Uniform Confinement Research Articles

Layered Porous Ring-Like Carbon Network Protected FeNi Metal Atomic Pairs for Bifunctional Oxygen Electrocatalysis and Rechargeable Zn-Air Batteries.

Bimetallic atom catalysts exhibit ultra-high oxygen electrocatalytic activity by harnessing mutual promotion and synergistic effects between adjacent metal active centers, surpassing the performance of single metal atomic catalysts. Herein, FeNi atom pairs protected by hierarchical porous annular carbon grids (P-FeNi-NPC) are introduced using a mediator-assisted MOFs-derived strategy. The introduction of the multi-block copolymer P123 ensures the uniform confinement and dispersion of metal ions, followed by thermal decomposition to form a "planetary-ring-like" carbon framework that anchors the bimetallic atomic pairs in the active region. The homogeneous distribution of adjacent Fe-N4 and Ni-N4 active sites significantly enhances catalytic activity and stability. Leveraging unique electronic and geometric structures, the resulting P-FeNi-NPC catalyst demonstrates exceptional ORR and OER activities with an ΔE value of 0.705 (E1/2 = 0.845V, Ej = 10 = 1.55V). Theoretical calculations unveil that FeNi bimetallic sites loaded on nitrogen-doped carbon frameworks with specific curvature effectively modulate the energy of d-band centers, thus balancing the free energy of oxygen-containing intermediates. This study presents a novel and versatile approach for synthesizing advanced bifunctional catalysts, poised to drive the future development of Zn-air batteries.

Confinement-induced self-assembly of a diblock copolymer within a non-uniform cylindrical nanopore.

The self-assembly of a diblock copolymer melt confined within a non-uniform cylindrical nanopore is studied using the self-consistent field theory. The non-uniformity manifests in the form of a converging-diverging cylindrical nanopore. The axial variation in pore diameter presents a range of curvatures within the same confinement pore as opposed to a single curvature in a uniform-diameter cylindrical pore. The introduction of multiple curvatures leads to the formation of novel microstructures not accessible in uniform cylindrical confinement. The well-known equilibrium structures like a single helix, double helices, and concentric lamella under cylindrical confinement transition into new morphologies such as hyperboloidal phases, microstructures containing rings with a bead, rings with spheres, and a squeezed helical phase as the pore diameter varies axially. The converging-diverging geometry of the confining pore renders the helical phases seen in the cylindrical pore less favorable. A phase diagram in the parametric space of the block fraction and the ratio of the smallest and largest pore radii has been constructed to depict the order-order transition of various microstructures. The ratio of radii, a measure of the non-uniformity of the pore, along with the pore length brings out some interesting morphologies. The mechanism of these structural transitions is understood as the interplay between the variation in pore curvature attributed to the non-uniformity, the spontaneous curvature of the block copolymer interface, and the enthalpic interaction between the segregated blocks.

Wall-bounded periodic snap-through and contact of a buckled sheet

Fluid flow passing a post-buckled sheet placed between two close confining walls induces periodic snap-through oscillations and contacts that can be employed for triboelectric energy harvesting. The responses of a two-dimensional sheet to a uniform flow and wall confinement in both equilibrium and post-equilibrium states are numerically investigated by varying the distance between the two ends of the sheet, gap distance between the confining walls and flow velocity. Cases with strong interactions between the sheet and walls are of most interest for examining how contact with the walls affects the dynamics of the sheet and flow structure. At equilibrium, contact with the wall displaces the sheet to form a nadir on its front part, yielding a lower critical flow velocity for the transition to snap-through oscillations. However, reducing the gap distance between the walls below a certain threshold distinctly shifts the shape of the sheet, alters the pressure distribution and eventually leads to a notable delay in the instability. The contact between the oscillating sheet and the walls at post-equilibrium is divided into several distinct modes, changing from sliding/rolling contact to bouncing contact with increasing flow velocity. During this transition, the time-averaged contact force exerted on the sheet decreases with the flow velocity. The vortices generated at the extrema of the oscillating sheet are annihilated by direct contact with the walls and merging with the shear layers formed by the walls, resulting in a wake structure dominated by the unstable shear layers.

