Core Topology Research Articles

Experimental and finite element analyses of a 3D printed sandwich with an auxetic or non-auxetic core

This work presents the results of experimental and numerical analyses of the static properties of architectural cores and the dynamic behavior of sandwich structures made with an auxetic or non-auxetic core. Three architectural cores have been studied which are re-entrant, rectangular and hexagonal honeycombs. Each configuration was produced with four relative densities depending on the number of cells in the width of the specimens. The specimens were made with additive manufacturing technology. The material used to make the specimens was polylactic acid with flax fibers. Several tensile tests were carried out on the architectural cores to analyze and understand the influence of the topology and the density of the core on the Poisson’s ratio and the Young’s modulus of these architectural structures. Then, vibration tests were carried out on the cores and the sandwich structures. The objective was to study the influence of these structures and their densities on the dynamic properties of sandwiches. The structural Poisson’s ratio shows a sensitive behavior to the core topology and density.

Synthesis, structures, and magnetic properties of butterfly-shaped hexanuclear [FeIII4LnIII2] single-molecule magnets

A series of new FeIII4LnIII2 complexes possessing a unique centrosymmetric chair-like core topology have been synthesized and characterized.

Reconstructing gene regulatory networks of biological function using differential equations of multilayer perceptrons

BackgroundBuilding biological networks with a certain function is a challenge in systems biology. For the functionality of small (less than ten nodes) biological networks, most methods are implemented by exhausting all possible network topological spaces. This exhaustive approach is difficult to scale to large-scale biological networks. And regulatory relationships are complex and often nonlinear or non-monotonic, which makes inference using linear models challenging.ResultsIn this paper, we propose a multi-layer perceptron-based differential equation method, which operates by training a fully connected neural network (NN) to simulate the transcription rate of genes in traditional differential equations. We verify whether the regulatory network constructed by the NN method can continue to achieve the expected biological function by verifying the degree of overlap between the regulatory network discovered by NN and the regulatory network constructed by the Hill function. And we validate our approach by adapting to noise signals, regulator knockout, and constructing large-scale gene regulatory networks using link-knockout techniques. We apply a real dataset (the mesoderm inducer Xenopus Brachyury expression) to construct the core topology of the gene regulatory network and find that Xbra is only strongly expressed at moderate levels of activin signaling.ConclusionWe have demonstrated from the results that this method has the ability to identify the underlying network topology and functional mechanisms, and can also be applied to larger and more complex gene network topologies.

Efficiency-oriented circuit parameter optimization of dual active bridge converter

The power carbon neutrality path is to build a new power system with new energy as the main body. Dual active bridge (DAB) converter is considered as the core topology of new power system mode due to its galvanic isolation, bi-directional power capability, and wide soft-switching range, which is responsible for inter-connection between DC buses of different voltage levels and various DC loads. However, the lack of fast and accurate quantitative circuit parameter optimization design methods in DAB converter affects the improvement of the full working domain efficiency. In this paper, a hierarchical filtering method considering the control parameter is proposed to avoid the full range exhaustive search, and the effectiveness and correctness of the method are verified experimentally. First layer circuit characteristics must fulfill output power and inductor current requirements. The second layer filters poor inductor RMS current and soft-switching parameters. The last layer filters out weak steady-state circuit characteristics and identifies optimal regions. The proposed method improves the efficiency while reducing the area of the circuit parameter region for calculating the loss function by 85% compared with the traditional full-scale search method based on the loss analysis model, thus improving the optimization speed. The optimal circuit parameter solving process provides a graphical representation of the relationship between DAB operating characteristics and the optimal parameter area, ensuring proper optimization. Besides, the idea of hierarchical filtering can be well applied to the optimal design of other converters, and better guide the industrialization of products. • Using hierarchical filtering method can speed up the design. • Visualization of parameters can ensure the correctness of optimization results. • The design of other converters can also use the hierarchical filtering method. • Optimal design of parameters can ensure the normal operation of the device and also improve the steady-state characteristics.

Heterotrimetallic Assemblies with 1,2,4,5-Tetrakis(diphenylphosphino)benzene Bridges: Constructs for Controlling the Separation and Spatial Orientation of Redox-Active Metallodithiolene Groups.

