Cellular Metal Research Articles

A new type of sandwich panel with periodic cellular metal cores and its mechanical performances

Many studies have been performed on the mechanical properties and optimization of truss PCMs (periodic cellular metals), but those on the fabrication process, which is one of key factors determining the survivability of PCMs in the market, have been relatively limited. This study introduces a new idea on the fabrication of quasi Kagome truss cored sandwich panels, which is based on the expanded-metal process. And the mechanical behavior of the sandwich panels is to be evaluated. The mechanical strengths and failure mechanisms under compression and bending load are estimated based on elementary mechanics of materials, and the optimal design is derived. Its validity is proved by comparison with the results of experiments. The results showed that the new idea is promising with respect to all three requirements, i.e., the morphology, fabrication cost, and raw materials. The simple mechanical analysis was sufficiently effective and accurate for estimating the performance and failure mode of the sandwich panels. In the experiments, sandwich panel specimens of three different designs were compared in their bending behaviors to demonstrate sensitivity of geometric parameters. Namely, although all the designs had little difference in their load capacity-per-weight, the failure mechanisms and the behaviors after a peak load were totally different.

Compressive strength of tube-woven Kagome truss cores

We tried to fabricate lattice truss structure cores from SUS 304 stainless steel tubes. The compressive behaviors of the cores were investigated. The micro- and macro-structures and failure mechanisms under compression were observed. It was seen that the tube-woven lattice truss structures could be fabricated from the tubes without any technical difficulty, although the process involved the helical formation of the tubes. The compressive strengths of the tube-woven lattice truss cores were found to be higher than those predicted by analytical solutions. The post-peak behavior was stable and wavy, thus absorbing sufficient energy before the final densification. The tube-woven lattice truss cores outperform most cellular metals except for hollow trusses.

On the acoustical properties of metallic hollow sphere structures (MHSS)

Well-known advantages of cellular metals are their high ability for energy absorption, good damping behavior and sound absorption at a high specific stiffness. This paper has a focus on the absorption coefficient representing the acoustical property. The absorption coefficient is analysed experimentally by an impedance tube. Results fit well to theoretical investigations described by Champoux and Allard.

Temperature-Dependent Sensitivity of a Marine Diatom to Cadmium Stress Explained by Subcelluar Distribution and Thiol Synthesis

This study examined the potential bioaccumulation and biochemical mechanisms (phytochelatin and other thiols induction) in the temperature-dependent sensitivity of a marine diatom Thalassiosira nordenskioeldii to cadmium (Cd) stress. A higher environmental temperature increased the sensitivity of diatoms to Cd toxicity. Either increased cellular Cd accumulation or a poorer detoxification ability was responsible for the higher concentration of metal-sensitive fraction (MSF)-Cd in the diatoms and subsequently the higher Cd sensitivity with increasing temperature. In addition, N-deficiency or glutathione depletion may partly explain the highest sensitivity at the highest tested temperature (30.5 degrees C). Although temperature affected the biochemical composition (e.g., the N/C ratio and phytochelatin induction), physiological processes (e.g., the growth rate, photosynthesis, Cd uptake, accumulation, and subcellular distribution) and the resulting differential tolerances, Cd concentration in MSF or organelles served as the best indicators of Cd toxicity in diatoms at different temperatures. Phytochelatins (PCs) were induced by increasing [Cd2+] and the significant relationship between the intracellular Cd and PC-SH concentration suggested that PC-SH is a biomarker for cellular metal stress. However, the intracellular Cd/ PC-SH ratio did not always explain the temperature-dependent metal tolerance. The functions of PCs other than metal chelation and detoxification need to be further examined.

