Pyramidal Core Research Articles

Reactivity of [(Cp*CoPh)(Cp*Co)(μ-TePh)(μ-k2-Te,H-TeBH3)] Toward [M(CO)5·THF] (M = Mo and W), CS2, and [Fe2(CO)9

Syntheses and structural elucidation of homo- and heterochalcogen-bridged complexes of cobalt are described. The photolytic reaction of bimetallic hydridoborate species [(Cp*CoPh)(Cp*Co)(μ-TePh)(μ-k2-Te,H-TeBH3)] (1) in the presence of [M(CO)5·THF] (M = Mo and W) afforded unprecedented tellurolate-bridged [(Cp*Co)2(μ-TePh)3]+[TePh{M(CO)5}2]- (M = Mo (2), W (3)) as ionic complexes with the release of BH3. Complex 2 has three bridged-TePh moieties between two Cp*Co fragments in the cation part, whereas the anionic part, [TePh{M(CO)5}2]-, shows a distorted trigonal pyramidal core. In order to synthesize mixed chalcogenate-bridged complexes having both S and Te, we carried out the photolytic reaction of 1 with CS2. Although the objective of generating mixed chalcogen-bridged complex [(Cp*Co)2(μ-TePh)2(μ-S)] was not achieved, the reaction yielded an unusual bimetallic thiotellurite complex [(Cp*Co)2(μ-S3TeS3-κ2S:κ2Te:κ2S')] (4). Complex 4 has two wings, each consisting of three sulfur atoms, that are connected to two Co-atoms and one Te-atom. Further, to synthesize the Fe analogue of 2 and 3, a similar reaction was carried out with [Fe2(CO)9]. However, the reaction led to the formation of the trimetallic complex [Cp*Co(CO)(μ3-Te)2{Fe2(CO)6}] (5). These complexes were characterized by employing different multinuclear NMR, IR spectroscopies, single-crystal X-ray diffraction analyses, and mass spectrometry. Additionally, computational analyses of these chalcogen-bridged neutral and ionic complexes were conducted to offer insight into their bonding.

Legendre–Ritz solutions for vibration characteristics of three-dimensional double-layer lattice truss sandwich plates

In this paper, Legendre–Ritz solutions for vibration characteristics of double-layer lattice truss sandwich plates are proposed based on three-dimensional (3-D) elasticity theory. Double-layer lattice truss sandwich plates consist of three face sheets and two cores. The face sheets are composed of fiber-reinforced composites and the cores are composed of pyramidal lattice trusses made of isotropic materials. The pyramidal lattice core is equated to a homogeneous plate according to equivalence principle. Based on 3-D elasticity theory and pseudo excitation method (PEM), each layer's energy expressions of double-layer lattice truss sandwich plates are constructed. After that, Legendre polynomials are adopted to describe displacement components in length, width and thickness directions. On this basis, the Rayleigh-Ritz method is used to solve energy functions to obtain motion equations of double-layer lattice truss sandwich plates. The accuracy and validity of the present method are corroborated by comparisons with references and finite element method (FEM). Additionally, in order to find out effects of relevant parameters on dynamical characteristics of double-layer lattice truss sandwich plates, parametric studies are carried out by means of some numerical examples.

Local damage and imperfection sensitivities of pyramidal core sandwich cylinders

Local damage and imperfections may affect the loading capacity of truss core sandwich cylinders. This study develops a numerical model to investigate the effects of missing lattice struts, unbound nodes, openings, and eigenmode-shape imperfections on the buckling and post-buckling behavior of pyramidal core sandwich cylinders. Results from the numerical model show that the pyramidal core sandwich cylinder is sensitive to missing struts and unbound nodes when local buckling is the main failure model. Critical loads show a gradual decrease as the opening damage increases. Pyramidal core sandwich cylinders are not sensitive to eigenmode-shape imperfections compared to the equivalent single-walled shells.

