Boundary Motion Research Articles

Crucial future observations and directions for unveiling magnetopause dynamics and their geospace impacts

The dynamics of Earth’s magnetopause, driven by several different external/internal physical processes, plays a major role in the geospace energy budget. Given magnetopause motion couples across many space plasma regions, numerous forms of observations may provide valuable information in understanding these dynamics and their impacts. In-situ multi-point spacecraft measurements measure the local plasma environment, dynamics and processes; with upcoming swarms providing the possibility of improved spatiotemporal reconstruction of dynamical phenomena, and multi-mission conjunctions advancing understanding of the “mesoscale” coupling across the geospace “system of systems.” Soft X-ray imaging of the magnetopause should enable boundary motion to be directly remote sensed for the first time. Indirect remote sensing capabilities might be enabled through the field-aligned currents associated with disturbances to the magnetopause; by harnessing data from satellite mega-constellations in low-Earth orbit, and taking advantage of upgraded auroral imaging and ionospheric radar technology. Finally, increased numbers of closely-spaced ground magnetometers in both hemispheres may help discriminate between high-latitude processes in what has previously been a “zone of confusion.” Bringing together these multiple modes of observations for studying magnetopause dynamics is crucial. These may also be aided by advanced data processing techniques, such as physics-based inversions and machine learning methods, along with comparisons to increasingly sophisticated geospace assimilative models and simulations.

Atomistic simulations of structure and motion of twin interfaces reveal the origin of twinning in NiTi shape memory alloys

Shape memory alloys (SMAs) are functional materials featuring unique shape recovery properties that make them suitable for key industrial applications. The essential process controlling this fascinating performance is microstructural twinning. Some twin systems are much more frequently observed than others, yet a fundamental mechanistic understanding of this evidence is missing, which hampers SMA design. Here, we consider the prototypical NiTi SMA to show that the emergence of twinning can be strongly affected by twin interface mobility. In this work, we adopt an integrated approach combining crystallographic theory, state-of-the-art atomistic modelling, topological model, and validation with high-resolution transmission-electron micrographs. Atomistic simulations confirm that the occurrence of twins is dictated by the driving force for twin boundary motion rather than interfacial energy. Moreover, our findings settle long-standing questions by elucidating the propagation mechanisms of twin interfaces, which the established martensite crystallography and kinetic theories could not address conclusively. The newly discovered understanding of the role of interface mobility in twin formation can be used to predict variant selection and guide the design of SMAs with improved functional performance.

Effect of thermal etching and oxidation on in situ characterisation of grain growth in carbon steel

This paper presents the results from a recent investigation into the impact of thermal etching and oxidation on grain growth across the surface and bulk of carbon steel during heat treatment. The study used in situ high temperature Scanning Electron Microscopy imaging, facilitated by a novel heat stage, to capture microstructural changes during heat treatments between 800 and 920 °C. The key observations made using this surface imaging included oxidation, the formation and development of thermal etching, and grain boundary movement. In situ data were further supported by ex situ compositional and optical microstructural data obtained by first sectioning the bulk material. Comparison between the results highlighted a significant discrepancy between the surface and bulk grain growth of the specimens during heat treatment at all temperatures. Further investigation concluded that the combination of thermal etching and oxidation lead to the retardation of grain growth on the surface of the carbon steel, but that grain growth in the bulk specimen appeared to be unaffected. The mechanism that causes the grain retardation is not dissimilar to that of Zenner pinning, where in this case oxide particles pin the newly exposed etched grain boundaries. Hence, oxidation formation within the boundaries decreases the energy of the overall system resulting in movement of the grain boundary becoming less energetically favourable. It is anticipated that these findings will be used to improve understanding of the surface effects that occur during the heat treatment of carbon steel in a vacuum environment.

