Anisotropic Strain Research Articles

A hypoplastic model for pre- and post-liquefaction analysis of sands

This article proposes an extended constitutive model for liquefaction analysis of sands. The proposed model is formulated based on the hypoplastic model for granular soils by von Wolffersdorf (1996), enhanced with Intergranular Strain Anisotropy by Fuentes et al. (2019), which is usually referred to as ISA-hypoplasticity. The proposed extended model includes some modifications that are indispensable for the correct prediction of liquefaction-related analysis: (i) a new Lode-angle-dependent function for post-liquefaction shear strain accumulation, (ii) a modification for fabric change effects, (iii) the theory of the so-called semifluidized state. The first modification allows the model to predict shear strain accumulation in extension and compression during cyclic mobility. The second and third modifications, were initially developed by Liao et al. (2022) for hypoplasticity with conventional intergranular strain based on the pioneer work by Barrero et al. (2020) for Sanisand, and enable the model to reproduce fabric change effects upon loading reversal, and stiffness and dilatancy degradation at low effective stress levels, respectively. With the consideration of the new Lode-angle function, the proposed model realistically predict the increasing shear strain accumulation in both extension and compression without adopting a circular critical state surface, as adopted in Liao et al. (2022). The proposed model was carefully calibrated and validated based on a series of monotonic and cyclic triaxial tests on Zbraslav and Karlsruhe fine sands, considering various testing conditions. The comparison between experimental measurements and numerical predictions of undrained cyclic tests suggests that the proposed model accurately describes the pre- and post-liquefaction stages, as well as the stress attractors.

Anisotropic Elastomer Ionomer Composite-Based Strain Sensors: Achieving High Sensitivity and Wide Detection for Human Motion Detection and Wireless Transmission.

Anisotropic strain sensors capable of multidirectional sensing are crucial for advanced sensor applications in human motion detection. However, current anisotropic sensors encounter challenges in achieving a balance among high sensitivity, substantial stretchability, and a wide linear detection range. To address these challenges, a facile freeze-casting strategy was employed to construct oriented filler networks composed of carbon nanotubes and conductive carbon black within a brominated butyl rubber ionomer (iBIIR) matrix. The resulting anisotropic sensor based on the iBIIR composites exhibited distinct gauge factors (GF) in the parallel and vertical directions (GF∥ = 4.91, while GF⊥ = 2.24) and a broad linear detection range over a strain range of 190%. This feature enables the sensor to detect various human activities, including uniaxial pulse, finder bending, elbow bending, and cervical spine movements. Moreover, the ion-cross-linking network within the iBIIR, coupled with strong π-cation interactions between the fillers and iBIIR macromolecules, imparted high strength (12.3 MPa, nearly twice that of pure iBIIR) and an ultrahigh elongation at break (>1800%) to the composites. Furthermore, the sensor exhibited exceptional antibacterial effectiveness, surpassing 99% against both Escherichia coli and Staphylococcus aureus. Notably, the sensor was capable of wireless sensing. It is anticipated that anisotropic sensors will have extensive application prospects in flexible wearable devices.

Non-singular straight dislocations in anisotropic crystals

A non-singular dislocation theory of straight dislocations in anisotropic crystals is derived using simplified anisotropic incompatible first strain gradient elasticity theory. Based on the non-singular theory of dislocations for anisotropic crystals, all dislocation key-formulas of straight dislocations are derived in generalized plane strain, for the first time. In this model, the singularity of the dislocation fields at the dislocation core is regularized owing to the nonlocal nature of strain gradient elasticity. The non-singular dislocation fields of straight dislocations are obtained in terms of two-dimensional anisotropic Green functions of simplified anisotropic strain gradient elasticity. All necessary Green functions, including the two-dimensional Green tensor of the twofold anisotropic Helmholtz-Navier operator and the two-dimensional F\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\varvec{F}$$\\end{document}-tensor of generalized plane strain, are derived as sum of the classical part and a gradient part in terms of Meijer G-functions. Among others, we calculate the regularization of the Barnett solution for the elastic distortion of straight dislocations in an anisotropic crystal. In the framework of simplified anisotropic first strain gradient elasticity, the necessary material parameters are computed for cubic materials including aluminum (Al), copper (Cu), iron (Fe) and tungsten (W) using a second nearest-neighbour modified embedded-atom-method interatomic potential. The elastic distortion and stress fields of screw and edge dislocations of 12⟨111⟩\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\frac{1}{2} \\langle 111\\rangle$$\\end{document} Burgers vector in bcc iron and bcc tungsten and screw and edge dislocations of 12⟨110⟩\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\frac{1}{2} \\langle 110\\rangle$$\\end{document} Burgers vector in fcc copper and fcc aluminum have been computed and presented in contour plots.

