Multilayered Shells Research Articles

Construction of layered double hydroxide-modified silica integrated multilayer shell phase change capsule with flame retardancy and highly efficient thermoregulation performance

Current energy problems have driven the development of thermal storage technology based on phase change materials (PCMs). However, the leakage and flammability of organic PCMs appeared as troublesome agendas that deserve attention. In this article, the strategy of constructing phase change capsules with paraffin wax (PW) core and multilayer shell was proposed aiming to address the above issues. For the integrated multi-layer shell, silica (SiO2) acts as initial layer to encapsulate the PW core, and then tannic acid (TA) was creatively taken to bridge the subsequent flame retardant layered double hydroxides (LDH) layer on the surface of the silica shell, and polyvinyl alcohol (PVA) layer was further introduced to improve the compatibility of phase change capsules with polymer matrix. Characterization of chemical structure and morphology confirmed that phase change capsules with LDH modified silica multilayer shell (M-EPCMs) was successfully prepared. The results indicated that M-EPCMs, particularly the representative M-EPCM-5, possessed outstanding thermal stability, excellent leak proofness, good thermal regulation performance as well as long-term cycling stability. Importantly, M-EPCM-5 with the thickest LDH layer can self-extinguish when exposed to fire, and especially can keep the integrity of its shell without breakage after being heated at high temperature. Furthermore, the silicone rubber foam (SRF) composite containing M-EPCM-5 can reach UL-94V-1 level, indicating the flame retardancy of SRF matrix was improved significantly. The possible flame retardant mechanism revels that LDH can not only accelerate the formation of dense ceramic protective layer in condensed phase, but also release non-combustible gases (H2O, CO2) in gas phase, thus improving the fire retardancy of M-EPCMs. Therefore, the construction strategy proposed in this article represents a powerful means to improve flame retardancy and prevent leakage of phase change capsules at the same time, which will greatly expand the application scope of PCMs.

Morphological structure of shell mould in investment casting

The stress state (SS) of multilayer shell mould (SM) is significantly influenced by its morphological structure, its variants, and the connections between the contacting layers. The purpose of this work is to establish the effect of sliding without friction of one of the layers of SS relative to the neighboring contacting layer on SS of the multilayer SM. The process of determining the stress-strain state (SSS) in the SM is modeled when it is filled with steel, in which there is a surface between the layers, where one layer of the SM is completely sliding relative to the adjacent neighboring layer. The task is to find the geometric location of a given surface by thickness of SM from the condition of the formulated objective function with the corresponding system of constraints. The construction of the mathematical model is based on equations of the linear theory of elasticity, the equations of thermal conductivity, solution of which is carried out by a proven numerical method. In the axisymmetric formulation, a complex three-component system is considered: liquid metal, solid metal, ceramic SM. Solid metal and SM are considered to be isotropic. Crack resistance of the SM is estimated by the stresses arising in it. On contact with the support filler (SF), it is possible to move the SM surface from the SF during the liquid metal cooling. In this case, the contact problem is solved – reassignment of the boundary conditions. An algorithm for solving the problem is compiled. The results of numerical modeling are displayed graphically in the form of plots. A detailed analysis of the obtained results was carried out. The inconsistency of manufacturing such a multilayer mould is shown. The results of the research can be useful in calculations of other functional multilayer shell systems.

Accurate Multilayered Shell Buckling Analysis via the Implicit-Mesh Discontinuous Galerkin Method

A novel formulation for the linear buckling analysis of multilayered shells is presented. High-order equivalent-single-layer shell theories based on the through-the-thickness expansion of the covariant components of the displacement field are employed. The novelty of the formulation regards the governing equations solution via implicit-mesh discontinuous Galerkin method. It is a high-order accurate numerical technique based on a discontinuous representation of the solution among the mesh elements and on the use of suitably defined boundary integrals to enforce the continuity of the solution at the inter-element interfaces as well as the boundary conditions. Owing to its discontinuous nature, it can be naturally employed with nonconventional meshes. In this work, it is combined with the implicitly defined mesh technique, whereby the mesh of the shell modeling domain is constructed by intersecting an easy-to-generate background grid and a level set function implicitly representing the cutouts. Several numerical examples are considered for the buckling loads of plates and shells modeled by different theories and characterized by various materials, geometry, boundary conditions, and cutouts. The obtained results are compared with literature and finite-element solutions, and they demonstrate the accuracy and the robustness of the proposed approach.