Axial compressive behavior of circular composite columns with external confinement

With the advance of externally confined composite columns, a generic model that can predict the ultimate axial compressive strength of both circular concrete-filled steel tube (CFST) and concrete-filled double skin steel tubes (CFDST) short columns with external confinement is very attractive. For this purpose, a rich experiment database of composite columns is assembled, guides to build up this database are outlined, and its limitations are also summarized. Based on some fundamental considerations, a simple formula for estimating ultimate axial compression of circular composite short columns is proposed first. The hoop and longitudinal stresses of outer and inner (if any) steel tubes are then determined by the stress analysis, from which the assumption frequently used in previous studies that the sandwiched concrete in a CFDST column is under uniform confinement is demonstrated to be unreasonable. Besides, the additional external confining pressure provided by external confinement in the form of steel spirals, rings, jackets, or tie bars is thoroughly investigated. Further, to comprehend the triaxial strength of infilled concrete in both CFST and CFDST columns, a novel concept of equivalent confining stress that can reflect both uniform and non-uniform confinement effects is defined, with which a modified Power-law failure criterion is established. Model validations illustrate that this generic model can reasonably estimate the strength of externally confined CFST and CFDST columns. Although it currently slightly underestimates the strength of ring-enhanced CFDST columns, this limitation can be easily overcome by recalibrating some coefficients without rebuilding the proposed framework.

Hyperuniform Disordered Solids with Morphology Engineering

AbstractHyperuniform disordered solid (HUDS) structures can provide large, uniform, complete, and isotropic light confinement at the nanoscale after precise design. Based on the HUDS structures, in‐plane light confinement for developing photonic integrated circuits is also explored. To improve the performance of HUDS devices, researchers have mainly focused on cell size or cell distribution optimization in HUDS, which suffers from time‐consuming computation or moderate photonic bandgap (PBG) modification. Here, a morphology engineering method is demonstrated to tailor HUDS PBGs and improve HUDS waveguide devices for transverse electric mode. The results show that the Bezier‐curve‐decorated HUDS devices can achieve a maximum of about 75% PBG width increase, 1.5 dB transmittance improvement in a 10 µm long HUDS waveguide, improved quality factors of HUDS‐cladding microring resonators, and device fabrication compatibility with foundry processing. This study opens new avenues for the development of unprecedented devices for exploring light field regulation, nonlinear optics, and sensing.

Damage evolution and full-field 3D strain distribution in passively confined concrete

The damage evolution of concrete under multiple stress states is complicated because the triaxial stress on the heterogeneous concrete affects mesoscale interactions between aggregates and mortar, which further alters the internal cracking of concrete and its load bearing mechanism. Hence, probing the internal cracking evolution of concrete under a complex stress state is the key to better understanding the characteristics and failure mechanism of concrete material. This study conducted a series of X-ray computed tomography (X-CT) tests on fiber-reinforced polymer (FRP) confined concrete with varied in situ axial load levels. Different cross-sections of concrete specimens—circular, square with round corners, and square with sharp corners—were designed to achieve uniform or nonuniform passive confinement conditions. The obtained volumetric images from X-CT clearly exhibited the internal damage evolution of concrete, where crack growth, shear banding, and failure localization were displayed for the concrete under varying triaxial stress states. The development of damage to concrete due to cracking with increasing load was also quantified by image segmentation. In addition, the digital volumetric correlation technique (DVC) was employed to produce the volumetric displacement field and strain distribution in the confined concrete according to the image variation of natural speckles. A three-dimensional internal strain analysis revealed that strain localization was mainly caused by mesoscale concrete heterogeneity and nonuniform confinement. More importantly, this study provides the first database of full-field strain tensors for FRP-confined concrete under different axial load levels. These data are valuable for the development of concrete mechanics, failure criteria of materials, and computational modeling of concrete materials and their structures, especially for concrete under complex stress states.