A nonlinear finite viscoelastic formulation relative to the viscous intermediate configuration applied to plants

AbstractIn the contribution at hand, a new formulation for finite strain viscosity relative to the viscous intermediate configuration is presented. The evolution of the viscous deformations is based upon a new numerical approach, which allows for a consistent consideration of anisotropic finite strain viscoelasticity, according to the authors knowledge. A standard Maxwell model is used to describe viscous behaviour at finite deformations. Furthermore, the orthotropic Yeoh material model is extended to include a distinction between behaviour under tensile and compression loading. The proposed formulation is validated, and parameters of the model are identified by material tests on Sorghum bicolor plants. Subsequently, numerical examples are shown to demonstrate the capabilities of the model. In general, the proposed Yeoh material formulation is shown to accurately represent the inability of fibres to carry compression loading. Furthermore, the viscoelastic approach, developed relative to the viscous intermediate configuration, is demonstrated to be capable of producing plausible results. Additionally, the mechanical behaviour of Sorghum bicolor plants is simulated using the introduced formulation. The results show that the contribution at hand describes a novel methodology to simulate the viscoelastic behaviour of plant materials reliably.

Ultra-High Temperature Operated Ni-Rich Cathode Stabilized by Thermal Barrier for High-Energy Lithium-Ion Batteries.

The pursuit of high energy density batteries has expedited the fast development of Ni-rich cathodes. However, the chemo-mechanical degradation induced by local thermal accumulation and anisotropic lattice strain is posing great obstacles for its wide applications. Herein, a highly-antioxidative BaZrO3 thermal barrier engineered LiNi0.8Co0.1Mn0.1O2 cathode through an in situ construction strategy is first reported to circumvent the above issues. It is found that the Zr ions are incorporated to Ni-rich material lattice and influence on the topotactic lithiation as well as enhance the oxygen electronegativity through the rigid Zr─O bonds, which effectively alleviates the lattice strain propagation and decreases the excessive oxidization of lattice oxygen for charge compensation. More importantly, the BaZrO3 thermal barrier with an ultra-low thermal conductivity validly impedes the fast heat exchange between electrode and electrolyte to mitigate the severe surface side reactions. This helps an ultra-high mass loading Li-ion pouch cell deliver a specific energy density of 690Wh kg-1 at active material level and an excellent capacity retention of 92.5% after 1400 cycles under 1 C at 25°C. Tested at a high temperature of 55°C, the pouch type full-cell also exhibits 88.7% in capacity retention after 1200 cycles.

Molten-Salt-Assisted Strategy Enables High-Rate Micron-Sized Single-Crystal Li-Rich, Mn-Based Layered Oxide Cathode Materials.

Li-rich Mn-based layered oxides (LMLOs) are expected to be the most promising high-capacity cathodes for the next generation of lithium-ion batteries (LIBs). However, the poor cycling stability and kinetics performance of polycrystalline LMLOs restrict their practical applications due to the anisotropic lattice stress and crack propagation during cycling. Herein, B-doped micron-sized single-crystal Co-free LMLOs were obtained by molten-salt (LiNO3 and H3BO3)-assisted sintering. The results reveal that the low-melting-point molten salt can serve as liquid-phase media to improve the efficiency of atomic mass transfer and crystal nucleation and growth. The modified single-crystal LMLO cathodes can resist the accumulation of anisotropic stress and strain during the cycling and reduce interface side reactions, thus achieving excellent high-voltage stability and kinetics performance. The reversible specific capacity of the single crystals is 210.8 mAh g-1 at 1C with a voltage decay rate of 1.95 mV/cycle and up to 161.1 mAh g-1 at 10C with a capacity retention of 81.06% after 200 cycles.