Two-dimensional cellular metals as multifunctional structures: topology optimization

Highly porous two-dimensional (2D) cellular metals have multifunctional attributes, with tailorable structures to achieve multifunctional performance. The focus of this study is to explore the optimal cellular topology of 2D cellular metals for heat dissipation, and to investigate the eligibility of different heat enhancement techniques for more efficient heat dissipation. An analytical approach for the optimal design of metallic 2D cellular materials, cooled by single-phase laminar forced convection in various flow configurations, is proposed and validated by comparison with full numerical simulations. The optimal design is characterized by two subsidiary dimensionless parameters: one reflecting the trade-off between convection and fluid friction, and the other reflecting the optimal balance between conduction and convection. A heat transfer enhancement technique––boundary layer redevelopment––is subsequently introduced and its feasibility examined experimentally. Future research directions in specific areas are discussed.

Failure Mechanisms during Periodic Cellular Metal Fabrication by Perforation Stretching

Periodic cellular metals (PCMs) are structurally efficient lightweight materials. Perforation stretching is a recently developed PCM fabrication method that plastically deforms perforated sheet precursors into a three-dimensional (3-D) array of load-supporting struts. The present study examines the onset and limit of useful plastic deformation during perforation stretching of a wrought 3003 aluminum alloy over a range of precursor microstructures and geometries. A compression platform was used to apply the forming forces such that force-displacement profiles could be obtained for each condition. The initial stage of plastic deformation was bending dominated, and it was found that a simple plastic bending cantilever model was able to account for the nearly order of magnitude range in plasticity onset force. On the other hand, unlike a previously reported pin punch through mechanism, it was found that for the present forming conditions, perforation-stretching failure could be attributed largely to tensile instability, suggesting that the tensile failure strain is a key parameter in determining the range of accessible perforation-stretching formed architectures.

Modelling of the multiaxial elasto-plastic behaviour of porous metals with internal gas pressure

The gas pressure built up within closed cells of porous or cellular metals influences the macroscopic behaviour during deformation. Another important process affected by internal pore pressure is the roll forming of structurally porous metals. During pressing and thermo-mechanical forming, the internal pressure of the pores and the temperature can rise to high levels. In this paper, the influence of the internal gas pressure on the mechanical behaviour of porous metals under different loading conditions is numerically investigated by the finite element method. It has been found that the internal gas pressure significantly influences the initial yielding as well as the macroscopic behaviour if the pressure is clearly less than a half of the yield strength of the base material. This can be found in scientific literature as a limit for a significant influence.

High Strength‐per‐Weight Cellular Metals Fabricated of Wires

In pursuit of high specific strength cellular metals, the authors have examined compressive strength of Wire-woven Bulk Kagome (WBK) specimens composed of two different wires, i.e., aluminum alloy wires and spring steel wires. Compression tests give the strength of 1.8 MPa at a density of 0.096 Mg/m 3 for the former and 7.1 MPa at 0.271 Mg/ m 3 for the latter. These two WBK specimens outperform most competitors of metal foams with respect to specific strength. In comparison with other Periodic Cellular Metals (PCMs), even though the relative density of the two WBK specimens is substantially lower, their compressive strength and energy absorptions are comparable to those of the square honeycomb and the pyramidal core, which are known as ones of the best PCMs.

Differential effects of phosphorus limitation on cellular metals in Chlorella and Microcystis

We investigated the effect of phosphate bioavailability on cellular metal quotas in two species of freshwater phytoplankton (the eukaryote Chlorella sp. UTCC522 and the cyanobacterium Microcystis sp. LE3), grown in semicontinuous culture over four controlled levels of phosphate availability, encompassing phosphorus (P) deplete to P replete conditions. P limitation caused reduced growth rate, high C: P (up to 1800 mol mol‐1), and increased alkaline phosphatase (APase) activity. Low P availability led to enriched cobalt (Co), cadmium (Cd), and zinc (Zn) in Chlorella (up to 2.8‐fold, 1.7‐fold, and 1.8‐fold, respectively, normalized to cellular N, relative to P‐replete control) but resulted in enriched Co and nickel (Ni) in Microcystis (up to 4.4‐fold and 3.0‐fold). In contrast, cellular iron (Fe), manganese (Mn) and copper (Cu) were largely unchanged (±~20%) in both organisms. Cd and Co may substitute for Zn in the APase of Chlorella while in Microcystis the dominant phosphatase may be strictly Co‐requiring, as has been reported for other prokaryotes and is consistent with its evolutionary emergence before the oxygenation of the atmosphere, when Co was relatively abundant in natural waters. By extension, the absolute Co requirement of the important marine cyanobacteria Synechococus and Prochlorococcus may be related in part to widespread depletion of orthophosphate (PO43‐) in the oligotrophic surface ocean. The enrichment of Ni in Microcystis may indicate increased activity of Ni‐requiring superoxide dismutase under P limitation or, speculatively, a co‐uptake of Ni and Co by a shared transport system. These results shed light on the interaction between trace metals, macronutrient availability, and phytoplankton assemblage composition, and suggest intensified biological cycling of Zn, Cd, Co, and Ni in low‐P freshwater and marine systems.