Metallodithiolene complexes of the type [(R2C2S2)M(η2-tpbz)] [R = CN, Ph, or p-anisyl; M = Ni2+, Pd2+, or Pt2+; tpbz = 1,2,4,5-tetrakis(diphenylphosphino)benzene] chelate transition metals ions to form trimetallic arrays [[(R2C2S2)M(tpbz)]2M']n+, where M' is square planar Pt2+, tetrahedral Cu+, Ag+, or Au+, or octahedral {ReBr(CO)}/{Re(CO)2}+. Forcing conditions (190 °C reflux in decalin, 72 h) are demanded for the Re+ compounds. With third-row metals at the nexus, the compounds are stable to air. Twelve members of the set have been characterized by X-ray diffraction and reveal dithiolene centroid-centroid distances ranging from 22.4 to 24.0 Å. Folding around each tpbz intrachelate P···P axis such that the MP2/M'P2 planes meet the tpbz P2C6P2 mean plane at non-zero values gives rise to core topologies that appear "S-like" or herringbone-like for M' = Pt2+ or {ReBr(CO)}/{Re(CO)2}+. Calculations reveal that departure from idealized D2h/D2d/C2v symmetries is induced by steric crowding between Ph groups and that dynamic, fluxional behavior is pertinent to the solution phase because multiple, lower-symmetry minima of comparable energy exist. Spectroscopically, the formation of the trimetallic arrays is marked by a shift of the open end 31P nuclear magnetic resonance signal from approximately -14.5 ppm to approximately +41, approximately +20.5, and approximately +28.5 ppm for M' = Pt2+, Au+, and {ReBr(CO)}/{Re(CO)2}+, respectively. Electrochemically, dithiolene-based oxidations are observed for the R = Ph and M' = Pt2+ or Au+ compounds but at potentials that are anodically shifted relative to charge-neutral [[(R2C2S2)M]2(μ-tpbz)]. The compounds reported clarify the possibilities for the synthesis of assemblies in which weakly coupled spins may be created in their modular (R2C2S2)M and M' parts.

Novel design of honeycomb hybrid sandwich structures under air-blast

In this study, dynamic explicit analysis was performed to examine the air-blast performance of various hybrid sandwich designs in terms of face plate deflections and energy dissipation capacity under the conventional weapons effects program (CONWEP) air-blast loads ranging from 3 kg to 8 kg trinitrotoluene for stand-off distance ranges from 150 mm to 200 mm. The blast resistance of honeycomb sandwich configurations was evaluated using steel honeycomb with different core topologies, crushable Al foam-filled steel honeycomb, and steel or steel with 3D Kevlar/polypropylene laminate employing fiber metal laminate (FML) front face. For an accurate prediction of the deformation mechanism of all steel parts, the Johnson-Cook (J-C) model was used. The composite failure criteria of Hashin, Puck, and Matzenmiller were implemented to accurately examine the fiber and matrix damage behavior. The novel hybrid design of the honeycomb sandwich structure’s blast resistance is improved by the employment of foam-filled honeycomb, an FML front face, and a circular honeycomb core. In comparison to other sandwich configurations, a novel designed hybrid sandwich construction composed of foam filled circular honeycomb with FML front facing and steel back facing (FCH-1KP0.5) achieved the highest blast resistance due to its lowest face deflection with the smallest plastic dissipation energy.

Numerical Investigation of Different Core Topologies in Sandwich-Structured Composites Subjected to Air-Blast Impact

Air-blast loading is a serious threat to military and civil vehicles, buildings, containers, and cargo. Applications of sandwich-structured composites have attracted increasing interest in modern lightweight design and in the construction of dynamic loading regimes due to their high resistance against blast and ballistic impacts. The functional properties of such composites are determined by the interplay of their face sheet material and the employed core topology. The core topology is the most important parameter affecting the structural behavior of sandwich composites. Therefore, this contribution presents a thorough numerical investigation of different core topologies in sandwich-structured composites subjected to blast loading. Special emphasis is put on prismatic and lattice core topologies displaying auxetic and classical non-auxetic deformation characteristics in order to illustrate the beneficial properties of auxetic core topologies. Their dynamic responses, elastic and plastic deformations, failure mechanisms, and energy absorption capabilities are numerically analyzed and compared. The numerical studies are performed by means of the commercial finite element code ABAQUS/Explicit, including a model for structural failure.