Sound transmission through baffled multilayered curved shells using a transfer matrix method

The present work describes the use of a transfer matrix method to define the acoustic behavior of multilayered and periodic baffled curved shells consisting of a generic arrangement of homogeneous and heterogeneous periodic layers of various nature (fluid, solid, and poroelastic). The dynamic stiffness matrix of a unit cell is manipulated in order to derive the through-radius transfer matrix of a cylindrical periodic layer. Thus, the acoustic radiation or transmission of multilayered shells can be assessed. The blocked pressure field due to an incident plane wave is defined by taking into account the infinite rigid baffle by means of a two-dimensional boundary element model. Analytical expressions for the cylindrical acoustic impedances are utilized to define the coupling with the bounding fluid media. Furthermore, a one-dimensional windowing technique is adopted to account for the finite length of the shells. The proposed approach is validated by systematic comparison with a full finite-boundary element method.

Hydrogen‐bonded polymer multilayer coatings via dynamic layer‐by‐layer assembly

AbstractWe developed the dynamic assembly of the hydrogen‐bonded multilayers of (poly(N‐vinylpyrrolidone/poly(methacrylic acid)) (PVPON/PMAA)) and compared their properties to the static multilayers. We found that dynamic multilayers, wherein a planar substrate is shaken during polymer adsorption, leads to a 15‐time faster deposition of the planar coatings. The thicknesses and roughness of the dynamic coatings were found to be ⁓30% larger than those of static (no shaking) multilayer films as measured by spectroscopic ellipsometry and atomic force microscopy. We examined the film growth, mechanical properties, wettability, hydration, and pH stability of the planar static and dynamic multilayers and demonstrated that these properties were insignificantly affected by the assembly mode. Both static and dynamic coatings produced microporous films when exposed to pH = 5.9, close to the film critical dissolution pH = 6. We discovered that during the release of the multilayer films into a solution to produce free‐standing films either as planar membranes or multilayer capsule shells, the molecular chain rearrangements result in the decreased roughness for both static and dynamic multilayers and lead to a decreased thickness of the dynamic multilayers. Our findings can help develop a rapid synthesis of thicker nanostructured polymer coatings for sensing and controlled delivery applications.

A suturable biohydrogel with mechanical matched property based on coating chitosan and polyethylene glycol shell for tissue patching

The mechanical mismatch between soft hydrated tissues and sutures has become a common negative impact on wound healing process. A novel method of coating multilayer polymer shells is thus reported to improve the mechanical performance of hydrogel sutures. It is suitable for tissue patching and shows advantages of convenient, efficient, and biosafety. Specifically, a precursor hydrogel (Cu@CMC) consisted of carboxymethyl chitosan and copper modified by carbon dots was used as the inner sheath, and then bonding the precursor hydrogel sheath with toughening polyethylene glycol network by anchoring sites composited from rigid chitosan shell integrated a whole structure. Subsequently, the whole system was soaked with EtOH, and rapid dehydration of EtOH was used to accelerate the entanglement process between the two coatings by constricting the molecular chains. Finally, an ideal suture (Cu-fiber) with both toughness and rigidness was obtained. The data showed that the tensile strength and biosafety of the hydrogel sutures prepared by the new strategy were significantly improved, and the skin, liver and vessel of rodents can be sutured without secondary damage. Moreover, it can inhibit inflammation response and promote the healing process of skin wound, indicating that the Cu-fiber will become a great candidate for tissue patching.

