {111} nano-twinning lead to dynamic nano-laminated dual-phase (NL-DP) structures, which advances the monotonic “dynamic Hall-Petch” effect in enhancing strength, strain-hardening ability, and ductility by dynamically tailoring the type and width of shear transformation bands. Our work provides a promising strategy for evading the strength-ductility dilemma via dynamically developing NL-DP structures through activating reversible shear transformations.

Geology along the Bedretto tunnel: kinematic and geochronological constraints on the evolution of the Gotthard Massif (Central Alps)

The unlined Bedretto tunnel crosses large parts of the pre-Triassic basement of the Gotthard massif (Central Alps), giving the possibility to study late-Variscan plutonic rocks (Rotondo granite) and their Caledonian (poly-)metamorphic host rocks (Tremola and Prato series). The Rotondo granite consists mostly of an equigranular, fine-grained granite and to a lesser extent of a porphyritic granite. Commonly, the Rotondo granite is massive or only slightly foliated. Ductile deformation is localized along discrete shear zones composed of granitic or quartz-biotite-rich lithologies. This paper reviews the geology of the Bedretto tunnel with emphasis on the Rotondo granite and presents constraints based on kinematic, microstructural, and U–Pb geochronological evidence, which can be summarized as follows: (1) Both granitic and quartz-biotite-rich shear zones (QB-SZ) in the Rotondo granite generally dip moderately to steeply towards north and are related to top-to-south reverse shearing, indicating south-verging backthrusting during the exhumation of the Gotthard massif. (2) Zircons from both the equigranular and porphyritic Rotondo granite show overlapping {}^{206}hbox {Pb}/{}^{238}hbox {U}-age ranges of 285–319 Ma and 280–335 Ma, respectively, which indicate that both are part of the same late-Variscan magmatic episode. Almost no older inherited cores are reported. (3) In zircons from a QB-SZ, 30% of the concordant age spots scatter between 339 and 589 Ma. This suggests that the parent material of the QB-SZ is unrelated to the magmatic episode that formed the Rotondo granite, but rather that the QB-SZ represent sheared xenoliths within the granite.

U-Pb zircon-titanite-apatite age constraints on basin development and basin inversion in the Kiruna mining district, Sweden

To constrain the tectonothermal evolution of the type locality for iron oxide-apatite deposits, we have obtained U-Pb zircon, titanite, and apatite age data for the Kiruna mining district in northernmost Sweden. The results indicate that the host basin initiated in an overall extensional regime as indicated by the deposition of alluvial conglomerates and greywackes. A volcanic intercalation in a conglomerate unit approximately 1 km northwest of the Luossavaara iron oxide-apatite deposit yields a U-Pb zircon concordia age of 1887 ± 3 Ma representing the timing of the earliest Orosirian volcanism in the central Kiruna mining district coinciding with the onset of basin development. In-situ analysis of titanite sitting on hydrothermally altered fracture planes within a cataclastic fault damage zone (c. 270 m from the fault core system associated with the Luossavaara iron oxide-apatite deposit) yields complex U-Pb data. Applying a strict discordance filter yields seven analyses (<1.5 % relative discordance which included six common Pb-corrected analyses and one analysis where no significant common Pb was detected) that yield a 207Pb/206Pb weighted average age of 1889 ± 26 Ma that we interpret as the most probable minimum age of fault initiation. The overlap in age of the host volcanic rock and the fault implies that during basin development, contemporaneous volcanism and syn-volcanic faults may have played an important role during iron ore emplacement. A U-Pb lower intercept age of apatite from the Nukutus iron oxide-apatite deposit provides a first indication that the area was subsequently buried and metamorphosed under upper greenschist-facies conditions and later tectonically exhumed and cooled below the apatite closure temperature at 1805 ± 26 Ma. Further temporal constraints on exhumation and basin inversion is given by syn-tectonic titanite along a brittle-ductile reverse shear zone to the east of the study area that shows limited presence of significant common Pb and is part of a sodic-calcic + Fe + Cl hydrothermal alteration assemblage. Titanite grains that show a well-developed zonation yield a U-Pb concordia age of 1812 ± 3 Ma, which we interpret as the onset of basin inversion. Titanite grains from the same sample that show less pronounced zonation yield a U-Pb concordia age of 1802 ± 8 Ma, tentatively indicating that the tectonothermal activity lasted up to c. 20 m.y.

Microstructure-mechanical properties evaluation of AISI 304 steel during back-annealing

ABSTRACT In this research, the effect of back-annealing on the microstructure and mechanical properties of deformed austenitic stainless steel was studied. After the annealing treatment, the density of defects including mechanical twins and strain-induced martensite (SIM) were reduced in the microstructure. At 700°C both diffusional and shear reversion mechanisms (DRM and SRM) were active, while at higher temperatures (800 and 900°C) the SRM was dominant. After the annealing at 700°C for 60 min, the microstructure changed significantly and new grains were widely observed which resulted from the reversion of γ through the DRM and SRM. The results showed a decrease in yield (940 MPa) and ultimate tensile (978 MPa) strengths in annealed sample at 700°C for 10 min with respect to the deformed steel, while the total elongation has not changed significantly and remains around 20%. By increasing the annealing time to 60 min, the yield and ultimate tensile strengths of steel decreased to 640 and 830.4 MPa, respectively, and the total elongation increased significantly to 40.5%. The fracture surface of annealed sample at 700°C for 10 min was heterogeneous. After 60 min, the fracture surface became homogeneous and fine dimples were uniformly observed throughout the surface.

