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Summary: Aqueous zinc batteries (AZBs) hold great promise for advancing applications in next‐generation energy storage devices because of their high safety, high energy density, and low cost. However, zinc metal anodes have greatly impeded the application in AZBs due to their poor cycle performance. Short lifespan, which is caused by dendritic growth, deformation, corrosion, and competing hydrogen evolution, is very tricky. Herein, a stable Sn@Cu foam, prepared by plating tin on copper foam, is reported as the substrate of Zn anodes. We evaluate the quality of plating tin layers, which are prepared by using different tin salt solutions, and Na2SnO3 solution is eventually selected. Electrochemical tests show that Sn@Cu foam can not only inherit the merits of Cu foam but also suppress hydrogen evolution reaction and lower the initial heterogeneous nucleation barrier of deposited Zn. Moreover, in situ observation by optical microscope demonstrates that Zn dendrite growth on Sn layer is suppressed during the plating‐stripping process. As a result, a compact Zn layer on Sn@Cu foam is obtained (Zn/Sn@Cu foam), symmetrical cells display superior cycling life of 1800 h at 1 mA cm−2 for 1 mAh cm−2, and full cells with VO2 cathode deliver remarkably better cycling stability and longer lifespan. [ABSTRACT FROM AUTHOR]

• Multiaxial properties of additively manufactured Kelvin foams are characterized. • Initial yield surface can be well fitted using a parabolic or an elliptic function. • The normalized initial yield surface is still relied on the strut diameter. • Effects of SLM defects and EPS foam filler on the yield behaviors are studied. Additively manufactured lattice structures (AMLS) exhibit substantially more freedom in design compared with traditional cellular materials such as honeycombs and stochastic foams. Prior to extensive applications, multiaxial mechanical behaviors of AMLS need to be thoroughly understood. In this study, open-cell Kelvin lattice structures (named as Kelvin foams) are fabricated through the selective laser melting (SLM) process using 316L stainless steel powder. Multi-cell numerical models are developed and validated against the uniaxial compressive results and then adopted to simulate virtual triaxial experiments. An energy dissipation point is adopted to define onset of yielding. Multiaxial yield surface of Kelvin foams is characterized in the von Mises and mean stress plane, which can be well fitted in terms of an elliptical or a parabolic yield function. The normalized yield surface using uniaxial yield strength is still relied on the strut diameter. It is found that the yield surface is gradually shrunk with increasing strut-diameter dimensional tolerance induced by the SLM process, which becomes more pronounced when its stress state is close to a hydrostatic compression. The yield surface is found to expand when the expanded polystyrene (EPS) foam is used as a filler material, but the influence of foam filler becomes weaker when gradually experiencing hydrostatic compression. [ABSTRACT FROM AUTHOR]

• High-temperature and dynamic compressive responses of Al foams are studied. • Initial failure surface of Al foams is identified under high temperature conditions. • A theoretical constitutive model is proposed involving strain-rate effects. • The strain-rate dependent macro-mechanics models are numerically evaluated. Metallic foams exhibit great application prospects in some extreme working conditions such as high temperatures and/or high-velocity impact environments, but predominantly, their mechanical behavior has remained to be fully understood to date. In this study the uniaxial and biaxial tests are conducted on closed-cell aluminum foams at elevated temperatures. It is indicated that both drop stress and initial failure strength exhibit approximately linear relationship with the applied temperature, while the densification strain keeps almost at a constant value. The higher foam density or lower applied temperature, the larger the initial failure surface characterized in the von Mises - mean stress plane. However, the normalized failure surfaces nearly do not depend on foam density or temperature, and can be well fitted in terms of elliptical or parabolic function. Dynamic compressive tests under constant strain-rates reveal that the compressive strength is correlated to strain-rate positively, but the densification strain negatively. A novel rate-dependent constitutive model is proposed to describe the compressive constitutive behavior of Al foams. Finally, the crushable foam model with the tabular input of yield ratio approach can produce satisfactory numerical predictions compared to dynamic experimental results. This study provides new insights into the intrinsic mechanical properties of metallic foams under some extreme conditions. [Display omitted] [ABSTRACT FROM AUTHOR]