Refined multilayered beam, plate and shell elements based on Jacobi polynomials

In this paper, theories of structures based on hierarchical Jacobi expansions are explored for the static analysis of multilayered beams, plates and shells. They belong to the family of classical orthogonal polynomials. This expansion is employed in the framework of the Carrera Unified Formulation (CUF), which allows to generate finite element stiffness matrices in a straightforward way. CUF allows also to employ both layer-wise and equivalent single layer approaches in order to obtain the desired degree of precision and computational cost. In this work, CUF is exploited for the analysis of one-dimensional beams and two-dimensional plates and shells, and several case studies from the literature are analysed. Displacements, in-plane, transverse and shear stresses are shown. In particular, for some benchmarks, the shear stresses are calculated using the constitutive relations and the stress recovery technique. The obtained results clearly show the convenience of using equivalent single layer models when calculating displacements, in-plane stresses and shear stresses recovered by three-dimensional indefinite equilibrium equations. On the other hand, layer-wise models are able to accurately predict the structural behaviour, even though higher degrees of freedom are needed.

Failure analysis and curvature-based failure criterion of super large cooling tower under strong equivalent static wind load

More and more super large cooling towers are used in recent years. However, investigations on them under strong wind are still insufficient and there is still not an agreement failure criterion. In this paper, we conducted the failure analysis of a super large cooling tower with 253 m height under the equivalent static wind load. The finite element analysis procedure incorporates the multi-layered shell element, the softened damage model of concrete and the two-level secant algorithm in one framework. The numerical results show that the nonlinear response of the tower can be divided into four stages, i.e., the initial linear stage, the nonlinear stage, the softening linear stage and the failure stage. The failure of the cooling tower is caused by the loss of material strengths, i.e., the cracking of the concrete and the following yield of the meridian rebar. Finally, a curvature-based failure criterion is proposed to evaluate the failure of the cooling tower, in which the structure fails when the global curvature variation ratio ϰ reaches some definite values. ϰ is defined as the ratio of the total curvature variation with the initial total curvature of the cooling tower geometry. It can evaluate the total curvature variation in a global view. It is recommended that ϰ can be used as an index in the design of the cooling tower, and 1.0% and 3.5% can be deemed as the nonlinear and failure index, respectively.

Precise mix-design of Ultra-High Performance Concrete (UHPC) based on physicochemical packing method: From the perspective of cement hydration

• A physicochemical packing method to optimize the design of UHPC is proposed. • A new equivalent particle size distribution of hydrated cement is calculated. • The macro characteristics of the newly developed UHPC is evaluated. • The hydration kinetics of the newly developed UHPC is evaluated. • The microstructure development of the newly developed UHPC is evaluated. It is widely accepted that Ultra-High Performance Concrete (UHPC) could be designed by the employment of Modified Andreasen and Andersen (MAA) particle packing model. However, the traditional MAA model only takes into account that dry particles reach the dense packing status under physical conditions, without considering the chemical hydration of wet cement particles. To solve this problem, this study adopts a physicochemical packing method to optimize the mix-design of UHPC through establishing a new equivalent particle size distribution of hydrated cement by applying a multilayer spherical shell model. Based on this, the mix proportion of UHPC is redesigned and the properties of the optimized UHPC are evaluated afterwards. The results show that the optimized mix-design leads to higher particle packing density of UHPC, thereby improving the durability on the premise of guaranteeing the workability and mechanical properties. Meanwhile, the optimized mix-design can also achieve denser micro structures of UHPC matrix, which provides a valuable reference to design UHPC more scientifically and reasonably.