Experimental evaluation of composite and non‐composite columns and braces in special concentrically braced frames

SummaryHollow structural section (HSS) and concrete‐filled tube (CFT) cross‐sections have been widely employed in the columns and braces of special concentrically braced frames (SCBFs). Square‐HSS cross‐section widely used in multistory frames is filled with concrete and converted to square‐CFT cross‐section to enhance the behavior of this cross‐section. However, some investigations indicated that circular‐HSS cross‐section filled with concrete (circular‐CFT) showed better behavior in comparison with square‐CFT cross‐section due to more uniform and larger concrete confinement in circular‐CFT cross‐section. The current study was experimentally undertaken to evaluate (1) the seismic performance and the global and local hysteresis responses of HSS and CFT members with various cross‐section shapes from initial elastic range to collapse in the system level of multistory SCBFs, (2) the behavioral differences between square cross‐section and circular cross‐section, and (3) the behavioral differences between HSS cross‐sections and CFT cross‐sections employed in the columns and braces of SCBFs. Four full‐scale one‐bay, two‐story SCBFs with four various cross‐sections, namely, square‐HSS, circular‐HSS, square‐CFT, and circular‐CFT, for columns and braces were subjected to cyclic lateral loading. Evaluating base shear–roof drift hysteretic loops of SCBF specimens demonstrated that SCBF specimens with CFT columns and braces (CFT‐SCBFs) experienced respectively around 107%, 58%, 28%, and 152% higher stiffness, post‐yielding and post‐buckling strengths, ductility, and energy dissipation capacity than SCBF specimens with HSS columns and braces (HSS‐SCBF). In addition, the experimental observations indicated that CFT braces experienced local buckling initiation, crack initiation, and fracture at respectively 2.22, 2.35, and 2.32 times of roof drifts of those exhibited by HSS braces. Moreover, assessing braces with various cross‐sections indicated that CFT braces showed an increase in compression strength, post‐buckling strength, compression axial deformation, and out‐of‐plane buckling approximately by 83%, 152%, 127%, and 100%, respectively, in comparison with HSS braces. Finally, square‐HSS/CFT braces sustained rupture propagation better than circular‐HSS/CFT braces.

Mechanical analysis and finite element modeling of FRP-ECC-HSC composite stub column under axial compression

A novel composite column, consisting of an outer fiber-reinforced polymer (FRP) tube, an inner high strength concrete (HSC) core and an engineered cementitious composite (ECC) ring, has been proposed and investigated. Compared with normal FRP-confined HSC column, the FRP-ECC-HSC composite column could exhibit superior deformability performance. In this study, mechanical analysis was firstly conducted on the composite column to investigate the interaction behavior among different components, i.e. HSC core, ECC ring and FRP tube. Modified analysis-oriented models were proposed for HSC and ECC under uniform FRP confinement. Furthermore, finite element (FE) models were also established with the use of accurate concrete damaged plasticity (CDP) model to simulate the behavior of the composite column, especially the ECC ring which is under non-uniform confinement. The material property data used in the FE models were generated by the modified analysis-oriented models. It is shown that the FE models can provide close predictions on the axial load-axial strain behavior and hoop strain-axial strain behavior compared with test results. Meanwhile, stress distribution over the composite column section as well as the influence of ECC ratio were discussed with the validated FE model.

Superposition of random plane waves in high spatial dimensions: Random matrix approach to landscape complexity

Motivated by current interest in understanding statistical properties of random landscapes in high-dimensional spaces, we consider a model of the landscape in RN obtained by superimposing M > N plane waves of random wavevectors and amplitudes and further restricted by a uniform parabolic confinement in all directions. For this landscape, we show how to compute the “annealed complexity,” controlling the asymptotic growth rate of the mean number of stationary points as N → ∞ at fixed ratio α = M/N > 1. The framework of this computation requires us to study spectral properties of N × N matrices W = KTKT, where T is a diagonal matrix with M mean zero independent and identically distributed (i.i.d.) real normally distributed entries, and all MN entries of K are also i.i.d. real normal random variables. We suggest to call the latter Gaussian Marchenko–Pastur ensemble as such matrices appeared in the seminal 1967 paper by those authors. We compute the associated mean spectral density and evaluate some moments and correlation functions involving products of characteristic polynomials for such matrices.