Metal foams are commonly used to withstand impact loading from different directions in real life applications attributable to their superior performance of energy absorption to weight. It has been of special interest to explore the complex yield/failure behavior of metal foams under dynamic impact recently. However, existing studies have mainly focused on crushing behavior under simple quasi-static loading conditions. Hence, this study aims to explore the multiaxial dynamic failure behavior of closed-cell aluminium foams. First, the uniaxial failure behavior of foams with three different apparent densities is experimentally investigated at varying strain rates (10−3-150 s−1) through quasi-static compression and drop weight tests, respectively. It is found that the initial failure strength exhibits evident strain-rate dependency. An empirical relation is established to associate the initial failure strength with relative density and nominal strain rate. Second, the multi-axial failure behavior is characterized based upon the developed microscopic computed tomography (micro-CT) image foam models. It is revealed that at low and medium strain rates, the hardening of the uniaxial failure strength is rate-dependent on the foam cell-wall base material. Under compression-shear and triaxial compression loadings, the initial failure surface in the von Mises - mean stress plane significantly expands with increasing strain rates. After normalized by the uniaxial failure strength at the corresponding strain rates, the failure surface is almost independent of loading or strain rates. The normalized failure surface can be well depicted by an elliptic or a parabolic function. Moreover, with use of suitable plastic Poisson's ratio, the normalized failure surface could be well characterized by Deshpande and Fleck (D&F) model and Miller model. The modified rate-dependent constitutive models are suggested for foam materials subject to quasi-static and dynamic loadings. Image 1 • Multiaxial properties of closed-cell Al foams are characterized based upon micro-CT based models. • Rate dependence of foam cell-wall leads to strain-rate sensitivity of the initial failure strength. • The normalized failure surface is independent of strain rate. • The modified Miller and D&F models are proposed with consideration of strain-rate effects. [ABSTRACT FROM AUTHOR]

As one of widely-used multi-functional materials, metallic foams are often subjected to multiaxial stress states in practical applications; in which the yield behaviors under different stress states need to be better characterized. However, it is difficult to conduct multiaxial mechanical tests on foam materials, especially under arbitrarily proportional triaxial loadings. In this study, numerical modeling of the yield properties of aluminum (Al) foam is performed based upon 3D image-based models. Real structural models of the Al foam are reconstructed using microscopic X-ray computed tomography (micro-CT) technique for multiaxial characterization computationally. Numerical simulation reveals that plastic collapse and fracture of cell-walls first occur in a relatively weak zone under prescribed uni/tri-axial loadings, whereas happen in the central section under biaxial loadings. An initial yield criterion is defined based upon energy dissipation. A constant stress proportion coefficient can be obtained under the stress-controlled triaxial proportional loading and its effectiveness is also validated by comparing the stress-strain responses with those under velocity-controlled uniaxial and hydrostatic compressive loading. It is found that the initial yield points of foam specimens can be obtained in different stress states in the von Mises-mean stress space. The normalized yield surface is approximately independent of relative density and can be well fitted to a parabolic or an elliptic function. Comparisons between the numerical yield surface and three typical theoretical yield criteria suggest that the Deshpande and Fleck's criterion provides more precise predictions than Gibson and Miller yield criteria when a proper plastic Poisson's ratio is adopted. Furthermore, it is shown that the early stage yield surface of metallic foams can be evolved in a geometrically self-similar manner. Image 1 • Multiaxial characterization of closed-cell Al foams based upon 3D image-based models. • The normalized initial yield surface is well fitted with a parabolic or an elliptic function. • Deshpande and Fleck's criterion provides more precise prediction. • The early stage of the yield surface of metallic foams is evolved in a geometrically self-similar manner. [ABSTRACT FROM AUTHOR]

• A novel approach for the hardening parameters identification of cell-wall of closed-cell aluminum foam. • The objective function considers both the indentation curve and the pile-up information. • The optimization process combines 2D with 3D numerical simulations to improve the efficiency. • The material properties of cell-wall of aluminum foam are experimentally verified. This study aims to develop an inverse approach to identifying the cell-wall material properties of closed-cell aluminum (Al) foams, which is based upon indentation tests, numerical simulation and optimization technique. Vickers nano-indentation tests are conducted on the cell-wall of foams, and the residual surface deformation is measured by a high definition confocal microscopy. To enhance identification efficiency, a combined 2D with 3D micromechanics modeling strategy is proposed here, in which the load-depth curve and residual imprint (pile-up) of the indentation tests are considered. In this study, the cell-wall material properties such as the yield strength and strain-hardening exponent are identified using this proposed inverse approach, while the Young's modulus is obtained directly for the unloading part of the indentation load-depth curves. The identification results indicate that the proposed inverse procedure can provide a well-posed solution to the cell-wall material properties by introducing the pile-up information. Microscopic computed tomography (μCT) technique is also utilized to reconstruct accurate 3D image-based representative volume element (RVE) model of foam structure, through which the numerical simulation is conducted for uniaxial compression. The identified cell-wall material parameters are validated by comparing the numerical simulation with the experimental data in terms of the deformation/failure modes and quantitative results. It is noted that the cell-wall of aluminum foams that are commonly made of melt foaming processes exhibits a quite different stress-strain relation when compared with the raw material of cell-wall. This study is expected to provide an effective approach for identifying the material properties that may be not easily determined through conventional testing methods. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Structural responses, deformation modes, blast resistance and energy absorption of foam core signify some major functional characteristics for design of sandwich panels. This study aimed to address these issues by investigating uniform and graded foam core configurations. First, an experimental study was performed and the testing results of blast-loaded sandwich panels were analyzed. Second, a numerical model was developed and validated by comparing the simulation results with the experimental results in terms of deformation modes and back facesheet deflection. Third, the blast resistance of sandwich panels was comprehensively studied based upon the developed numerical models. Due to the high attenuation ability of the shock induced stress wave, the foam core with descending gradient of layer density across the thickness direction provided the highest blast resistance of all the core configurations considered here and its advantage could be further improved by enlarging the density difference of the core layer. While keeping total facesheet thickness unchanged, a relatively thick back facesheet is beneficial to enhance the blast resistance under relative low blast intensity. Finally, an optimization study was performed to improve the blast resistance of graded core sandwich panels. For the single objective optimization, the maximum back facesheet deflection of the optimum design decreased by 24.58% in comparison with that for the initial baseline design. For the multiobjective optimization, the optimal designs obtained from the Pareto solution can significantly enhance weight efficiency without compromising the resistance. Image 1 • A numerical model of sandwich panel against blast resistance was developed and experimentally validated. • The foam core with descending gradient of layer density across the thickness direction provided the highest blast resistance. • A relatively thick back facesheet is beneficial to enhance the blast resistance under low blast intensity. • Single/multi-objective optimization design is conducted to improve the blast resistance of sandwich panel. [ABSTRACT FROM AUTHOR]