Nickel and oxygen-containing functional groups co-decorated graphene-like shells as catalytic sites with excellent selective hydrogenation activity and robust stability

Encapsulation of metal nanoparticles is one of the promising strategies to overcome the instability of supported metal catalysts. However, improving the hydrogenation activity of multilayer graphene-like encapsulationremains a critical challenge. To address this issue, multilayer graphene-like shells (MGSs) doped with oxygen-containing functional groups (OFGs) encapsulated Ni nanoparticles catalysts (Ni@OC) were synthesized via calcining the calcination of Ni-based metal-organic framework. The Ni@OC catalysts exhibited 100 % nitroaromatics conversion, excellent product selectivity, and superior stability in harsh conditions. Experimental results indicate that the dissociation of H2 and the activation of nitrobenzene compounds can be achieved with the OFGs doped MGSs as the catalytic site in Ni@OC catalysts. In addition, OFGs promote the electron transfer from Ni core to graphene-like shells and result in structural defects of the MGSs to adsorb hydrogenation substrates. Thus, a reasonable design concept was provided to improve the hydrogenation activity of MGSs encapsulated catalysts with the stable existence of metal.

Confined high-entropy-alloy nanoparticles within graphitic shells for synergistically improved photothermal conversion

High-entropy-alloy nanoparticles (HEA-NPs) have exhibited great potential in solar steam generation, in which their photothermal conversion performances can be optimized through the interband transition (IBTs) between the composing elements. In this work, the HEA-NPs were in-situ confined in the multi-layer graphitic shells (HEA@CNPs) by the arc-discharged plasma approach to achieve a synergistic improvement in the solar steam generation performances. It can be recognized that the graphitic shells not only serve as optical absorbers but also improve the surface temperature ascribed to their low thermal conductivities. The numerical simulation reveals that the electric fields can be accumulated in the graphitic shells over the wavelength regions of 1000 to 2500 nm. As a result, the most optimized FeCoNiTiVCrMnCu@C nanocapsules demonstrated an evaporation rate of 2.66 kg m−2h−1 under one sun irradiation with an energy conversion efficiency of 98%, and the surface temperature can increase to ∼105 °C within 90 s, demonstrating an effective solar steam generation performance. The present study indicates an insight into the synergistic optical absorption behaviors between HEA-NPs and graphitic shells, and the nanocapsules could be expanded to other solar-thermal conversion applications.

Testing sand and soil from selected playgrounds in Lublin for eggs of nematodes of the genus: Ascaris, Toxocara, Trichuris

Abstract Children need to play outdoors. It is a natural tendency for young children to put everything in their mouths. Hygienic condition of playgrounds is important for maintaining their health. Companion animals (dogs and cats) as well as wild animals can transmit parasites that cause zoonoses in humans. Such infections often affects children playing in sandpits and playgrounds. Sand samples taken from specific locations (sandboxes, playgrounds) can be tested for the presence of parasite eggs specific to humans and animals (Ascaris, Toxocara, Trichuris). They cause ascariasis, toxocarosis, trichurosis. Invasive eggs of the parasites due to the very thick, multi-layered egg shells are very resistant to the influence of climatic factors and to chemicals present in the environment. The only way to get rid of parasite eggs from locations where they endanger human health is to remove the top layer of sand or soil or completely replace the sand. However, this is a laborious and costly procedure. The aim of the project was to examine samples from selected playgrounds in Lublin (Polnad) in terms of the presence of Ascaris, Toxocara, and Trichuris eggs. Thirty five samples of sand and soil obtained from 7 playgrounds in Lublin were obtained in May 2022 and tested for the presence of Ascaris, Toxocara, and Trichuris eggs with flotation method. In none of the examined samples the parasite eggs were found. The tested playgrounds in Lublin are hygienic and safe from eggs of Ascaris, Toxocara, and Trichuris.