Heavy metals generate reactive oxygen species in terrestrial and aquatic ciliated protozoa

Reactive oxygen species (ROS) induction by exposure to heavy metals (Cd, Cu or Zn) in diverse free-living ciliated protozoa ( Tetrahymena sp. and three strains of Colpoda steinii, isolated from freshwater and soils with different level of metal pollution) has been evaluated. Using specific fluorophores, such as 2′,7′-dichlorofluorescein diacetate, hydroethidine and dihydrorhodamine 123, and a fluorescence microscope with the program MetaMorph Imaging System 4.0, we have analyzed both the average fluorescence emission and the heterogeneous distribution of fluorescence in control and treated cells. This is the first time that these fluorophores are used to detect ROS production in ciliated protozoa. All metals generate ROS, mainly superoxide and peroxides, showing a remarkable inter- and intra-specific variations. Likewise, resistance against each metal was also very diverse. Cu and specially Cd, the most toxic heavy metal for these ciliates, are the best oxidative stress inducers. However, a correlation between fluorescence emission intensity and cellular metal sensitivity for each strain cannot be established. Results are discussed and compared with similar findings previously published in other unicellular and pluricellular organisms.

Plastic Hinging Collapse of Periodic Cellular Truss Cores

Periodic cellular metals (PCMs) have considerable potential as a new type of hybrid material for sandwich panel cores, due to their high architectural efficiency and load-bearing capability at relatively low mass. The mechanical performance of these materials is controlled by both architectural and microstructural parameters. In the case of PCM struts that have intermediate slenderness ratios, the peak load capacity is determined by the inelastic buckling stress, in which the rotation of the strut ends is opposed by their plastic hinging resistance. Strut rotation is, therefore, a key component of the overall PCM failure mechanism. In the present study, a method is developed for measuring the plastic hinging strength by allowing the truss core nodes to spread radially outward during collapse. Both finite element (FE) and experimental methods were used to study this behavior in AA3003 truss cores; the effect of work hardening, interfacial friction, and specimen size was examined. Direct measures for the plastic hinging resistance can be obtained and it was possible to demonstrate that while work hardening during PCM stretch-forming fabrication introduces significant work hardening in the near-hinge region, not all of the strengthening is available to resist plastic hinging collapse by virtue of the Bauschinger effect.

Loss of Zhf and the tightly regulated zinc-uptake system SpZrt1 inSchizosaccharomyces pombereveals the delicacy of cellular zinc balance

Abstract Zinc is an essential micronutrient, and yet it can be toxic when present in excess. Zinc acquisition and distribution are dependent on tightly controlled transport of Zn(2+) ions. Schizosaccharomyces pombe represents a second eukaryotic model to study cellular metal homeostasis. In several ways its micronutrient metabolism is fundamentally different from Saccharomyces cerevisiae. We identified the first Zn(2+)-uptake system in S. pombe and named it SpZrt1. Knock-out strains for all three ZIP (Zrt, Irt-like protein) transporters in fission yeast were constructed. Only zrt1Delta cells were unable to grow at low Zn(2+) and showed reduced (65)Zn(2+) uptake. Elemental profiles revealed a strong decrease in zinc accumulation. Cd(2+) ions inhibited uptake but Fe(2+) or Mn(2+) did not. Both mRNA abundance and protein amount are tightly regulated. Zrt1 activity is rapidly shut down upon transfer of zinc-deficient cells to zinc-replete conditions. In cells lacking Zhf, a transporter mediating endoplasmic reticulum storage of zinc, this response is about 100-fold more sensitive. Thus, removal of excess of zinc from the cytosol is largely Zhf dependent. Moreover, cells deficient for both transporters are no longer able to adjust to changing external Zn(2+) concentrations. Optimal growth is restricted to a narrow range of Zn(2+) concentrations, illustrating the fine balance between micronutrient deficiency and toxicity.