Static and dynamic response of pyramidal lattice sandwich plate with composite face sheets reinforced by graphene platelets

For the pursuit of lightweight structures with excellent mechanical performance, sandwich structures with lightweight cores and strengthened face sheets have become popular in the advanced engineering fields in recent years. In this paper, the nonlinear static and dynamic responses of the sandwich plate constructed with the aluminum pyramidal lattice core and functionally graded graphene platelets reinforced composite (FG-GPLRC) face layers are analyzed. The partial differential equations of the pyramidal lattice sandwich plate considering the geometric nonlinearity are achieved based on the Reddy’s third order shear deformation theory (TSDT), which are solved by the combination of finite element model, Raphson’s method and Newmark numerical integration method. Four different types of the impact loads including the step loading, triangular loading, half-sine loading and exponential loading with the same peak value and duration time are investigated. The influences of the thickness-to-truss radium ratio and the angle of the truss core, as well as the weight fraction and distribution patterns of graphene platelets (GPLs) over the face sheets under different impact loads and different boundary conditions are analyzed. According to the numerical results, it is concluded that the sandwich plate with higher weight fraction of GPLs, lower thickness-to-truss radium ratio, and higher angle of the truss core can exhibit better performance in both static and dynamic loading conditions. The FG-X distribution of GPLs presents the best dynamic performance as compared to the other GPL distributions. The combination of lightweight truss core with the advanced GPLRC face sheets is instructive for potential applications and further research.

Optimizing Carbon-Based Perovskite Solar Cells with Pyramidal Core–Shell Nanoparticles for High Efficiency

Optimizing Carbon-Based Perovskite Solar Cells with Pyramidal Core–Shell Nanoparticles for High Efficiency

Theoretical and DFT Study of Atypical Pentanuclear [(iPr3P)Ni]5Hn (n = 4, 6, 8) Clusters: What are the Rules?

The structure, bonding, and properties of a series of atypical pentanuclear nickel hydride clusters supported by electron-rich iPr3P of the type [(iPr3P)Ni]5Hn (n = 4, 6, 8; H4, H6, H8) and their anionic models where iPr3P are substituted by H- (H4', H6', H8') were investigated by density functional theory (DFT) calculations. All clusters were calculated to adopt a similar square pyramidal core geometry. Calculations indicate singlet ground states with small singlet-triplet gaps for H4 and H6, similar to previously reported experimental values. Molecular orbital theory description clusters were investigated using the simplified model complexes [HNi]5Hn5- (n = 4, 6, 8; H4', H6', H8'). The results show that there are three skeletal electron pairs (SEPs) in H4'. The addition of two molecules of H2 to form H6' and H8' results in the partial or full occupation of two degenerate MOs (e* set) that give two SEPs and one SEP, respectively. Indeed, the occupation of these low-lying weakly antibonding orbitals governs the multielectron chemistry available for these clusters and plays a role in their unique reactivity.

Effect of geometrical parameters on compression performance and energy absorption of pyramidal thin-walled tube core sandwich panel

Sandwich panels with pyramidal cores made of thin-walled tubes absorb energy very well, but their main limitation is the complexity of producing such a structure. This study utilized a novel self-interlocking assembly technique to fabricate the lattice core, significantly reducing fabrication time and material requirements. Experimental tests and finite element analyses were performed to investigate the effect of geometrical parameters on the out-of-plane characteristics of sandwich panels with pyramidal thin-walled tube cores and relative densities ranging from 1.39% to 3.96%. Finite element predictions for deformation mechanisms, compressive strength, and energy absorption match experimental results. The results reveal that the proposed approach for producing the nodes worked successfully, with no brazed nodes breaking. The amount of energy absorbed per unit of mass reduces by 22% and 27%, respectively, when the slenderness is increased from 3 to 5 and subsequently from 5 to 7. In addition, when the angle of the tubes is increased from 50° to 55°, it makes them 23% stronger and absorbs 13% more energy per unit mass. Regarding strength and energy absorption per unit volume, pyramidal thin-walled tube cores are better than traditional lightweight sandwich panels, especially at lower relative densities.

Effect of truss core on sound radiation behavior of sandwich plate structures under structure borne excitation

Compared with traditional honeycomb and stiffened sandwich structures, lattice-based structures are considered an ideal substitute for traditional core structures due to their high stiffness and other potential multifunctional application characteristics. Based on that, the sound radiation characteristics of the sandwich plate with different truss cores under structure borne excitation were investigated in the current paper, wherein three truss cores, including pyramidal, tetrahedral and 3D-kagome cores types, are considered. The governing equations for the vibration and sound radiation analysis of the sandwich plate structure are carried out using the static equilibrium method, and then solved via the Navier approach and Rayleigh integral. By comparing the experimental results, the validity of the proposed theoretical model is verified. The theoretical model is subsequently used to investigate the influences of truss core geometric parameters and types, face sheet-core face sheet thickness ratio and aspect ratio on sandwich plate sound radiation characteristics. The results indicate that, in the range [ 5 ∘ ≤ θ ≤ 52 ∘ ] and [ 52 ∘ < θ ≤ 85 ∘ ] , the tetrahedral and 3D-Kagome core types have the maximum natural frequency values, respectively, while the resonance peaks of sound pressure level curves move to lower frequency region with the increase in truss core radius and face sheet-core face sheet thickness ratio, and the sandwich plate with the 3D-kagome core shows better sound radiation characteristics in the wide frequency range.