Baric properties of quantum dots of the type of core (CdSe)-multilayer shell (ZnS/CdS/ZnS) for biomedical applications

Baric properties of quantum dots of the type of core (CdSe)-multilayer shell (ZnS/CdS/ZnS) for biomedical applications

Analytical Study of Dynamic and Vibrational of Composite Shell with Piezoelectric Layer using GDQM Method

Piezoelectric materials, due to their electromechanical coupling properties, are widely used as actuators and sensors in intelligent structures to control vibrations and bends of multilayer sheets with piezoelectric layers. In this paper, the response of free vibrations of a multilayer composite shell with the new Generalized Differential Quadrature Method (GDQM) for different boundary conditions is investigated. The governing equations are obtained by assuming first-order shear theory and using Hamilton's principle. The generalized quadrature differential method is used to solve the obtained equations. To use this method, coding has been done in MATLAB software. Due to the same thickness of the layers, as the number of composite layers increases and the total thickness is constant, the thickness of each layer decreases, and consequently the thickness of the piezoelectric layer decreases. Comparing the results of this method with the work of other researchers shows that this method has good accuracy.

On the flexoelectric effect on size-dependent static and free vibration responses of functionally graded piezo-flexoelectric cylindrical shells

The flexoelectric effect depends on the strain gradient, which naturally appears in intelligent structures at micro and nano scales. Therefore, the flexoelectric phenomenon significantly affects electro-mechanical behavior of structures in these scales. In this study, the first-order shear deformation theory and the reformulated flexoelectric theory are applied to derive coupling equations of motion for a size-dependent static and dynamic responses of multilayered composite shell with simply supported and clamped edges. Constitutive equations are defined based on assumption that the internal energy function depends not only on strains and polarization tensors but also on strains and polarization gradient tensors. The piezo-flexoelectric structure is made of an isotropic functionally graded core and two orthotropic layers. Reynolds transport theorem and variational Hamilton principle are used to derive equations of motion expressed by forces and displacements, and corresponding boundary conditions. In order to check the correctness of the formulation, and solution of the problem obtained by Galerkin method, static and free vibrations analyses of macro-/micro-/nanoshell are investigated. Diagrams of deflection and electrical potential variations of the structure under the load are obtained for the direct flexoelectric effect. Additionally, the influence of various parameters, e.g., geometric properties, size effect, power-law index, and flexoelectric layer thickness, on the deflection, potential function, and natural frequency of the microshell have been investigated. The numerical results and discussion present that above parameters significantly affect a mechanical behavior of the microshell under consideration.

3-D analytical solution of non-homogeneous transversely isotropic thick closed cylindrical shells

This paper presents an effective analytical method based on displacement potential functions (DPF) for solving 3D static problem of thick and multilayer transversely isotropic cylindrical shells with simply supported end boundary conditions. By using the DPF method, the three-dimensional elasticity equations are simplified and decoupled into two linear partial differential equations of fourth and second order as governing differential equations. The governing equations are solved by the separation of variable method in terms of fields that exactly satisfy end boundary conditions and the continuity of a closed cylinder in the hoop direction. The analysis covers a straightforward solution process for handling problems on multilayered cylindrical shells of transversely isotropic material, adopting all boundary and continuity conditions. Extensive sets of general radial loads located on the inner and outer faces of the cylindrical shell may be stated and examined with in a systematic manner. Comparisons are performed to other existing analytical results for one and multilayered cylindrical shells, and show excellent agreement for different materials, thicknesses and aspect ratios of the shell. In addition, various more involved problems are studied and solved analytically for single and three-layered shells of transversely isotropic material with different sets of radial loading functions at the outer and inner shell surfaces. The results of the present study can be used as benchmark solutions for other studies.

In situ-formed cobalt nanoparticles embedded within carbonaceous matrix as highly efficient and selective catalysts for the hydrogenation of nitroarenes