Process–microstructure–property relationships in AA3003 expanded metal periodic cellular truss cores

Despite their significant potential as ultra-lightweight composite materials, comparatively little attention has been given to the microstructure of deformation formed periodic cellular metals (PCMs). Because shape plays such a determining role in their performance, it is the spatial distribution of microstructure which controls both the useful range of cellular architectures and their resultant mechanical properties. The present study examines the effects of non-uniform recrystallization in expanded AA3003 sheet precursors on the PCM composite formability and mechanical performance. Because fabrication induced work-hardening and crack formation is localized to the hinge region, the pre-annealing temperature prior to fabrication provides a trade-off between the resultant compressive modulus and inelastic buckling strength of the PCM.

In SituX-Ray Tomography Studies of Microstructural Evolution Combined with 3D Modeling

AbstractSynchrotron x-ray microtomography is a characterization technique increasingly used to obtain 3D images of the interior of optically opaque materials with a spatial resolution in the micrometer range. As a nondestructive technique, it enables the monitoring of microstructural evolution duringin situexperiments. In this article, examples from three different fields of metals research illustrate the contribution of x-ray tomography data to modeling: deformation of cellular materials, metal solidification, and fatigue crack growth in Al alloys. Conventionally, tomography probes the 3D distribution of the x-ray attenuation coefficient within a sample. However, this technique is also being extended to determine the local crystallographic orientation in the bulk of materials (diffraction contrast tomography), a key issue for the modeling of microstructure in metals.

Thermal Conductivity of Cellular Metals Measured by the Transient Plane Source Method

The thermal conductivity of a collection of cellular metals has been measured by the Transient Plane Source (TPS) method. Using this method, it has been possible to cover different volumes of selected samples and to study their in-homogeneities from their surface to their inner part. Additionally, these samples have been characterized by tomography. With the TPS method, in combination with tomography, it has been possible to analyse the in-homogeneity of the samples as well as to characterize the thermal conductivity of a single in-homogeneous sample as a complete collection of different porosity specimens. This is the corrected version of the paper by Solórzano et al., Adv. Eng. Mater. 2008, 10, 371, which was unfortunately published in an uncorrected version.

Edge effects in compression testing periodic cellular metal sandwich cores

Compression testing of cellular sandwich core materials is often complicated by the presence of edge effects, in which the cells on the outside of the specimen deform at lower stresses than those in the bulk. As a result, minimum specimen length-to-cell-size ratios have been established in the literature for metallic foams. Periodic cellular metals (PCMs) are a recently developed class of materials that have received considerable interest due to their greater architectural efficiency and enhanced mechanical properties compared to conventional metal foams. In this study, edge effects of PCM core materials have been measured in compression using a new test platform which evaluates the properties of the core as a stand-alone material. This approach introduces uniform and periodically rigid boundary conditions to the PCM nodes, resulting in the same inelastic buckling failure mechanism that occurs in reference PCM sandwich panels. Edge effects were comparatively small and samples down to 2 × 2 unit cells were found to be representative of bulk-like cores.