Strain Partitioning along Terrane Bounding and Intraterrane Shear Zones: Constraints from a Long-Lived Transpressional System in West Gondwana (Ribeira Belt, Brazil)

Abstract Shear zones are zones of localized high strain accommodating differential motion in the lithosphere and impacting the crustal rheology and deformational history of orogenic belts. Although terrane bounding shear zones are widely studied, intraterrane shear zones and their tectonic significance, especially in association with supercontinent assembly, is a largely unexplored topic. The Ribeira Belt (SE Brazil), a Neoproterozoic-Cambrian orogenic belt from West Gondwana, is dissected by a crustal-scale NE-trending transcurrent shear zone system that juxtaposes composite terranes. Despite its extensive coverage and complexity, this shear zone system remains poorly investigated. In this paper, we explore the thermal and deformational regimes, and timing of ductile shearing using a multiscale approach combining structural analysis derived from remote sensing and field-based structural data, microstructures, quantitative structural analysis, and multimineral U–Pb geochronology (zircon, titanite, monazite, and xenotime). Our data, combined with previously published data, indicate a transitional northeastward increase in metamorphic conditions from lower greenschist to granulite facies conditions (from 250–300 to 750–800°C), reflecting the different crustal levels that are exposed. Vorticity and finite strain data indicate a complex strain regime with varied contributions of pure and simple shear and oblate-shape ellipsoids in strike-slip shear zones and prolate-shaped ellipsoids in dip-slip reverse shear zones. The strain set suggests that all shear zones were developed under subsimple shear deformational regimes involving thrusting and folding followed by wrench tectonics. The pure shear component of deformation was accommodated in folded domains between shear zones. Geochronological data suggest intermittent ductile shear zone activations from ca. 900–830 to 530 Ma, partially coeval with at least two major episodes of terrane accretion at 850–760 Ma and 610–585 Ma. The spatial and temporal record of shear zones within the Ribeira Belt indicates that some relate to assembly of the belt and represent either terrane bounding structures (e.g., Itapirapuã shear zone) or intraterrane structures (e.g., Ribeira, Figueira, and Agudos Grandes shear zones), whereas others are terrane bounding, postcollisional shear zones (e.g., Taxaquara shear zone) reactivated in an intracontinental setting (560–535 Ma).

A thermogelling organic-inorganic hybrid hydrogel with excellent printability, shape fidelity and cytocompatibility for 3D bioprinting

Alginates are the most commonly used bioink in biofabrication, but their rheological profiles make it very challenging to perform real 3D printing. In this study, an advanced hybrid hydrogel ink was developed, a mixture of thermogelling diblock copolymer, alginate and clay i.e. Laponite XLG. The reversible thermogelling and shear thinning properties of the diblock copolymer in the ink system improves handling and 3D printability significantly. Various three-dimensional constructs, including suspended filaments, were printed successfully with high shape fidelity and excellent stackability. Subsequent ionic crosslinking of alginate fixates the printed scaffolds, while the diblock copolymer is washed out of the structure, acting as a fugitive material/porogen on the (macro)molecular level. Finally, cell-laden printing and culture over 21 d demonstrated good cytocompatibility and feasibility of the novel hybrid hydrogels for 3D bioprinting. We believe that the developed approach could be interesting for a wide range of bioprinting applications including tissue engineering and drug screening, potentially enabling also other biological bioinks such as collagen, hyaluronic acid, decellularized extracellular matrices or cellulose based bioinks.

A Closure for Lee Wave Drag on the Large-Scale Ocean Circulation

AbstractA new, energetically, and dynamically consistent closure for the lee wave drag on the large-scale circulation is developed and tested in idealized and realistic ocean model simulations. The closure is based on the radiative transfer equation for internal gravity waves, integrated over wavenumber space, and consists of two lee wave energy compartments for up- and downward propagating waves, which can be cointegrated in an ocean model. Mean parameters for vertical propagation, mean–flow interaction, and the vertical wave momentum flux are calculated assuming that the lee waves stay close to the spectral shape given by linear theory of their generation. Idealized model simulations demonstrate how lee waves are generated and interact with the mean flow and contribute to mixing, and document parameter sensitivities. A realistic eddy-permitting global model at 1/10° resolution coupled to the new closure yields a globally integrated energy flux of 0.27 TW into the lee wave field. The bottom lee wave stress on the mean flow can be locally as large as the surface wind stress and can reach into the surface layer. The interior energy transfers by the stress are directed from the mean flow to the waves, but this often reverses, for example, in the Southern Ocean in case of shear reversal close to the bottom. The global integral of the interior energy transfers from mean flow to waves is 0.14 TW, while 0.04 TW is driving the mean flow, but this share depends on parameter choices for nonlinear effects.