Comparative analysis of two intergranular strain-based hypoplastic models through elemental and centrifuge testing

While hypoplastic models have demonstrated accurate predictions of sand behavior under monotonic loading, their accuracy diminishes when applied to cyclic loading conditions. To address this limitation, the intergranular strain approach is used as an extension to the model. The current investigation focuses on the analysis of two variants: the original Intergranular Strain (IS) approach proposed by Niemunis and Herle (1997) and the Intergranular Strain Anisotropy (ISA) by Fuentes et al. (2019). Although both models have the same objective, they present distinct mathematical structures and therefore different repercussions on the simulations. In this study, sand Hypoplasticity is enhanced with IS and ISA, and employed to simulate a series of experimental tests conducted on Fontainebleau sand. These tests encompass isotropic compression, drained monotonic triaxial, and undrained cyclic triaxial tests, while considering different initial densities and test characteristics. Furthermore, the calibrated models were applied to simulate a series of centrifuge tests, involving a pile embedded in the same sand, which is subjected to various episodes of monotonic and cyclic lateral loading. A comparison and discussion of the similarities and differences in elemental and finite element predictions, arising from the two intergranular strain formulations is presented.

Experimental and numerical investigation of the yield point phenomenon and strain partitioning behavior in a dual-phase steel with lamellar structure

Severe rolling techniques show potential for enhancing the strength and ductility of metallic materials, but the resulting microstructural anisotropy affects the mechanical behavior. The study investigated the anisotropic yield point phenomenon (YPP) and strain partitioning behavior in a dual-phase steel with ultrafine lamellar structure, fabricated through severe cold- and warm-rolling procedures. Experimental results show that tensile specimens aligned parallel to the rolling direction exhibit YPP and higher ductility, while those oriented normal to the rolling direction show continuous yielding behavior and decreased ductility. Using Digital Image Correlation techniques, we studied the evolution of the strain distribution on the surface of the gauge segment, revealing that the strain within the Lüders band was almost constant during the Lüders band propagation. Strain-induced martensitic transformation (SIMT) was observed within the Lüders band and the volume fraction of martensite keeps almost constant during the Lüders band propagation. Numerically, we integrated the mechanisms of SIMT and YPP into a dislocation density-based J2 plasticity constitutive framework. Simulated tensile tests indicate a smaller Lüders strain resulted from the initial higher strain hardening rate. Additionally, SIMT suppresses local instability and therefore promotes the stable propagation of Lüders bands. Simulations verify that the lamellar orientation and SIMT significantly affect the strain hardening rate and void growth. Our findings provided a new perspective on the intrinsic mechanism of the anisotropic YPP and ductility in lamellar dual-phase steels.

Anisotropic Strain-Tailoring Nonlinear Optical Response in van der Waals NbOI2.

Two-dimensional (2D) NbOI2 demonstrates significant second-harmonic generation (SHG) with a high conversion efficiency. To unlock its full potential in practical applications, it is desirable to modulate the SHG behavior while utilizing the intrinsic lattice anisotropy. Here, we demonstrate direction-specific modulation of the SHG response in NbOI2 by applying anisotropic strain with respect to the intrinsic lattice orientations, where more than 2-fold enhancement in the SHG intensity is achieved under strain along the polar axis. The strain-driven SHG evolution is attributed to the strengthened built-in piezoelectric field (polar axis) and the enlarged Peierls distortions (nonpolar axis). Moreover, we provide quantifications of the correlation between strain and SHG intensity in terms of the susceptibility tensor. Our results demonstrate the effective coupling of orientation-specific strain to the anisotropic SHG response through the intrinsic polar order in 2D nonlinear optical crystals, opening a new paradigm toward the development of functional devices.

Systematic DFT Modeling van der Waals Heterostructures from a Complete Configurational Basis Applied to γ-PC/WS2.

Periodic boundary conditions in density functional theory (DFT)-based modeling of bilayer van der Waals heterostructures introduce an artificial lock to a metastable configuration. Depending on the initial supercell, geometric optimization may reach local energy minima at a fixed twist-angle in a restricted strain-space. In this work, an algorithm was introduced for generating a complete scope of ways to combine two monolayer unit cells into a common supercell. In its application to γ-PC/WS2, 18,123 bilayer supercells were derived, for which the constituting monolayers possessed isotropic strains, anisotropic strains, or intralayer shear strains. Based on analysis, 45 isotropically strained configurations were carefully chosen for optimization by DFT. Geometric and energetic features and band structures were revealed and compared, following the variations at different strains and twist-angles. As such, this case study brought to resolution the impacts of supercell construction on DFT's outcomes and the merits of in-depth screening of the different options. Repetitions and extensions to the demonstrated approach may be applied to characterize van der Waals heterostructures and derivatives in the future.