Inhibiting the side reactions meanwhile promoting the hydrogenation of aromatic nitro compounds are the target for the production of functional amines. In this work, an easy-to-prepare heterogeneous catalyst with multilayered graphitic shells was successfully synthesized and applied. First of all, the structural features of catalyst reveal two possible catalytic mechanisms; in simple terms, 1) the metallic nanoparticles are covered with thin carbon layers with small cracks, where H2 can be diffused through and activated for the hydrogenation, and 2) the outer graphitic shell can be activated by the electronic interaction between inner metallic nanoparticles and outer graphene layer. Subsequently, the catalytic properties were tested in the hydrogenation of nitroarenes by a series of reaction conditions, hydrogen sources and substrates, and most of the nitro aromatics with functional groups were well tolerated in an excellent yield even under very mild industrially viable and scalable conditions. More surprisingly, this catalyst preformed highly selective hydrogenation on –NO2 and can further catalyze N-methylation for various tertiary amines by tandem reaction; not only that, a slight loss of catalytic activity was observed after recycling up to eight times, suggesting a potential routs to produce functional amines in scale-up application.

Experimental and numerical investigation on seismic performance of semi-precast concrete sandwich shear wall

This study investigated the seismic performance of an innovative semi-precast concrete sandwich shear wall (SCSSW) system. The system consists of two precast reinforced concrete (RC) wythes, a core cast-in-place RC wythe, a core thermal insulation layer, the fiber reinforced polymer connectors and the steel trusses. A total of three RC shear wall specimens were fabricated and tested under in-plane cyclic load. They consists of one conventional cast-in-place RC shear wall, one structural wythe of SCSSW (i.e., the assemble of a precast and a cast-in-place RC wythe), and one typical SCSSW. The failure mode, hysteretic curve, ductility and energy dissipation of the three specimens were studied and compared. Furthermore, numerical simulation based on multi-layer shell element was conducted to reproduce the test, and parametric analysis was conducted to facilitate a better understanding on the SCSSW. It was concluded that the SCSSW presented a ductile failure behavior; the seismic performance of the SCSSW including hysteretic curves, skeleton curves, stiffness degradation and the energy dissipation was similar to that of the cast-in-place RC shear wall, while the ductility of the SCSSW was slightly lower; and the facade precast RC wythe contributed few effect on the seismic performance of the SCSSW.

Isogeometric analysis of multilayer composite shell structures: Plasticity, damage, delamination and impact modeling

A comprehensive Isogeometric Analysis framework for damage modeling of laminated composite structures is presented. The formulation is based on a multilayer approach that employs Kirchhoff–Love shell theory coupled with anisotropic elastoplastic damage to model the mechanical behavior of the individual plies. The plies are connected at their interfaces through a mixed-mode cohesive damage model that is used to represent delamination. The ply no-interpenetration condition is enforced using a penalty formulation. The formulation ensures a smooth transition from the opening mode, which is governed by the cohesive damage law, to the closing mode, which is governed by the penalty approach, and results in a significantly more stable numerical methodology overall. The resulting framework is deployed on a series of simulation cases with increasing complexity of the geometry and mechanical phenomena modeled. In all cases, experimental data is used for model validation purposes and for demonstrating the superior robustness and predictive capabilities of the formulation presented.

Flutter characteristics of multi-layered composite shell panels under supersonic flow with curvature effect

ABSTRACT This study presents the finite element (FE) solutions to the aeroelastic flutter behaviour of multi-layered composite shell panels with flat and cylindrical geometry under supersonic flow based on third-order shear deformation mid-plane kinematics. The shell panel is discretized by a nine-noded isoparametric shell element with nine nodal degrees of freedom. The effect of the aerodynamic load is incorporated through first-order piston theory. The numerical model's accuracy and validity are justified by comparing the present solutions (free vibration frequency, coalescence frequency, and the corresponding critical aerodynamic pressure) with the existing numerical results. Also, the current natural frequencies are compared with the values from in-house experimental tests. The influence of parameters such as the flow angle, fibre orientation, material anisotropy, thickness ratio, and curvature ratio on the supersonic flutter boundaries of the shell panels subjected to simply supported and clamped conditions is investigated. The results are deliberated in detail, and it is observed that the fibre orientation and material anisotropy affect the flutter boundary differently under the simply supported and clamped conditions. Moreover, the first coalescence is greatly influenced by the flow angle instead of the curvature of the curved shell panels.