Numerical Solution of the Newtonian Plane Couette Flow with Linear Dynamic Wall Slip

An efficient numerical approach based on weighted-average finite differences is used to solve the Newtonian plane Couette flow with wall slip, obeying a dynamic slip law that generalizes the Navier slip law with the inclusion of a relaxation term. Slip is exhibited only along the fixed lower plate, and the motion is triggered by the motion of the upper plate. Three different cases are considered for the motion of the moving plate, i.e., constant speed, oscillating speed, and a single-period sinusoidal speed. The velocity and the volumetric flow rate are calculated in all cases and comparisons are made with the results of other methods and available results in the literature. The numerical outcomes confirm the damping with time and the lagging effects arising from the Navier and dynamic wall slip conditions and demonstrate the hysteretic behavior of the slip velocity in following the harmonic boundary motion.

An internal variable model of macroscopic twin boundary dynamics

Depending on whether the experiments are quasi-static or fast dynamics, the measured twin boundary velocity values range from zero to the material’s sound speed. The twin boundary velocity is not yet predicted theoretically in the continuum mechanics framework. The extension of continual description is provided in the paper by means of internal variables. It is shown that a diffusional slow motion of twin boundaries can be represented using a single internal variable. The dual internal variable technique is employed for the description of the fast dynamics of twin boundaries.

Hexagonal vortices enable faster colloidal crystal grain coarsening.

We find that localized rotations of hexagonal clusters of particles occur during rapid dissolution of grain boundary loops in two-dimensional colloidal crystals. These particle vortices, or rotating "granules," are distinct from established models for grain boundary diffusion, which predict that a crystal grain enclosed within another crystal will dissolve at a constant rate. Our measurements of colloidal crystal experiments and Brownian dynamics simulations reveal grain boundary motion that is described by two distinct processes: slow dissolution due to the diffusion of individual particles, and rapid dissolution due to collective granule rotation. In the latter process, hexagonal clusters of particles rotate together in granules whose shape and position are determined by the underlying moiré pattern. Furthermore, these vortices guide cooperative strings of particles that move along the edges of the hexagonal granules. Including this vortex mechanism may improve models for grain coarsening in polycrystalline materials, ultimately offering improved predictions for the time evolution of material properties.

Thermal runaway front propagation characteristics, modeling and judging criteria for multi-jelly roll prismatic lithium-ion battery applications

Large-format prismatic Li-ion batteries (LIBs) are prominent energy storage devices in electric transportation applications. However, large-format LIB induces severe thermal runaway (TR) disasters. Battery failure commonly initiates from a local point of one jelly roll and then propagates to the whole cell, called thermal runaway front (TRF) propagation. This study investigates the TRF propagation mechanism of multi-jelly roll-based LIBs through experiments, modeling, and theoretical analysis for thermal runaway propagation (TRP) mitigation. Experiments prove that battery venting changes along the jelly roll-safety valve directions during the TRF boundary movement. Besides, TRF propagation speed is found to be accelerated inside each cell (from 3.6 to 10.6 mm/s) during TRP, driven by a significant temperature gradient, chemical reactions, and gas flow along the TRP direction. The in-cell TRF acceleration behavior is more noticeable for batteries with more jelly rolls. The TRF speed-jelly roll index equations are proposed to reveal the propagation acceleration principle mathematically. Furthermore, a thermal-physical model is developed to precisely simulate in-cell TRF propagation behavior, which is validated by experimental data. Moreover, the TRF boundary temperature equation and “No TRP” judging criteria are proposed through theoretical analysis. This study proposes promising strategies for potential TRP suppression, contributing to future safe battery system design.

Slip Rate for the Rose Canyon Fault through San Diego, California, Based on Analysis of GPS Data: Evidence for a Potential Rose Canyon–San Miguel-Vallecitos Fault Connection?