Techniques for applying reinforcement learning to routing and wavelength assignment problems in optical fiber communication networks

We propose a novel application of reinforcement learning (RL) with invalid action masking and a novel training methodology for routing and wavelength assignment (RWA) in fixed-grid optical networks and demonstrate the generalizability of the learned policy to a realistic traffic matrix unseen during training. Through the introduction of invalid action masking and a new training method, the applicability of RL to RWA in fixed-grid networks is extended from considering connection requests between nodes to servicing demands of a given bit rate, such that lightpaths can be used to service multiple demands subject to capacity constraints. We outline the additional challenges involved for this RWA problem, for which we found that standard RL had low performance compared to that of baseline heuristics, in comparison with the connection requests RWA problem considered in the literature. Thus, we propose invalid action masking and a novel training method to improve the efficacy of the RL agent. With invalid action masking, domain knowledge is embedded in the RL model to constrain the action space of the RL agent to lightpaths that can support the current request, reducing the size of the action space and thus increasing the efficacy of the agent. In the proposed training method, the RL model is trained on a simplified version of the problem and evaluated on the target RWA problem, increasing the efficacy of the agent compared with training directly on the target problem. RL with invalid action masking and this training method outperforms standard RL and three state-of-the-art heuristics, namely, k shortest path first fit, first-fit k shortest path, and k shortest path most utilized, consistently across uniform and nonuniform traffic in terms of the number of accepted transmission requests for two real-world core topologies, NSFNET and COST–239. The RWA runtime of the proposed RL model is comparable to that of these heuristic approaches, demonstrating the potential for real-world applicability. Moreover, we show that the RL agent trained on uniform traffic is able to generalize well to a realistic nonuniform traffic distribution not seen during training, thus outperforming the heuristics for this traffic. Visualization of the learned RWA policy reveals an RWA strategy that differs significantly from those of the heuristic baselines in terms of the distribution of services across channels and the distribution across links.

Multifunctional cellular sandwich structures with optimised core topologies for improved mechanical properties and energy harvesting performance

This paper developed a multifunctional composite sandwich structure with optimised design on topological cores. As the main concern, full composite sandwich structures were manufactured with carbon fibre reinforced polymer (CFRP) facesheets and designed cores. Three-point bending tests have been performed to assess the mechanical performance of designed cellular sandwich structures. To evaluate the energy harvesting performance, the piezoelectric transducer was integrated at the interface between the upper facesheet and core, with both sinusoidal base excitation input and acceleration measured from real cruising aircraft and vehicle. It has been found that the sandwich with conventional honeycomb core has demonstrated the best mechanical performance, assessed under the bending tests. In terms of energy harvesting performance, sandwich with re-entrant honeycomb manifested approximately 20% higher RMS voltage output than sandwiches with conventional honeycomb and chiral structure core, evaluated both numerically and experimentally. The resistance sweep tests further suggested that the power output from sandwich with re-entrant honeycomb core was twice as large as that from sandwiches with conventional honeycomb and chiral structure cores, under optimal external resistance and sinusoidal base excitation.

Influences of skin thickness, core topology, depth and direction on flexural deformation and ductile failure of Al honeycomb-based sandwich structures

To systematically explore the effects of skin thickness, core topology, core depth and core direction on crushing deformation, failure behavior, mode and mechanism of aluminum (Al) honeycomb-based sandwich structures, a series of sandwich panels with various honeycomb core structures and skin thicknesses are prepared and deformed in the out-of-plane three-point bending deformations. Particularly, auxetic and non-auxetic honeycomb structures with an ultrathin cell wall thickness are investigated. Finite element simulations of all flexural deformations are conducted with the mixed Swift-Voce constitutive model which accurately describes plastic deformation. The numerical model is well validated by comparisons of the experimental load-deflection responses and simulation results. Ductile failure modes in Types I, II and III are identified, and their behaviors and mechanisms are numerically reproduced. Although core topology has a negligible effect on the failure mode, skin thickness, core depth, and core direction do. Additionally, using an auxetic honeycomb core, such as a reentrant unit, improves peak load, energy absorption, and the corresponding specific values of honeycomb-based sandwich structures. Increases in core depth and skin thickness, on the other hand, do not result in a consistent increase in specific peak load. To achieve a lighter and stronger Al honeycomb-based sandwich structure, utilizing a reentrant honeycomb core rather than a traditional non-auxetic core is more effective than increasing core depth and skin thickness.

Performance Evaluation of Sandwich Structures Printed by Vat Photopolymerization.

Additive manufacturing such as vat photopolymerization allows to fabricate intricate geometric structures than conventional manufacturing techniques. However, the manufacturing of lightweight sandwich structures with integrated core and facesheet is rarely fabricated using this process. In this study, photoactivatable liquid resin was used to fabricate sandwich structures with various intricate core topologies including the honeycomb, re-entrant honeycomb, diamond, and square by a vat photopolymerization technique. Uniaxial compression tests were performed to investigate the compressive modulus and strength of these lightweight structures. Sandwich cores with the diamond structure exhibited superior compressive and weight-saving properties whereas the re-entrant structures showed high energy absorption capacity. The fractured regions of the cellular cores were visualized by scanning electron microscopy. Elastoplastic finite element analyses showed the stress distribution of the sandwich structures under compressive loading, which are found to be in good agreement with the experimental results. Dynamic mechanical analysis was performed to compare the behavior of these structures under varying temperatures. All the sandwich structures exhibited more stable thermomechanical properties than the solid materials at elevated temperatures. The findings of this study offer insights into the superior structural and thermal properties of sandwich structures printed by a vat photopolymerization technique, which can benefit a wide range of engineering applications.