Bioinspired Integrated Multidimensional Sensor for Adaptive Grasping by Robotic Hands and Physical Movement Guidance

AbstractThe construction of piezoresistive sensors capable of distinguishing multiple mechanical stimuli is important for sensing higher level applications. However, the mutual interference between sensing signals is a technical bottleneck for sensors to recognize multiple mechanical stimuli. Inspired by the structure of human skin and muscle, a multidimensional sensor is designed by integrating three sub‐sensors. Each sub‐sensor is only sensitive to stimulus components in one of the three orthogonal axes, whereas it remains insensitive to others because of its anisotropic sensing properties. Specifically, an omnidirectional gradient wrinkled polyurethane film with MXene‐embedded ZnO nanowire arrays serves as a strain‐insensitive pressure sub‐sensor, while two aligned segmental polyimide/polyurethane films through orthogonal stacking act as two pressure‐insensitive anisotropic strain sub‐sensors. A unique characteristic of multidimensional sensor is its ability to distinguish and measure the type, magnitude, and direction of strain, pressure, and shear. Moreover, multidimensional sensor exhibits maximal gauge factor of 863.7 for strain and highest sensitivity of 187.71 kPa−1 for pressure. Importantly, multidimensional sensor exhibits an unprecedented ability to quantitatively evaluate shear using a library of electrical responses. The adaptive grasping of robotic hands and free‐throw training of players have been demonstrated to initiate the development of robotic object manipulation and physical movement guidance.

Decomposition of the anisotropic strain in 3D-structure GaN layers using Raman spectroscopy

Strain engineering for gallium nitride has been studied by many researchers to improve the performance of various devices (i.e., light-emitting diodes, laser diodes, power devices, high electron mobility transistors, and so on). Further miniaturization of gallium nitride devices will clearly continue in the future, and therefore an accurate understanding of the strain state in the devices is essential. However, a measurement technique for axially resolved evaluation of the strain in microareas has not yet been established. In this study, we revealed that the anisotropic strain state induced in c-plane growth gallium nitride is linked to the split state of Raman peaks, which were measured with z(xx)z¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$z(xx)\\overline{z }$$\\end{document} and z(yx)z¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$z(yx)\\overline{z }$$\\end{document} polarized configurations. The anisotropic strain state in c-plane gallium nitride was induced in the 3D-structure by epitaxial lateral overgrowth, which enabled successful performance of our work. This result allowed us to axially decompose the strain in c-plane gallium nitride through Raman spectroscopy and establish a measurement technique for axially resolving the strain. This measurement technique is feasible using a conventional Raman spectrometer. Furthermore, the method was indicated to be applicable to all wurtzite-type crystals, including gallium nitride, silicon carbide, and aluminum nitride. Our work provides a new perspective for understanding the complex strain state in microareas for wurtzite materials. Comprehending the strain state, which strongly affects device performance, will help promote the research and development of III-V semiconductor devices.

Anisotropic dynamic permeability model for porous media

Based on the tortuous capillary network model, the relationship between anisotropic permeability and rock normal strain, namely the anisotropic dynamic permeability model (ADPM), was derived and established. The model was verified using pore-scale flow simulation. The uniaxial strain process was calculated and the main factors affecting permeability changes in different directions in the deformation process were analyzed. In the process of uniaxial strain during the exploitation of layered oil and gas reservoirs, the effect of effective surface porosity on the permeability in all directions is consistent. With the decrease of effective surface porosity, the sensitivity of permeability to strain increases. The sensitivity of the permeability perpendicular to the direction of compression to the strain decreases with the increase of the tortuosity, while the sensitivity of the permeability in the direction of compression to the strain increases with the increase of the tortuosity. For layered reservoirs with the same initial tortuosity in all directions, the tortuosity plays a decisive role in the relative relationship between the variations of permeability in all directions during pressure drop. When the tortuosity is less than 1.6, the decrease rate of horizontal permeability is higher than that of vertical permeability, while the opposite is true when the tortuosity is greater than 1.6. This phenomenon cannot be represented by traditional dynamic permeability model. After the verification by experimental data of pore-scale simulation, the new model has high fitting accuracy and can effectively characterize the effects of deformation in different directions on the permeability in all directions.

Strain-Tunable Hyperbolic Exciton Polaritons in Monolayer Black Arsenic with Two Exciton Resonances.