ABSTRACT The Rose Canyon fault is the southern extension of the larger Newport–Inglewood–Rose Canyon fault system, which represents a major structural boundary in the Inner Continental Borderland (ICB) offshore of southern California. Ten to fifteen percent of total plate boundary motion in southern California is thought to be accommodated by the faults of the ICB, but the exact distribution of slip is uncertain. With an onshore segment, the Rose Canyon fault offers an opportunity to measure the slip rate using traditional geodetic methods. In this study, we use Global Positioning System (GPS) surface velocities from a combined campaign and continuous GPS network to constrain elastic models of the Rose Canyon fault. We then compare the observed surface velocities with proposed conceptual models of regional fault connections that facilitate the transfer of slip into the Rose Canyon fault to assess how well the observations are explained by the models. The results of elastic half-space models suggest that the Rose Canyon fault may be slipping toward the higher end of geologic estimates, with the preferred model indicating a slip rate of 2.4 ± 0.5 mm/yr. Although limited in terms of near-fault benchmarks, we find an improved model fit using an asymmetrical elastic half-space model and a higher slip rate, suggesting a potential rheological contrast across the Rose Canyon fault, similar to observations from the northern Newport–Inglewood fault segments. Observed GPS surface velocities, background seismicity, and gravity anomalies south of San Diego Bay point toward a more easterly trace for the Rose Canyon fault, suggesting a possible connection with the San Miguel–Vallecitos fault system. Such a connection could increase the potential rupture lengths of future earthquakes and have important consequences for regional seismic hazards.

Single grain pIRIR dating of glacigenic deposits in the Yuzhu Peak area of Kunlun Mountains of Tibetan Plateau revealed the glaciations during Holocene period

The variations of glaciers in the Kunlun Mountains of the northern Tibetan Plateau are influenced by the complex interaction of the East Asia summer monsoon (EASM), Indian summer monsoon (ISM) and Westerlies, as well as human activity during the Holocene period. Consequently there is ongoing debates regarding the evolution of glaciers and the factors driving their changes. The reconstruction of glacial evolutions in these regions has been hindered by insufficient chronological data for moraines and other glacial landforms. In this study, glacial sediment samples were collected from five moraine sequences located on the southern and northern slopes of the Yuzhu Peak in the Kunlun Mountains. These poorly bleached moraine samples were dated using the single-grain quartz optically stimulated luminescence (OSL) and K-feldspar post-infrared infrared stimulated luminescence (pIRIR) dating methods. The luminescence characteristics analysis of quartz grains shows that single grain quartz OSL dating cannot be used to date Holocene moraine samples due to the low brightness of quartz OSL signals. Various tests were conducted to assess the reliability of K-feldspar pIR50IR170 dating, including anomalous fading tests, dose recovery, and residual dose tests. The K-feldspar pIR50IR170 ages, determined using the Minimum Age Model (MAM), indicate that during the early Holocene, glaciations have expanded by ∼800 m in length at ∼ 8 ka, and during the end of the Neoglacial period, they extended by ∼200 m in length at ∼ 1 ka. The strengthened ISM precipitation and northward movement of ISM boundary likely contributed to the glacial expansion in the early Holocene. During the end of the Neoglacial period, the increase in westerlies precipitation and cold events may have played a role in the advancement of glaciers.

Microstructural Evolution and Mechanical Property of Cu–Cr–Zr–ZrB2 Composites Subjected to Cryorolling and Aging Treatment

A new strategy has been developed to combine the nanotwins and dual‐scale particles into copper matrix composites and the comprehensive properties of Cu–1Cr–0.3Zr–1ZrB2 exhibit excellently with the addition of intermediate aging and cryorolling. The effects of different deformation processes on the evolution of microstructure, room temperature, and elevated‐temperature mechanical properties are investigated. The result demonstrates that the number of nanoscale Cr precipitates increases obviously after intermediate aging. The nanosized Cr precipitates impede the movement of grain boundaries and dislocations, resulting in the refinement of deformation bands and the dislocation tangle. The combined effect of intermediate aging and cryorolling also improves the formation of nanotwins, which plays an important role in enhancing the tensile strength of composites. The tensile strength, elongation, and conductivities of the composites subjected to two‐step cryorolling reach 653 MPa, 8.02%, and 79.51% IACS, respectively, showing an optimum comprehensive property. In addition, the stable nanotwins and the uniform distribution of dual‐scale particles inhibit the recrystallization process at elevated temperatures, contributing to improving the mechanical behavior at elevated temperatures and heat‐resistant performance of composites.