The Chronology of Monte d’Accoddi (Sardinia, Italy) – New Radiocarbon Dates

The shrine at Monte d’Accoddi constitutes an architectural unicum in the context of the Mediterranean of the 4th millennium cal. BC. The building comprised of a terrace with an access ramp, a form that has led to an ongoing debate as to the possible origins of this architectural model. In its earliest phase, attributable to the first half of the 4th millennium cal. BC, the edifice consisted of a truncated pyramidal core. During the second half of the same millennium this was englobed by a second building, similar to the first in general shape, but much larger and with a central, possibly stepped, core. The site was occupied during the 3rd millennium cal. BC and occasionally so during the following proto-historic and subsequent phases of history. This paper will present new radiocarbon dates that will help to define the construction and occupation phases of the monument as well as the settlement that grew around it.

Heat transfer property of C/SiC composite pyramidal lattice core sandwich structures

An explicit analytical model for predicting the heat transfer in C/SiC composite pyramidal lattice core sandwich structures is proposed with considering the radiation emitted from the struts. Temperature gradient in thickness direction of the lattice core sandwich structuresis considered in the proposed model. The predictions are compared with the published experimental data and analytical results. It indicates the effect of the radiation emitted from the struts on the equivalent thermal conductivity becomes more significant at high temperature and cannot be overlooked. The present model is more accurate in estimating the high-temperature equivalent thermal conductivity of pyramidal lattice core sandwich structures than those models without considering the radiation of struts. The effects of geometry, solid emissivity, and temperature on the equivalent thermal conductivity of pyramidal lattice core sandwich structures are well discussed.

Nonlinear vibration responses of lattice sandwich beams with FGM facesheets based on an improved thermo-mechanical equivalent model

An investigation on the nonlinear vibration behaviors of a lattice sandwich beam with pyramidal truss core and functionally graded material (FGM) facesheets under thermo-mechanical loads is performed with consideration of the temperature-dependency of material properties. In present work, an improved equivalent methodology is proposed to determine the transverse shear modulus of pyramidal core subjected to a non-uniform thermal field across thickness direction and makes lattice truss core transformed to a continuous layer. Finally, the lattice sandwich beam is modeled as a three-layered sandwich structure. The facesheets are made of FGMs with mixture of ceramics and metals in a pow-law form. The outer surfaces of facesheets are ceramic-rich, while the inner surfaces are metal-rich. The nonlinear strain–displacement relations are established based on the von Kármán large deflection and classical beam theory. The Lagrange method are implemented to yield equations governing the free and forced vibration behaviors. With the help of Newton-Raphson iteration technique as well as the Newmark-β method, the nonlinear time-independent responses of the sandwich beam under thermal environment are solved. A comprehensive parameter study is directed to address the effects of non-uniform thermal environment, FMG facesheets, external load, and lattice core on the nonlinear vibrations of the beams.

Analyzing sandwich panel with new proposed core for bending and compression resistance

Sandwich panels are used in many industries for their lightweight compared to high strength. Most of the sandwich panels application are bending and compression, which relies on the core type of the panel. Widely used in additive manufacturing is pyramid cell cores. In this article, two new cores, the reinforced pyramid cell model and the C-half circle cell model, are proposed to replace the pyramidal core and to verify their advantages and disadvantages with respect to it compression and in bending. The comparison was done in the ABAQUS simulation. A semi-analytical method was used as well as experimental tests were carried out to verify the numerical simulation on ABAQUS. The results have been validated, the difference remains below 10%. According to the simulations, the deformation of the skin of the half circle cell panel decreases by 15% in compression while the deflection of the reinforced pyramid cell panel decreases by 26% in bending compared to the pyramid cell panel. However, the most effective results in absorbing compression are half circle cell which is allowed to make impact insulation.