• Experimental studies on aluminum foam-core sandwiches with three different facesheet materials namely aluminum alloy, steel, and carbon fiber reinforced plastic (CFRP) subjected to blast impulse. • Analysis of deformation/failure modes of the whole sandwich panels as well as the front facesheet, foam core, and back facesheet. • Influence of facesheet materials and configuration on the blast resistance of sandwich panels. • Effect of core density gradients on the blast resistance as per the permanent deflections of back facesheets. Sandwich panels with an energy-absorbing core material have exhibited great potential in lightweight structures for blast protection. In this study, the deformation/failure modes of sandwich panels against blast impulse were investigated experimentally. The blast tests were conducted on the aluminum foam-core sandwich panels with different facesheet materials, namely aluminum alloy, steel, and carbon fiber reinforced plastics (CFRP); and the cores involve uniform foam and graded foam. The deformation modes of the whole sandwich panels as well as the front facesheet, foam core, and back facesheet were analyzed systematically. It is shown that the deformation patterns are fairly sensitive to the impulse intensity, facesheet material, and foam core gradient. Based upon the measurements, the back facesheet deflection increases linearly with the impulse, apart from the petal-tearing failure of front facesheet. When considering the specific impulse and the same metallic back facesheets, the blast resistance of the sandwich specimen with CFRP front facesheet is superior to these of the metallic front facesheet specimens. Interestingly, the sandwich panels with the aluminum front and steel back facesheet perform better in blast resistance than those with the steel front and aluminum back facesheet. The blast resistance of sandwich panels with a positive gradient of core density (i.e. core density linearly decreased along the blast direction) is superior to those with a negative gradient of core density; and the performance increases with increasing density difference. Compared with the uniform core, the positively-graded foam core with a larger density difference exhibits a stronger blast resistance, while those with a smaller density difference present a weaker blast resistance. The study is expected to provide some fundamental data and design guide for a more efficient sandwich structure with lighter weight and higher capacity of blast protection. Image, graphical abstract [ABSTRACT FROM AUTHOR]

As a class of effective lightweight energy absorption materials, periodic closed-cell foams have been widely applied in engineering, in which the Kelvin and Octet-B foams have demonstrated great value in the research of multiaxial mechanical characteristics. For this reason, this study aims to develop a series of realistic finite element analysis (FEA) models for investigating their uniaxial, compression-shear, and arbitrary triaxial compression performance. Under uniaxial loading conditions, the mechanical responses and deformation modes of the two foams are compared and analyzed with different densities. The influence of different loading angles is also considered under compressive-shear loading. The deformation pattern of foams subject to equal biaxial and hydrostatic loading are compared with uniaxial compression. Based on sufficient simulation data, the initial yield surfaces of the two foams are plotted in the von Mises and mean stress plane, and fitted by three theoretical yield criteria characterized in terms of quadratic functions. It is found that the Miller criterion can better describe the initial yield surface shape of Kelvin foams than the yield models of Deshpande–Fleck and Zhang et al.; while the above yielding models are all of high fitting accuracy for the Octet-B foam. Further, the ability to resist initial yield of the Kelvin foam has proven superior to Octet-B foams by calculating the curve integration. The study is anticipated to provide new insights into novel design and extensive applications of periodic closed-cell foam materials in practice. • The realistic and systematic multiaxial simulation for polymetric foam. • Effect of relative density on mechanical performance of polymetric foam. • Effect of relative density on the initial yield surfaces of polymetric foam. • Identification of macroscopic yield constitutive relationship of polymetric foam. [ABSTRACT FROM AUTHOR]