Hot deformation behavior and dynamic recrystallization of 2195 Al–Li alloy with various pre-precipitation microstructures

In this work, 2195 Al–Li alloys with various precipitation microstructures were obtained by homogenization treatment followed by air-cooling (AC), discontinuous cooling (DC), and furnace-cooling (FC), and then tested by hot compression at different temperatures. The results show that the flow stresses of all specimens decrease with temperature and the peak stresses of AC, DC and FC specimens decrease in order at the same temperature. For FC samples, coarse pre-precipitates diminish the deformation resistance due to the reduction of solid solution strengthening and precipitation strengthening. Dynamic softening at low temperatures is significantly greater than that at high temperatures, except for the anomalous softening of the FC specimen at 520 °C due to stress release by cracks. At 370–420 ​°C, the dynamic softening of the AC specimen is more significant than the other samples, resulting from dynamic precipitation and precipitate coarsening. Furthermore, there is considerable dynamic recrystallization (DRX) in FC samples and not in AC and DC samples, although their precipitates coarsen to similar levels at low temperatures. This suggests that DRX is associated with the particle-stimulated nucleation mechanism by regularly arranged precipitates. The banded or regularly arranged precipitates divide the Al matrix into multiple confined units, hindering dislocations and (sub)grain boundary movement, and thus promoting the development of sub-grains and DRX.

Global Solutions to an Initial-Boundary Value Problem of a Phase-Field Model for Motion of Grain Boundaries

Global Solutions to an Initial-Boundary Value Problem of a Phase-Field Model for Motion of Grain Boundaries

Reorientation induced plasticity in full αʺ martensite Ti-9V-1Fe-4Al alloy

The microstructure and deformation mechanism of a full orthorhombic αʺ martensite Ti-9V-1Fe-4Al (wt.%) alloy were investigated by XRD, TEM, EBSD analyses and tensile tests. The results show that the quenched alloy has a twinned-martensite microstructure and {111}αʺ type I internal twins are formed as the lattice invariant shear for martensite transformation. The alloy plastically deforms by a complex reorientation of αʺ martensite variants via the movement of the inter-variant boundaries of <211>α′′ type Ⅱ twin, and deformation twinning of {111}α′′ type I internal twin and of newly generated {011}αʺ compound twin in primary twinned martensites. {130}α′′<3¯ 10>α′′ and {110}α′′<1 1‾ 0>α′′ plastic twins were not observed in the alloy. Such a kind of deformation induced martensite reorientation results in a good combination of strength and plasticity with yielding strength of 480 MPa, tensile strength of 1030 MPa and elongation of 23% in the alloy. The calculated results further show that the shears of {111}α′′ type I, <211>α′′ type II and {011}α′′ compound twins and the shuffle of {111}α′′ type I twin increase, while the shears of {130}α′′<3‾ 10>α′′ and {110}α′′<1 1‾ 0>α′′ twins and the shuffle of {130}α′′<3‾ 10>α′′ twin decrease with an increase of the lattice parameter ratio bα′′/aα′′. The shears of these activated twinning systems are larger than those of {130}α′′<3‾ 10>α′′ and {110}α′′<1 1‾ 0>α′′ twins, and the shuffle of {111}α′′ type I twin is also bigger than that of {130}α′′<3‾ 10>α′′ twin in the present alloy, which implies that the operative twining modes cannot be derived simply in terms of the shear and shuffle magnitude in full αʺ martensite Ti based alloys.

Significant improvement in tensile shear properties of friction stir lap welded nano TiB2/2024 Al composite joints via a novel tool pin geometry design

A novel designed tool pin with two shoulders and pins (stepped pin, S-pin) was performed to fabricate the friction stir lap welded nano-TiB2/2024 Al composite joints for the interface migration optimization and tensile shear strength improvement purposes. Compared with the conventional tapered pin (T-pin) joints, broken and dispersedly distributed hook, significantly restrained cold lap were observed in the S-pin joints. Submicron or hundreds of nanometers grains were detected in the stir zone (SZ), which should be attributed to the existence of nano-TiB2 hindering the movement of grain boundaries and limiting the growth of recrystallized grains. A wedge-shaped microhardness distributions of the S-pin joints were found, which would be better for the joint bearing capacity. Tensile shear loads of the S-pin joints were much higher than those of the T-pin joints. The optimal average tensile shear strength, 7.3 kN or 484 N/mm, were obtained when the S-pin was performed, dominantly fracturing in the heat affected zone (HAZ) rather than the SZ.