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.

Dynamics of Small Particle Inertial Migration in Curved Square Ducts

Microchannels are well known in microfluidic applications for the control and separation of microdroplets and cells. Often the objects in the flow experience inertial effects, resulting in dynamics that is a departure from the underlying channel flow dynamics. This paper considers small neutrally buoyant spherical particles suspended in flow through a curved duct having a square cross-section. The particle experiences a combination of inertial lift force induced by the disturbance from the primary flow along the duct, and drag from the secondary vortices in the cross-section, which drive migration of the particle within the cross-section. We construct a simplified model that preserves the core topology of the force field yet depends on a single parameter $\kappa$, quantifying the relative strength of the two forces. We show that $\kappa$ is a bifurcation parameter for the dynamical system that describes motion of the particle in the cross-section of the duct. At large values of $\kappa$ there exists an attracting limit cycle in each of the upper and lower halves of the duct. At small $\kappa$ we find that particles migrate to one of four stable foci. Between these extremes, there is an intermediate range of $\kappa$ for which all particles migrate to a single stable focus. Noting that the positions of the limit cycles and foci vary with the value of $\kappa$, this behavior indicates that, for a suitable particle mixture, duct bend radius might be chosen to segregate particles by size. We evaluate the time and axial distance required to focus particles near the unique stable node, which determines the duct length required for particle segregation.

Bending properties of sandwich sheets with metallic face sheets and additively manufactured 3D CFRP lattice cores

• Sandwich sheets with representative shell-lattice, truss-lattice and plate-lattice cores are proposed. • Effects of core topologies on mechanical properties and bendability of sandwich sheets are clarified. • Theoretical predictions of failure modes during bending of sandwich sheets with 3D lattice cores. • Bendable sandwich sheets with 3D lattice cores are successfully designed and produced. • Bendable sandwich sheets with multifunctional application potentials. To improve structural performance, bendability and potential functionality of metal-based sandwich sheets, the 3D lattice cores were sandwiched between thin metallic face sheets. The bending properties of sandwich sheets with 3D printed carbon fiber reinforced plastic (CFRP) lattice cores originating from basic topologies of spherical shell, tetrahedral truss and tetrahedral plate were systematically investigated. The effects of core topologies, core relative densities, core heights, face sheet thicknesses on structural properties were clarified. The common failure modes during bending of sandwich sheets, such as face buckling and shear failure of core, were deeply investigated by theoretical models and experimental tests. At a prescribed radius of 60 mm, the sandwich sheets with the bilayered dome, octet truss and plate lattice cores of relative density of 50 %, height of 6 mm and face sheet thickness of 0.5 mm are bendable. This study demonstrates the feasibility of design and production of bendable sandwich sheets with 3D lattice cores based on the theoretical and experimental validations. The designed bendable sandwich sheets can be adopted to replace conventional heavy monolithic metal sheets in various engineering applications, which is anticipated to fulfill the high demand for lightweight functional materials.

Investigation on the flexural properties of sandwich beams with auxetic core

Availing cellular structures as the core of sandwich beams is an innovative approach to improve the efficiency of them. Nonetheless, the flexural characteristics of sandwich beams are affiliated to the core topology. Accordingly, choosing an appropriate core can have a significant efficacy on the performance of sandwich beams. The purpose of the present study is to assess the influence of using auxetic cores in flexural properties of sandwich beams. Specifically, experimental and finite element approaches were implemented to evaluate the flexural behavior, energy absorption and the stiffness of fully integrated 3D printed polymeric sandwich beams, made of square node anti-tetra chiral, arrowhead and re-entrant auxetic cores, compared with the conventional honeycomb core. Fabrication of specimens was performed using the FDM 3D printing method, and three-point bending tests were conducted on the printed specimens. Results indicated that selection of proper core topology has remarkable effect on the flexural properties of sandwich beams, and using auxetic core is potentially an efficient method to enhance mechanical properties of sandwich beams due to high load bearing capacity.