Hyperbolic polaritons have been attracting increasing interest for applications in optoelectronics, biosensing, and super-resolution imaging. Here, we report the in-plane hyperbolic exciton polaritons in monolayer black-arsenic (B-As), where hyperbolicity arises strikingly from two exciton resonant peaks. Remarkably, the presence of two resonances at different momenta makes overall hyperbolicity highly tunable by strain, as the two exciton peaks can be merged into the same frequency to double the strength of hyperbolicity as well as light absorption under a 1.5% biaxial strain. Moreover, the frequency of the merged hyperbolicity can be further tuned from 1.35 to 0.8 eV by an anisotropic biaxial strain. Furthermore, electromagnetic numerical simulation reveals a strain-induced hyperbolicity, as manifested in a topological transition of iso-frequency contour of exciton polaritons. The good tunability, large exciton binding energy, and strong light absorption exhibited in the hyperbolic monolayer B-As make it highly suitable for nanophotonics applications under ambient conditions.

The experimental and numerical analysis of elastic rock mechanical properties in tight conglomerate rock samples: a case study in Junggar Basin

Tight conglomerate rocks consist of gravels and rock matrices. The existence of these stiff gravels leads to heterogeneity in conglomerates and makes it difficult to characterize rock mechanical properties, which then affects drilling and hydraulic fracturing operations in tight conglomerate hydrocarbon-bearing reservoirs. This case study introduces a series of experimental and numerical analyses for the better understanding of rock deformation and elastic wave propagation patterns in a tight conglomerate reservoir in Junggar Basin, China. Tri-axial compression tests, acoustic test, and finite element modeling of rock deformation and elastic wave propagation in conglomerate rocks are presented. Experimentally tested samples exhibit good brittleness and shearing failure patterns, while well correlated static-dynamic elastic moduli and P-S wave velocities are captured. Numerical results show that the existence of stiff gravels leads to strong direction-dependent stress and strain anisotropies. Stress concentrations are also induced by gravels radially and axially. In the elastic wave domain, stiff gravels facilitate the propagation of elastic waves. The gravel close to the wave source also induces stronger compressive/tensile states in the wave domain, indicating that the existence of gravels in conglomerates can alter waveforms. This integrated approach improves the quantitative understanding of stress, strain, and elastic wave responses in heterogeneous tight conglomerates. This case study also serves as a reference for the brittleness evaluation and geomechanical evaluation in the study area. The contribution of this work is primarily about the integrated experimental study, solid deformation modeling, and elastic wave modeling of tight conglomerate rocks.

Large elasto-electric response of the charge-ordered perovskite SmBaMn2O6 under an anisotropic strain

The interplay among various order parameters in quantum materials frequently results in exotic ground states and may facilitate revolutionary functional control. In the A-site-ordered manganite double perovskite SmBaMn2O6, it was demonstrated that an anisotropic strain of less than 0.1% can modulate electrical transport by over 6% near the Neel temperature. It is hypothesized that this phenomenon is due to the high sensitivity of spin fluctuation near the antiferromagnetic ordering to lattice distortion, resulting in significant changes in transport properties. This study offers a compelling approach for investigating the interaction between the electric properties of SmBaMn2O6 and in situ anisotropic strain.

Controlled Preparation of Highly Stretchable, Crack-Free Wrinkled Surfaces with Tunable Wetting and Optical Properties.

Constructing wrinkles by utilizing strain-driven surface instability in film-substrate systems is a general method to prepare micronano structures, which have a wide range of applications in smart surfaces and devices such as flexible electronics, reversible wetting, friction, and optics. However, cracks generated during the preparation and use process significantly affect the uniformity of wrinkled surfaces and degrade the functional properties of the film devices. The realization of crack-free wrinkles with high stretchability in hard film systems is still a great challenge. Here, we report on a facile technique for controllable preparation of large-area, highly stretchable, crack-free wrinkled surfaces by ultraviolet ozone (UVO) treatment of Ecoflex. The thickness dependence of the wrinkles and the in situ wrinkling process during mechanical loading are investigated. The wrinkles including striped, labyrinth-like, herringbone, and transitional structures are controllable by changing strain mode (uniaxial or biaxial), loading history (simultaneous or sequential), strain anisotropy, and gradient loading. The wrinkled surfaces obtained using UVO-treated Ecoflex have tunable wetting and optical properties and can maintain excellent mechanical stability under large strains. This study provides a facile method for the preparation of large-area, crack-free wrinkles, which is simple, fast, low-cost, and robust. The resulting wrinkled surfaces remain stable under high stretching, which is beneficial for many practical applications, especially in the cases of large strains.