A plasticity constitutive model for concrete under multiaxial compression

Structural members with confined concrete are becoming increasingly popular in civil engineering applications because of their superior strength and ductility. In these structural members, the concrete is subjected to dilation-induced (passive) lateral compressive stresses from the confining device (e.g., a steel tube). Existing research has led to theoretical models that predict closely the stress–strain behavior of concrete under uniform confinement (e.g., concrete in circular steel tubes under concentric axial compression), but theoretical models with a similar capability have not been achieved for the more common situation of concrete under non-uniform confinement (e.g., concrete in rectangular steel tubes). This paper presents a three-dimensional (3D) plasticity constitutive model that is accurate in predicting the stress–strain behavior of concrete in various scenarios of confinement. In the proposed model, a well-established open strength surface with associated open yield surfaces is combined with a hardening/softening rule compatible with both plastic volumetric compaction and dilation. In addition, a novel potential surface with a triangle-like deviatoric trace is proposed and calibrated with available experimental data of non-uniformly confined concrete. The implementation of the constitutive model in finite element analysis with an enhanced stress-return algorithm suitable for the novel potential surface is explained. While the focus of the present work is on monotonic compression-dominated loading, the model can be combined with fracture and damage theories to depict the behavior of concrete under tension-dominated and cyclic loading conditions. The performance of the proposed model is evaluated by comparing its predictions with a wide range of experimental data covering uniform active, uniform passive, and non-uniform passive confinement conditions, which demonstrates the capability and high accuracy of the proposed model.

Uniform Deposition and Effective Confinement of Lithium in Three-Dimensional Interconnected Microchannels for Stable Lithium Metal Anodes.

Lithium dendrite formation has hindered the practical implementation of lithium metal batteries with higher energy densities compared with those of conventional lithium-ion batteries. Herein, a nanoconfinement strategy to access dendrite-free lithium metal anodes comprising three-dimensional (3D) hollow porous multi-nanochannel carbon fiber embedded with TiO2 nanocrystals (HTCNF) is reported. The transport of the lithium ions is facilitated by the 3D architecture. Functioning as nanoseeds, the TiO2 nanocrystals guide the lithium ions toward forming uniform deposits, which are further confined inside the hollow carbon fibers and the 3D HTCNF layer. Site-selective deposition coupled with the nanoconfinement of lithium metal modifies the Li plating/stripping behavior and effectively suppresses the dendrite growth. The HTCNF-Li cell delivers a stable cycling performance of 1300 h with a voltage hysteresis as low as 6 mV. The assembled HTCNF-Li//LiFePO4 full cell displays a compelling rate performance and enhanced cycling stability with high capacity retention (90% after 400 cycles at 0.5 C). Our results demonstrate a new and potentially scalable route to resolve the lithium dendrite growth issue for enhanced electrochemical performances, which can be further extended to other metal battery systems.

Improved concrete plastic-damage model for FRP-confined concrete based on true tri-axial experiment

The constitutive relationship of concrete under passive confinement of fibre reinforced polymer (FRP) is one of the fundamental requirements for mechanical analysis of FRP-confined concrete members. The existing tri-axial constitutive models are commonly established based on actively confined concrete or uniform passively confined concrete. True tri-axial experiments and corresponding constitutive models for non-uniform passively confined concrete are rare. In this study, based on the pioneering work of true tri-axial testing on concrete cubes associated with passive confinement and the corresponding database assembled by the corresponding author, a plastic-damage based constitutive model for non-uniform passively confined concrete is established. The main parameters for the plastic-damage model i.e., damage variable, hardening/softening rule (cohesion stress) and flow rule (dilation angle) are determined. Non-uniformity factor and maximum lateral confinement stiffness, the key parameters for passively confined concrete, are used to define the cohesion stress and dilation angle curves. The proposed model is validated and then applied in the analysis of FRP fully and partly confined circular columns (uniform passive confinement) and FRP confined square columns (non-uniform passive confinement). The well-matched performance demonstrates the applicability of the proposed model in simulating mechanical response of FRP confined concrete with complex stress fields.