Effect of the atomic structure of complexions on the active disconnection mode during shear-coupled grain boundary motion

The migration of grain boundaries leads to grain growth in polycrystals and is one mechanism of grain-boundary-mediated plasticity, especially in nanocrystalline metals. This migration is due to the movement of dislocationlike defects, called disconnections, which couple to externally applied shear stresses. While this has been studied in detail in recent years, the active disconnection mode was typically associated with specific macroscopic grain boundary parameters. We know, however, that varying microscopic degrees of freedom can lead to different atomic structures without changing the macroscopic parameters. These structures can transition into each other and are called complexions. Here, we investigate [111¯] symmetric tilt boundaries in fcc metals, where two complexions—dubbed domino and pearl—were observed before. We compare these two complexions for two different misorientations: In Σ19b[111¯](178) boundaries, both complexions exhibit the same disconnection mode. The critical stress for nucleation and propagation of disconnections is nevertheless different for domino and pearl. At low temperatures, the Peierls-like barrier for disconnection propagation dominates, while at higher temperatures the nucleation is the limiting factor. For Σ7[111¯](145) boundaries, we observed a larger difference. The domino and pearl complexions migrate in different directions under the same boundary conditions. While both migration directions are possible crystallographically, an analysis of the complexions' structural motifs and the disconnection core structures reveals that the choice of disconnection mode and therefore migration direction is directly due to the atomic structure of the grain boundary. Published by the American Physical Society 2024

Generation of quasi-traveling waves in a finite rectangular membrane with two internal viscoelastic line supports

In this work we study the forced vibration of a finite rectangular membrane driven by arbitrarily distributed boundary motion on two adjacent edges and internally coupled with multiple viscoelastic line supports, as an extension of the analysis of coexisting vibrations and waves in one-dimensional elastic strings and ducts. Using the static solution for the membrane displacement in the absence of interior supports, the response of the nonclassically damped system is obtained through a normal-mode expansion. A traveling-wave index based on complex orthogonal decomposition is utilized to identify and optimize the traveling waves in the rectangular membrane. A vibration localization condition in a semi-infinite membrane is analytically derived, from which the complex boundary excitations and constraints in a finite membrane are specified to effectively realize pure traveling waves and confine the vibration to a restricted area. Then the membrane is edge-driven by a simpler time-periodic, spatially sinusoidal excitation for practical realization, with the line-support parameters optimized using the traveling-wave index function and a derivative-free optimization routine with lower-bound constraints. Analytical results show that quasi-traveling waves are produced for ranges of line-support parameters (location, stiffness and damping) following optimization using the traveling-wave index. The developed wave patterns are examined with a power-flow analysis and numerically verified through finite element analysis. Wave localization is demonstrated to be valid in a finite membrane with specific boundary conditions and multiple viscoelastic line supports. The proposed method shows the predictive ability of the orthogonally stiffened membrane configuration as the basic unit cell for the design of periodic structures with directional wave propagation as well as vibration localization dynamics.

The influence of annealing temperature on the microstructure and mechanical properties of Fe-0.52 C-11Mn-5.14Al-1Cr lightweight steel