Thermal Conductivity of Cellular Metals Measured by the Transient Plane Sour Method

The thermal conductivity of a collection of cellular metals has been measured by the Transient Plane Source (TPS) method. Using this method, it has been possible to cover different volumes of selected samples and to study their in-homogeneities from their surface to their inner part. Additionally, these samples have been characterized by tomography. The density of the different volumes covered by the heat flow has been calculated from the tomographic slices and it has been related to the thermal conductivity measurements. These results have shown a similar trend to those obtained characterizing the bulk samples. With the TPS method, in combination with tomography, it has been possible to analyse the in-homogeneity of the samples as well as to characterize the thermal conductivity of a single in-homogeneous sample as a complete collection of different porosity specimens.

Defect sensitivity of bulk PCMs composed of octet and Kagome trusses to mechanical behaviors subjected to compression

The Kagome truss has been attracting attention, because it has equivalent or even higher strength compared to the octet truss with the same material and density. In this work, another aspect, which seems to be important for its practical applications, that is, defect sensitivity of bulk PCMs (periodic cellular metals) composed of Kagome trusses to mechanical behaviors subjected to compression was compared with a counterpart composed of octet trusses. In order to investigate the mechanical characteristics of bulk PCMs composed of the two trusses, a hybrid approach was taken in this work. First, assuming perfectly uniform structure and deformation of WBK, the behavior of the bulk PCMs composed of infinite number of trusses was simulated by finite element analysis for a unit cell with periodic boundary conditions. From the results, the force-displacement response of a single strut composing the trusses in each bulk PCM was estimated. Then, the effects of geometric imperfections and the inhomogeneous material properties were evaluated by network analyses, in which the force-displacement responses were used to characterize mechanical behaviors of the networks. The imperfections were modeled to have Gaussian distributions, and the analysis results of the two bulk PCMs were compared to evaluate their defect sensitivities. For the geometric imperfections, the maximum strength of both bulk PCMs decreased gradually as the imperfection level increased. For material property imperfections, the maximum strength maintained nearly unchanged for the PCM composed of Kagome trusses. On the other hand, for that composed of octet trusses, it slightly dropped as the imperfection level increased. The octet truss PCM was found to be more sensitive to the property imperfections than the other.

Recent Advances in the Prediction of the Thermal Properties of Syntactic Metallic Hollow Sphere Structures

Metallic hollow sphere structures (MHSS) constitute a group of innovative materials which are characterised by more constant material properties compared to classical cellular metals. Their big potential lies within multifunctional applications where combinations of their properties yield symbiotic advantages. In this paper, the effective thermal conductivity of MHSS materials is investigated. Three different approaches, namely a Finite Element Method, a Lattice Monte Carlo Method and an analytical Maxwell model, are used. It is shown that all approaches complement each other and that the results are in excellent agreement.

Catalytic metal ion switching in zinc‐dependent deacetylases

The metallohydrolase UDP‐3‐O‐((R)‐3‐hydroxymyristoyl)‐N‐acetylglucosamine deacetylase (LpxC) catalyzes the first committed step in Lipid A biosynthesis, a critical component of the outer leaflet of gram‐negative bacteria. LpxC activity has previously been shown to be activated by a divalent transition metal ion (Zn(II), Co(II), or Ni(II)) and has been described as a mononuclear zinc enzyme. Fe(II) has not yet been considered as the in vivo catalytic metal ion. However, LpxC reconstituted with Fe(II) exhibits increased catalytic activity vs. Zn(II) and the activity of LpxC in E. coli cell extracts is oxygen‐sensitive. When LpxC is purified anaerobically from E. coli grown in media with defined metal concentrations, the ratio of iron/zinc bound to LpxC varies linearly with the iron/zinc ratio in the cell lysate, suggesting that the catalytic metal ion of LpxC depends on the cellular conditions. Binding of Fe2+ vs. Zn2+ has been measured and compared to free cellular metal concentrations. Two possibilities arise from these results – either LpxC lacks specificity for its active site metal, or the enzyme is subject to a regulatory mechanism that responds to intracellular metal concentrations. Preliminary results indicate another Zn‐dependent deacetylase, human histone deacetylase 8 (HDAC8), may also be able to use Fe(II) in vivo, suggesting this may be a broader theme in “zinc”‐dependent deacetylases.