The Mitigation of Eddy-Current Losses in Ferromagnetic Samples Produced by Laser Powder Bed Fusion

We study the use of topology optimization in the design of low-loss ferromagnetic core structures for additively manufactured electrical machines. The test case was a simple toroid core with a primary and a secondary winding. A 2D axisymmetric finite element method model was implemented for the toroid, and the core topology was optimized for minimum losses and maximum secondary flux linkage. The optimized core was then modified for additive manufacturing, and test samples were built via laser powder bed fusion. The B-H characteristics and losses of the core were measured in several operation points. The losses were compared against an additively manufactured solid core, a laminated core, and an additively manufactured core with evenly placed air gaps (i.e., grooves). The results show that the losses in the topology-optimized core are on the same level as the losses in the laminated core and considerably smaller than those in the solid core, which is a considerable improvement to previous published works.

Ditriphenylenothiophene butterfly-shape liquid crystals. The influence of polyarene core topology on self-organization, fluorescence and photoconductivity

Two series of regio-isomeric mesomorphous, luminescent and conductive compounds, based on a ditriphenylenothiophene core (α/β-DTPT), were successfully synthesized by the Suzuki–Miyaura cross-coupling/Scholl cyclo-dehydrogenation reactions tandem.

Laser Powder Bed Fusion of a Topology Optimized and Surface Textured Rudder Bulb with Lightweight and Drag-Reducing Design

This work demonstrates the advantages of using laser powder bed fusion for producing a rudder bulb of a moth class sailing racing boat via laser powder bed fusion (LPBF). The component was designed to reduce weight using an AlSi7Mg0.6 alloy and incorporated a biomimetic surface texture for drag reduction. For the topological optimization, the component was loaded structurally due to foil wing’s lift action as well as from the environment due to hydrodynamic resistance. The aim was to minimize core mass while preserving stiffness and the second to benefit from drag reduction capability in terms of passive surface behavior. The external surface texture is inspired by scales of the European sea bass. Both these features were embedded to the component and produced by LPBF in a single run, with the required resolution. Drag reduction was estimated in the order of 1% for free stream velocity of 2.5 m s−1. The production of the final part resulted in limited geometrical error with respect to scales 3D model, with the desired mechanical properties. A reduction in weight of approximately 58% with respect to original full solid model from 452 to 190 g was achieved thanks to core topology optimization. Sandblasting was adopted as finishing technique since it was able to improve surface quality while preserving fish scale geometries. The feasibility of producing the biomimetic surfaces and the weight reduction were validated with the produced full-sized component.

Phononic Bandgap Optimization in Sandwich Panels Using Cellular Truss Cores

The development of custom cellular materials has been driven by recent advances in additive manufacturing and structural topological optimization. These contemporary materials with complex topologies have better structural efficiency than traditional materials. Particularly, truss-like cellular structures exhibit considerable potential for application in lightweight structures owing to their excellent strength-to-mass ratio. Along with being light, these materials can exhibit unprecedented vibration properties, such as the phononic bandgap, which prohibits the propagation of mechanical waves over certain frequency ranges. Consequently, they have been extensively investigated over the last few years, being the cores for sandwich panels among the most important potential applications of lattice-based cellular structures. This study aims to develop a methodology for optimizing the topology of sandwich panels using cellular truss cores for bandgap maximization. In particular, a methodology is developed for designing lightweight composite panels with vibration absorption properties, which would bring significant benefits in applications such as satellites, spacecraft, aircraft, ships, automobiles, etc. The phononic bandgap of a periodic sandwich structure with a square core topology is maximized by varying the material and the geometrical properties of the core under different configurations. The proposed optimization methodology considers smooth approximations of the objective function to avoid non-differentiability problems and implements an optimization approach based on the globally convergent method of moving asymptotes. The results show that it is feasible to design a sandwich panel using a cellular core with large phononic bandgaps.

Design of a novel multi-walled tube-reinforced aluminum foam for energy absorption

In this paper, a novel multi-walled tube-reinforced aluminum foam (MWTRF) was proposed in an attempt to improve quasi-static compression performances and energy absorption. The quasi-static compression performance of the MWTRF fabricated by combining extrusion and electro-discharge machining (EDM) was investigated through using a combined experimental and numerical method. It is shown that the MWTRF has higher peak load and energy absorption capacity than those of the sum of empty multi-walled tube (EMWT) and aluminum foam (AF). The strengthening mechanism is that AF in MWTRF can stabilizes buckling and changes the compressive deformation mode of EMWT, resulting in elevating compression performance and energy absorption of MWTRF. Moreover, numerical parametric studied on MWTRF reveals that MWTRF with increasing density from the outer foam to the inner foam is the best combination mode with outstanding energy absorption efficiency, and the density of AF and the thickness of EMWT has an impact on the energy absorption capability. Furthermore, in comparison with competing core topologies, the energy absorption of the proposed MWTRF is outstanding on the material selection map.