Axial Compressive Performance of Corroded Concrete Columns Strengthened by Alkali-Activated Slag Ferrocement Jackets

Chloride-induced corrosion of reinforcement has endangered the safety of reinforced concrete (RC) structures. It is, therefore, necessary to strengthen the corroded RC members to ensure structural safety. This study aims to investigate the effectiveness of alkali-activated slag (AAS) ferrocement jackets in strengthening corroded RC columns. AAS ferrocement specimens with various layers of stainless steel wire mesh (SSWM) were subjected to direct tensile tests. Square RC columns suffered artificially accelerated corrosion and were subsequently strengthened by AAS ferrocement jackets. Axial compressive tests were conducted on the column specimens. Experimental results have shown that corroded specimens suffer severe losses in loading capacity up to 46% as compared with the control one. Volume fraction of transverse SSWM (ρv) plays primary role in loading capacity and ductility of ferrocement and its confinement on column specimens. Ferrocement with ρv of 0.266% can rehabilitate loading capacity of specimens with corrosion degrees of 8.9% and 18.3% by 37% and 46%, respectively. Corroded specimen strengthened by ferrocement with ρv of 0.532% achieves approximately two times the ductility than the one without strengthening. Ferrocement jackets provide better and uniform confinement to core concrete than new stirrups. Analytical models are proposed to predict tensile strength of AAS ferrocement and loading capacity of specimens strengthened by ferrocement jackets. The prediction is in good agreement with experimental results.

RC frame structures retrofitted by FRP-wrapping: A model for columns under axial loading and cyclic bending

Abstract In order to mitigate the seismic risk of existing RC frame structures not designed with seismic criteria, a widespread strengthening strategy is based on increasing strength and ductility of RC columns by means of Fiber Reinforced Polymer wrapping. The existing models for RC cross-sections wrapped by FRP sheets were developed principally considering pure axial loads with uniform confinement pressure. In seismic areas, RC columns are instead usually subjected to axial load and cyclic bending. In the present work, in order to consider the effective loading conditions, an iterative cyclic model for square RC cross-sections wrapped by composite FRP sheets subjected to axial force and cyclic bending is proposed. The model considers the strain gradient-effect over the cross-section due to the bending loads that change significantly the confinement level of RC cross-section. Moreover, the model has been validated by comparing the numerical outcomes with various cyclic experimental results. The model has been also implemented in an open-source software with distributed plasticity finite elements in order to perform pushover analyses of an existing RC frame structure with different retrofitting strategies to improve the ductility of the columns for lateral forces.

Mechanical Properties of Aluminium Metal Matrix Nanocomposites Manufactured by Assisted-Flake Powder Thixoforming Process

This study discusses the superior effect of thixoforming process on enhancing the tensile properties of aluminium matrix composite produced using flake metallurgy route. The flake metallurgy process was utilised to manufacture aluminium matrix composites followed by thixoforming process. Microstructural investigations carried out using transmission electron microscope have shown the synergic effect of thixoforming process on rendering uniform distribution of SiC nanoparticles associated with lower porosity content. X-ray diffraction characterisations have revealed the promising effect of uniform dispersion of SiC nanoparticles on restricting the grain growth of aluminium matrix within nanoscale regime (90 nm) even at high semi-solid thixoforming temperatures (575 °C). The achieved results of tensile tests have shown a profound effect of flake metallurgy of aluminium powder through dual speed ball milling. These results are higher than those achieved by low speed and high speed even with higher SiC content. This was attributed to the uniform confinement of SiC nanoparticles within the samples produced using flake-assisted forming process compared to the ones manufactured using ball milling-assisted processes.

Exciton Spatial Coherence and Optical Gain in Colloidal Two-Dimensional Cadmium Chalcogenide Nanoplatelets.