Steel used in the automotive industry must strike a delicate balance between strength and ductility to maintain the structural integrity of vehicles and achieve intricate designs. Traditional methods of reducing weight by using high-strength low-carbon steels have limitations. As a result, a new dual-phase lightweight steel with an austenite-ferrite structure and the composition Fe-0.52 C-11Mn-5.14Al-1Cr was developed. The relationship between the microstructure and mechanical properties of this lightweight steel, which underwent various annealing processes (700°C-1000°C) after cold rolling, was examined using specialized equipment like a universal testing machine, electron microscopy, and X-ray diffractometer. The findings reveal that the cold-rolled test steel (CR) exhibits high tensile strength (1500 MPa) but low elongation at break (3.9 %). The performance of the experimental steel post-annealing treatment has shown significant improvement, with the average grain size increasing with higher annealing temperatures. The γ phase generally shows an increasing trend, with finer grains post-annealing, and the distribution of the α phase displays a consistent pattern along γ boundaries. Additionally, a substantial number of annealing twins appear in the matrix. These twin boundaries absorb some dislocations, and slip leads to the movement of twin boundaries, effectively reducing stress concentration from deformation and enhancing the ability of twin boundaries to accommodate plastic strain, creating twin dislocation interaction. The interplay among dislocations, stacking faults, and twins regulates the balance between strength and plasticity. Following treatment at 850°C × 1 min + 500°C × 3 min, the steel displays excellent mechanical properties, including ultimate tensile strength (836 MPa), elongation (53 %), and strength-ductility product (43,723 MPa·%). This study identifies a specific heat treatment parameter that achieves a harmonious equilibrium between outstanding strength and plasticity (strength-ductility product) within the designed composition.

Study of a mechano-electrochemical model: a numerical and experimental approach

The mechanochemical effects of elasticity and plasticity are introduced into a peridynamic (PD) corrosion model. A PD equation that couples the mechanics and kinetics of electrochemistry is proposed for the first time. This clarifies the influence of the mechanical load in governing the occurrence of diffusion during corrosion. The phase changes experienced by a material are used to characterize the movement of the corrosion boundary, and the concentration of material points is used to characterize the degree and extent of damage caused to the chosen metal. Immersion tests and in situ electrochemical tests are carried out, and the results are used to explore the effects of stress and/or load on the kinetics of environment-induced damage to an aluminum alloy. The model predictions are in good agreement with the experimental observations. The results of this study demonstrate that a coupled mechano-electrochemical PD corrosion model can capture corrosion-induced damage and can be used to study damage propagation upon exposure to an aggressive environment.

Volume-of-fluid-based method for three-dimensional shape prediction during the construction of horizontal salt caverns energy storage

Construction prediction is the key for the shape control of energy storage salt caverns, which benefits with the storage capacity and long-term operational safety. However, the conventional grid discretization methods using elastic grid could not accurately tracking the three-dimensional boundary movements of salt cavern. This paper introduced a novel construction prediction model of salt cavern using a Volume-of-fluid based method. The tracking of the salt caverns’ dissolving boundary is successfully reconstructed and tracked by the fluid volume fractions (0-1) in structural grids. The model was validated by indoor experiment and field data. In the simulation of indoor experiment, the lateral expansion, which was difficult to reproduce in previous models, is successfully simulated. The volume of the simulation chamber is 392.8 ml with an error of 1.9 %. During the simulation of Volgograd horizontal cavern construction, the simulated cavern shape is close to the sonar detection, with an average error in radius about 3.6 %. And the brine-discharge concentration is consistent with the site monitoring, with an average error about 4.5 %. These results validate the capability of the proposed method in three-dimensional dynamic boundary tracking and shape prediction of salt cavern.

Modification and strengthening mechanism of high strength-toughness as-cast Al–11Si–3Cu alloy modified with minor Sr and Er content

The strength of Al–11Si–3Cu requires improvement to meet the growing demands of manufacturing and expand its application in the automotive market. A new high strength-toughness as-cast Al–11Si–3Cu alloy with the ultimate tensile strength and elongation up to 294 MPa and 3.5 % was developed by using minor Sr and Er modifiers. The TEM and the first principles calculations showed that Sr and Er atoms adsorbed on the eutectic Si surface and prompted the formation of twins that branched in 70.5° and 39° directions, and the synergistic effects of Sr and Er atoms significantly reduced the size of eutectic Si to ∼500 nm. Moreover, the ∼10 nm Al3Er and ∼200 nm Al8Cu4Er particles formed in the alloy, which have positive effects on enhancing the mechanical properties of the alloy. The dislocation lines were stretched when passing through the Al3Er particles and eventually formed dislocation rings, while the motion of the grain boundary was hindered by the Al8Cu4Er particle. Additionally, the modification mechanism of Sr and Er modifiers on the eutectic Si and the strengthening mechanism of the modified alloy were discussed.