Computational modeling of coupled mechanical damage and electrochemistry in ternary oxide composite electrodes

Performance degradation of ternary layered oxide cathodes largely originates from their loss of structural integrity in cyclic usage. Mechanical damage, such as intergranular fracture of the active particles, is not only a mechanical cleavage process but also interferes with electrochemical kinetics such as infiltration of liquid electrolyte, surface corrosion of the constituent primary particles, and may eventually isolate the primary grains from the electron conducting network. Here we develop a computational framework that integrates electrochemistry of a LiNixMnyCo1−x−yO2 (NMC) composite cathode with mechanical damage of the active particles. To fully examine the intricate chemomechanical behavior of the electrode, we evaluate the effects of the anisotropic material properties, the influence of mechanical potential on Li transport, and the concurrent intergranular fracture and electrolyte penetration along the grain boundaries upon multiple cycles. Electrolyte infiltration benefits capacity retention but aggravates further mechanical damage by corrosion. Structural failure mostly occurs in the first charging due to the anisotropic mechanical strain between the primary grains, while the resulting damage remains stable in the later few cycles. The results are consistent with experimental observations and the integration of electrochemistry and mechanical failure enables a step further understanding of the complex mechanism of battery degradation.

Anisotropic model to describe chemo-mechanical response of Ni-rich cathode materials

In the context of lithium-ion battery technology, LiNixMnyCozO2 (x ≥ 0.8) (Ni-rich NMC) is considered a promising cathode material for next-generation batteries due to its high energy density. However, rapid capacity fade caused by mechanical failure hinders commercialization in the battery market. Anisotropic deformation in the basal and normal directions is the main source of mechanical damage to Ni-rich NMC. In this study, we developed a fully coupled chemo-mechanical model that rigorously accounts for the anisotropic features of anisotropic diffusivity, anisotropic stress-induced diffusion and anisotropic mechanical deformation. Using the model, we investigate the effects of anisotropic and concentration-dependent lattice strains on the chemo-mechanical behavior of a single-crystalline Ni-rich NMC particle through a comparative study with the cases of a fully isotropic model, constant properties and an isotropic diffusion approximation. Numerical simulations reveal that due to the anisotropic features, Ni-rich NMC materials generate larger concentration gradients and associated higher stresses than isotropic materials, thereby enhancing the possibility of mechanical fractures. The comparative study reveals that the anisotropy in diffusivity plays an important role in high stress generation of anisotropic electrode materials. On the other hand, the anisotropy in stress-induced diffusion has small effect on the stress level of anisotropic materials; thus, isotropic approximation of the stress-induced diffusion term is reasonably allowed in the anisotropic chemo-mechanical models. The simulation results indicate that although anisotropic electrode materials are used in a single crystal structure, they are not advantageous compared to isotropic materials in terms of mechanical stability. This study provides fundamental insight into the role of the anisotropic chemo-mechanical behavior of Ni-rich cathode materials, which will help in the better design of robust, high-capacity batteries.

The Effects of Strain Rate and Anisotropy on the Formability and Mechanical Behaviour of Aluminium Alloy 2024-T3

The present study focuses on the mechanical behaviour and formability of the aluminium alloy 2024-T3 in sheet form with a thickness of 0.8 mm. For this purpose, tensile tests at quasi-static and intermediate strain rates were performed using a universal testing machine, and high strain rate experiments were performed using a split Hopkinson tension bar (SHTB) facility. The material’s anisotropy was investigated by considering seven different specimen orientations relative to the rolling direction. Digital image correlation (DIC) was used to measure specimen deformation. Based on the true stress–strain curves, the alloy exhibited negative strain rate sensitivity (NSRS). Dynamic strain aging (DSA) was investigated as a possible cause. However, neither the strain distribution nor the stress–strain curves gave further indications of the occurrence of DSA. A higher deformation capacity was observed in the high strain rate experiments. The alloy displayed anisotropic mechanical properties. Values of the Lankford coefficient lower than 1, more specifically, varying between 0.45 and 0.87 depending on specimen orientations and strain rate, were found. The hardening exponent was not significantly dependent on specimen orientation and only moderately affected by strain rate. An average value of 0.183 was observed for specimens tested at a quasi-static strain rate. Scanning electron microscopy (SEM) revealed a typical ductile fracture morphology with fine dimples. Dimple sizes were hardly affected by specimen orientation and strain rate.