Surface etching-dependent geometry tailoring and multi-spectral information of Au@AuAg yolk-shell nanostructure with asymmetrical pyramidal core: The application in Co2+ determination

In this paper, a novel Au@AuAg yolk-shell heterogeneous nanostructure is designed as plasmonic spectroscopic sensor based on surface etching for ultrasensitive detection of trace cobalt ions (Co2+). Due to the surface diffusion of gold atoms, the Ag at one end of the core gold nanobipyramids (Au NBPs) is retained, and Au@AuAg yolk-shell nanostructure with asymmetric core is prepared. The alloy shell is coupled to Au NBPs and the interface of asymmetric Ag respectively, the two local surface plasmon resonance bands will have obvious reverse changes depending on the surface morphology of the shell. By using this distinct plasmon response generated by Co2+ induced surface etching, which is driven by discrepancy of double-peaks, a sensing method has been established to realize multi-information spectral detection of Co2+. There is a good linear relationship between the intensity ratio and the Co2+ concentration in the range of 1–100 nM, in which the limit of detection is 0.2 nM. This method further improves the sensing capability by combining multiple pieces of strongly changing spectral information, and demonstrates great advantages and potential of Au@AuAg yolk-shell heterogeneous nanostructure as a multi-information plasmonic sensor based on etched shell surface for trace detection.

Effect of high-low temperature on the compressive and shear performances of composite sandwich panels with pyramidal lattice truss cores

Composite sandwich panels with pyramidal lattice truss cores (CSPPLTCs) were manufactured employing waterjet-cutting technology and interlocking assembly. The effect of high-low temperature environments on the out-of-plane compressive and shear performance of the panels was studied using theoretical and experimental methods. In particular, the out-of-plane compressive stiffness, strength of sandwich panels with pyramidal lattice truss cores, their shear stiffness, and strength in high-low temperature environments were predicted using theoretical equations. The study found that in low-temperature environments, the movement of molecular chain segments in the epoxy is hindered, futhermore, the mismatched thermal expansivity of carbon fiber and epoxy resin leads to the improvement of interface bonding performance, thus improving the out-of-plane compressive and shear performance of CSPPLTCs; in high temperature environments, the movement of molecular chain segments in the epoxy gets more active and tends to move freely, so the resin turns into a flexible state with high elasticity from the stiff glass state, which finally causes a deterioration in out-of-plane compressive and shear performance of CSPPLTCs. According to observations, the failure mode depends on temperature environments. Brittle fracture and crushing failure happen in the composite struts at low temperature; plastic microbuckling may happen in the composite struts at high temperature.

Bending performance of a sandwich beam with sheet metal pyramidal core

Metallic sandwich structures with pyramidal cellular cores have proven to be highly effective in the industry of advanced lightweight materials thanks to their high strength-to-weight ratios. This paper presents the investigation of the bending performance of a sandwich structure based on a novel pyramidal cellular core. The effective bending and shear stiffness are investigated using numerical and experimental approaches. Furthermore, the finite element model created for the four-point bending scenario is in good agreement with the experimental one and can be subsequently used for further product development. This represents a cost-efficient method used for structural optimisation and may lead to improved mechanical properties and higher lightweight capabilities. The study includes a comparison to other existing periodic core topologies which shows that the investigated pyramidal structure has high potential to be used for the construction of sandwich panel assemblies.

Modeling and simulation of static and dynamic behavior in composite sandwich plates with hourglass lattice cores based on reduced-order model

The composite sandwich plate with hourglass lattice cores (CSP-HLC) is a novel cellular structure that can increase the width-to-length ratio and reduce the inter-node spacing. However, its static and dynamic behaviors are difficult to analyze due to the complex microstructures. In this work, a computational homogenization method is proposed for calculating the constitutive parameters. A reduced-order plate model is then derived through dimensional reduction from the three-dimensional orthotropic thermoelasticity framework. The effectiveness and accuracy of the proposed model were verified by comparing with the static-displacement and free-vibration results of 3D direct numerical simulations. The parameter analysis showed that the different material and structural parameters of the hourglass lattice core had different effects on the equivalent stiffnesses and natural frequencies of the CSP-HLC. Compared with the composite sandwich plate with pyramidal lattice cores, the displacement of the CSP-HLC was smaller under the same load and boundary conditions, and the natural frequencies were also smaller, which may have been because the additional equivalent density of the CSP-HLC influenced the frequency more predominantly than the extra equivalent stiffness.