Two-dimensional (2D) cadmium chalcogenide (CdX, X = Se, S, Te) colloidal nanoplatelets (NPLs) make up an emerging class of quantum well materials that exhibit many unique properties including uniform quantum confinement, narrow thickness distribution, large exciton binding energy, giant oscillator strength, long Auger lifetime, and high photoluminescence quantum yield. These properties have led to their great performances in optoelectrical applications such as lasing materials with a low threshold and large gain coefficient. Many of these properties are determined by the structure and dynamics of band-edge excitons in these 2D materials. Motivated by fundamental understanding of both 2D nanomaterials and their applications, the properties of 2D excitons have received intense recent interest. This Account provides an overview of three key properties of 2D excitons: how big is the 2D exciton (i.e., exciton center-of-mass coherent area); how the exciton moves in 2D NPLs (i.e., exciton in-plane transport mechanism); how multiple excitons interact with each other (i.e., biexciton Auger recombination); and their effects on the optical gain mechanism and threshold of colloidal NPLs. After a brief introduction in Section 1, the current understandings of 2D electronic structures of cadmium chalcogenide NPLs, and type-I CdSe/CdS and type-II CdSe/CdTe core/crown NPL heterostructures are summarized in Section 2. Section 3 discusses the direct measurement of exciton center-of-mass coherent area in 2D CdSe NPLs, its dependence on NPL parameters (thickness, lateral area, dielectric environment, and temperature), and the resulting giant oscillator strength transition (GOST) effect in 2D NPLs. 2D exciton diffusive in-plane transport in CdX NPLs and the comparison of exciton transport mechanisms in 2D NPLs and 1D nanorods are reviewed in Section 4. How Auger recombination lifetime depends on nanocrystal dimensions in NPLs, quantum dots, and nanorods is discussed in Section 5. The lateral area and thickness dependent Auger recombination rates of NPLs are shown to be well described by a model that accounts for the different dependence of the Auger recombination rates on the quantum confined and nonconfined dimensions. It is shown that Auger recombination rates do not follow the "universal volume scaling" law in 1D and 2D nanocrystals. Section 6 describes optical gain mechanisms in CdSe NPLs and the dependence of optical gain threshold on NPL lateral size, optical density, and temperature. The differences of optical gain properties in 0D-2D and the bulk materials are also discussed, highlighting the unique gain properties of 2D NPLs. At last, the Account ends with a summary and perspective of key remaining challenges in this field in Section 7.

Synthesis of mesoporous carbon-polymeric hybrid material for energy storage application

The overarching goal of this study is fabrication and evaluation of mesoporous carbon-polymeric hybrid electrode materials derived by in situ polymerization of aniline on mesoporous carbon. The mesoporous carbon (CMK-3) was prepared using mesoporous silica SBA-15 as a hard template. The characteristics and functional groups of synthesized mesoporous carbon-polyaniline composite confirmed by Fourier-transform infrared spectroscopy, Raman spectroscopy, Thermo gravimetric analysis, X-ray powder diffraction, and BET surface area analysis. The electrochemical performance of carbon-polyaniline composite was evaluated through its supercapacitor behavior in the electrolyte Potassium bicarbonate (KHCO3). Synthesized carbon-polyaniline was used as the working electrode after modification with Nafion solution on glassy carbon electrode. The hybrid material reveals high current density with increased storage efficiency due to uniform confinement of polyaniline into the pore structure of CMK-3. The high specific capacitance of 487 F/g was observed on carbon-polyaniline electrode at 0.2 A/g in KHCO3, and also reveals better stability, retained 90% efficiency after 1000 charge–discharge cycles. Thus, the prepared carbon-polyaniline composite exhibit as a good candidate in supercapacitor application.

Chemically-Engineered Host Materials Enabling Safe Sodium Metal Anodes

As an anode material, sodium (Na) metal is the most promising alternative for lithium for the next‐generation energy storage systems. Nevertheless, its practical implementation is impeded by the huge volume change and severe Na metal dendrite growth during electrochemical stripping/plating. Herein, the employment of chemically-engineered porous copper (Cu) and titanium carbide (Ti3C2) MXene as stable host for metallic Na anode is presented. By treating the commercial Cu foam through a facile and cost‐effective method, a composite matrix consists of cylindrical core–shell skeleton is achieved, facilitating uniform impregnation and confinement of Na within the matrix pores promoted by the chemical interaction between Na and the matrix. While by treating Ti3C2 via a facile cetyltrimethylammonium bromide prepillaring followed by subsequent Tin cation (Sn2+) pillaring, a Sn2+ pillared Ti3C2 MXene matrix is obtained, guiding the Na nucleation/growth within the matrix interlayer space and contributing to uniform Na deposition facilitated by the chemical interaction between Na and Sn-based nanocomplexes encapsulated within the MXene layers. The unique characteristic of the chemically-engineered host materials can well accommodate hostless Na+, suppressing the volume change and mossy/dendritic Na growth during cycling. A stable Na cycling behavior is demonstrated in carbonate electrolyte without any additives at a high capacity up to 3 mAh/cm2 with a current density up to 2 mA/cm2. While in ether electrolyte, a stable Na performance at a high capacity up to 5 mAh/cm2 along with a high current density up to 10 mA/cm2 is achieved. Furthermore, electrochemical measurements of a full cell made of the Na composite matrix anodes clearly reveal the superior performance over that using bare Na metal. We believe that our approach provides facile approaches to the fabrication of stable Na metal anodes for high‐energy Na‐based batteries, and could be a viable strategy for other metallic anode systems.[1,2] Reference： [1] C.Wang, H. Wang, E. Matios, X. Hu, W. Li, Adv. Funct. Mater, 2018, 28, 1802282. [2] J. Luo, † C. Wang, † H. Wang, X. Hu, E. Matios, X. Lu, W. Zhang, X. Tao, W. Li, Adv. Funct. Mater, 2018, 1805946. Figure 1