Mechanics of controlled fragmentation by cold drawing

Cold drawing is a mature and widely adopted technique in the shaping of metallic and polymeric materials in industry. Interestingly, cold drawing of a ductile cladding containing a brittle core wire or a ductile substrate supporting a deposited brittle film has recently emerged as a method to produce micron sized rods and ribbons through controlled fragmentation induced by local necking. While this method shows tremendous potential in providing an economic yet efficient technological platform for large-scale manufacturing of structures at the micro- and nanoscale, there is so far no theoretical guideline on how to control the size of the fragmented components. Here, we develop a theory of controlled fragmentation in cold drawing of both axisymmetric core-cladding and plane-strain film-substrate systems. The theory reveals that the process is governed by a reverse shear lag effect which gives rise to a peak tensile stress leading to controlled fragmentation near the necking zone, where the material properties of both the brittle core/film and ductile cladding/substrate play critical roles. Of particular interest is how the feature size of the fragmented components can be reduced toward the nanoscale. To this end, our theory shows that the fragmentation size mainly depends on the interfacial shear strength, geometrical dimension and stiffness of the brittle material, and can be reduced via increasing the strength of interfacial interactions and/or decreasing geometrical dimensions such as the core radius or film thickness.

Towards fully-predictive transport modelling in ASDEX Upgrade H-modes

The common way to predict energy confinement in future devices such as ITER is to use scaling laws, based on parameters regression of large cross-machine databases. However, this approach is limited: the regression variables are not purely engineering parameters, physics quantities such as the plasma density n e are also input; power regressions fail to capture important physics such as regime transitions; profile effects such as T i/T e or reverse magnetic shear are not retained. As a consequence, the scatter is large, but even some dependences are known to be of limited validity, such as the n e or P dependences of the IPB98(y, 2) scaling. Dimensionless physics, if validated, provides a reliable basis for predicting confinement in a future device. However, there are no experimental data to use as boundary condition, nor empirical knowledge based on that device. Also, the use of full gyro-kinetic codes with all relevant ingredients is computationally unfeasible for a full-radius modelling. Integrated modelling with the recently developed IMEP workflow allows to simulate from the separatrix to the plasma centre, without making use of any experimental input. Although physics-based models are used to predict core transport, core transport is shown to be predicted with less accuracy than the pedestal energy. Therefore, we validate the most established quasi-linear models TGLF and QuaLiKiZ in different regimes and experimental conditions, assessing their strengths and limits. The quasi-linear models are shown to predict transport accurately in a variety of experimental conditions, including dominant ion and electron heating, respectively. The well-known shortcoming near the pedestal top is solved, while a new collision operator in the QuaLiKiZ model improves the electron temperature simulation significantly. Also the Neural Network version of QuaLiKiZ, with very fast computation time, appears to be well applicable in ion heated H-modes.

Plasma Stability in a Tokamak with Reactor Technologies Taking into Account the Pressure Pedestal

Studying stationary regimes with high plasma confinement in a tokamak with reactor technologies (TRT) [1] involves calculating the plasma stability taking into account the influence of the current density profiles and pressure gradient in the pedestal near the boundary. At the same time, the operating limits should be determined by the parameters of the pedestal, which, in particular, are set by the stability limit of the peeling–ballooning modes that trigger the peripheral disruption of edge localized modes (ELM). Using simulation of the quasi-equilibrium evolution of the plasma by the ASTRA and DINA codes, as well as a simulator of magnetohydrodynamic (MHD) modes localized at the boundary of the plasma torus based on the KINX code, stability calculations are performed for different plasma scenarios in the TRT with varying plasma density and temperature profiles, as well as the corresponding bootstrap current density in the pedestal region. At the same time, experimental scalings for the width of the pedestal are used. The obtained pressure values are below the limits for an ITER-like plasma due to the lower triangularity and higher aspect ratio of TRT plasma. For the same reason, the reversal of magnetic field shear in the pedestal occurs at a lower current density, which causes the instability of modes with low toroidal wave numbers and reduces the effect of diamagnetic stabilization.

Directional shear jamming of frictionless ellipses.

In this work we study shear reversals of dense non-Brownian suspensions composed of cohesionless elliptical particles. By numerical simulations, we show that a new fragility appears for frictionless ellipses in the flowing states, where particles can flow indefinitely in one direction at applied shear stresses but shear jam in the other direction upon shear stress reversal. This new fragility, absent in the isotropic particle case, is linked to the directional order of the elongated particles at steady shear and its reorientation at shear stress reversal, which forces the suspensions to pass through a more disordered state with an increased number of contacts in which it might get arrested.