Comparative study on the blast load response of woven and lattice core metallic sandwich panels

Sandwich structures are potential alternatives to monolithic plates for the purpose of absorbing energy and managing the impulse associated with blast loading. The study of sandwich structures subjected to blast loading is a rapidly expanding area of activity. Sandwich structures are extensively used in blast dissipation applications on account of their excellent physical and mechanical properties. These sacrificial cladding structures absorb energy through progressive plastic deformation of the front-facing plate and the core layer; thus minimizing the transfer of the peak force to the non-sacrificial structure. The core absorbs most of the energy and hence has a significant influence on the blast behavior of sandwich structures. The core layer can have several topologies, which in turn have various configurations. The present study numerically evaluated and compared the effectiveness of using Triangular Woven and Pyramidal Lattice core configurations in sandwich panels for resisting blast loads. The parametric study consisted of the effect of change in outer layer thicknesses of sandwich panels and the application of successive blast loads in the performance of the sandwich panels. The study was conducted for seven outer layer thickness combinations modeled in ANSYS Workbench Explicit Dynamics. All the models were subjected to a blast load with the same scaled distance. The comparison of the simulated results was used to determine the more suitable core configuration for dissipating blast loads. Pyramidal lattice panels were found to be 5% and 48% more efficient than a triangular woven panel of comparable relative core density under normal blast load and successive blast load respectively.

Dislocation core structure and motion in pure titanium and titanium alloys: A first-principles study

The deformation mode of some titanium (Ti) alloys differs from that of pure Ti due to alloying elements in the α-phase. Herein, we investigated all possible slip modes in pure Ti and the effects of Al and V solutes as typical additive elements on the dislocation motion in α-Ti alloys using density functional theory (DFT) calculations. The stacking fault (SF) energy calculations indicated that both Al and V solutes reduce the SF energy in the basal plane. In contrast, Al solute increases the SF energy in the prismatic plane, making the slip motion in different planes more comparable. DFT calculations were subsequently carried out to simulate dislocation core structures. The energy landscape of the transition between all possible dislocation core structures and the barriers for dislocation glide in various slip planes clarified the nature of dislocation motion in pure Ti; i) the energy of prismatic core is higher than the most stable pyramidal core, and thereby dislocations need to overcome the energy barrier of the cross-slip (22.8 meV/b) when they move in the prismatic plane, ii) the energy difference between the prismatic and basal cores is higher (127 meV/b), that indicates the basal slip does not activate, iii) however, the Peierls barrier for motion in the basal plane is not as high (16 meV/b) once the dislocation exists stably in the basal plane. Direct calculations for the dislocation core around solutes revealed that both Al and V solutes facilitate dislocation motion in the basal plane by reducing the energy difference between the prismatic and basal cores. Thus, the effect of solutes characterizes the difference in the deformation mode of pure Ti and α-Ti alloys.

Experimental and numerical investigation of adhesively bonded additive manufactured sandwich structures with a pyramidal lattice core

ASBTRACT The application of adhesively bonded joints has increased in a large variety of different industrial sectors over the last decades. In comparison to other joining techniques, adhesively bonded joints can offer easier assembly, weight reduction, lower stress concentration, etc. Additive Manufacturing (AM) as a transformational approach in Industry 4.0 can even improve the structural performance of such joints in terms of more weight reduction, making more homogenous stresses in the adhesive layer of the bonded area. In this work, an adhesively bonded single lap joint (SLJ) with metallic sandwich structures and a pyramidal lattice core as adherend by using AM was designed, produced and tensile tested. The result of this study showed that in addition to the significant savings in the weight of the adhesively bonded joint, the additive manufactured sandwich adherend produces a more homogenous stress distribution compared to conventional adherends with the same material. Furthermore, two different finite element (FE) approaches were used for modelling the fracture behaviour of the additive manufactured joint, namely a solid element formulation and a simplified model using shell-beam formulation. The simplified shell-beam formulation reduces the modelling and calculation efforts massively and shows a good agreement with experimental results.

Additive manufactured sandwich structures: Mechanical characterization and usage potential in small aircraft

The developments in manufacturing technologies, in particular through the establishment of additive manufacturing (AM) processes, offer new possibilities in sandwich design. With the use of AM it is possible to build a full metallic sandwich plate without the need of adhesive connections. This results in a more reliable bond. In this paper, AM metallic sandwich structures with pyramidal cores and their application as load carrying members in small aircraft are investigated. For this, analytical and numerical models describing the sandwich properties are first derived and then experimentally validated. The tested specimens are produced from AlSi10Mg using Laser Powder Bed Fusion (LPBF). These models are then used to derive equations which are needed to implement a homogenized element for numerical calculations. Afterwards the element is used to analyze and optimize a small aircraft wing. At last, the resulting wing is compared to an equivalent wing using a conventional structure. It is shown that compared to conventional structures, high weight savings can be reached by using AM sandwich structures, but also that with AlSi10Mg no sufficient qualities can be reached to obtain the needed structural performance.