Modified plastic-damage model for passively confined concrete based on triaxial tests

Plasticity-based models are used as the constitutive relationship of concrete under passive confinement of fiber reinforced polymers (FRPs). Triaxial cube tests are needed for adjusting the parameters included in a model. Most of the existing plasticity models are developed from actively confined tests or by uniform passively confined column tests. Methods for developing a plasticity model based on non-uniform passively confined concrete tests and applied to non-uniform passive confinement are rare and needed. This study reports more than one hundred triaxial concrete cube tests under uniform and non-uniform passive confinement. Six grades of concrete were tested under monotonic and cyclic compression loads. The lateral stiffness ratio was the main parameter for designing the tests. Using the reported tests, a new approach is devised for deriving parameters of a plastic-damage model for practical application to concrete structures under non-uniform passive confinement. The lateral stiffness ratio is found to be a key factor for plasticity model parameters involving dilation angle, hardening rule, and damage variable. Based on the test results and using finite element analysis (FEA), explicit empirical models are developed for the plasticity parameters. FEA analyses using the developed plasticity-damage model performs well compared with test results.

Enabling a Safe Metallic Sodium Anode Using Chemically-Engineered Porous Copper Matrix with Cylindrical Core-Shell Skeleton

Sodium (Na) metal is the most promising alternative for lithium metal as an anode material for the next-generation energy storage systems due to its high theoretical capacity, low cost and high natural abundance. However, huge volume change and severe dendrite growth of Na metal anode during repeated electrochemical stripping/plating result in rapid electrode degradation, low Coulombic efficiency, and even the risk of explosion caused by short circuit of the batteries. Because of its very soft nature, Na metal is susceptible to deform and degrade during both battery assembly process and electrochemical cycling. The volume and morphology change of the “hostless” Na severely aggravates the growth of Na dendrites. Thus, it is essential to seek an ideal host to support Na metal so as to maintain the high integrity of the electrode. Here we present the employment of a chemically engineered 3D porous copper (Cu) matrix with a cylindrical core-shell skeleton structure as a highly stable host for metallic Na anode, enabling a high Na areal mass loading of 70 mg cm-2, through a facile and cost-effective surface treatment on commercially available Cu foam in forming high performance composite anode for Na-based batteries. We find that the unique surface characteristics of the as-obtained matrix can not only facilitate uniform impregnation and confinement of Na within the matrix pores promoted by the chemical interaction between Na and the matrix, but also can divert the Na plating from the matrix skeleton towards the Na reservoirs within the pores upon cycling. Benefiting from our delicately surface-engineered matrix as a host for Na, we demonstrate an excellent Na anode cycling stability in carbonate electrolyte without any additives over 100 cycles (300 hours) at a current density up to 2 mA cm-2 with a high cycling capacity up to 3 mAh cm-2. A stable rate performance up to 3 mA cm-2 is also demonstrated. A full cell made of Na3V2(PO4)3 as cathode and the as-prepared surface-treated Na composite as anode is further tested, showing superior cycling performance and high rate capability (at 5C) compared with that using bare Na metal as anode. In addition to performance improvement, we systematically investigate the interfacial interactions between treated/untreated Cu matrixes and metallic Na to reveal how the surface property of the matrix skeleton greatly influences the electrochemical stability of Na anode.